Key Ratio

[Yardbird47@aol.com]

Deniis Johnson rote, 6/20:
<< If the key ratio is so underleveraged that the repositioned capstans will
not sit under the cushions, is there no good alternative to completely
redesigning the frame and moving the balance rail?>>

Dennis, you've probably heard this from a number o fsides by now, but what
Keith McGavern saw is the simplest solution to the problem of poor action
ratio.

Bruce Clark (in his days with Santi Falcone before Falcone Piano Co.) used to
move balance rails and key balance holes to fix poor ratios. (When we say
poor ratios, in general this means high ratios, or as David Stanwood measures
it the Strike/Balance Ratio.) But as Bruce described it, it's a bloody awful
lot of work. Moving the wippen by itself does little: whatever the capstan
moves under the cushion, the knuckle will move on the lever, and in the same
direction.

Moving the capstan is where the correction wants to be made. Interestingly,
we talk about correcting the overall action ratio at the capstan as adjusting
the key ratio, but the major effect of that move is on the wippen's leverage.
Move the cap .95mm in towards the BRail, and that .95mm figures very little
in the proportions of the key lever's arms. In the context of the wippen's
much shorter arms, .95mm has a much bigger effect and here, the leverage is
being reduced (while the key leverage is being increased).

As far as relocating the wippen heel, David Stanwood has done plenty of this,
Chris Robinson as well, and probably many other Ninja-class rebuilders. Just
for fooling around, you can grab your Renner sample box, and put a Steinway
wippen flange on the universal body ('though the screwhole-CP distance will
increase by 0.11" because of the Steinway flange, that's pure vertical and of
no consequence). See if any of the available heels will locate correctly over
the desired cap point. But what is involved once you've found the desired cap
point and can locate it on the wippens, is (as Keith McGavern saw) slicing
off the existing wippen heel with a band saw jig, and if you not too proud
simply regluing it in the correct spot (with its height reduced by the kerf
thickness), or if you *are* too proud, setting up a router table jig to
locate and mill a dado for the selected Renner wippen heel.

Once again, the trade-off in total action ratio is between the weight you can
lift and how far you have to lift it. For a given hammer weight, a lower
Strike/Balance Ratio (essentially the overall action ratio measured by how
mass translates from one end of the action to the other, rather than the
linear measurement of the lever arms involved), will take less energy to move
that payload, but for a given hammer blow (say, 1.75") the key will have to
move farther. David Stanwood is the real wizard here, and once his patent
comes through a bunch more of his ideas will become available.


Bill Ballard RPT  "Never try to teach a pig to sing. It
NH Chapter, PTG        wastes time and  annoys the pig."
          Sign on the wall of a college voice  teacher's studio.