Interesting question:
I'm reinstalling a set of new upright hammers on a piano (100
year-old Knabe) which should have had new butts under them. In
measuring the hammer bore specs, the one thing I notice is that the
rake in the top section is 0º (with the rest of the hammer boring
being a standard 5º). I've talked with the technician for whom I'm
doing this, who says that the boring is the supply company's, and
they followed whatever was on the original samples.
New butts and shanks along with however I choose to do the reboring
of the replacement hammers. I can get the hammers to hit their strike
points regardless of the rake. Just a matter of shank length. I'd be
inclined to use the rake in the lower sections. I was remembering
that this morning, at the piano, I was confirming the strike point on
string #88, using the original shank and replacement hammer (at 0º
rake), busted out of the "dead-meat" butt (go ahead, RicB, I dare
you...), that the hammer was striking square to the string, and that
after a little hammer reshaping and then locating strike point #88 it
sounded promising.
That was with the new butt as well (Pratt-Win). The interesting thing
is that when I get an old and new butt side by side with action
centers matching and the top surfaces (with the bore) parallel, the
shank on the new butt leans backwards by 4º. So re-introducing a rake
in the hammer bore added to this extra angle in the butt's bore will
actually swing more the butt's center of gravity closer to above the
center pin.
The 0º rake starts at #72, which is about halfway through the top
section, so if I had to bet, I'd say that it was somebody's accident.
As I said, in inclined (pun intended) to make a constant rake. But if
anyone knows what advantage there might be to a 0º rake in the top
octave, I'd be happy to hear about it.
Bill Ballard RPT
NH Chapter, P.T.G.
"If you are in a dilemma about where to park your car, ask your
hostess. If she is engaged, ask some responsible person who can
indicate a convenient spot"
...........Betty White's Teenage Dance Book (paperback, 1959)
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