Hammer Boring Angle

[Richard Brekne]

Hi Terry, some pianos (grands too)  use a different angle then 90 degrees. Some
by design...hehe...and some by acident me thinks. Bob Hoff wrote a nice series
in the journal recently that touches on this..tho its more on the lines of
finding the right bore length to fit any given piano configuration. And I think,
if I am not mistaken thats set up for a 90 degree angle...I will have to recheck
that tho.. in anycase it would be good reading.

Your question as I understand it is more a question of action geometry then
anything else. And I suspect you will get a few involved replies in that
direction. Thats good too... cuz we havent really gotten so much into upright
action geometry so much in the recent past.

I look forward to some interesting responses... :)

Farrell wrote:

> Is there ever any good reason to bore a hammer on an upright such that the
> long axis of the hammer & core and the shank form an angle less than 90
> degrees? I'm putting new hammers and butts on an upright and don't want to
> repeat original mfg. errors. I should think the hammer/shank angle should be
> exactly 90 degrees and the boring distance should be like on a grand - just
> a hair longer than where the shank becomes parallel with the strings, just
> to allow for a small amount of hammer wear. Original hammer core/shank angle
> is about 88 degrees.
>
> (Why is there 1/2" of felt on the top half of hammer and about 5/8" on the
> bottom? Did someone file the top only, or can gravity do that much? It makes
> it pretty funny looking because you can see so clearly that the flat surface
> of  the string imprint at the strike point is centered well below the center
> of the hammer core - a good argument for why we file the top AND the bottom
> of hammers!)
>
> Or is it better to not hold to hard and fast rules and rather put new sample
> parts on piano and see if it works better with the small angle?
>
> Close examination of the new Abel butts show that the shank hole is about a
> half-shank-diameter toward the back of the piano from the original location
> when the butt top is horizontal. So is it better to shorten the boring
> length to make the shank parallel with the strings, or might it be better to
> keep the boring length about the same and have the shank never quite get to
> parallel with the strings (and thus exaggerating the present hammer/shank
> angle) - but having the hammer hit the strings when it is perpendicular?
>
> A confusing array of possibilities here. I realize on the upright you likely
> have a bit of geometrical leeway anyway, but even if I don't achieve
> perfection, I want to push myself in that direction as far as is reasonable.
> To do that I need to understand what perfection is (theoretical at least),
> or our best guestimate of perfection.
>
> "It's always something!"
> Terry Farrell

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no