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Seating strings

  • 1.  Seating strings

    Posted 04-14-2005 04:23 
    From "Michael Gamble" <michael@gambles.fsnet.co.uk>

Hello List and Ron who said: (inter alia) 
Here's the mantra... Strings don't climb bridge pins, and seating 
neither pins, nor strings cures the cause of false beats. It just 
does further damage to the cap.

I must confess to tapping strings on the bridge to get rid of false beats. Most times it works. Rarely it doesn't. There has to be a reason for that. So.... what is the preferred method of getting rid of those false beats?
Regards
Michael G.(UK)


  • 2.  Seating strings

    Posted 04-14-2005 06:32 
    From Ron Nossaman <rnossaman@cox.net>

Michael Gamble wrote:
> Hello List and Ron who said: (inter alia)
> Here's the mantra... Strings don't climb bridge pins, and seating
> neither pins, nor strings cures the cause of false beats. It just
> does further damage to the cap.
>  
> I must confess to tapping strings on the bridge to get rid of false 
> beats. Most times it works. Rarely it doesn't. There has to be a reason 
> for that. So.... what is the preferred method of getting rid of those 
> false beats?
> Regards
> Michael G.(UK)


How often do you do it? Every tuning? If you do it on a regular 
basis with tuning, how long do you suppose that false beat you got 
rid of stayed gone? Was it a year, a month, a week, a day, or at 
least long enough for you to get out of the house? The cause 
typically is loose bridge pins. When touching the side of the 
speaking side bridge pin of the false string (opposite the string) 
with a screwdriver stops the beat, that's it. Seating the string 
often temporarily wedges the pin enough that it doesn't flagpole and 
cause the beat. Beat goes away. The tuner thinks he's fixed it, but 
it comes back as the string goes back where it was and the loose pin 
can again flagpole. The fix is to make the pin solid in the cap at 
the surface of the cap. CA or epoxy will do that, but it's not a 
casual field repair. For the most part, the customers don't hear (or 
at least don't mind) these noises. It's the tuners that are driven 
nuts by them. I usually just ignore them and press on. At most, and 
not often, I'll press down on a string just forward of the bridge 
pin with my thumb nail. I know it doesn't do anything good, but I 
haven't done any harm, and it sometimes makes a real screamer less 
bad temporarily. In my opinion, if the venue requires a piano 
utterly free of false beats, then it warrants a thorough job of 
repairing the cause, not a band aid seating of strings. The 
important thing here is that seating strings isn't something that is 
necessary to get the strings back down on the bridge, because they 
are already down on the bridge. It's almost always the loose pin 
that causes the false beat. Strings don't climb bridge pins.

Ron N


  • 3.  Seating strings

    Registered Piano Technician
    Posted 04-14-2005 06:34 
    From "Robert Edwardsen" <eedward2@rochester.rr.com>

It's almost always the loose pin
> that causes the false beat. Strings don't climb bridge pins.
>
> Ron N
>


I just saw a presentation by Don Mannino in Syracuse, NY which included some
high tech films of pianos in action.  One film was of a string moving up &
down at the bridge and it sure looked like that string might creep up the
pin after awhile, great presentation if you get a chance to see it.

Rob E.
/pianotech


  • 4.  Seating strings

    Posted 04-14-2005 07:25 
    From Ron Nossaman <rnossaman@cox.net>

> I just saw a presentation by Don Mannino in Syracuse, NY which included some
> high tech films of pianos in action.  One film was of a string moving up &
> down at the bridge and it sure looked like that string might creep up the
> pin after awhile, great presentation if you get a chance to see it.
> 
> Rob E.

Against positive downbearing, against a string offset angle, and pin 
inclination, how is it physically possible for a string to climb, 
creep, or otherwise get up a pin so it is no longer in contact with 
the bridge cap, and stay there? I don't buy it. I'd like to see 
anyone take a reasonably normal piano and make a string stay up a 
pair of bridge pins without touching the cap. Most everyone seems to 
take it on faith that this happens naturally and ubiquitously, but 
no one seems able or willing to demonstrate that it is indeed 
possible by doing it, and proving it by sliding something under the 
string between bridge pins.

Ron N


  • 5.  Seating strings

    Registered Piano Technician
    Posted 04-14-2005 09:32 
    From "Robert Edwardsen" <eedward2@rochester.rr.com>

I think I'll take the spark plug feeler gauges out on the road and check it
out.

Rob E


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 6.  Seating strings

    Posted 04-14-2005 20:23 
    From William Ballard <yardbird@vermontel.net>

At 11:32 AM -0400 4/14/05, Robert Edwardsen wrote:
>I think I'll take the spark plug feeler gauges out on the road and check it
>out.

Or a dial indicator with a magnetic base on the plate and its 
business end on the wire at the bridge.

I am just as skeptical as Ron N. about strings defying the prevailing 
(and increasing) frictional forces in their climb up the bridge pins 
(allowing of course, for indented bridge pins--who was that who first 
reported that on this list, Marcel Carey maybe two years ago?). What 
I do observe is wire wandering laterally across the bridge away from 
the pin. How do I observe this? When I tap the first time (and it 
only takes a very light tap), I see the string move. When I tap a 
second time, it doesn't move.

At 7:32 AM -0500 4/14/05, Ron Nossaman wrote:
>How often do you do it? Every tuning?

When during the course of a tuning, I first hear a false beat or 
nasal sound which clears up with a lateral tap, I then stop and tap 
every string from there outwards (usually this means upwards into the 
treble). Nothing before this first offender got tapped because 
because it didn't need to be tapped. Typical example is a local 
recording studio where NRBQ does their stuff (as well as Ken Burns). 
The next tuning after Terry Adams, I'm tapping strings.

Bill Ballard RPT
NH Chapter, P.T.G.

"Can you check out this middle C?. It "whangs' - (or twangs?)
     Thanks so much, Ginger"
     ...........Service Request
+++++++++++++++++++++


  • 7.  Seating strings

    Posted 04-14-2005 11:47 
    From "Michael Spalding" <spalding48@earthlink.net>

And, as a practical matter, where do you find the most false beats and do
the most string seating?  Octave 5 and above, where the vibrational
displacement of the string is barely, or not, large enough to see.   And
does it occur as often on verticals, where the direction of the hammer
impact should help to seat the string?  Now, which string was shown in the
film?  I'm guessing it was a long heavy bass string, as they would have the
largest / slowest displacement and make the most interesting film.   I'm
inclined towards Ron's vision of what's happening at the bridge pins.

Mike


> [Original Message]
> From: Ron Nossaman <rnossaman@cox.net>
> To: Pianotech <pianotech@ptg.org>
> Date: 4/14/2005 8:21:08 AM
> Subject: Re: Seating strings
>
> > I just saw a presentation by Don Mannino in Syracuse, NY which included
some
> > high tech films of pianos in action.  One film was of a string moving
up &
> > down at the bridge and it sure looked like that string might creep up
the
> > pin after awhile, great presentation if you get a chance to see it.
> > 
> > Rob E.
>
> Against positive downbearing, against a string offset angle, and pin 
> inclination, how is it physically possible for a string to climb, 
> creep, or otherwise get up a pin so it is no longer in contact with 
> the bridge cap, and stay there? I don't buy it. I'd like to see 
> anyone take a reasonably normal piano and make a string stay up a 
> pair of bridge pins without touching the cap. Most everyone seems to 
> take it on faith that this happens naturally and ubiquitously, but 
> no one seems able or willing to demonstrate that it is indeed 
> possible by doing it, and proving it by sliding something under the 
> string between bridge pins.
>
> Ron N
> _______________________________________________
> pianotech list info: http://www.ptg.org/mailman/listinfo/pianotech


  • 8.  Seating strings

    Posted 04-14-2005 13:53 
    From "Michael Gamble" <michael@gambles.fsnet.co.uk>

Hello Ron (and List)
Your statement about false beats is a "must read" for all interested in 
tuning pianos. I concur with all you have said. It all makes profound sense. 
I now eagerly await a "trial by fire". I have therefore put your obiter 
dictum on the List for all to read.
Kind regards
Michael G.(UK)

    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 9.  Seating strings

    Member
    Posted 04-14-2005 14:04 
    From Phillip Ford <fordpiano@earthlink.net>

>Against positive downbearing, against a string offset angle, and pin
>inclination, how is it physically possible for a string to climb,
>creep, or otherwise get up a pin so it is no longer in contact with
>the bridge cap, and stay there? I don't buy it. I'd like to see
>anyone take a reasonably normal piano and make a string stay up a
>pair of bridge pins without touching the cap. Most everyone seems to
>take it on faith that this happens naturally and ubiquitously, but
>no one seems able or willing to demonstrate that it is indeed
>possible by doing it, and proving it by sliding something under the
>string between bridge pins.
>
>Ron N

OK, just for fun (or for the sake of argument, if you prefer) I'll take a 
crack at this.  I thought I would throw a little math at this.

My assumptions:

String tension T = 150 lbs.
Side bearing angle 8 degrees
Down bearing angle 1 degree
Bridge pin angle (relative to cap surface) 15 degrees

Friction between string and bridge pin is given by static friction formula
FR = u N

where:

u = coefficient of friction between string and bridge pin.  This will 
depend on the material of the string and the material of the bridge pin and 
on surface finishes of each.  For high polished steel on highly polished 
brass it would be on the order of 0.2.  For rusty steel on rusty steel it 
might be on the order of 1.0 or more.

N = normal force (force perpendicular to bridge pin) exerted by the string

The side bearing force is given by SB = T sin (8 deg) = 150 (.139) = 20.9 LB

The down bearing force is given by DB = T sin (1 deg) = 150 (.017) = 2.7 LB

Each of these forces will have components normal to the bridge pin and 
parallel to the bridge pin.

FOR THE SIDE BEARING:

Normal force N1 = 20.9 cos (15 deg) = 20.2 LB (note that this is towards or 
into the bridge pin)

Parallel force P1 = 20.9 sin (15 deg) = 5.4 LB (note that this force is 
down toward the bridge cap)

FOR THE DOWN BEARING:

Normal force N2 = 2.7 sin (15 deg) = 0.7 LB (note that this is away from 
the bridge pin and is counteracting the normal force from the side bearing)

Parallel force P2 = 2.7 cos (15 deg) = 2.6 LB (note that this is down 
toward the bridge and is adding to the parallel force from the side bearing)

TOTAL FORCES:

N = N1 + N2 = 20.2 - 0.7 = 19.5 LB

P = P1 + P2 = 5.4 + 2.6 = 8.0 LB

If the force parallel to the pin is higher than the friction generated by 
the normal force then the string will want to move down the pin.  If the 
friction force is higher than the force parallel to the pin then the string 
will want to stay where it is (even if it's above the bridge cap).

FRICTION FORCE:

This is going to depend on the friction coefficient that you assume:  I 
think a reasonable number might be 0.6.  For this assumption friction force is:

FR = u N = 0.6 (19.5) = 11.7 LB

In this case the string will want to stay where it is, and not move down 
the bridge pin.  For this set of assumptions (which I think are probably 
representative of pianos out there) the string will want to stay above the 
bridge cap.  I can imagine another set of assumptions (perhaps also 
representative of other pianos out there with different side bearing angle, 
different down bearing angle, different bridge pin angles, and different 
coefficient of friction from different bridge pin materials or surface 
smoothness) where the numbers would work out the other way and the string 
would want to move down the pin.

A few things to note:

As the piano ages the string and the bridge pin are probably going to get 
some corrosion which is going to raise the coefficient of friction, making 
the string less likely to move down the pin.

The higher the string is above the bridge cap the greater the side to side 
displacement (the greater the side bearing angle) because of the angled 
bridge pins, and the greater the down bearing angle, which will increase 
all of the normal and parallel forces.  However, the friction force will go 
up fastest, making the string less likely to move down the pin.  This is 
somewhat counterintuitive to me, but there you are.

None of these forces will make the string move up the pin.  So, the string 
won't 'climb' the pin.  However, if due to humidity increase the bridge cap 
swells and raises the string, then the string isn't going to follow it back 
down (at least in the situation given in the example above) when the cap 
shrinks back down on a humidity decrease.  So, the idea of tapping the 
strings down periodically is perhaps not unsound practice.

On a practical note I have to agree with David I that my experience in 
prepping new pianos is that on tapping the strings down (and I'm talking 
about a light tap) I often see a noticeable downward movement of the string 
and will often hear a noticeable improvement in the tone.  I don't have an 
explanation for why strings on newly strung pianos would end up some 
distance off the bridge cap, but my perception is that they do.  I don't do 
too much prepping of new pianos these days, but I'll be happy to try to 
stick a feeler gage or piece of paper under some strings the next time I'm 
around an unprepped new piano.  I'll report back.

Phil Ford
San Francisco


  • 10.  Seating strings

    Posted 04-14-2005 15:30 
    From Ron Nossaman <rnossaman@cox.net>

> If the force parallel to the pin is higher than the friction generated by 
> the normal force then the string will want to move down the pin.  If the 
> friction force is higher than the force parallel to the pin then the string 
> will want to stay where it is (even if it's above the bridge cap).

And when you throw in vibration from play, and the movements from 
thermal effects, the forces will overcome friction and the string 
will stay with the bridge cap. We know that over time, strings will 
render across the bridge, which takes overcoming friction  at the 
pins. That ought to work vertically at least as well as, probably 
better than, horizontally.


> On a practical note I have to agree with David I that my experience in 
> prepping new pianos is that on tapping the strings down (and I'm talking 
> about a light tap) I often see a noticeable downward movement of the string 
> and will often hear a noticeable improvement in the tone.  I don't have an 
> explanation for why strings on newly strung pianos would end up some 
> distance off the bridge cap, but my perception is that they do.  

There are two possibilities that I can think of, given positive 
front and overall bearing. Either the string isn't touching the cap 
at all, in which case a feeler gage should slide between the string 
and bridge cap in the middle of the section between the pin rows, or 
the notch edge is already crushed to where it is just barely 
touching the string at the pin. It is my opinion that the second 
condition, and a less than solid pin, accounts for this fuzzy tone. 
The string is contacting the notch edge too much to let the pin 
flagpole enough to beat, but not enough to prevent pin flagpoling 
altogether, which is why seating the string "clears" it up. If you 
take a string off of a new piano, you'll almost certainly see a 
groove in the bridge cap. It will be wider (and deeper) at the notch 
edge than in the middle.


