hammer acceleration

[David Love]

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Roger:

It is a Steinway from the 1980's and its a bit of a mess.  Sharps and =
naturals have different key ratios (oops).  The Renner wippens I put on =
have a higher profile which forces the capstans a bit lower, but it =
actually put the cap/heel contact more on the convergence line than it =
was.  I wonder if a longer knuckle radius would result in a faster rate =
of acceleration through the swing arc.   And if it does, would that =
contribute to a feeling of less control because once the static friction =
is broken the key would accelerate more easily, i.e., it might feel like =
the key is flying away from you too fast?  Just a thought.


David Love =20
  ----- Original Message -----=20
  From: jolly roger=20
  To: pianotech@ptg.org=20
  Sent: August 25, 2001 3:19 AM
  Subject: Re: hammer acceleration



  Hi David,
                The Abel shanks are lighter than the Renner, this can =
add to you observations.  Also no graphite depending on the humidity in =
your area, this can be a significant difference re friction.  These are =
the two reasons I prefer the Abel shanks.
  It's been a while since I used Renner shanks, so things may have =
changed.
    I have not noticed any thing amiss with any of Wally's knuckles with =
regards to friction, and I know he is very vigilant with regards to =
dimensions,  alignment and friction.  He gets a lot of feed back, so =
talk to him, he may have some extra ideas.
  Is this a Steinway?  If so the capstan and heel geometry is critical.  =
1mm change can mean a whole lot, so check carefully.
  Just some random thoughts.
  Roger


  At 11:48 AM 8/24/01 -0700, you wrote:=20

    Roger/Newton:

    In this case it is new parts.  Renner wippens, Abel shanks.  Center =
pins are fine everything is lubricated properly and adequately.  I am =
aware of the static friction element but it seems more than that.   I do =
notice that the leather on the Abel shanks is much different than the =
leather on Renner shanks, which I have generally used in the past.  The =
Abel knuckles seem not as smooth and soft as Renner's.  Any comments on =
that? =20

    David Love
        ----- Original Message -----=20
        From: jolly roger=20
        To: pianotech@ptg.org=20
        Sent: August 24, 2001 10:13 AM=20
        Subject: Re: hammer acceleration


        Hi David,=20
                        Are you noticing this on new parts?  Once static =
friction is broken, I have noted that this happens more frequently with =
worn or loose keybushings. e.g.  Changing a prehung set of Yamaha =
shanks, with out rebushing keys. At one time I used to change just the =
hammer sets at the University.  Now I insist on rebushing keys along =
with hammer replacement.  It makes a big difference.=20
        If the friction is high on the knuckle and centre pinning =
friction is very low it can give similar results. To trouble shoot.  =
Remove a hammer and wippen assembly,  and measure the friction of the =
flange C/P's, Holding the flange horizontal, if it drops under it's own =
weight, will give you a quick check, but start measuring and repinning =
if there seems to be problems. This eliminates these as the cause. Next =
examine the capstan, and wippen cloth,  polish the capstan, and if it's =
old capstans steam out the cup, dry iron smooth, and burnish in some =
teflon powder.=20
        FWIW. I have repinned more than one set of flanges on new parts. =
=20
        With friction happening with the right amounts in the right =
places, the key should go down nice and and steady. Many new Korean =
pianos have way too much friction on the knuckles, shrinking the C/P =
bushings has been a common practice to over come friction.  It will mask =
the problem,  and give acceptable DW readings. Change the knuckles, and =
WOW, watch the the friction figures change.=20
        To to look at geometry issues you have to start with the magic =
line, key ratio, etc.=20
        The old adage, "divide and conquer", applies here.  Just =
eliminate one thing at a time.=20
        Regards Roger








        At 09:00 AM 8/24/01 -0700, you wrote:=20
          I notice, when I am doing a weigh-off on a key board, that on =
some actions as the hammer rises the acceleration is relatively slow and =
steady.  Other times, once the hammer starts to rise, the acceleration =
is quite rapid.   What is responsible for that difference?  Friction =
would seem to be the logical answer, but friction where?  I heavily =
lubricate actions before I do a weigh-off.  There seems to be something =
else at work in the geometry/leverage.  Among other things, with the =
rapidly accelerating hammer, it is more difficult to determine the =
measured downweight.  I there any way around that problem? =20


          David Love






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