Pianotech

  • 1.  Yamaha C7 hammer bobble

    Member
    Posted 10-23-2022 16:40

     I am looking for help in getting the hammers on a C7 to check when the piano is played at all volume levels. According to my Little Red School House manual and training the hammers should check high on the backcheck. Many where not doing this and I made some slight adjustments to the backchecks inward to the keys. I also used a checkering file to score the tails and take off glaze down near the tip. Although this improved the checking I am not satisfied and definitely want to improve checking to be consistent and reliable .
    Presently the hammer flange friction is low such as 3.5 to 4 swings, letoff was set in the piano by sound like David Anderson taught. I think the rep springs may need a bit more tension put in them but an wondering if the pinning in the jacks and rep-lever needs to be tighter or looser. I have the opportunity to try various things on the piano since it is close to home and available to me. The church that it is in has not been good at keeping the piano in the shape it should be. More and more some talented and higher level pianists are playing it and require more out of the piano . Any tips, techniques, magic potions are welcome

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    James Kelly
    Owner- Fur Elise Piano Service
    Pawleys Island SC
    (843) 325-4357
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  • 2.  RE: Yamaha C7 hammer bobble

    Registered Piano Technician
    Posted 10-23-2022 17:33
    checking.... There is a difference between the leather not grabbing the hammer tail and the hammer actually bouncing off the back check.  We will assume the repetition lever pinning is no more than 5 grams, and the friction of the spring is properly addressed.  If not, the rep lever will fight the hammer upon its rebound, and compromise checking.   

       no need for rough tails if the back check angle ( perhaps 5º off parallel to the hammer centerline) and tail radius (1/2 the shank length) are correct.  Glazed back check leather should be sanded.   You want springs that cannot be felt in the key, and you want to make sure you have sufficient (.040-50") aftertouch.  You also need to ascertain that the jacks are not jamming against their stop felt when the key is depressed, as that can lock up the repetition lever enough to bounce the shank off of it.  

        Beyond that, your friction at the mortise can come into play, as drag upon rebound will absorb what might be enough hammer rebound speed to keep it from checking. 

    That should be enough to start with. 
    Regards, 



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  • 3.  RE: Yamaha C7 hammer bobble

    Registered Piano Technician
    Posted 10-23-2022 17:56
    James

    Don't just "rough" the tail, make sure it's rounded. Take your sandpaper paddle and round the lower edge of the tail. And, as Ed said, sand the leather of the check, too. 

    Last, while the hammer should check, even if it doesn't, just make sure it doesn't bounce up and hit the string on the rebound. This can be adjusted with the drop screw. Fudge with it a little to allow the hammer to drop a little more. 



    Original Message


  • 4.  RE: Yamaha C7 hammer bobble

    Registered Piano Technician
    Posted 10-23-2022 21:39
    James,

    So far you're getting good advice. I assume you are working with the original hammers? If not, you may have a bore distance or tail arcing problem. I would suggest you examine the end notes. If the end notes perform correctly then you can proceed with the assumption that your situation is a problem with wear. Knuckles may be flat or hammers overly shaped throwing the action geometry out of "whack". One area sometimes overlooked is wippen butt wear. The wippen butt felt may become concave to the point where the action movement goes into "dampening" mode. This is where a given change in key dip travel results in a decreasing rate of wippen/hammer travel. As a last resort you may try bolstering the wippen butt felt. Fortunately, Yamaha incorporates a bi-felt design enabling you to insert a small felt between the two felt pads. I use thin key bushing felt.



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    Roger Gable RPT
    Gable Piano
    Everett WA
    (425) 252-5000
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    Original Message