>I don't do 
> too much prepping of new pianos these days, but I'll be happy to try to 
> stick a feeler gage or piece of paper under some strings the next time I'm 
> around an unprepped new piano.  I'll report back.
> 
> Phil Ford

Thanks, I'm interested.
Ron N


  • 11.  Seating strings

    Posted 04-14-2005 23:06 
    From Roger Jolly <roger.j@sasktel.net>

Theory.

I agree that it is highly improbable that the string climbs up the pin.


However the pin can rise out of the bridge, due to hydraulics. As moisture 
is absorbed by the bridge, force is applied to the bottom of the pin, 
moving it upward.  This is the same principal as rocks appearing in a 
farmers field every spring.  Movement of water , pumps these rocks to the 
surface.   The string is held against the pin with friction, and rises with 
the pin.

For a number of years I have been using West systems epoxy as a driving 
fluid for installation of bridge pins.  The pin acts as a pump and forces 
the epoxy down the capillaries of the grain structure, making the hole/pin 
impervious to these moisture fluctuations.  The number of false beats to 
appear in bridges with this treatment is way less than no treatment.  Many 
of us have repaired bridges with epoxy, putting the epoxy in hole #1 and 
watching come out #2.

If the pin has moved upwards, then this can explain why a light tap will 
seat the pin and string, and be a partial cure for several years.  The 
hydraulics with begin to do it's evil work again.
   New pianos going to a very dry climate will exhibit shrinkage of the 
bridge, and can show a lot of falseness. Seating the strings by tapping the 
bridge pins cleans up a lot of the garbage, and lasts for a number of years.

I have had several long conversations with a Professor that specializes in 
soil Hydraulics, and does a lot of consultant work for major power 
corporation's , with regards to transmission lines.   The telegraph poles 
that you see beside the highway, leaning every way but vertical. Are moved 
by the following. #1 Hydraulics. #2 wind shear. #3 load.

He felt that my theory was a high probability.

Regards Roger.

PS I will keep tapping the falsies out.


  • 12.  Seating strings

    Registered Piano Technician
    Posted 04-15-2005 09:11 
    From "David Chadwick" <chadwick61@cox.net>

Greetings, 
I really don't think that there is enough down bearing on the bridge cap to positively terminate the power generated by the wave pattern of the string. I'm certainly no authority and I'm probably just pondering. Try holding one end of a rope while another person quickly moves the other end up and down similarly to string vibration. Even standing on the "bridge end" of the rope would require more down bearing power to keep it from leaking beyond the point of termination and continued vibration would undoubtedly wear the surface on either the rope/string or the stopping point, whichever is the strongest material. Cementing the bridge pin in place might be OK for the pin to wood relationship but I feel it leaves me with fewer options to service this point such as tapping the bridge pins. I like Roger J's solution that I picked up at a seminar once....by gently sliding the thick side of the felt mute wedge slowly up the speaking length to the bridge with slight down pressure the seating can be accomplished without the tapping on the strings. I usually do it as needed through the course of tuning. It also is a lot quieter and is less alarming to the client as the tapping can be quite noisy. My only question is how come it more in the treble section than in other area's. 

More than "two cents" worth but I had to comment. 

David Chadwick


  • 13.  Seating strings

    Posted 04-16-2005 11:28 
    From Ron Nossaman <rnossaman@cox.net>

Phil,

I put a spreadsheet together about four years ago, for estimating 
these friction and force levels. I get somewhat different results. 
Having no formal engineering education, I did what I thought looked 
right and was supportable by what reference material I could find 
(and understand). It's subject to revision if better information is 
available, so I have some questions, if I may.


> OK, just for fun (or for the sake of argument, if you prefer) I'll take a 
> crack at this.  I thought I would throw a little math at this.

For fun, absolutely, and for education, which is also fun.


> My assumptions:
> 
> String tension T = 150 lbs.
> Side bearing angle 8 degrees
> Down bearing angle 1 degree
> Bridge pin angle (relative to cap surface) 15 degrees
> 
> Friction between string and bridge pin is given by static friction formula
> FR = u N
> 
> where:
> 
> u = coefficient of friction between string and bridge pin.  This will 
> depend on the material of the string and the material of the bridge pin and 
> on surface finishes of each.  For high polished steel on highly polished 
> brass it would be on the order of 0.2.  For rusty steel on rusty steel it 
> might be on the order of 1.0 or more.
> 
> N = normal force (force perpendicular to bridge pin) exerted by the string
> 
> The side bearing force is given by SB = T sin (8 deg) = 150 (.139) = 20.9 LB
> 
> The down bearing force is given by DB = T sin (1 deg) = 150 (.017) = 2.7 LB

The sin function gets less accurate as the angle increases, but yes, 
close enough.


> Each of these forces will have components normal to the bridge pin and 
> parallel to the bridge pin.
> 
> FOR THE SIDE BEARING:
> 
> Normal force N1 = 20.9 cos (15 deg) = 20.2 LB (note that this is towards or 
> into the bridge pin)
> 
> Parallel force P1 = 20.9 sin (15 deg) = 5.4 LB (note that this force is 
> down toward the bridge cap)

This puzzles me. I got 5.4 for the down force all right, but how can 
the total of 20.2 lb horizontal, and 5.4 lb vertical be more than 
the 20.9 lb the side bearing angle generates? Is this just an 
artifact of the inaccuracy of the sin and cos method at these big 
angles?


> FOR THE DOWN BEARING:
> 
> Normal force N2 = 2.7 sin (15 deg) = 0.7 LB (note that this is away from 
> the bridge pin and is counteracting the normal force from the side bearing)

This also puzzles me. The downbearing force should have nothing to 
do with the side bearing forces since it is acting directly on the 
bridge top and isn't bearing on the pin at all. I don't understand 
why this is here.


> Parallel force P2 = 2.7 cos (15 deg) = 2.6 LB (note that this is down 
> toward the bridge and is adding to the parallel force from the side bearing)

Double puzzlement. How can side bearing reduce downbearing force 
(absent friction), and again, how can the sum of these two numbers 
exceed the total downbearing force of 2.7 lb?


> TOTAL FORCES:
> 
> N = N1 + N2 = 20.2 - 0.7 = 19.5 LB
> 
> P = P1 + P2 = 5.4 + 2.6 = 8.0 LB
> 
> If the force parallel to the pin is higher than the friction generated by 
> the normal force then the string will want to move down the pin.  If the 
> friction force is higher than the force parallel to the pin then the string 
> will want to stay where it is (even if it's above the bridge cap).
> 
> FRICTION FORCE:
> 
> This is going to depend on the friction coefficient that you assume:  I 
> think a reasonable number might be 0.6.  For this assumption friction force is:
> 
> FR = u N = 0.6 (19.5) = 11.7 LB

I didn't break it out like this, but calculate a static resistance 
(with your quite reasonable 0.6 coefficient) moving down the pin at 
6.7lb, and up the pin at 17.5lb. By my reckoning, the 2.6lb of 
downbearing and the 5.4lb down force from the pin slant and side 
bearing exceeds the static resistance, and the string will seat on 
the bridge automatically. I show a break even point of friction 
against down force at either a 13.25? pin angle, or a 0.666 (did you 
do that intentionally? <G>) friction coefficient. Enlighten me, please.


  • 14.  Seating strings

    Registered Piano Technician
    Posted 04-14-2005 16:35 
    From "David Love" <davidlovepianos@comcast.net>

In my experience, the only time strings climb pins is when there is a
notch carved in the bridge pin from the friction of the string over
time.  Then the string will want to seat itself in the notch in the pin.
As the bridge is indented from friction (and/or string tapping) the
notch on the bridge pin no longer aligns itself with the string being
seated on the bridge top and it can appear that the string is "climbing"
the pin.  Tapping down the string in such cases tends to be a temporary
measure as the string will want to seat itself in the groove cut into
the bridge pin.  Otherwise, Ron is correct, the bearing combined with
the bridge pin angles will keep the string seated firmly on the bridge.

Belief is the wound that knowledge heals.  

David Love
davidlovepianos@comcast.net 


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 15.  Seating strings

    Member
    Posted 04-14-2005 17:07 
    From V T <pianovt@yahoo.com>

Hello List,

I too saw Don's high speed film and was very impressed
with it.  The main thing I came away with is that life
at the bridge pin is incredibly violent.  I don't
remember seeing if the string momentarily lifted off
the bridge.  I can however see how a pin can pull out
of the bridge, and how the hole in the bridge cap can
enlarge where the pin exits the wood.  In fact, I am
amazed that the system works as well as it does!

This film is really worth seeing, along with some
others Don shows.

Vladan

==============================
I just saw a presentation by Don Mannino in Syracuse,
NY which included some
high tech films of pianos in action.  One film was of
a string moving up &
down at the bridge and it sure looked like that string
might creep up the
pin after awhile, great presentation if you get a
chance to see it.

Rob E.



		
__________________________________ 
Do you Yahoo!? 
Yahoo! Small Business - Try our new resources site!
http://smallbusiness.yahoo.com/resources/


  • 16.  Seating strings

    Posted 04-14-2005 17:10 
    From Ric Brekne <ricbrek@broadpark.no>

Hi folks.

We've been through this one many times. It seems perfectly obvious to 
me, and has for about 6 years now since I first heard this << strings 
dont climb the pins >> claim, that for whatever reasons, the strings do 
indeed and in the face of positive downbearing, find themselves on 
frequent occasion up the pins and away from the bridge just a tad.  You 
can measure the conditon of downbearing, make sure there is positve crow 
and still find strings not seated.  The fact that it is difficult to 
understand how this can be does change this fact.  Indeed, the lack of 
an explanation for any phenomena says only <<we do not understand>>.  It 
is in itself not an arguement for or against anything.

Just measure downbearing, crown, and whatever else you can think of on 
the occasion you find yourself in a string seating situation. I have and 
most often when I find strings needing seating, I find positive 
downbearing a plenty.  The report of Don's video does not suprise me in 
the slightest, I'd love to see it.

Cheers
RicB


>/ I just saw a presentation by Don Mannino in Syracuse, NY which included some
/>/ high tech films of pianos in action.  One film was of a string moving up &
/>/ down at the bridge and it sure looked like that string might creep up the
/>/ pin after awhile, great presentation if you get a chance to see it.
/>/ 
/>/ Rob E.
/
Against positive downbearing, against a string offset angle, and pin 
inclination, how is it physically possible for a string to climb, 
creep, or otherwise get up a pin so it is no longer in contact with 
the bridge cap, and stay there? I don't buy it. I'd like to see 
anyone take a reasonably normal piano and make a string stay up a 
pair of bridge pins without touching the cap. Most everyone seems to 
take it on faith that this happens naturally and ubiquitously, but 
no one seems able or willing to demonstrate that it is indeed 
possible by doing it, and proving it by sliding something under the 
string between bridge pins.

Ron N


  • 17.  Seating strings

    Posted 04-14-2005 17:11 
    From "Alan" <tune4u@earthlink.net>

Just like our discussion on why pianos go flat over time, I find it
interesting that, once again, we are tossing around ideas, strong opinions,
anecdotal evidence, theories, and assumptions about a piano topic that is
very important to our profession and yet ...

...no one really knows.

Pianos have had wild strings for as long as we've had pianos (a longish
time); you'd think the research had been done and definitive answers
published, by now.

Alan R. Barnard
Salem, MO



    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 18.  Seating strings

    Member
    Posted 04-14-2005 17:17 
    From Phillip Ford <fordpiano@earthlink.net>

>>If the force parallel to the pin is higher than the friction generated by 
>>the normal force then the string will want to move down the pin.  If the 
>>friction force is higher than the force parallel to the pin then the 
>>string will want to stay where it is (even if it's above the bridge cap).
>
>And when you throw in vibration from play, and the movements from thermal 
>effects, the forces will overcome friction and the string will stay with 
>the bridge cap.

There is vibration from play.  I don't know how much variation in the 
forces at the pin it yields.  I would think it would be fairly small even 
for a hard blow.  It might be enough to overcome the frictional forces.  I 
suppose it depends on how close the so-called Parallel force is to the 
Frictional force.  If it's close, then the periodic increase from the 
vibration should be enough to overcome the frictional force and cause the 
string to move.  If the frictional force is significantly higher, because 
of geometry, materials, or surface condition, then the force increase from 
the vibration wouldn't cause the string to move. I don't know what you mean 
by movement from thermal effects.

>  We know that over time, strings will render across the bridge, which 
> takes overcoming friction  at the pins. That ought to work vertically at 
> least as well as, probably better than, horizontally.

They will, but not always.  I think once again it's a matter of whether or 
not the forces are high enough to overcome the frictional forces.  If the 
mismatch in tension between speaking length and back length is high enough 
to overcome the friction at the pins then the string will move.  If that 
mismatch was just below the amount needed to overcome the friction, then 
the periodic increase in force from the string vibration would cause the 
string to move.  If the mismatch is far below the amount needed to overcome 
friction then string vibration would not cause it to move.



>>On a practical note I have to agree with David I that my experience in 
>>prepping new pianos is that on tapping the strings down (and I'm talking 
>>about a light tap) I often see a noticeable downward movement of the 
>>string and will often hear a noticeable improvement in the tone.  I don't 
>>have an explanation for why strings on newly strung pianos would end up 
>>some distance off the bridge cap, but my perception is that they do.
>
>There are two possibilities that I can think of, given positive front and 
>overall bearing. Either the string isn't touching the cap at all, in which 
>case a feeler gage should slide between the string and bridge cap in the 
>middle of the section between the pin rows,

Which would mean what, in your opinion?  That the forces aren't in fact 
sufficient to keep the string seated against the bridge cap, or that there 
hasn't been sufficient time for the vibration and thermal movement to cause 
the string to move down against the cap?

>or the notch edge is already crushed to where it is just barely touching 
>the string at the pin.

If side bearing and down bearing are sufficient to keep the string against 
the cap, why wouldn't they also keep the string firmly down against the 
notch edge?

>  It is my opinion that the second condition, and a less than solid pin, 
> accounts for this fuzzy tone. The string is contacting the notch edge too 
> much to let the pin flagpole enough to beat, but not enough to prevent 
> pin flagpoling altogether, which is why seating the string "clears" it 
> up. If you take a string off of a new piano, you'll almost certainly see 
> a groove in the bridge cap. It will be wider (and deeper) at the notch 
> edge than in the middle.

