Hammer Boring Angle

[Mike and Jane Spalding]

Terry,

I started a reply in which I was explaining how a small change in hammer
bore distance can make a big change in how much gravity assists hammer
return, but as I thougth about it I realized that's not true.  Assuming
there is no difference in the size and shape of the hammers, and you adjust
the bore angle to keep the hammer perpendicular to the string, the hammer
bore distance has no effect on the amount of gravity assist, nor on how the
hammer strikes or rebounds from the string.  The most direct way to affect
these important parameters is by altering the distance of the butt flange
center from the string.  It seems to me that the only thing you'd be
changing if you square up the hammers to the shanks is the angular
relationships of the butts to the jack tips, and it's hard to imagine that a
degree or two would make a big difference.  Wear and compaction of the butt
cushions should be a much bigger factor than this.

My take on the theory, anyway.

It will be interesting to hear about someone' actual experience with this.

Mike



----- Original Message -----
From: Farrell <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: Monday, August 27, 2001 6:47 AM
Subject: Hammer Boring Angle


> 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
>
>
>