Weighing off by balance weight

[Mark Cramer]

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Ed,

thanks for this excellent research.

I've been keeping your post on my screen, in hopes that others better
equipped to discuss this with you would respond, this is such a cool idea!

I hope you will keep us in the loop Ed.

For the meantime, I appreciate you pushing through with the experiment, and
look forward to future discussions when more of our colleagues are on hand.

Mark Cramer,
Brandon University

  -----Original Message-----
  From: caut-bounces@ptg.org [mailto:caut-bounces@ptg.org]On Behalf Of Ed
Sutton
  Sent: Wednesday, June 09, 2004 1:35 PM
  To: Caut@ptg.org
  Subject: Weighing off by balance weight


  Dear List-

  During our discussion of inertia in piano actions a few months ago, Jim
Ellis presented some of his thoughts on the problem, including the
suggestion that weighing off should be done relative to a target balance
weight.

  I liked his thoughts, and intended to try them as soon as I could.
Opportunity came in the form of a small Knabe action in which just about
every design decision was wrong.

  To interpret Jim's idea, I made three pairs of weights, representing
varying amounts of friction with a 37.5 gram balance weight, thus:
25u+25=50d; 22.5u+30=52.5d; 20u+35=55d.  In each weight pair, the first
weight is the upweight, the second added to it produces the associated
downweight.

  I found these weights delightful to work with, as they enable you to
assess the action in terms of relative speeds.  The goal is to produce equal
speeds of and down movement for each pair, but faster as you compare the
25/50 weights with the 22.5/52.5 weights and then the 20/55 weights.

  On this action I made several geometry changes (increased the hammer
weight, shortened the wippen heels, changed the capstan angle and finally
moved the natural capstans forward to equalize the key ratios with the
accidentals).  Observation with the weight pairs made the improvements of
each change very obvious.

  Finally they led me on a fine chase for tiny friction devils.  Seeing the
action move this way makes tiny moments of friction easy to spot.  For
instance, things may move smoothly with the 55 and 52.5 gram pairs, but
there will be a slight delay with the 50 gram downweight.  This could be
just a fuzz between wippens or a rough place on a keypin.

  Although it may seem complex in description, in practice it was a fast and
easy way to work through the weigh off.  Comparing the speed of hammer
movement with two pairs of weights gives very clear information.  The amount
of time spent wondering, subtracting and second-guessing was minimal.

  My hat's off to Jim for this idea.

  Ed Sutton





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