It seems that if there were a well defined groove into which the string 
wasn't firmly sitting (which raises the question of how it became a well 
defined groove), then tapping it down would push it straight down into the 
groove which would also seem to be moving it down away from the bridge pin, 
which I wouldn't guess would clarify the tone.  To keep it firmly against 
the pin and the notch it would have to move down parallel to the bridge 
pin.  This would seem to require widening of the string groove in the hard 
maple.  I wouldn't think that a light tap could accomplish this.

Phil Ford



>>I don't do too much prepping of new pianos these days, but I'll be happy 
>>to try to stick a feeler gage or piece of paper under some strings the 
>>next time I'm around an unprepped new piano.  I'll report back.
>>Phil Ford
>
>Thanks, I'm interested.
>Ron N


  • 19.  Seating strings

    Posted 04-14-2005 21:33 
    From Ron Nossaman <rnossaman@cox.net>

> There is vibration from play.  I don't know how much variation in the 
> forces at the pin it yields.  I would think it would be fairly small even 
> for a hard blow.  

I really don't know either, but it is a real world dynamic 
complication to your static model.

>It might be enough to overcome the frictional forces.  I 
> suppose it depends on how close the so-called Parallel force is to the 
> Frictional force.  If it's close, then the periodic increase from the 
> vibration should be enough to overcome the frictional force and cause the 
> string to move.  If the frictional force is significantly higher, because 
> of geometry, materials, or surface condition, then the force increase from 
> the vibration wouldn't cause the string to move. I don't know what you mean 
> by movement from thermal effects.

Strings change length with temperature changes. I would expect a 
change in length of the various string segments to have an affect on 
the friction points. Another dynamic complication to the static model.


  > They will, but not always.  I think once again it's a matter of 
whether or
> not the forces are high enough to overcome the frictional forces.  

I disagree. I have no data to support it (can't be everywhere at 
once), but I think the strings are continually rendering back and 
forth across the bearing points (including the bridge pins) with 
both thermal cycling, and humidity changes over longer time periods. 
I would agree (were it offered) that the various segments of any 
given string at any given time will most likely not all be at the 
same tension, but I also think those tension differences go back and 
forth depending on the present climate conditions and the immediate 
past conditions. In other words, I would expect to find the speaking 
length segment of a given string of higher tension than the rear 
duplex of that string one day, and quite possibly lower the next. 
I'm not sure of the time scale, but I expect that everything is 
moving to some degree all the time.


>>There are two possibilities that I can think of, given positive front and 
>>overall bearing. Either the string isn't touching the cap at all, in which 
>>case a feeler gage should slide between the string and bridge cap in the 
>>middle of the section between the pin rows,
> 
> 
> Which would mean what, in your opinion?  That the forces aren't in fact 
> sufficient to keep the string seated against the bridge cap, or that there 
> hasn't been sufficient time for the vibration and thermal movement to cause 
> the string to move down against the cap?

I don't think there is ever a time in a reasonably functional piano 
when the string is not in contact with the bridge. I don't see how 
it's possible, nor any indication that it happens.



> If side bearing and down bearing are sufficient to keep the string against 
> the cap, why wouldn't they also keep the string firmly down against the 
> notch edge?

Because a past high humidity cycle, or fifty, with the friction of 
the string on the pin, has crushed the edge of the notch. The string 
under tension will attempt to describe a straight line between 
support points. Vertically, the support point on the bridge cap 
being somewhat back from the edge (because the edge was crushed by 
the pin friction BENDING the wire between the center of the bridge 
and the pin and putting the stress on the notch edge), the string no 
longer touches the notch edge. Note that during wet cycles, few 
false beats are noticed, because the string is once again clamped to 
the cap close to the pin by the expanding bridge cap. The real 
screamers always appear in the dry cycles, where the (nominally) 
vertically straight shot between the string support point on the 
bridge, and the agraffe, doesn't contact the bridge cap at the pin. 
Note that if the pin was solid in the cap, no false beat would be 
manifest regardless of the condition of the notch edge. The pin is 
the termination, not the notch edge, and there are plenty of pianos 
out there with bridges notched well back of the pin that don't 
exhibit false beats because of it. The friction numbers dictate 
that. It's only when the pin isn't firm in the cap at the cap 
surface that we get these noises.


> It seems that if there were a well defined groove into which the string 
> wasn't firmly sitting (which raises the question of how it became a well 
> defined groove), then tapping it down would push it straight down into the 
> groove which would also seem to be moving it down away from the bridge pin, 
> which I wouldn't guess would clarify the tone. 

It clarifies tone by providing a temporary clamp that prevents the 
pin from flagpoling, which is the probable cause of the false beat 
and lack of clarity (a matter of degree).


  • 20.  Seating strings

    Member
    Posted 04-14-2005 17:17 
    From Phillip Ford <fordpiano@earthlink.net>

>...Against what seems should be so... the strings will indeed <<climb>> 
>the pins one way or the other and the side bearing math model is quite 
>obviously in error or not a complete enough model to describe the 
>condition adequatly.

My apologies for not choosing my words more carefully.  I should have said 
that this particular model shows no mechanism for the strings to climb the 
pin.  The point of the model was to offer one possible explanation for why 
the strings might not move down the pin if they were above the bridge cap, 
regardless of how they got there.  A model is just that, a model, not the 
real thing.  It is limited by the parameters modeled and the assumptions 
made.  To the extent that it is a good or useful model it will illuminate 
something about the real thing, provide a basis for discussion, or yield 
ideas for further investigation.  At least it looks like it wasn't a 
failure at providing a basis for discussion.

>  And, if you do actually take the time to see how long each string 
> seating job stays seated... you will find that most often they stay down 
> quite long.

Why would that be if the strings want to climb the pins?


>"There is a diety hiding in just about every dark corner of what is 
>commonly refered to as knowledge"  Alfred Lodge
>RicB

What's a diety?

Phil Ford


  • 21.  Seating strings

    Posted 04-14-2005 17:57 
    From Ric Brekne <ricbrek@broadpark.no>

Hi again.

Well, like I say... Do the measurements as well as doing the math.  Make 
observations that put /all/ claims to the test, instead of simply 
hopping from one set of taken for granteds to another. If you do 
actually observe all the stated relative conditions carefully on enough 
pianos then you will find the exact quandry that so many have cited 
through the years so many times. Against what seems should be so... the 
strings will indeed <<climb>> the pins one way or the other and the side 
bearing math model is quite obviously in error or not a complete enough 
model to describe the condition adequatly. And, if you do actually take 
the time to see how long each string seating job stays seated... you 
will find that most often they stay down quite long.

"There is a diety hiding in just about every dark corner of what is 
commonly refered to as knowledge"  Alfred Lodge
 
RicB


In my experience, the only time strings climb pins is when there is a
notch carved in the bridge pin from the friction of the string over
time.  Then the string will want to seat itself in the notch in the pin.
As the bridge is indented from friction (and/or string tapping) the
notch on the bridge pin no longer aligns itself with the string being
seated on the bridge top and it can appear that the string is "climbing"
the pin.  Tapping down the string in such cases tends to be a temporary
measure as the string will want to seat itself in the groove cut into
the bridge pin.  Otherwise, Ron is correct, the bearing combined with
the bridge pin angles will keep the string seated firmly on the bridge.

Belief is the wound that knowledge heals.  

David Love
davidlovepianos@comcast.net <mailto:davidlovepianos@comcast.net>


  • 22.  Seating strings

    Posted 04-14-2005 23:59 
    From Piano Forte Supply <pianoforte@pianofortesupply.com>

In a number of voicing classes and seminars across the country, I have 
experienced (seen and heard) how tapping the bridge pin can reduce or 
remove false beats and even strengthen and focus the tone of that 
string.  I don't claim to know all the physics involved, or whether or 
not strings can climb, or jump, for that matter.  I'll leave that 
discussion to others with a better grasp of the math. 

In the meantime, (even if it isn't a "permanent" fix, just as my tuning 
isn't) I'll go on tapping pins here and there as needed,  improving the 
tone of the pianos I work on and satisfying my clients <G>.

Jurgen Goering


  • 23.  Seating strings

    Registered Piano Technician
    Posted 04-15-2005 00:26 
    From "David Love" <davidlovepianos@comcast.net>

While I agree that tapping seems to provide a temporary fix.  I think
you would be better off securing the bridge pin by the use of thin CA
glue wicked into the base of the pin to secure it and keep it from
oscillating.  Tapping the pin (not the string) can lower the groove that
gets cut into the side of the pin so that it is closer to the surface of
the bridge, but the false beats tend to come from pins which are loose
in the bridge cap.  As Roger J. pointed out, pins that are held secure
with epoxy rarely have problems with false beats-unless the false beat
comes from poor terminations at the other end.  
 
David Love
davidlovepianos@comcast.net 

    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 24.  Seating strings

    Posted 04-15-2005 03:50 
    From Ric Brekne <ricbrek@broadpark.no>

Hi Phil

Nice posts. I appreciate the way you take due caution to relating maths 
modling to real life situations instead of simply spinning off a few 
figures and declaring universal truths. The point you bring up below is 
one (amoung several) that hasnt really been looked at.  It is simply 
assumed that the strings force upwards for even a hard blow is not 
enough to contribute to the string moving upwards on the pin. I dont 
know myself how much of a yank there is there... but it has to be pretty 
signifiacant to get the mass that the soundboard is along with the 
string plane to vibrate in a large enough amplitude to create the volume 
of sound we hear.  I did do a cute little experiement a while back... 
put a penny on the string just at the bridge pin and whack the key.  
Dont get in the way of the penny... :)

Another moment that bothers me which I see no one looking at is the fact 
that the string is forced into an unatural curve across the bridge 
surface to begin with. A string pushed up by a flat surface the width of 
a bridge will not (without bridge pins) lay perfectly flat on that 
surface. It will tend to bend around the surface being highest in the 
middle.  The bridge pins force the string to flatten out, creating 
essentially two fulcrum points where the string contacts the bridge. 
Which forces are doing what in this regard I dont know... but it would 
seem to me that since the string wont be comfortable just laying flat as 
it were. 

A third point which relates to the friction by the pins that seems 
totally over looked is that these also are vibrating in their own 
fashion. For that matter the whole assembly is moving around, components 
phasing in and out .... all in all a pretty complicated picture.

Seems to me that  carefull observation clearly reveals that strings do 
indeed somehow climb up these pins.  Just how remains perhaps a mystery. 

I sure would like to hear more about Maninnos video tho.... :)

Cheers
RicB



Phil Ford writes

There is vibration from play.  I don't know how much variation in the 
forces at the pin it yields.  I would think it would be fairly small even 
for a hard blow.  It might be enough to overcome the frictional forces.  I 
suppose it depends on how close the so-called Parallel force is to the 
Frictional force.  If it's close, then the periodic increase from the 
vibration should be enough to overcome the frictional force and cause the 
string to move.  If the frictional force is significantly higher, because 
of geometry, materials, or surface condition, then the force increase from 
the vibration wouldn't cause the string to move. I don't know what you mean 
by movement from thermal effects.


  • 25.  Seating strings

    Posted 04-15-2005 11:13 
    From David Andersen <david@davidandersenpianos.com>

> 
> David Love writes:
> 
> While I agree that tapping seems to provide a temporary fix.  I think you
> would be better off securing the bridge pin by the use of thin CA glue wicked
> into the base of the pin to secure it and keep it from oscillating.
> 
> Hi, David---do you have a protocol to do that without removing strings,
> on-site?
> 
> That would be groovy.....
> 
> David Andersen


  • 26.  Seating strings

    Member
    Posted 04-15-2005 12:31 
    From Phillip Ford <fordpiano@earthlink.net>

Phil F writes:
>>.....I don't know what you mean by movement from thermal effects.

Ron N writes:
>Strings change length with temperature changes. I would expect a change in 
>length of the various string segments to have an affect on the friction 
>points. Another dynamic complication to the static model.

Certainly the real situation is a dynamic one and the static model is a 
(gross) simplification.


>  > They will, but not always.  I think once again it's a matter of whether or
>>not the forces are high enough to overcome the frictional forces.



>I disagree. I have no data to support it (can't be everywhere at once), 
>but I think the strings are continually rendering back and forth across 
>the bearing points (including the bridge pins) with both thermal cycling, 
>and humidity changes over longer time periods.

I'm skeptical.  There is the static friction at the bridge pins that has to 
be overcome.  If my numbers were in the ballpark that amounts to about 10 
pounds or more at each pin.  I don't think that the small changes in length 
of the string segments due to the sort of temperature ranges that a piano 
is normally exposed to would cause that much change in string tension.  So, 
I think the string will stay put at the friction points and the string 
segments will grow or shrink between them due to temperature changes.  How 
would humidity change affect the string?  As I see it the change would mean 
soundboard movement up or down, which would change string tension and would 
probably affect the speaking portion and backscale portion 
differently.  Perhaps enough to cause a 10 pound tension mismatch if the 
movement was great enough.  However, if there is some other mechanism, such 
as string vibration causing some minute movement of the string on the pin, 
this may break the static friction and cause the strings to move past the 
pins with much smaller tension mismatches.


>>If side bearing and down bearing are sufficient to keep the string 
>>against the cap, why wouldn't they also keep the string firmly down 
>>against the notch edge?
>
>Because a past high humidity cycle, or fifty, with the friction of the 
>string on the pin, has crushed the edge of the notch. The string under 
>tension will attempt to describe a straight line between support points. 
>Vertically, the support point on the bridge cap being somewhat back from 
>the edge (because the edge was crushed by the pin friction BENDING the 
>wire between the center of the bridge and the pin and putting the stress 
>on the notch edge), the string no longer touches the notch edge.

I'm not sure I understand the mechanism that you're describing here.  Are 
you talking about the bridge cap trying to move up on a wet cycle, but the 
pin holds the string in place, crushing it into the cap?

>  Note that during wet cycles, few false beats are noticed, because the 
> string is once again clamped to the cap close to the pin by the expanding 
> bridge cap. The real screamers always appear in the dry cycles, where the 
> (nominally) vertically straight shot between the string support point on 
> the bridge, and the agraffe, doesn't contact the bridge cap at the pin. 
> Note that if the pin was solid in the cap, no false beat would be 
> manifest regardless of the condition of the notch edge. The pin is the 
> termination, not the notch edge, and there are plenty of pianos out there 
> with bridges notched well back of the pin that don't exhibit false beats 
> because of it. The friction numbers dictate that. It's only when the pin 
> isn't firm in the cap at the cap surface that we get these noises.

