From "David Love" <davidlovepianos@comcast.net>
No, I don't always install vertical hitches. It depends on the backscale
length, the scope of the job, customer attitudes about modifications, other
factors. I have an early model O in the shop getting everything which has
the cast-in aliquots and I will grind those off and install vertical hitches
at least in the capo section. The bass bridge will get redesigned so I
haven't decided whether to put them there yet. It does help in the bass
where the backscale lengths can be quite short (as does a bass float). It
also helps where the plate dips and compromises the bridge, especially in
the treble, allowing you to set a more uniform bridge height and not having
to worry about whatever the plate did while it was cooling. But I don't do
it on every piano or on the entire piano necessarily.
I don't preload the board because I'm doing an RC&S board and using rib
deflection formulas and they seem to come out pretty close.
Last question, yes, I want the bridge height to be at a specific value
determined by my rib deflection calculations and the targeted residual
bearing (and crown). I also like to make the bridge caps the right height
to begin with which is important if you are doing laminated caps since
planning down the bridge is more difficult and you will invariably plane
through some of the laminations and it looks sloppy (if you are using thin
laminations and/or if you like to leave the top of the bridge without black
graphite-which I like to do). Mainly though I just like to make the bridge
cap the right height to begin with because I hate cutting those little
slots, it takes too long and it's too easy to make a mistake. Although,
as I mentioned, I cut them slightly thicker (about 1 mm if I can) and sand
them to the final height.
David Love
www.davidlovepianos.com
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf
Of William Truitt
Sent: Tuesday, January 12, 2010 3:04 PM
To: pianotech@ptg.org
Subject: Re: [pianotech] Rebuilding tips
Thanks David, for sharing this. Should I be assuming that all your
rebuilds, Steinways included, have the vertical hitch pins installed? If so
that would make the following question moot: How close to your predicted
deflections are you coming after the piano is strung? I'm still a neophyte
at this, but I have been loading the board in the belief that loading the
board will be more accurate at achieving the targeted deflection than an
unloaded one. (That's not a claim on my part, I don't yet have enough of a
body of experience on which to make such a claim). I am working with
calculations that are based on loading and driving the board down to a
measured deflection before then measuring and trimming the bridge to set
downbearing. I am curious as to what your experience has been. I am not
using vertical hitch pins but rather the string rests and aliquots that come
with the plate.
Making the bridge cap the right height to begin with - do I take that to
mean that you want the bridge height to be near or at a specific value once
bearing, plate height, etc. have been set?
Will
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf
Of David Love
Sent: Tuesday, January 12, 2010 10:49 AM
To: pianotech@ptg.org
Subject: Re: [pianotech] Rebuilding tips
I started doing it a bit differently a few years back. I created two wedges
marked with incremental thickness indications (1mm, 2mm, 3mm etc) sort of
like what Ron N uses to slide under the stretched string when you test crown
(which I use these for as well). The two wedges (picture attached-sorry for
the poor quality) I use are: the smaller one for the string rest area and
the larger one for the bridge top. I do this procedure, btw, with the
bridge decapped, the bridge screwed to the soundboard and the soundboard
screwed to the rim with the plate height determined and set. I don't
prestress the board. The smaller gauge is used for string rest area and the
thickness point at which the string contacts this is calculated based on
the anticipated deflection and the targeted residual bearing. So if I want
to target say 3 degrees of predeflection bearing then I calculate the string
contact point on the gauge (in millimeters) as .44 x number of degrees x
backscale length (in inches) + the height of the string rest (or height
above the plate of the vertical hitch if there is one). The number .44 mm
comes from sin of 1 degree = .0175" converted to mm). Let's say that number
is 5 mm. I do this, btw, with the bridge decapped and if it's a new board
with the board screwed together and screwed down to the inner rim, the plate
height located. I don't prestress the board. So then stretching the string
from the agraffe or capo to the string rest point behind the bridge I rest
the string on the small gauge at the 5 mm point with the gauge sitting where
the string rest will be. The string is then stretched over the top of the
uncapped bridge and there will be a gap of some distance, of course, over
the bridge. I take the other gauge and slide it under the string on top of
the uncapped bridge until it just touches the string. That gauge, btw, is
made about the width of the bridge pin array-though it doesn't really
matter, it should positioned ideally where the strings would be touching the
bridge. Whatever the thickness of the gauge is at that point is the
thickness of my bridge cap. I do this along the entire bridge every
whatever marking on the bridge top the thickness of the to be made cap.
Then I make the cap to the desired thickness usually with the front edge of
the bridge about 1 mm higher than the back to insure positive front
bearing-this may vary depending on the piano though. Typically I make the
bridge about 1 mm higher than needed and then sand it back to the final
desired height. If you are using laminated bridge caps this allows you to
make the bridge cap the right height to begin with (important) and otherwise
not have to deal with cutting those stupid little slots. Having a plate
float system and/or vertical hitches gives you some wiggle room should you
need to tweak the final settings later.
David Love
www.davidlovepianos.com
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf
Of William Truitt
Sent: Monday, January 11, 2010 9:30 PM
To: pianotech@ptg.org
Subject: Re: [pianotech] Rebuilding tips
Scoop out the bridge under the string line until the string just grazes the
top of the bridge whilst held tight and down onto the particular shim. Done
at 3 locations on the bass bridge and about 9 or 10 on the treble bridge.
Then plane the bridge tops down to those markings.
Will
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf
Of David Love
Sent: Monday, January 11, 2010 11:34 PM
To: pianotech@ptg.org
Subject: Re: [pianotech] Rebuilding tips
What is your "as usual from there"?
David Love
www.davidlovepianos.com
I just reach into the box and get the thickness I want, run the string
through the agraffe and over the bridge, and lower it onto the top of the
shim. Adjust bridge height as usual from there.
Will Truitt