Fw: bore distance: was Re: hammer replacement

[Ron Overs]

Dale, David and Newton,

David wrote:

>It's not just the friction reduction that changes the resisitance as 
>the shank rises.  The function that describes the change in force 
>required as the hammer rises is exponential (y/cos0--don't have the 
>symbol for theta).  So the rate of reduction of resisitance as the 
>hammer goes through it's arc is not constant.  If by raising the 
>shank 2mm a reduction of 4 grams in the force required to get the 
>hammer moving is achieved, the next 2mm will not achieve the same 
>amount.  (I'll have to review my trigonometry to describe it 
>mathmatically.)  Anyway, if you graph out the change in the required 
>force to move the hammer through the stroke, you will see that there 
>is a point (approximately 1/2-2/3 through the stroke) where the 
>change in force for the duration of the stroke becomes nominal. 
>Let's say, for arguments sake, that at that point the force required 
>to further raise the hammer is 40 grams.  If you then move the shank 
>closer to the string at the start (as a result of short-boring or 
>over-centering by 2 mm, then the range of total change in weight 
>becomes 46 - 40 or 6 grams rather than 50 - 40 or 10 grams.  The 
>action is not just lighter, but the stroke should feel more 
>consistent from beginning to end.

Agreed - there's less deviation of force required. Any other views out there?

Ron O.
-- 
Overs Pianos
Sydney Australia
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Web site: http://www.overspianos.com.au
Email:     mailto:ron@overspianos.com.au
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