Hammer Boring Angle

[jolly roger]

Hi Terry,
              For max efficiency the hammer needs to strike the string at
90 degrees.  The regulation parameters will help determine blow distance,
Typically 1 3/4" to 1 and 7/8"  range.   Since the flange centre, is
forward of the hammer shank line/ radius when the hammer is in contact with
the string,  some rake is needed to maintain the 90 degrees of string to
molding centre at contact.
Same principal as over and under centering on a grand.
Depending on turning radius, the length of shank and butt above centre,
will determine rake.. eg.   Lots of rake on compressed console actions.  2
to 3 degrees on the average upright.
The bore distance,  combined with blow distance, will determine the
relationship of the butt to the jack.  Too long a bore, you will have to
set the back rail to the rear to obtain blow distance, and you can end up
with problems with the jack returning and getting under the butt

The jack contact point on the butt must be very close to horizontal.   This
is not carved in stone because some actions have considerable toe.  (
bottom of action is mounted in towards the plate.)    
Now this leads into all the goodies associated with the key sticks.   OMG
fudge factors creeping in all over the place.

I have been working on a complete vertical series for the Journal, but have
only completed the first 40 pages.

 Now to cut a long story short duplicate what is there, unless some thing
is obviously wrong.   <G>

Just some random thoughts.

Roger



At 07:47 AM 8/27/01 -0400, you 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
>