Capstan Relocation

[Bill Ballard]

At 7:42 AM +1000 10/21/00, Overs Pianos wrote:
>At 10:30 PM -0400 19/10/00, Bill Ballard wrote:
>>Agreed. My point however was not quite so concrete. It was just to 
>>say that with .52-3 KRs, his SWs still needed to be pretty good to 
>>avoid high FWs. Already the BWs are in the mild mid-30s. What we 
>>need to know now is what the FWs are that will tell if what is 
>>being balanced @ 35g BW is a serious (or slight mismatch) of SWs 
>>and SBRs, or whether it's a naturally mild-feeling action, ie. well 
>>hung.
>
>>(The acronyms have been introduced earlier in this thread. What, 
>>you weren't paying attention?)
>
>I confess Bill, I must get up to speed with 'acronym speak'. While I 
>understand the forces at work in an action, I've basically worked 
>this stuff through from my own research while designing my own 
>action last year. I realise that much work has been by David 
>Stanwood and others, which has resulted in new definitions and 
>terms. However, I'll promise to widen my piano tech vocab' to 
>include the acronyms ASAP.

I apologize. (Boy, did I learn my lesson.) All terms below are as per 
David Stanwood
SW: Strike Weight, or the weight of the hammer as measured at the far 
end of the hammershank
FW: Front Weight, or how much heavier the front half of the key (with 
its leads) is than the back half (with the capstan and backchecks).
BW: Balance  Weight, or how much heavier the back half of the key is, 
once loaded with the wight of the action parts as they sit on the 
capstan .
SBR: Strike Balance Ratio, or the ratio of a note's Strike Weight as 
inferred at the front of the key, by a series of tares.  This is the 
expression of the action's overall leverage as measure by weight. 


>>Very nice graphic. You're still defining the problem in the linear. 
>>What we're selling to the pianist is not linear but but in the 
>>dimension of mass and weight (more specifically, inertial and 
>>gravitational forces). At what point do you move from adjusting 
>>length to adjusting weight?
>
>I presume you are referring to the relationship between leverage 
>ratios and arc relationships (and the way in which we might approach 
>design solutions for an action in a dynamic sense, as apposed to the 
>static measurements we might make). While these are separate matters 
>which both influence dynamic performance, when designing and action, 
>I would consider the arc relationship as a first consideration, 
>since the overall layout of the action will determine the arc 
>relationships. Nonetheless, leverage ratios must also be factored in 
>to allow the final design to function efficiently with the desired 
>key dip and hammer blow distance.

My point has already been made, and we diverge, respectfully. The 
motion of arcs is the rotational version of distance. You're working 
the problem in the linear dimension. David's New Metrology works it 
in the weight dimension. Certainly you can resize lever arms and 
relocate pivots to arrive at a desired overall leverage ratio, 
coinciding with the proper relationship of axes and contact points. 
But still missing from this view is a direct view of what happens you 
load the weight of a hammer on the payload end of this lever train. 
Certainly,
	Hammer/key ratio = (B/A)*(D/C)*(E/F)
will tell you how much the action leverage will increase the hammer 
weight as encountered at the front of the key. But without a weight 
measure of the existing balance of the key (FW, or how much heavier 
the front of the key than the back), there is no indication of 
whether the above mentioned hammer is too heavy for the given action 
(however neatly its arms and axes have been revised).

The notion that leverage can be expressed just as well by weight 
measurements as linear may be a new one, but it is very attractive to 
me.

>>To my knowledge there's only one shank which will achieve [an 
>>optimal relationship to the line-of-centres] and that's the aeolean 
>>shank of the '20s, in which reducing the knuckle to the one 
>>quadrant of it actually used by the jack, cut the height of the 
>>standard knuckle by 1/2.
>
>I should like to see a jpeg of this action if anybody has one 
>(please send to ron@overspianos.com.au).

I doubt if a mechanical drawing of this action exists. It was found 
typically in 1920's Marshall&Wendells.

Bill Ballard RPT
NH Chapter

"We mustn't underestimate our power of teamwork."
     ...........Bob Davis RPT, pianotech '97