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Front Weight Tolerances

  • 1.  Front Weight Tolerances

    Registered Piano Technician
    Posted 03-01-2021 17:19
    I have been gravitating toward David Stanwood's concept of a chosen smoothly scaled front weight spec as a design feature.  I have also been paying attention to Nick Gravagne's series in the Journal where he describes the reduction of front weight as a combination of removing key leads, and drilling out lead for subtler adjustments.

    Somewhere I recall seeing a clinician speak about reasonable tolerances when modifying front weight. but I can't find that segment as I go hunting in the resources available to me.  I high degree of precision is possible, but at what point does one experience diminishing returns?  When it comes to front weight, how much variation do you think can be present before it becomes perceptible to a discerning pianist?

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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 2.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-01-2021 17:53
    By way of context, I am reviewing the work I did on a Yamaha C3 just over 7 years ago.  At that time, I chose specs for hammer weight and balance weight with an eye to having front weight land somewhere around 4 grams under Stanwood's front weight ceiling spec as put forth in his manual for the Touch Designer's tool kit.  My final step at that time was to add and subtract key leads to achieve a consistent balance weight.  Today's fresh measurement of front weight produced data with a trend line very close to what I was aiming for, but with a fair amount of scatter.  All but eleven keys fell within 4 grams of Stanwood's front-weight-ceiling-minus-3-grams.  Of the eleven outside of that window, four notes had lower front weight, and seven higher.  The widest variations were found below note 27.

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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 3.  RE: Front Weight Tolerances

    Member
    Posted 03-01-2021 18:44
    2 grams differential has been stated by numerous folks.

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    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
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  • 4.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-01-2021 18:46
    Thanks Jim!

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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 5.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-02-2021 03:23
    I don't think that's quite the right way to ask the question.

    First, a smooth front weight (FW) curve results when there is a smooth strikeweight (SW) curve, the Action Ratio (AR) is exactly the same from note to note, and the balance weight is also uniform.  Any irregularities in the SW curve, AR or a Balance Weight (BW) that is not uniform will result in variations in the FW curve.

    The strikeweight curve can be easily measured and controlled, short of measurement error.  In a weigh off to determine the BW (again assuming no measurement error of the DW and UW), the BW can be uniformly set.  The AR is never exactly uniform note to note due to inevitable execution irregularities in things like capstan line, balance rail pin locations, knuckle hanging, punchings, etc.

    So if you are going to set a smooth FW curve to parallel the SW curve exactly you will always have some irregularities in the BW.  That seems unavoidable.  The decision to be made, then, assuming you create a smooth SW curve, is whether to compromise a smooth FW curve or a uniform BW.  If you decide a uniform BW is important then you will not have a smooth FW curve, it will be a bit bumpy depending on the inconsistency in the AR.  If you decide that a smooth FW curve is important then you will have a non uniform BW.  The degree to which the AR is exactly uniform will determine how much compromise there is.  I generally opt for uniform BW because the effect of slight variations in the FW to inertia is minimal.  Where the perceptions of differences in BW occur I can't say, I don't have any real evidence.

    The most important relationship in setting up an action is the AR to the SW as that determines the inertia, which will always be greater in the bass than in the treble (due to greater hammer mass in the bass).  That relationship also determines the general amount of lead required to balance the action at a given BW.  Excessive FWs, or too many leads, result from a poor relationship between AR and SW.  High inertia in the system, or a heavy feeling action, is not primarily due to too many leads, it's due to the poor AR/SW relationship.  Too few leads, or too low a front weight is also not good as it results in inertia that is too low which can leave the pianist feeling like that can't control the action or can't feel the throw of the hammer.  Low inertia actions that come about as a function of very low ARs also can require excessive key dip as the hammer travel is reduced relative to the key travel the lower you go.  That can also be unpleasant.

    I have found that the simplest indication of whether that relationship between AR and SW is ideal in the Stanwood system is to use the FW maximums as a guide.  Approximately 80-85% of the FW maximum as indicated in the Stanwood system places the action in about the ideal place or, as Fandrich and Rhodes put it, "An action to die for".  Actions are certainly acceptable within a range of that target but I generally try not to go outside of 75% - 90% and generally try and hit that 80-85% target.  In addition I usually aim for that in the middle section(s) of the piano.  If my SW curve, assuming it's a relatively normal range, pushes the FW up a bit in the treble, or down a bit in the bass outside of that ideal range I don't really think it's of much consequence.  Again, the inertia will always be lower in the treble and higher in the bass anyway.  Aside from uniform BW the pianist will react positively to predictable inertia at a reasonable BW, or in the feel of the throw of the hammer.