Any ideas about why a flagpoling bridge pin causes false beats?

Phil Ford


  • 27.  Seating strings

    Posted 04-15-2005 17:30 
    From Ron Nossaman <rnossaman@cox.net>

> Certainly the real situation is a dynamic one and the static model is a 
> (gross) simplification.

Gotta start somewhere though.


> I'm skeptical.  There is the static friction at the bridge pins that has to 
> be overcome.  If my numbers were in the ballpark that amounts to about 10 
> pounds or more at each pin.  I don't think that the small changes in length 
> of the string segments due to the sort of temperature ranges that a piano 
> is normally exposed to would cause that much change in string tension.  

Possibly not. The point is it's movement, and the difference between 
the static friction supposedly holding a string above the bridge cap 
and the combination of downbearing, pin slant, and string offset 
angle trying to pull it down is much closer than 10 lbs.

>So, 
> I think the string will stay put at the friction points and the string 
> segments will grow or shrink between them due to temperature changes.  How 
> would humidity change affect the string?  

It wouldn't, directly, but the bridge would move relative to the 
pins. Again, I haven't measured it, but I don't see how the pins 
could avoid moving relative to one another (at least somewhat) as 
the bridge changes dimension more or less continuously.

>As I see it the change would mean 
> soundboard movement up or down, which would change string tension and would 
> probably affect the speaking portion and backscale portion 
> differently.  Perhaps enough to cause a 10 pound tension mismatch if the 
> movement was great enough.  

It isn't. There is much more tension change resulting from the 
bridge moving strings up and down diverging pins. Incidentally, 
while the soundboard is moving, the bridge top, and presumably the 
string, is also moving on the pin - breaking the friction enough for 
the string to render through from segment tension differences. 
That's going up. It remains to be seen if anyone can demonstrate 
that the string stays stuck to the pin enough to lose contact with 
the cap in the dry cycles.



>However, if there is some other mechanism, such 
> as string vibration causing some minute movement of the string on the pin, 
> this may break the static friction and cause the strings to move past the 
> pins with much smaller tension mismatches.

This is what I think happens.


> I'm not sure I understand the mechanism that you're describing here.  Are 
> you talking about the bridge cap trying to move up on a wet cycle, but the 
> pin holds the string in place, crushing it into the cap?

Exactly. I've directly measured an 0.011" difference in pin height 
above the cap surface in a bridge model I cycled through a couple of 
cycles of from 4% - 12% MC. The force required to push the string up 
the divergently slanted pins is half again that required to render a 
string straight past a pin. That's a heck of a PSI load on a maybe 
0.010" wide groove in a maple cap. Take a pin out of the speaking 
side of an old bridge. Hold a short length of straightened piano 
wire in the existing string groove with a screwdriver of knife blade 
at a right angle to the wire. hold down in the middle of the bridge 
first and note that the wire is pretty much parallel to the bridge 
top. Now hold it closer to the notch edge, and closer, and at the 
bridge pin hole and watch the tangent angle of that groove go to 
maybe 15? at the notch edge. Now imagine a wire under tension 
resting on the center of the bridge, and going down at a generous 1? 
angle to the agraffe. It will pass the pin hole some distance above 
the cap. The string has NOT climbed the pin. The notch edge simply 
doesn't reach the strings natural path any more because it has been 
crushed too low to make contact unless the bridge is in the 
expansion cycle. Forcing it down to contact by tapping the string or 
driving the pin has no chance of keeping it down there. It will once 
again seek it's straight line path and lose contact with the notch 
edge until the next expansion cycle.


> Any ideas about why a flagpoling bridge pin causes false beats?
> 
> Phil Ford 

Yes. The pin has nearly no stress on it below the surface of the 
bridge, so it hasn't greatly deformed the wood that surrounds it. At 
the cap surface, the side stress of the cap pushing the string up a 
slanted pin (combined with the normal side bearing) pushes the pin 
against the side of the hole. The deformation the pin makes in the 
hole is like the deformation the string makes in the bridge top. It 
curves, because the pin is slightly sprung by the forces involved 
just like the string is, only less because the pin is stiffer. So 
here's a pin, tight in the bottom of the hole, and looser at the 
top. At some point below the surface of the cap is the place where 
the back side (away from the string) of the pin parts company with 
the cap and is free to flagpole. It becomes a spring. The pin is 
still the string's vertical termination point, just like it always 
was if the bridge was notched deeply enough at manufacture. But the 
horizontal termination is a spring with a more solid termination 
somewhat beyond the spring on the bridge surface. The beat is the 
difference between the vertical excursion frequency and the 
horizontal excursion frequency of the string caused by the lossy 
horizontal termination. Tapping the string or driving the pin clamps 
the string down to the cap closer to the pin , courtesy of friction 
between string and pin and string and cap, and restricts horizontal 
movement of the springy pin. This makes the horizontal and vertical 
excursion frequencies close enough to the same to kill, or minimize 
the beat. If the friction between string and pin isn't sufficient to 
hold the string tightly against the notch edge, or if the pin or 
notch edge is too damaged to provide the necessary clamp, it doesn't 
"fix" the false beat. The unfocused sound that seating clears up is 
the string grazing, but not clearing the cap enough to produce a 
clear beat. Seating these, especially by driving the pins, should 
produce really nice false beats soon enough. In all these cases, the 
mechanism that produces the beat is the bridge pin that is not solid 
in the cap at the surface and can flagpole. It doesn't take much. I 
think we see this only in the top two sections because the 
differences in the two apparent speaking lengths the flagpoling pin 
provides quits producing clear beats as that difference becomes a 
small enough percentage of the speaking length and resulting 
frequency. The longer strings absorb the difference better, like 
they will in unison tuning.

I need an animation. This would be so much simpler and more obvious 
to watch than to describe.


  • 28.  Seating strings

    Posted 04-15-2005 19:57 
    From "Cy Shuster" <741662027@theshusters.org>

Geez, Ron, if you're going to blue-sky some crazy wild-ass idea, at least 
put together some semblance of a cogent argument, with at least a touch of 
logic and some teeth in it.... :-)  :-)  :-)

--Cy--


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 29.  Seating strings

    Posted 04-15-2005 20:18 
    From Ron Nossaman <rnossaman@cox.net>

> Geez, Ron, if you're going to blue-sky some crazy wild-ass idea, at 
> least put together some semblance of a cogent argument, with at least a 
> touch of logic and some teeth in it.... :-)  :-)  :-)
> 
> --Cy--


Aw heck, I'm going to have to start from scratch...
Whozitz


  • 30.  Seating strings

    Member
    Posted 04-15-2005 12:31 
    From Phillip Ford <fordpiano@earthlink.net>

>Theory.
>
>I agree that it is highly improbable that the string climbs up the pin.
>
>
>However the pin can rise out of the bridge, due to hydraulics. As moisture 
>is absorbed by the bridge, force is applied to the bottom of the pin, 
>moving it upward.

This would seem to argue against bottoming the pin in the hole.  Some 
rebuilders (maybe some builders too, I don't know) drill the holes deep and 
don't drive the pins to the bottom of the hole.  Do you think this would 
prevent this?

>  ...
>If the pin has moved upwards, then this can explain why a light tap will 
>seat the pin and string, and be a partial cure for several years.  The 
>hydraulics with begin to do it's evil work again.
>   New pianos going to a very dry climate will exhibit shrinkage of the 
> bridge, and can show a lot of falseness. Seating the strings by tapping 
> the bridge pins cleans up a lot of the garbage, and lasts for a number of 
> years.
>...
>Regards Roger.

Would tapping the strings down without tapping the pins down not accomplish 
the same thing?

Phil Ford


  • 31.  Seating strings

    Posted 04-15-2005 17:39 
    From Ron Nossaman <rnossaman@cox.net>

>>However the pin can rise out of the bridge, due to hydraulics. As moisture 
>>is absorbed by the bridge, force is applied to the bottom of the pin, 
>>moving it upward.
> 
> 
> This would seem to argue against bottoming the pin in the hole.  Some 
> rebuilders (maybe some builders too, I don't know) drill the holes deep and 
> don't drive the pins to the bottom of the hole.  Do you think this would 
> prevent this?

I drill deeper just to not have to file the tops of the pins, but 
yes. That's another good reason. It's an even better reason not to 
drive pins to seat strings, because the pins will be pushed right 
back up where they were in the next dry cycle. Even with the hole 
deeper than the pin, the bridge will still push the strings up and 
down the pin with humidity cycles. The point of zero relative 
movement between the pin and the bridge tends to be somewhere toward 
the bottom of the cap. Perhaps the glue line has something to do 
with it. I have more tests planned, with epoxied in pins, and some 
with my latest capping material. I want to see what it takes to 
eliminate this curse in rebuilding or manufacture. Yea, I know Del, 
bridge agraffes.



> Would tapping the strings down without tapping the pins down not accomplish 
> the same thing?
> 
> Phil Ford

It would, with fewer complications.


  • 32.  Seating strings

    Member
    Posted 04-15-2005 12:31 
    From Phillip Ford <fordpiano@earthlink.net>

>Hi Phil
>
>...It is simply assumed that the strings force upwards for even a hard 
>blow is not enough to contribute to the string moving upwards on the pin. 
>I dont know myself how much of a yank there is there... but it has to be 
>pretty signifiacant to get the mass that the soundboard is along with the 
>string plane to vibrate in a large enough amplitude to create the volume 
>of sound we hear.  I did do a cute little experiement a while back... put 
>a penny on the string just at the bridge pin and whack the key.
>Dont get in the way of the penny... :)

Hi Ric,

Yes, that is my assumption.  But I don't have any experimental evidence to 
back it up.  The force or the movement may be a lot greater than I imagine.

>Another moment that bothers me which I see no one looking at is the fact 
>that the string is forced into an unatural curve across the bridge surface 
>to begin with. A string pushed up by a flat surface the width of a bridge 
>will not (without bridge pins) lay perfectly flat on that surface. It will 
>tend to bend around the surface being highest in the middle.

Which may be one of the reasons that the cap gets crushed at the notch.
Perhaps the top of the bridge should be curved to accomodate this.

>   The bridge pins force the string to flatten out, creating essentially 
> two fulcrum points where the string contacts the bridge. Which forces are 
> doing what in this regard I dont know... but it would seem to me that 
> since the string wont be comfortable just laying flat as it were.

And if these fulcrum points are actually slightly back from the edge of the 
notch because of the way the pins are holding down the string, then the up 
and down movement of the string would be tending to crush the edge of the 
notch, especially if the string movement really is violent.  Perhaps the 
idea of notching slightly back from the pin is a good one.  I wonder if 
long term this type of notching tends to exhibit less false beat development.

>A third point which relates to the friction by the pins that seems totally 
>over looked is that these also are vibrating in their own fashion.
 
I don't think it's overlooked.  I think this is what Ron, and maybe Roger, are
saying.  Because the string is not firmly down on the bridge at the pin, the pin
is flagpoling, which is causing the false beat, by some mechanism which I don't
think I've seen described.

>For that matter the whole assembly is moving around, components phasing in and 
>out .... all in all a pretty complicated picture.

Agreed.

>
>Seems to me that  carefull observation clearly reveals that strings do 
>indeed somehow climb up these pins.

I also think we may need to clarify what we mean by climbing the pin.  Are 
you talking about the whole string lifting itself off of the bridge cap or 
the portion of the string at the notch not wanting to stay down in the 
groove that tends to form with time?

>   Just how remains perhaps a mystery.
>I sure would like to hear more about Maninnos video tho.... :)
>
>Cheers
>RicB

Me too.  I wonder if he'll have them at the upcoming convention?

Phil Ford


  • 33.  Seating strings

    Registered Piano Technician
    Posted 04-15-2005 19:19 
    From "David Love" <davidlovepianos@comcast.net>

A very thin tipped 2 oz hypo oiler.  Put a very small amount of thin CA
into it so that the application is easier to control.  Apply to the non
string side of the bridge pin and let it wick into the cracks.  Blot the
excess up with a paper towel or a piece of newspaper if needed.  I don't
usually take the strings off. 
 
David Love
davidlovepianos@comcast.net 

    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
                                                        Original Message


  • 34.  Seating strings

    Member
    Posted 04-16-2005 16:36 
    From Phillip Ford <fordpiano@earthlink.net>

>Phil,
>
>I put a spreadsheet together about four years ago, for estimating these 
>friction and force levels. I get somewhat different results. Having no 
>formal engineering education,

Hopefully you spent four years doing something more enjoyable and 
ultimately more lucrative (oh, wait, you went into the piano business - 
well, hopefully you spent four years doing something more enjoyable).

>  I did what I thought looked right and was supportable by what reference 
> material I could find (and understand). It's subject to revision if 
> better information is available, so I have some questions, if I may.

Sheesh.  Someone's actually gonna check my numbers?  Now I'm in trouble.

>..
>>My assumptions:
>>String tension T = 150 lbs.
>>Side bearing angle 8 degrees
>>Down bearing angle 1 degree
>>Bridge pin angle (relative to cap surface) 15 degrees
>>Friction between string and bridge pin is given by static friction formula
>>FR = u N
>>where:
>>u = coefficient of friction between string and bridge pin.  This will 
>>depend on the material of the string and the material of the bridge pin 
>>and on surface finishes of each.  For high polished steel on highly 
>>polished brass it would be on the order of 0.2.  For rusty steel on rusty 
>>steel it might be on the order of 1.0 or more.
>>N = normal force (force perpendicular to bridge pin) exerted by the string
>>The side bearing force is given by SB = T sin (8 deg) = 150 (.139) = 20.9 LB
>>The down bearing force is given by DB = T sin (1 deg) = 150 (.017) = 2.7 LB
>
>The sin function gets less accurate as the angle increases, but yes, close 
>enough.

I'm sure that Ptolemy won't be happy to hear that.  I don't know what you 
mean about the sin function getting less accurate as the angle increases.



