Pianotech

  • 1.  Key Return Bounce

    Posted 02-12-2019 18:25
    How much allowable bounce during key return is a "manageable" amount?

    I've attached a video in real time and one in slow motion showing a bit of bounce of the key during its return from a fully depressed soft blow (no backcheck involved).

    This is my first time dealing with this and would like to know if the action needs to be a bit tighter. If it should be tighter how is it accomplished?

    Natural Time
    YouTube remove preview
    Natural Time
    Uploaded by coby jay on 2019-02-12.
    View this on YouTube >


    Slow Mo
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    Slow Mo
    Uploaded by coby jay on 2019-02-12.
    View this on YouTube >


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    Cobrun Sells
    cobrun94@yahoo.com
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  • 2.  RE: Key Return Bounce

    Registered Piano Technician
    Posted 02-13-2019 08:33
    Have you specifically compared this "bounce" with other pianos and deem it out of the ordinary?  Also, is it bothering the player in some way?  I'm not sure it's beyond normal.  But I could be wrong.

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
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  • 3.  RE: Key Return Bounce

    Member
    Posted 02-13-2019 09:56
    Seems that would be an upweight problem from too heavy a hammer





  • 4.  RE: Key Return Bounce

    Registered Piano Technician
    Posted 02-13-2019 10:11
    ..and/or too little friction at key pin contact points (front-rail and balance-rail key pin bushings, and especially the balance pin hole) as well as hammer flange and wippen flange pinning.

    Alan

    P. S. Also curious about how your slow-motion video of this key compares with one that does not seem, to the naked eye, to be bouncing too much. The key stop rail (AKA shipping rail) is properly adjusted?

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    Alan Eder, RPT
    Herb Alpert School of Music
    California Institute of the Arts
    Valencia, CA
    661.904.6483
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  • 5.  RE: Key Return Bounce

    Registered Piano Technician
    Posted 02-13-2019 10:48
    Hey Cobrun,

    Difficult to observe this video and experience exactly what you're experiencing as a problem which may be DW/UW related, but I'll try to break down what I'm able to observe from the slow motion video.

     in the slow motion version there are three distinct events. some tiny bounces, then a big bounce and then some more tiny bounces.

    the first two or three tiny bounces occur after the rep lever spring pushes the whippen down away from the knuckle which in turn pushes the key back up. The tiny bounces that occur could potentially indicate that the balance hole on the key is too loose. This must be confirmed before taking any action 

    then there is a big bounce which occurs when the gravity pulling the hammer down finally catches up with the whippen that was catapulted downward. This bounce is normal. 

    the tiny bounces after that could again indicate a balance hole that is too loose or hammer pinning that is too loose. This is all based on observations far removed from your experience so you must take a closer look before accepting what I said to be the case.


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    Daniel DeBiasio
    Brooklyn, NY
    646.801.8863
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  • 6.  RE: Key Return Bounce

    Registered Piano Technician
    Posted 02-13-2019 10:59
    What you are observing is the oscillation rate of the action. Like any mechanical system in a one g environment there will be a natural period of movement to the mechanism. As Daniel explained when the rep spring is applying its' influence the period is faster. And then when the jack has reset the period slows to that of the inertia of the whole.

    The largest variables are the inertia of the hammer and the leverage at the hammer shank, (Knuckle position). More leverage there, and less hammer inertia, and the oscillation period of the action increases dramatically.

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    Edward McMorrow
    Edmonds WA
    425-299-3431
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