    So targeting 4 grams under maximum on a note whose front weight max is 20 grams would be exactly 80%.  However, four grams under a note that had a FW maximum of 40 grams would be 90%, and 4 grams under a note whose FW max is 5 grams would be 20%.  So I don't think the 4 gram target makes sense except, perhaps, in the center of the keyboard.

    My preferred method then is to determine the AR/SW relationship that produces in the center of the piano a FW of 80-85% of the Stanwood maximum and I then smooth the SW curve based on the given set.  On most sets the hammer weights vary a total of about 5 grams +/- from bass to treble.  After everything is installed I generally do a weigh off to calculate the BW on each note, address friction anomalies and then set a uniform BW allowing small variations in the FW curve.

    Sometimes, if I find a note that the BW on a given note is too low and would drop the FW too far below the curve that would result from the removal of lead, I might, instead, add back weight to the key--add a lead behind the balance rail.  The logic there is that if the SW curve is smooth and the key is weighing off too low it means that the AR on that note is lower than the other surrounding notes.  That will lower the inertia on that note.  Without altering the SW, the best way to compensate for that (i.e. to add inertia) is to leave the amount of lead in the front of the key in the general realm of the FW curve and add lead to the back of the key to satisfy the BW requirements.  That additional lead will then not only satisfy the BW requirement but add some inertia.  Probably not quite enough as the leads aren't responsible for that much of the inertia, but it will add some.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 6.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-02-2021 18:47
    Well said Mr. Love,
    I set a smooth front weight curve and let the balance weight float as it will, this is a result of procedure.
    After setting a smooth SW curve, I manually set balance weight on sample notes. I then fill in the rest on the scale using the Stanwood jig.
    The scale is very accurate and I prefer working with it. Leading ends up with a very nice pattern look with the trim lead slowly marching across.
    this can only be accomplished if at first you have a smooth SW curve matching correctly set AR, as you said.

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    Fenton Murray, RPT

    Fenton
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  • 7.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-03-2021 16:43
    I did some more analysis of my measurements on this 1969 Yamaha C3, and using Stanwood's protocol for determining strike ratio, and separating out my data for naturals and sharps, I came up with an average strike ratio of 5.4 for the naturals and 5.9 for the sharps.  I further understand that the apparently unavoidable scatter in terms of strike ratios across the keyboard is what keeps us from "having it both ways" in terms of a graduated front weight, and close consistency of balance weight.

    My understanding is that even balance weight is particularly desirable for soft playing, and that evenness of inertia has more relevance at higher dynamic ranges.  It occurred to me yesterday that a higher strike ratio would increase the inertial load for the player, and that elevating the front weight to compensate would further increase that inertial load.  This would seem to argue, from an inertial perspective, for giving preference to a carefully graduated front weight over close-to-perfect evenness of balance weight.

    Is the choice between favoring the balance weight spec versus the front weight spec essentially a choice as to which end of the dynamic range will be optimized in terms of responsiveness?  Is the sacrifice greater in one direction than the other?

    Jon, I'd love to hear you chime in, either here on the list or privately.


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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 8.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-03-2021 20:05

    The added lead to compensate for a high strike weight ratio isn't the main driver of high inertia. It's the mass of the hammer combined with the high ratio that is the problem. A 5.9 SWR calls for a lighter hammer to avoid high levels of inertia.  A 5.4 SWR will perform differently and will accommodate a somewhat heavier hammer.

    Inertia is the main event for touchweight dynamics. The DW associated with any BW setting simply represents the minimum force required to actuate the key. The force required to accelerate the key to its maximum velocity can be some 20 times the force required to simply get the key moving. But what pianists feel is the resistance to acceleration more than the static balance weight, or down weight. Complicating things is that we don't play the key in the same position fore and aft which affects the SWR and thereby the inertia-as well as the BW!


    it's probably not worth laboring over smooth FW versus uniform BW. Various techs do it both ways with perfectly good results. In your case, trying to have a smooth FW with two different SWRs will be impossible, though you can smooth each the sharps and the naturals separately. 


    But the dynamic differences between the naturals and sharps is already there even if the SWRs are the same owing to differences in key length. Of course you can have two different capstan lines: one for the sharps and one for the naturals to correct that if you want to do that.  

    Pick your poison. 



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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 9.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-04-2021 00:06
    Thanks David. I am enjoying your posts.

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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 10.  RE: Front Weight Tolerances

    Posted 03-04-2021 16:14
    Anybody knows what happened to Northwest Specialty Woods of Elma WA. I used to buy soundboard panels from them by dozen every 4-5 years and nobody answered the ph , messages, email. Do you know who took over the company or can supply soundboard panels in reasonable prices? Thanks!

    Alexander Brusilovsky




  • 11.  RE: Front Weight Tolerances

    Registered Piano Technician
    Posted 03-04-2021 21:02
    They closed, sadly. Not sure if anyone bought them. I used to buy all my sitka panels from them.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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