>>Each of these forces will have components normal to the bridge pin and 
>>parallel to the bridge pin.
>>FOR THE SIDE BEARING:
>>Normal force N1 = 20.9 cos (15 deg) = 20.2 LB (note that this is towards 
>>or into the bridge pin)
>>Parallel force P1 = 20.9 sin (15 deg) = 5.4 LB (note that this force is 
>>down toward the bridge cap)
>
>This puzzles me. I got 5.4 for the down force all right, but how can the 
>total of 20.2 lb horizontal, and 5.4 lb vertical be more than the 20.9 lb 
>the side bearing angle generates? Is this just an artifact of the 
>inaccuracy of the sin and cos method at these big angles?

The force on the pin is a vector having magnitude 20.9 and direction along 
a line in the horizontal direction (to be more correct, which I'll now 
define as a horizontal line lying in the horizontal plane and perpendicular 
to the string speaking length - and to be more correct, being positive in 
the direction of the bridge pin - none of which is strictly correct, but 
more on that in a moment).  I'm breaking down that vector into mutually 
perpendicular components (by using the sin and cos functions).  The vector 
summation of those components is the square root of the sum of the squares 
[(20.9)^2 = ((20.2)^2 + (5.4)^2)^.5], if that makes sense.  An easier way 
to think of it is that the force 20.9 is the hypotenuse of a right 
triangle, with the components 5.4 and 20.2 being the sides of the 
triangle.  The square of the length of the hypotenuse is the sum of the 
squares of the side lengths.  Clear as mud?  Sorry, I'm not a math teacher, 
so I hope I haven't said something not strictly correct here.  Caveat emptor.

Please note that the 5.4 LB component is not strictly speaking a 'down 
force'.  It is parallel to the bridge pin, but generally in the down 
direction (in other words, towards the bridge cap rather than away from it).

As I mentioned before, defining the side force on the pin as being in the 
horizontal direction and perpendicular to the string speaking length is not 
strictly correct.  The string bends around the pins (because of the side to 
side displacement of the string and also the portion of the string between
the pins is probably not in the same plane as the speaking length).
So the direction of the force will not be quite perpendicular to the
speaking length of the string and will probably not be quite in the
horizontal plane.  But for talking purposes let's call it close enough.



>>FOR THE DOWN BEARING:
>>Normal force N2 = 2.7 sin (15 deg) = 0.7 LB (note that this is away from 
>>the bridge pin and is counteracting the normal force from the side bearing)
>
>This also puzzles me. The downbearing force should have nothing to do with 
>the side bearing forces since it is acting directly on the bridge top and 
>isn't bearing on the pin at all. I don't understand why this is here.

If the string is firm against the cap then you're correct.  The point of my 
little exercise was to show that if the string was in fact above the cap 
that it might not want to slide down.  So I was assuming that the string 
was not against the cap, in which case the down bearing will tend to pull 
the string down (and slightly away from the pin - depending on the pin 
angle.  I think you can see that if the bridge pin angle was very severe 
and the string was up off the bridge that the down bearing would want to 
move the string down away from the bridge pin.  The same thing is happening 
for very small pin angles, it's just that the component of the downbearing 
perpendicular to the pin is very small - as you see here, only 0.7 LB - I 
could have safely ignored it).



>>Parallel force P2 = 2.7 cos (15 deg) = 2.6 LB (note that this is down 
>>toward the bridge and is adding to the parallel force from the side bearing)
>
>Double puzzlement. How can side bearing reduce downbearing force (absent 
>friction),

It doesn't.  The sidebearing and downbearing forces are two independent 
vectors.  I'm doing a vector summation of those forces.  I find it a little 
simpler or clearer to work with the components.  Both of these vectors have 
components perpendicular to the bridge pin and parallel to the bridge 
pin.  In this case the components parallel to the bridge pin are additive 
and the components perpendicular to the bridge pin are not.

>  and again, how can the sum of these two numbers exceed the total 
> downbearing force of 2.7 lb?

The summation talked about above.



>>TOTAL FORCES:
>>N = N1 + N2 = 20.2 - 0.7 = 19.5 LB
>>P = P1 + P2 = 5.4 + 2.6 = 8.0 LB
>>If the force parallel to the pin is higher than the friction generated by 
>>the normal force then the string will want to move down the pin.  If the 
>>friction force is higher than the force parallel to the pin then the 
>>string will want to stay where it is (even if it's above the bridge cap).
>>FRICTION FORCE:
>>This is going to depend on the friction coefficient that you assume:  I 
>>think a reasonable number might be 0.6.  For this assumption friction force is:
>>FR = u N = 0.6 (19.5) = 11.7 LB
>
>I didn't break it out like this, but calculate a static resistance (with 
>your quite reasonable 0.6 coefficient) moving down the pin at 6.7lb, and 
>up the pin at 17.5lb.

I don't understand why you have a different number for moving down the pin 
and moving up the pin?  Static friction is dependent on the normal force 
between the string and bridge pin and the coefficient of friction.  The 
initial force to start an infinitesimal movement of the string should be 
the same whether it moves up the pin or down.

>  By my reckoning, the 2.6lb of downbearing and the 5.4lb down force from 
> the pin slant and side bearing exceeds the static resistance, and the 
> string will seat on the bridge automatically.

Perhaps you can give me a little more detail on how you arrived at your 6.7 
LB static resistance number.

>  I show a break even point of friction against down force at either a 
> 13.25 deg pin angle,

I'll make my unknown angle a.

Total Normal Force on Pin = N = 20.9 cos a - 2.7 sin a
Static friction = FR = uN = 0.6(20.9 cos a - 2.7 sin a)

Total Parallel Force = P = 20.9 sin a + 2.7 cos a

String will move when P = FR, so

0.6(20.9 cos a - 2.7 sin a) = 20.9 sin a + 2.7 cos a

Solving gives a = 23.6 degrees

So, for this scenario you need a fairly steep pin angle for the string to 
want to slide down strictly under static load.

>  or a 0.666 (did you do that intentionally? <G>) friction coefficient.

Guess who made me do it? <G>

>  Enlighten me, please.

Notice that this is incompatible with my calcs, since I assumed a 0.6 
coefficient of friction and showed that the string wouldn't move.  So, if 
we're going to leave the pin angle alone and change the coefficient of 
friction so that the string will move it has to get lower, not higher.

Assuming I'm leaving the 15 degree pin angle alone, then from the numbers 
above, and solving for Coefficient of Friction u:

Friction = FR = uN = u (20.9 cos 15 - 2.7 sin 15) = 19.49 u

Parallel Force from above P = 8.0 LB

String will move when these are equal, so

19.49u = 8.0

u = 0.41

which is a fairly slippery interface.

Happy calculating,

Phil Ford


  • 35.  Seating strings

    Posted 04-17-2005 09:00 
    From Ron Nossaman <rnossaman@cox.net>

> Hopefully you spent four years doing something more enjoyable and 
> ultimately more lucrative (oh, wait, you went into the piano business - 
> well, hopefully you spent four years doing something more enjoyable).

Intermittently, though not necessarily work related.


> Sheesh.  Someone's actually gonna check my numbers?  Now I'm in trouble.

Nope, it's only math challenged me. You're safe.


> I'm sure that Ptolemy won't be happy to hear that.  I don't know what you 
> mean about the sin function getting less accurate as the angle increases.

Something I thought I had figured out about downbearing angles a 
long time ago. I can't find an example of the code anymore, and I 
don't remember exactly what I did - except that it was likely wrong.


> The square of the length of the hypotenuse is the sum of the 
> squares of the side lengths.  Clear as mud?  Sorry, I'm not a math teacher, 
> so I hope I haven't said something not strictly correct here.  Caveat emptor.

Got it. Yes, that does make sense.


> If the string is firm against the cap then you're correct.  The point of my 
> little exercise was to show that if the string was in fact above the cap 
> that it might not want to slide down.  

Ok, got it.


> I don't understand why you have a different number for moving down the pin 
> and moving up the pin?  Static friction is dependent on the normal force 
> between the string and bridge pin and the coefficient of friction.  The 
> initial force to start an infinitesimal movement of the string should be 
> the same whether it moves up the pin or down.

The difference is the downbearing and vector force from the pin 
tilt. Going down, the vector is in your favor. Going up, it is 
resistance. What I was originally looking for with this spreadsheet 
was an indication of the PSI load placed on the bridge cap by the 
expanding cap pushing the string up the pin. I wanted ammunition for 
my cyclic destruction scenario of cap damage. This seating thing was 
an afterthought.


>> By my reckoning, the 2.6lb of downbearing and the 5.4lb down force from 
>>the pin slant and side bearing exceeds the static resistance, and the 
>>string will seat on the bridge automatically.
> 
> 
> Perhaps you can give me a little more detail on how you arrived at your 6.7 
> LB static resistance number.

It's the static resistance less the down force vector. Hmmm. Going 
back to my spreadsheet and untangling and simplifying what I did to 
get there I find I was using the down vector from pin tilt twice. 
That figures. So I'd still have the 6.7lb resistance down with only 
the 2.6 lb downbearing force to overcome it, so in theory, it should 
be possible for a string to remain up on the pins. In practice, I 
don't see any evidence that this happens. I see strings in contact 
with bridge caps with crushed edges, so I'm assuming that string 
movement from play and the continual moisture and temperature 
induced dimensional changes of everything involved are partially 
overcoming the static friction and the down vector force seats the 
string on the bridge. Until reports of feeler gages going under 
strings on bridge caps start poring in, I won't believe it happens. 
The easily observable fact that the notch edges of old bridges, and 
not so old bridges, are crushed at an angle far exceeding any 
downbearing angle the bridge ever supported means that a string 
seated on the bridge top is quite likely not touching the notch 
edge, and can still be measurably forced down there.

Thanks for the clarification on the calcs.

Ron N


  • 36.  Seating strings

    Member
    Posted 04-17-2005 21:47 
    From Phillip Ford <fordpiano@earthlink.net>

>.......
>>I don't understand why you have a different number for moving down 
>>the pin and moving up the pin?  Static friction is dependent on the 
>>normal force between the string and bridge pin and the coefficient 
>>of friction.  The initial force to start an infinitesimal movement 
>>of the string should be the same whether it moves up the pin or 
>>down.
>
>The difference is the downbearing and vector force from the pin 
>tilt. Going down, the vector is in your favor. Going up, it is 
>resistance. What I was originally looking for with this spreadsheet 
>was an indication of the PSI load placed on the bridge cap by the 
>expanding cap pushing the string up the pin. I wanted ammunition for 
>my cyclic destruction scenario of cap damage. This seating thing was 
>an afterthought.

OK.  I think I see what you're saying.  In order to push the string 
up, the bridge cap has to exert enough force on the string to 
overcome the static friction and what I'm calling the Parallel force. 
 From my previous calculations, with the assumptions that I made, the 
static friction was 11.7 LB and Parallel force along the pin from the 
down bearing and side bearing was 8.0 LB.  So the bridge cap has to 
exert 19.7 LB along the bridge pin to move the string up.  Since the 
surface of the cap is presumably moving straight up that means that 
the force it has to exert on the string has to be great enough that 
the component of that force along the bridge pin is 19.7 LB or more. 
So, that means that the force P applied to the string (assuming a 15 
degree pin angle) has to be at least:

P cos 15 = 19.7 LB

P = 20.4 LB

To get some idea of the bearing stress on the cap we'll have to 
assume some bearing area.  This is easier said than done.  In theory 
since the string has a circular cross section it has a line contact 
on the bridge cap, which means that in theory the bearing stress is 
infinite (which also means that it should easily be able to indent 
the bridge cap).  In more practical terms the string and cap will 
indent a little and there will be some realistic bearing area.  I'm 
proposing that we make the width of the bearing area half the 
diameter of a large string, say 0.020 inch, and the effective length 
(the distance back from the notch) .250 inch.  I think that both of 
these numbers are generous.  In reality I think they will both be 
smaller.  But, for now, assume that bearing area is:

A = .25 x .020 = .005 IN ^ 2 (that's square inches in case the 
symbols don't come through)

So, bearing stress = 20.4/.005 = 4080 PSI

My wood handbooks say that compression perpendicular to the grain for 
maple is on the order of 1500 PSI.  So, guess what?

>...I see strings in contact with bridge caps with crushed edges, so 
>I'm assuming that string movement from play and the continual 
>moisture and temperature induced dimensional changes of everything 
>involved are partially overcoming the static friction and the down 
>vector force seats the string on the bridge.

Sounds reasonable.

>  Until reports of feeler gages going under strings on bridge caps 
>start poring in, I won't believe it happens.

I'll try to do my part on that front.

>  The easily observable fact that the notch edges of old bridges, and 
>not so old bridges, are crushed at an angle far exceeding any 
>downbearing angle the bridge ever supported means that a string 
>seated on the bridge top is quite likely not touching the notch 
>edge, and can still be measurably forced down there.

This also sounds reasonable.

Phil F

>
>Thanks for the clarification on the calcs.
>
>Ron N


  • 37.  Seating strings

    Posted 04-17-2005 15:16 
    From Ron Nossaman <rnossaman@cox.net>

Here are a couple of photos, if they're small enough to get by. One 
is an example of the capping material I'm now using, and the other 
is an illustration of how badly, and at how high an angle, a notch 
edge is crushed as a piano ages. We'll see how this works.

Ron N


  • 38.  Seating strings

    Posted 04-17-2005 22:25 
    From Greg Newell <gnewell@ameritech.net>

Excelent notching Ron! Any pics of that machine yet?

Greg



At 05:16 PM 4/17/2005, you wrote:
>Here are a couple of photos, if they're small enough to get by. One is an 
>example of the capping material I'm now using, and the other is an 
>illustration of how badly, and at how high an angle, a notch edge is 
>crushed as a piano ages. We'll see how this works.
>
>Ron N
>
>
>
>
>_______________________________________________
>pianotech list info: http://www.ptg.org/mailman/listinfo/pianotech

Greg Newell
Greg's piano Fort?
mailto:gnewell@ameritech.net


  • 39.  Seating strings

    Member
    Posted 04-17-2005 23:15 
    From Phillip Ford <fordpiano@earthlink.net>

>Here are a couple of photos, if they're small enough to get by. One 
>is an example of the capping material I'm now using,

That's a nice looking bridge Ron.  Are you planning to make this 
capping material available to the rest of us once you have it 
perfected?  And will I be able to notch it with my puny little hand 
chisel?

>  and the other is an illustration of how badly, and at how high an 
>angle, a notch edge is crushed as a piano ages. We'll see how this 
>works.
>
>Ron N

The bridge pin wear seems pretty apparent in these photos as well, or 
is that just my imagination?

