Gram weighing of parts

[Farrell]

"...with special attention given to key bushing friction control."

What do you recommend for key bushing friction? Minimal/near-zero without inducing slop? Some number of grams friction? What are the advantages to having near-zero and having some amount? Thanks.

Terry Farrell

----- Original Message ----- 
> When one studies piano friction weights (D-U)/2  they find that, with 
> uniform flange frictions, on average the friction weight drops by about 4g 
> from bass to treble.   This of course is due to the fact that hammers are 
> heavier in the bass and push the parts together with more force causing 
> more friction in the bass end.
> 
> Many of us sort friction with high in the bass and low in the treble and 
> this exaggerates this natural tapering of friction even more.  So what 
> you've done is to make friction weight even less tapered than normal by 
> putting the lower friction hammer flanges in the bass.
> 
> One finds that a change of one gram of rotational friction measured at a 
> 32mm radius on the hammer flange a gram will create a difference in the 
> friction weight of about one gram which means a change of 1g in both down 
> and up weight.
> 
> So if your sort yields say one gram rotational in the bass to say 5 grams 
> in the treble then your offsetting the natural decrease of friction bass to 
> treble of 4g with an increase bass to treble of 4g giving a more or less 
> uniform friction weight bass to treble so if the down weights are weighed 
> off to be a uniform level bass to treble the up weights will be uniform as 
> well.
> 
> If, in this case, you sorted with high friction in the bass to low in the 
> treble the up weights in the bass would be much much slower than in the 
> treble, with a uniform down weight.
> 
> If your going to sort by friction I think it makes more sense doing what 
> you've done because it creates a more consistent friction weight bass to 
> treble which in turn creates the possibility to weigh off to a more 
> consistent down weight and up weight bass to treble.  I'm sure that many 
> pianists would notice and like that kind of set up.
> 
> I actually prefer, in the case of shanks, to sort by shank strike weight 
> then working the flange frictions to be as uniform as can be from bass to 
> treble, with special attention given to key bushing friction 
> control.  Friction comes and goes but weight is pretty constant by 
> comparison...
> 
> Whew!
> 
> David Stanwood
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