hammer acceleration

[jolly roger]

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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.  
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. 
Regards Roger




At 09:00 AM 8/24/01 -0700, you wrote: 
>
> 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?  
>  
> David Love




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