Phil F


  • 40.  Seating strings

    Posted 04-18-2005 06:55 
    From Ron Nossaman <rnossaman@cox.net>

> That's a nice looking bridge Ron.  Are you planning to make this capping 
> material available to the rest of us once you have it perfected?  And 
> will I be able to notch it with my puny little hand chisel?

I think Terry might just be standing by with a few gallons of epoxy 
and a big veneer order to do just that. It notches by hand, but it's 
a battle.


  > The bridge pin wear seems pretty apparent in these photos as 
well, or is
> that just my imagination?
> 
> Phil F

Not your imagination. That's real damage.

Ron N


  • 41.  Seating strings

    Member
    Posted 04-18-2005 09:29 
    From Phillip Ford <fordpiano@earthlink.net>

>>That's a nice looking bridge Ron.  Are you planning to make this 
>>capping material available to the rest of us once you have it 
>>perfected?  And will I be able to notch it with my puny little hand 
>>chisel?
>
>I think Terry might just be standing by with a few gallons of epoxy 
>and a big veneer order to do just that. It notches by hand, but it's 
>a battle.

Have you provided details of your notching machine?  If so I somehow missed it.

>
>
>  > The bridge pin wear seems pretty apparent in these photos as well, or is
>>that just my imagination?
>>
>>Phil F
>
>Not your imagination. That's real damage.
>
>Ron N

I still think bridge pins could use some attention.  Something harder 
and with a slippier interface with steel.  Perhaps solid nickel, 
rather than the nickel plated whatever that we have now.  I don't 
know how this would affect the tone or the string wear rate.

Phil F


  • 42.  Seating strings

    Posted 04-18-2005 09:58 
    From J Patrick Draine <draine@comcast.net>

On Apr 18, 2005, at 11:28 AM, Phillip Ford wrote:

>
> I still think bridge pins could use some attention.  Something harder 
> and with a slippier interface with steel.  Perhaps solid nickel, 
> rather than the nickel plated whatever that we have now.

Mason & Hamlin is using stainless steel bridge pins.

Patrick


  • 43.  Seating strings

    Posted 04-18-2005 11:03 
    From Ron Nossaman <rnossaman@cox.net>

> Mason & Hamlin is using stainless steel bridge pins.
> 
> Patrick


Is anyone anywhere selling something like these?

Ron N


  • 44.  Seating strings

    Posted 04-18-2005 13:08 
    From J Patrick Draine <draine@comcast.net>

On Apr 18, 2005, at 1:02 PM, Ron Nossaman wrote:

>> Mason & Hamlin is using stainless steel bridge pins.
>> Patrick
>
> Is anyone anywhere selling something like these?

Well, when Bruce Clark was leading a factory tour for the Boston PTG 
Chapter in November, he said "Sure, we'll be happy to sell these to 
technicians!"
Now I'm sure that doesn't mean that supplying them to technicians would 
be a *priority* but you could give Bruce a call if you're interested.

Patrick


  • 45.  Seating strings

    Posted 04-20-2005 14:51 
    From Greg Newell <gnewell@ameritech.net>

Patrick,
         How does one call Bruce Clark? Do you have a number for him?

Greg Newell



At 03:07 PM 4/18/2005, you wrote:

>On Apr 18, 2005, at 1:02 PM, Ron Nossaman wrote:
>
>>>Mason & Hamlin is using stainless steel bridge pins.
>>>Patrick
>>
>>Is anyone anywhere selling something like these?
>
>Well, when Bruce Clark was leading a factory tour for the Boston PTG 
>Chapter in November, he said "Sure, we'll be happy to sell these to 
>technicians!"
>Now I'm sure that doesn't mean that supplying them to technicians would be 
>a *priority* but you could give Bruce a call if you're interested.
>
>Patrick
>
>_______________________________________________
>pianotech list info: http://www.ptg.org/mailman/listinfo/pianotech

Greg Newell
Greg's piano Fort?
mailto:gnewell@ameritech.net


  • 46.  Seating strings

    Posted 04-20-2005 15:07 
    From J Patrick Draine <draine@comcast.net>

Give him a call at the M&H factory, probably during the morning shift 
(7 AM to 3 PM, I think). (978) 374-8888

Patrick Draine

On Apr 20, 2005, at 4:50 PM, Greg Newell wrote:

> Patrick,
>         How does one call Bruce Clark? Do you have a number for him?
>
> Greg Newell


  • 47.  Seating strings

    Posted 04-20-2005 15:13 
    From Greg Newell <gnewell@ameritech.net>

Thank you Patrick! That's a BIG help!!

Greg


At 05:06 PM 4/20/2005, you wrote:
>Give him a call at the M&H factory, probably during the morning shift (7 
>AM to 3 PM, I think). (978) 374-8888
>
>Patrick Draine
>
>On Apr 20, 2005, at 4:50 PM, Greg Newell wrote:
>
>>Patrick,
>>         How does one call Bruce Clark? Do you have a number for him?
>>
>>Greg Newell
>
>_______________________________________________
>pianotech list info: http://www.ptg.org/mailman/listinfo/pianotech

Greg Newell
Greg's piano Fort?
mailto:gnewell@ameritech.net


  • 48.  Seating strings

    Posted 04-18-2005 10:44 
    From Ron Nossaman <rnossaman@cox.net>

> Have you provided details of your notching machine?  If so I somehow 
> missed it.

Not yet - I'll get there.


> I still think bridge pins could use some attention.  Something harder 
> and with a slippier interface with steel.  Perhaps solid nickel, rather 
> than the nickel plated whatever that we have now.  I don't know how this 
> would affect the tone or the string wear rate.
> 
> Phil F

Better material sure couldn't hurt, but stabilizing (petrifying) the 
cap to minimizing the vertical movement of the string on the pin 
will take care of a fair amount of pin wear. Illustration? Pull pins 
from an old bridge and compare front pins with back pins.
Ron N


  • 49.  Seating strings

    Member
    Posted 04-16-2005 18:11 
    From Phillip Ford <fordpiano@earthlink.net>

>>>However the pin can rise out of the bridge, due to hydraulics. As 
>>>moisture is absorbed by the bridge, force is applied to the bottom of 
>>>the pin, moving it upward.
>>
>>This would seem to argue against bottoming the pin in the hole.  Some 
>>rebuilders (maybe some builders too, I don't know) drill the holes deep 
>>and don't drive the pins to the bottom of the hole.  Do you think this 
>>would prevent this?


Ron N writes:
>I drill deeper just to not have to file the tops of the pins, but yes. 
>That's another good reason. It's an even better reason not to drive pins 
>to seat strings, because the pins will be pushed right back up where they 
>were in the next dry cycle. Even with the hole deeper than the pin, the 
>bridge will still push the strings up and down the pin with humidity cycles.

I thought you were saying in a previous post that the pin was being pushed 
up.  I think you mentioned measuring an 0.011 inch change in height above 
the cap over a humidity cycle.  But here you're saying that the string will 
be pushed up and down the pin by the bridge cap.  Are both happening?

>  The point of zero relative movement between the pin and the bridge tends 
> to be somewhere toward the bottom of the cap.

How did you determine that?

>  Perhaps the glue line has something to do with it.

Maybe so.  Perhaps the drill bit doesn't enlarge the hole in that region as 
much because of the presence of the bond.  I suppose the ideal situation 
would be if the point of zero relative movement between the pin and cap 
were at the cap surface.  I wonder if there's some way you could bond the 
pin to the cap right at this point.

One idea:  I'm not sure how much interference you normally look for between 
hole and pin.  The supply house drills and pins tend to give about 3 - 5 
thousands interference.  For the sake of discussion let's say we're going 
to use 5 thousands of interference.  Suppose you had a bridge pin that was 
not intended to bottom in the hole.  This bridge pin was also turned down 
on its lower end to be 5 thousands smaller diameter than its upper 
end.  The upper end is sized to give 5 thousands of interference to the 
hole.  The pin goes into the hole smaller diameter first.  It would be a 
nominal fit going into the hole until it reached the larger diameter 
portion of the pin, at which point it would be driven a millimeter or two 
further.

>I have more tests planned, with epoxied in pins, and some with my latest 
>capping material.

What is your latest capping material?

This brings up another topic.  I know that Steinway uses a lot of maple in 
their pianos, so it probably has some magical acoustical properties, and 
was specifically chosen to complete the magic circle of sound.  But since 
you're experimenting, perhaps some other materials might be 
interesting.  As far as American woods go, maple is not the hardest 
according to my various wood manuals.  There are several which are harder:

Hickory
Some Oaks (specifically Live Oak)
Locust
Persimmon (of which golf club heads used to be made, back in the old days 
when 'woods' were
      made out of wood)
Osage Orange (which I think may be one of the hardest American woods - I 
would think some of this
      might be found in your section of the country)

A couple of potential problems here.  There are many hickories and oaks, 
some of which are harder than maple and many of which are not.  So, getting 
the right one from your wood merchant might not be easy.

The woods that tend to be very hard also seem not to be very dimensionally 
stable for some reason.  That's a disadvantage versus maple.  But, if you 
put a thin top lamination on a more stable base laminate perhaps it would 
hold together and provide a hard top surface.

Also, there are tropical hardwoods which are probably harder than American 
woods.  Lignum vitae comes to mind.  Ron Overs may know about some 
interesting woods from down under.  Perhaps Tasmanian Devilwood or 
Queensland Kangeroowood or some such would be a lot harder than what we can 
get here and perhaps might be more stable.

Also, I wonder if anyone has tried putting a thin layer of metal on the top 
of the bridge.  Say a 15 or 20 thousandths sheet of steel (or other metal) 
bonded to the top of the bridge.  I would think it would keep the strings 
from indenting the cap and also the pins from enlarging their holes.  Don't 
know how it would affect the magic circle of sound.  Notching might be a 
little tricky.  Think your notching machine might be up to it?  In a 
factory environment I wouldn't think it would be too hard to deal with, but 
it might be more problematic for rebuilders.

>  I want to see what it takes to eliminate this curse in rebuilding or 
> manufacture. Yea, I know Del, bridge agraffes.

I think agraffes or something like them are ultimately where we want to 
go.  But until such time, it seems like time well spent to improve on the 
bridge pin design if possible.  As the numbers we've been throwing around 
show, at least for static loads, the bridge pin angles, side to side offset 
of the string, choice of pin material and pin surface finish all affect the 
string to pin friction.  I don't know how much thought or investigation has 
been put into optimizing this.

Also, there seems to be some thought that the string is trying to describe 
a straight line between some point back behind the notch and the front 
string termination.  If that's the case it seems likely that the further 
toward the pin line the edge of the notch is, the more likely it is to be 
crushed.  We know that moving the notch back from the pin line doesn't 
cause false beats.  This might reduce the crushing of the notch edge.  It 
may, however, slightly reduce support for the pin because more wood is 
taken away, so over time might lead to loose pins and flagpoling.  I'm 
curious as to which notching method remains most beat free over time.

There's also the suggestion that I made to Ric, perhaps curve the top of 
the bridge to describe the path that the string naturally wants to 
take.  This might result in less string grooving at the notch 
edges.  Perhaps this is impractical or provides little return on investment.

Phil Ford




>>Would tapping the strings down without tapping the pins down not 
>>accomplish the same thing?
>>Phil Ford
>
>It would, with fewer complications.


  • 50.  Seating strings

    Posted 04-17-2005 09:37 
    From Ron Nossaman <rnossaman@cox.net>

> I thought you were saying in a previous post that the pin was being pushed 
> up.  I think you mentioned measuring an 0.011 inch change in height above 
> the cap over a humidity cycle.  But here you're saying that the string will 
> be pushed up and down the pin by the bridge cap.  Are both happening?

If the pin is seated in the hole by tapping it down, if the MC of 
the bridge ever gets lower than at the point the pins were tapped 
in, the bottom of the hole will become the point of zero relative 
movement between the bridge and pin, and the shrinking bridge will 
push the pin up. Once the pin is clear of the hole bottom, the point 
of ZRM will be somewhere near the base of the cap.


  >> The point of zero relative movement between the pin and the 
bridge tends
>>to be somewhere toward the bottom of the cap.
> 
> 
> How did you determine that?

By measurement of tested samples. If, for instance, the pin height 
above the bridge changed 0.011" through a 4%-12% MC cycling, the 
bridge root changed 0.021", and the cap changed 0.009", the point of 
ZRM is within a couple of thousandths of the base of the cap. In 
this case it's in the root.


> Maybe so.  Perhaps the drill bit doesn't enlarge the hole in that region as 
> much because of the presence of the bond.  I suppose the ideal situation 
> would be if the point of zero relative movement between the pin and cap 
> were at the cap surface.  I wonder if there's some way you could bond the 
> pin to the cap right at this point.

I doubt it, but the cap could be made much denser and more 
dimensionally stable. Just going to a laminated cap (1.5mm 
laminations) lowered the 0.011" pin height difference to 0.004". An 
even denser cap should be even better.


> One idea:  I'm not sure how much interference you normally look for between 
> hole and pin.  The supply house drills and pins tend to give about 3 - 5 
> thousands interference.  For the sake of discussion let's say we're going 
> to use 5 thousands of interference.  Suppose you had a bridge pin that was 
> not intended to bottom in the hole.  This bridge pin was also turned down 
> on its lower end to be 5 thousands smaller diameter than its upper 
> end.  The upper end is sized to give 5 thousands of interference to the 
> hole.  The pin goes into the hole smaller diameter first.  It would be a 
> nominal fit going into the hole until it reached the larger diameter 
> portion of the pin, at which point it would be driven a millimeter or two 
> further.

I'd just drive the third one I installed upside down and screw up 
the whole process. Given my attention span,  I'd rather keep the 
process simple and try to improve the cap material.


> What is your latest capping material?

It's 8 epoxied laminations of 0.6mm (0.023") maple veneer, with 
another 3mm slab of maple underneath to give me enough depth to 
notch it. It is thoroughly impregnated with epoxy, and amounts to a 
fiber reinforced plastic. I expect that it won't change dimension a 
heck of a lot with humidity changes, that the point of ZRM will be 
very close to the top, and that if there is any change in pin height 
at all with humidity cycles, the cap is far more resistant to 
crushing than anything else I've tried, seen, or heard of. This 
ought to keep a clean termination with minimal wear for a very long 
time. At least that's the intent.


