Hello Paul,
> Can someone explain how drilling the hole in the middle on
> the half-round Steinway balance rail block would negate the acceleration
> effect on the hammer? As far as I can tell, having the hole in the
> middle doesn't negate the effect.
I am not sure if I understand your question re. acceleration, but if I do,
here is what I think:
On a regular action with flat bearings (punchings), the pivot point shifts
as the key goes through its stroke. I see that Ron N. already responded
about that. To visualize this, imagine an exaggerated key dip where the key
pivots against the player side of the punching edge when fully depressed
and against the opposite side when up. Indeed, the hole in the key wears
slightly because of that.
There is even a "dirty" trick for changing the key ratio where you
intentionally place a raised step under the punching, a short distance away
from the pin with the intention of forcing the key to pivot about that
point and not where the pin is. This elongates the hole more.
The regular flat felt punching (especially the thick ones) tends to
compress and tilt with the paper punchings as the key moves, so it's not a
really precise fulcrum point either.
In the case of the S&S half round, the contact point is better defined when
the hole is centered on the half round. However, _if_ they really did
intentionally drill the holes off-center, then I can see how the fulcrum point would shift distinctly. Of course, the hole in the key would not be
nice and round after a short while (and that is also the reason why I am
not fond of placing shims on one side of the balance pin underneath flat
punchings).
Vladan
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