hammer acceleration

[David Love]

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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
  Subject: Re: hammer acceleration


  Hi David,
                  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.
  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.
  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.
  To to look at geometry issues you have to start with the magic line, =
key ratio, etc.
  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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