> This brings up another topic.  I know that Steinway uses a lot of maple in 
> their pianos, so it probably has some magical acoustical properties, and 
> was specifically chosen to complete the magic circle of sound.  But since 
> you're experimenting, perhaps some other materials might be 
> interesting.  As far as American woods go, maple is not the hardest 
> according to my various wood manuals.  There are several which are harder:
> 
> Hickory
> Some Oaks (specifically Live Oak)
> Locust
> Persimmon (of which golf club heads used to be made, back in the old days 
> when 'woods' were
>       made out of wood)
> Osage Orange (which I think may be one of the hardest American woods - I 
> would think some of this
>       might be found in your section of the country)
> 
> A couple of potential problems here.  There are many hickories and oaks, 
> some of which are harder than maple and many of which are not.  So, getting 
> the right one from your wood merchant might not be easy.
> 
> The woods that tend to be very hard also seem not to be very dimensionally 
> stable for some reason.  That's a disadvantage versus maple.  But, if you 
> put a thin top lamination on a more stable base laminate perhaps it would 
> hold together and provide a hard top surface.

All of the above is why I'm using this new material.


> I think agraffes or something like them are ultimately where we want to 
> go.  But until such time, it seems like time well spent to improve on the 
> bridge pin design if possible.  As the numbers we've been throwing around 
> show, at least for static loads, the bridge pin angles, side to side offset 
> of the string, choice of pin material and pin surface finish all affect the 
> string to pin friction.  I don't know how much thought or investigation has 
> been put into optimizing this.

Very little, I'd guess. I figure if I can virtually eliminate the 
relative movement between the pin and cap surface, the rest is 
rather a moot point. I'll see what the samples do when I run them 
through the MC range.


> Also, there seems to be some thought that the string is trying to describe 
> a straight line between some point back behind the notch and the front 
> string termination.  If that's the case it seems likely that the further 
> toward the pin line the edge of the notch is, the more likely it is to be 
> crushed.  

Right, but not because the string is trying to describe the straight 
line. The crush isn't a downbearing angle artifact, it's from 
friction at the pin with an expanding bridge cap pushing the string up.


>We know that moving the notch back from the pin line doesn't 
> cause false beats.  This might reduce the crushing of the notch edge.  It 
> may, however, slightly reduce support for the pin because more wood is 
> taken away, so over time might lead to loose pins and flagpoling.  I'm 
> curious as to which notching method remains most beat free over time.

Too many other factors of cap density and environmental differences 
to "pin" it down...  Sorry.


> There's also the suggestion that I made to Ric, perhaps curve the top of 
> the bridge to describe the path that the string naturally wants to 
> take.  This might result in less string grooving at the notch 
> edges.  Perhaps this is impractical or provides little return on investment.
> 
> Phil Ford

It won't, because the downbearing angle isn't what crushes the notch 
edge. Again, with a straightened length of wire and an old bridge, 
determine the tangent angle of that string groove at the notch edge 
and you'll see the downbearing angle had nothing at all to do with 
it beyond the first degree or so.


  • 51.  Seating strings

    Member
    Posted 04-17-2005 23:08 
    From Phillip Ford <fordpiano@earthlink.net>

>>I thought you were saying in a previous post that the pin was being 
>>pushed up.  I think you mentioned measuring an 0.011 inch change in 
>>height above the cap over a humidity cycle.  But here you're saying 
>>that the string will be pushed up and down the pin by the bridge 
>>cap.  Are both happening?
>
>If the pin is seated in the hole by tapping it down, if the MC of 
>the bridge ever gets lower than at the point the pins were tapped 
>in, the bottom of the hole will become the point of zero relative 
>movement between the bridge and pin, and the shrinking bridge will 
>push the pin up.

Or the bridge will move down along the pin.  Semantics.  The result 
will be the same.

>  Once the pin is clear of the hole bottom, the point of ZRM will be 
>somewhere near the base of the cap.
>
>
>  >> The point of zero relative movement between the pin and the bridge tends
>>>to be somewhere toward the bottom of the cap.
>>
>>
>>How did you determine that?
>
>By measurement of tested samples. If, for instance, the pin height 
>above the bridge changed 0.011" through a 4%-12% MC cycling, the 
>bridge root changed 0.021", and the cap changed 0.009", the point of 
>ZRM is within a couple of thousandths of the base of the cap. In 
>this case it's in the root.

Interesting.  I wonder why?  I wonder if it has something to do with 
the different grain angles of the bridge body and cap, so that when 
you run the drill bit down through both, the pin ends up being 
tighter in the cap than the body.

>
>
>>Maybe so.  Perhaps the drill bit doesn't enlarge the hole in that 
>>region as much because of the presence of the bond.  I suppose the 
>>ideal situation would be if the point of zero relative movement 
>>between the pin and cap were at the cap surface.  I wonder if 
>>there's some way you could bond the pin to the cap right at this 
>>point.
>
>I doubt it, but the cap could be made much denser and more 
>dimensionally stable. Just going to a laminated cap (1.5mm 
>laminations) lowered the 0.011" pin height difference to 0.004". An 
>even denser cap should be even better.

Do you think there's a correlation between density and stability?

>
>
>>One idea:  I'm not sure how much interference you normally look for 
>>between hole and pin.  The supply house drills and pins tend to 
>>give about 3 - 5 thousands interference.  For the sake of 
>>discussion let's say we're going to use 5 thousands of 
>>interference.  Suppose you had a bridge pin that was not intended 
>>to bottom in the hole.  This bridge pin was also turned down on its 
>>lower end to be 5 thousands smaller diameter than its upper end. 
>>The upper end is sized to give 5 thousands of interference to the 
>>hole.  The pin goes into the hole smaller diameter first.  It would 
>>be a nominal fit going into the hole until it reached the larger 
>>diameter portion of the pin, at which point it would be driven a 
>>millimeter or two further.
>
>I'd just drive the third one I installed upside down and screw up 
>the whole process. Given my attention span,  I'd rather keep the 
>process simple and try to improve the cap material.

It would be easy enough to mark the bottom end in some way, with a 
different color, etc.  Not a show stopper.

>
>
>>What is your latest capping material?
>
>It's 8 epoxied laminations of 0.6mm (0.023") maple veneer, with 
>another 3mm slab of maple underneath to give me enough depth to 
>notch it. It is thoroughly impregnated with epoxy, and amounts to a 
>fiber reinforced plastic. I expect that it won't change dimension a 
>heck of a lot with humidity changes, that the point of ZRM will be 
>very close to the top, and that if there is any change in pin height 
>at all with humidity cycles, the cap is far more resistant to 
>crushing than anything else I've tried, seen, or heard of. This 
>ought to keep a clean termination with minimal wear for a very long 
>time. At least that's the intent.

It sounds like you're making Permali.

http://www.permalidehoplast.co.uk/

I think somewhere I have a sample of the Hydulignum made by this 
company.  Maybe I could whack a piece off for you to experiment with, 
assuming I have anything that will cut it (which isn't a trivial 
assumption - I think I got this sample when visiting a waterjet 
cutting operation - I think the point of it was something like, we 
can even cut this stuff).

I wouldn't think that maple would absorb the epoxy well since it's not porous.

If you're essentially making a cap out of epoxy, why not make it a 
carbon fiber composite, rather than a wood fiber composite?  It seems 
that it would be stronger and harder.

>
>>I think agraffes or something like them are ultimately where we 
>>want to go.  But until such time, it seems like time well spent to 
>>improve on the bridge pin design if possible.  As the numbers we've 
>>been throwing around show, at least for static loads, the bridge 
>>pin angles, side to side offset of the string, choice of pin 
>>material and pin surface finish all affect the string to pin 
>>friction.  I don't know how much thought or investigation has been 
>>put into optimizing this.
>
>Very little, I'd guess. I figure if I can virtually eliminate the 
>relative movement between the pin and cap surface, the rest is 
>rather a moot point.

I agree, as far as the movement of the string up and down the pin is 
concerned.  There's still the matter of the string rendering at the 
pins.  Some attention to pin material, surface finish, and side 
bearing offset might improve matters in that regard at least.  While 
we're on that subject, I don't know how much of the resistance to 
rendering comes from the string friction on the bridge cap.  I think 
the resistance of the cap to down bearing (and to humidity movement) 
takes place mostly near the bridge pins.  So the area of the cap 
between the pins is really doing nothing but increasing the 
resistance to rendering.  Perhaps the cap should have a relief 
between the pins.

>  I'll see what the samples do when I run them through the MC range.
>
>Also, there seems to be some thought that the string is trying to 
>describe a straight line between some point back behind the notch 
>and the front string termination.  If that's the case it seems 
>likely that the further toward the pin line the edge of the notch 
>is, the more likely it is to be crushed. 
>
>Right, but not because the string is trying to describe the straight 
>line. The crush isn't a downbearing angle artifact, it's from 
>friction at the pin with an expanding bridge cap pushing the string 
>up.

OK.  But the crushing seems to be more severe at the notch edge. 
Because of the path that the string is taking it has a fulcrum point, 
if you will, at the notch edge (which I believe Ric mentioned).  So, 
the bridge is trying to lift the string up at the edges of the two 
notches and they're being crushed.

>
>
>>We know that moving the notch back from the pin line doesn't cause 
>>false beats.  This might reduce the crushing of the notch edge.  It 
>>may, however, slightly reduce support for the pin because more wood 
>>is taken away, so over time might lead to loose pins and 
>>flagpoling.  I'm curious as to which notching method remains most 
>>beat free over time.
>
>Too many other factors of cap density and environmental differences 
>to "pin" it down...  Sorry.

One of the things on the list of things to investigate.

>
>
>>There's also the suggestion that I made to Ric, perhaps curve the 
>>top of the bridge to describe the path that the string naturally 
>>wants to take.  This might result in less string grooving at the 
>>notch edges.  Perhaps this is impractical or provides little return 
>>on investment.
>>
>>Phil Ford
>
>It won't, because the downbearing angle isn't what crushes the notch 
>edge. Again, with a straightened length of wire and an old bridge, 
>determine the tangent angle of that string groove at the notch edge 
>and you'll see the downbearing angle had nothing at all to do with 
>it beyond the first degree or so.

I'm not sure that I agree.  Because of the present geometry, as the 
bridge moves up, it is essentially lifting the string up at two 
points - the notch edges.  If the top of the bridge described the 
curve that the string naturally wanted to take, as the bridge tried 
to lift the string up, it would be lifting it along the entire length 
of contact with the bridge, which would lower the bearing stress 
considerably and perhaps prevent indenting of the cap.

Phil F


  • 52.  Seating strings

    Posted 04-18-2005 06:50 
    From Ron Nossaman <rnossaman@cox.net>

>> ZRM is within a couple of thousandths of the base of the cap. In this 
>> case it's in the root.
> 
> 
> Interesting.  I wonder why?  I wonder if it has something to do with the 
> different grain angles of the bridge body and cap, so that when you run 
> the drill bit down through both, the pin ends up being tighter in the 
> cap than the body.

I'm not sure. I assumed the glue line the pin passed through was a 
factor. I'll have to make up a horizontally laminated root and see 
what happens.


>> I doubt it, but the cap could be made much denser and more 
>> dimensionally stable. Just going to a laminated cap (1.5mm 
>> laminations) lowered the 0.011" pin height difference to 0.004". An 
>> even denser cap should be even better.
> 
> 
> Do you think there's a correlation between density and stability?

Not per se, but I expect these thin laminations saturated with epoxy 
won't be soaking up much moisture, and will be pretty difficult to 
crush.


> It sounds like you're making Permali.
> 
> http://www.permalidehoplast.co.uk/

It does, or a considerably less sophisticated version, at any rate.


> I think somewhere I have a sample of the Hydulignum made by this 
> company.  Maybe I could whack a piece off for you to experiment with, 
> assuming I have anything that will cut it (which isn't a trivial 
> assumption - I think I got this sample when visiting a waterjet cutting 
> operation - I think the point of it was something like, we can even cut 
> this stuff).

Spitfire propeller blades! I'd love a sample if the hacksaw survives.


> I wouldn't think that maple would absorb the epoxy well since it's not 
> porous.

This is 0.6mm sliced veneer. By the time a blade is pushed through a 
saturated flitch to shave it off, there's not much structural 
integrity left cross grain. The epoxy presses clear through the 
stuff in the clamps.


> 
> If you're essentially making a cap out of epoxy, why not make it a 
> carbon fiber composite, rather than a wood fiber composite?  It seems 
> that it would be stronger and harder.

Functionally, there's no reason not to other than notching 
difficulty (and maybe carbon fiber dust). Psychologically, might be 
another problem. The appearance of normalcy carries more weight than 
it probably should. Eventually...


> While we're on 
> that subject, I don't know how much of the resistance to rendering comes 
> from the string friction on the bridge cap.  I think the resistance of 
> the cap to down bearing (and to humidity movement) takes place mostly 
> near the bridge pins.  So the area of the cap between the pins is really 
> doing nothing but increasing the resistance to rendering.  Perhaps the 
> cap should have a relief between the pins.

Given the same friction coefficient between the string and cap for 
all forces, the down vector force alone, 5.4lb for each pin, sort of 
overpowers the 2.7lb from downbearing - and it's at the pin, not in 
the middle. Where does the curved bridge top to take downbearing 
force off of the notch edge fit in here?


  > OK.  But the crushing seems to be more severe at the notch edge. 
Because
> of the path that the string is taking it has a fulcrum point, if you 
> will, at the notch edge (which I believe Ric mentioned).  So, the bridge 
> is trying to lift the string up at the edges of the two notches and 
> they're being crushed.

Look at your own PSI figures and decide how much of the damage is 
done by downbearing and how much by pin friction and bridge 
dimensional changes. Then look at the photo I posted, and tell me 
how a string on that bridge crushed the notch edge at that angle 
from downbearing. I don't believe that piano ever had a 20? front 
bearing angle. In the world of science, how could downbearing alone 
EVER crush a notch edge past the point where the string can touch 
it????? I don't see this as being geometrically possible.


> I'm not sure that I agree.  Because of the present geometry, as the 
> bridge moves up, it is essentially lifting the string up at two points - 
> the notch edges.  If the top of the bridge described the curve that the 
> string naturally wanted to take, as the bridge tried to lift the string 
> up, it would be lifting it along the entire length of contact with the 
> bridge, which would lower the bearing stress considerably and perhaps 
> prevent indenting of the cap.
> 
> Phil F

The friction is still there, and the PSI load is still there. The 
cap would still crush at the edges as the bridge cap expanded, and 
the string would lose contact with the notch edge in dry seasons 
even sooner than with a flat cap.

Ron N


  • 53.  Seating strings

    Member
    Posted 04-18-2005 09:52 
    From Phillip Ford <fordpiano@earthlink.net>

>
>>I think somewhere I have a sample of the Hydulignum made by this 
>>company.  Maybe I could whack a piece off for you to experiment 
>>with, assuming I have anything that will cut it (which isn't a 
>>trivial assumption - I think I got this sample when visiting a 
>>waterjet cutting operation - I think the point of it was something 
>>like, we can even cut this stuff).
>
>Spitfire propeller blades! I'd love a sample if the hacksaw survives.

OK.  I'll give it a shot, assuming I can locate the sample.  If the 
hacksaw doesn't work I'll fire up the laser cutter.

>
>
>>I wouldn't think that maple would absorb the epoxy well since it's 
>>not porous.
>
>This is 0.6mm sliced veneer. By the time a blade is pushed through a 
>saturated flitch to shave it off, there's not much structural 
>integrity left cross grain. The epoxy presses clear through the 
>stuff in the clamps.

I see.

>
>
>>
>>If you're essentially making a cap out of epoxy, why not make it a 
>>carbon fiber composite, rather than a wood fiber composite?  It 
>>seems that it would be stronger and harder.
>
>Functionally, there's no reason not to other than notching 
>difficulty (and maybe carbon fiber dust). Psychologically, might be 
>another problem. The appearance of normalcy carries more weight than 
>it probably should. Eventually...

Yes, I see your point.

>
>
>>While we're on that subject, I don't know how much of the 
>>resistance to rendering comes from the string friction on the 
>>bridge cap.  I think the resistance of the cap to down bearing (and 
>>to humidity movement) takes place mostly near the bridge pins.  So 
>>the area of the cap between the pins is really doing nothing but 
>>increasing the resistance to rendering.  Perhaps the cap should 
>>have a relief between the pins.
>
>Given the same friction coefficient between the string and cap for 
>all forces, the down vector force alone, 5.4lb for each pin, sort of 
>overpowers the 2.7lb from downbearing - and it's at the pin, not in 
>the middle. Where does the curved bridge top to take downbearing 
>force off of the notch edge fit in here?

It wouldn't be helping things in that regard.  You can't have everything.

>
>
>  > OK.  But the crushing seems to be more severe at the notch edge. Because
>>of the path that the string is taking it has a fulcrum point, if 
>>you will, at the notch edge (which I believe Ric mentioned).  So, 
>>the bridge is trying to lift the string up at the edges of the two 
>>notches and they're being crushed.
>
>Look at your own PSI figures and decide how much of the damage is 
>done by downbearing and how much by pin friction and bridge 
>dimensional changes. Then look at the photo I posted, and tell me 
>how a string on that bridge crushed the notch edge at that angle 
>from downbearing. I don't believe that piano ever had a 20? front 
>bearing angle. In the world of science, how could downbearing alone 
>EVER crush a notch edge past the point where the string can touch 
>it????? I don't see this as being geometrically possible.

I agree that downbearing couldn't crush the notch edge past the point 
where the string is making contact with it.  I also agree that the 
damage is (mostly) not being done by downbearing.  It's being done as 
the cap moves up and the string doesn't.  Let's remove the pins and 
the notch.  The bridge is now a square block of wood.  Run a stiff 
string over it so that it's coming off the square block at a 1.5 
degree angle on both sides.  What are you going to see?  The string 
will be contacting the block at the edges and up in the air in 
between.  The bearing stress at those contact points is going to be 
very high.  If you try to lift the block up it will concentrate even 
more load right at the edges of the block.  If you curve the top of 
the block so that the string is coming off tangent to that curve on 
both sides of the block and is in contact over the whole upper 
surface of the block the bearing stress is going to be a lot lower. 
Try to raise it up a little bit and the stress wouldn't go up much. 
This was my thinking.  Now put the pins back in and things get more 
complicated.  The pin is providing a concentrated down force, because 
of the friction, against the string's upward movement.  Even if the 
top of the bridge was curved the string may get crushed down into the 
cap in the vicinity of the pin, as you say.  I'm inclined to think 
that moving the notch back away from the pin might make this crushing 
a little less.

>
>
>>I'm not sure that I agree.  Because of the present geometry, as the 
>>bridge moves up, it is essentially lifting the string up at two 
>>points - the notch edges.  If the top of the bridge described the 
>>curve that the string naturally wanted to take, as the bridge tried 
>>to lift the string up, it would be lifting it along the entire 
>>length of contact with the bridge, which would lower the bearing 
>>stress considerably and perhaps prevent indenting of the cap.
>>
>>Phil F
>
>The friction is still there, and the PSI load is still there. The 
>cap would still crush at the edges as the bridge cap expanded, and 
>the string would lose contact with the notch edge in dry seasons 
>even sooner than with a flat cap.
>
>Ron N

I'll agree with that.

Phil F

>_______________________________________________
>pianotech list info: http://www.ptg.org/mailman/listinfo/pianotech


  • 54.  Seating strings

    Posted 04-18-2005 11:01 
    From Ron Nossaman <rnossaman@cox.net>

>> Spitfire propeller blades! I'd love a sample if the hacksaw survives.
> 
> 
> OK.  I'll give it a shot, assuming I can locate the sample.  If the 
> hacksaw doesn't work I'll fire up the laser cutter.

I'll round you up a sample of my veneer lamination and we can 
exchange prisoners.


> I agree that downbearing couldn't crush the notch edge past the point 
> where the string is making contact with it.  I also agree that the 
> damage is (mostly) not being done by downbearing.  It's being done as 
> the cap moves up and the string doesn't.  Let's remove the pins and the 
> notch.  The bridge is now a square block of wood.  Run a stiff string 
> over it so that it's coming off the square block at a 1.5 degree angle 
> on both sides.  What are you going to see?  The string will be 
> contacting the block at the edges and up in the air in between.  The 
> bearing stress at those contact points is going to be very high. 

But not nearly as high as what the pins produce. Yes, I understand 
the thinking here, but I don't think rounding the bridge top will 
provide a benefit. First: how do you determine the proper curve for 
the tangent? Oops, a bit too deep! Second: how do you practically 
produce this curve in a step notched bridge? Third: By curving the 
top, you have eliminated the "pad" that the cyclic crushing from pin 
friction had before the notch edge is below tangent. I see it 
producing false beats quicker than ever.


  >Even if the top of the bridge was curved the string
> may get crushed down into the cap in the vicinity of the pin, as you 
> say.  

I don't see what would prevent it with a humidity reactive cap.


>I'm inclined to think that moving the notch back away from the pin 
> might make this crushing a little less.

I expect that's right, and if the pin could be kept solid in the cap 
at the top, it would remain a clean termination.

Ron N


  • 55.  Seating strings

    Posted 04-18-2005 08:05 
    From "Cy Shuster" <741662027@theshusters.org>

It's strange that everywhere else in a piano where a string changes 
direction, the acute angle goes over a strip of metal (front bearing bar, 
pressure bar, agraffe/capo, rear duplex)... except the front and back notch 
edges of the bridges.

I guess this is one of the smallest angular deflections... (assuming 
positive downbearing).

--Cy--


  • 56.  Seating strings

    Member
    Posted 04-18-2005 09:18 
    From Phillip Ford <fordpiano@earthlink.net>

>It's strange that everywhere else in a piano where a string changes 
>direction, the acute angle goes over a strip of metal (front bearing 
>bar, pressure bar, agraffe/capo, rear duplex)... except the front 
>and back notch edges of the bridges.
>
>I guess this is one of the smallest angular deflections... (assuming 
>positive downbearing).
>
>--Cy--

Well, I made the suggestion to put a thin sheet of metal on top of 
the bridge.  But I seemed to get no takers on the idea.

Phil Ford


  • 57.  Seating strings

    Posted 04-18-2005 10:38 
    From Ron Nossaman <rnossaman@cox.net>

Phillip Ford wrote:
>> It's strange that everywhere else in a piano where a string changes 
>> direction, the acute angle goes over a strip of metal (front bearing 
>> bar, pressure bar, agraffe/capo, rear duplex)... except the front and 
>> back notch edges of the bridges.
>>
>> I guess this is one of the smallest angular deflections... (assuming 
>> positive downbearing).
>>
>> --Cy--
> 
> 
> Well, I made the suggestion to put a thin sheet of metal on top of the 
> bridge.  But I seemed to get no takers on the idea.
> 
> Phil Ford

I've already got a bridge agraffe design I like a lot better than 
this. I think I'll try my petrified cap for a while first and see if 
it proves to be good enough.

Ron N


  • 58.  Seating strings

    Posted 04-18-2005 13:55 
    From "Calin Tantareanu" <calin.tantareanu@gmx.net>


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 59.  Seating strings

    Posted 04-18-2005 14:12 
    From Ron Nossaman <rnossaman@cox.net>

> Ron,
> 
> What does your bridge agraffe look like?
> 
> Calin Tantareanu


Hey, I can't tell you that! Might want to patent it...
Ron N


  • 60.  Seating strings

    Posted 04-18-2005 17:15 
    From Avery Todd <avery1@houston.rr.com>

Hey, you must have talking to Bernhard! >:-}

Avery

At 03:12 PM 4/18/05, you wrote:
>>Ron,
>>What does your bridge agraffe look like?
>>Calin Tantareanu
>
>
>Hey, I can't tell you that! Might want to patent it...
>Ron N
>_______________________________________________
>pianotech list info: http://www.ptg.org/mailman/listinfo/pianotech


  • 61.  Seating strings

    Posted 04-17-2005 11:08 
    From "Michael Gamble" <michael@gambles.fsnet.co.uk>

Hello List
I thought I would add a little "je ne sais quoi" to the battle. Although I am not a real devotee of John Broadwood they had some very revolutionary designs. And good for them! R&D is a cause worth pursuing - without it Ron Overs would not have developed his rather elegant new grand action design - just to mention one. Broadwoods were very innovative. They developed the "barless" grand, the repetition spring in upright pianos and, the point in question now (under the Collen-Broadwood banner) the fully agraffed strung frame. In this we find brass agraffes throughout, not only at the top end but on the bridge also. I cannot say I like the quality of the tone these pianos produce but I wonder what they were like when new? These brass agraffes are not fitted like the standard model but are attached by a screw through a counter-sunk hole. String spacing is by the holes on one side and string speaking-length is terminated on the rim opposite. I have not heard any false strings on one of these yet.
Regards during a respite from cutting the grass in my Sussex garden
Michael G.(UK)


  • 62.  Seating strings

    Member
    Posted 04-17-2005 23:12 
    From Phillip Ford <fordpiano@earthlink.net>

>Hello List
>I thought I would add a little "je ne sais quoi" to the battle. 
>Although I am not a real devotee of John Broadwood they had some 
>very revolutionary designs. And good for them! R&D is a cause worth 
>pursuing - without it Ron Overs would not have developed his rather 
>elegant new grand action design - just to mention one. Broadwoods 
>were very innovative. They developed the "barless" grand,

I'm a fan of the barless grand concept.  We've talked about that 
before on the list.

>the repetition spring in upright pianos and, the point in question 
>now (under the Collen-Broadwood banner) the fully agraffed strung 
>frame. In this we find brass agraffes throughout, not only at the 
>top end but on the bridge also. I cannot say I like the quality of 
>the tone these pianos produce but I wonder what they were like when 
>new? These brass agraffes are not fitted like the standard model but 
>are attached by a screw through a counter-sunk hole.

I'm having a little trouble picturing this.  Could you provide more 
description?

>String spacing is by the holes on one side and string 
>speaking-length is terminated on the rim opposite.

String speaking length terminated on the rim?  Now you've completely 
lost me.  Any possibility of some pictures?

>  I have not heard any false strings on one of these yet.
>Regards during a respite from cutting the grass in my Sussex garden
>Michael G.(UK)

I just picked the first rose from my tiny San Francisco garden today. 
We're getting a late start as we've had lots of rain and unseasonably 
cold weather.

Phil Ford


  • 63.  Seating strings

    Posted 04-17-2005 18:17 
    From David Ilvedson <ilvey@sbcglobal.net>

This is probably a dumb question, but for some reason your picture reminded of recyled plastic...has anyone tried plastic for a bridge?   Probably it doesn't conduct energy well enough...

David I.








Original message
From: Ron Nossaman
To: Phillip Ford , Pianotech
Received: Sun, 17 Apr 2005 16:16:22 -0500
Subject: Re: Seating strings


Here are a couple of photos, if they're small enough to get by. One
is an example of the capping material I'm now using, and the other
is an illustration of how badly, and at how high an angle, a notch
edge is crushed as a piano ages. We'll see how this works.

Ron N


  • 64.  Seating strings

    Posted 04-17-2005 19:22 
    From Ron Nossaman <rnossaman@cox.net>

> This is probably a dumb question, but for some reason your picture 
> reminded of recyled plastic...has anyone tried plastic for a bridge?   
> Probably it doesn't conduct energy well enough...
> 
> David I.


I think I just did, at least for the cap.
Ron N


  • 65.  Seating strings

    Registered Piano Technician
    Posted 04-17-2005 20:38 
    From "David Love" <davidlovepianos@comcast.net>

Nice notching!  Is that your new machine?

David Love
davidlovepianos@comcast.net 


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 66.  Seating strings

    Posted 04-17-2005 20:58 
    From Ron Nossaman <rnossaman@cox.net>

> Nice notching!  Is that your new machine?
> 
> David Love


It is. I love toys!

Ron N


  • 67.  Seating strings

    Posted 04-18-2005 11:18 
    From David Ilvedson <ilvey@sbcglobal.net>

What at about a capo surface inset at the notch.   Something round like a bridge pin but on it's side...possibly the vertical bridge pin and horizontal pin would buzz

David I.


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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  • 68.  Seating strings

    Registered Piano Technician
    Posted 04-18-2005 13:46 
    From "David Love" <davidlovepianos@comcast.net>

Pianotek is selling nickel plated pins.  

David Love
davidlovepianos@comcast.net 


    
                                                
    
					
                                                    

        
                                                
				
    
                                                
    
                                                    
                                                        
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