Hammer Boring Angle

[Farrell]

Thank you Roger, and thank you all for all the input so far. There are even
a few I have not read yet - will this afternoon - my wife runs her business
on the computer also and I sometimes have limited access to computer. This
excercise has really opened my eyes to upright geometry - now I have a
little idea about what I don't know - I'll figure out the rest of what I
don't know after the fact!

I had not even realized that upright hammer bores are not 90 degrees. I
checked out a 1912 or so Mason & Hamlin in my shop and those are bored at 84
degrees!!! I will be taking my current project action to the client's piano
today with a new sample butt/shank/hammer to double check hammer angle to
string, etc.

Your advice to keep it close to original I'm sure is good. I will keep it as
close as possible, but the new Abel butts (the Renner's also) do have
slightly different dimensions than the originals, so I want to be sure that
all will work out. I will fully regulate the sample note with the new butt
and be sure that blow, hammer angle to string, etc. is all OK.

What fun being on the new end of the process! Something.....er, ahh, many
things new every day!

Terry Farrell

----- Original Message -----
From: "jolly roger" <baldyam@sk.sympatico.ca>
To: <pianotech@ptg.org>
Sent: Tuesday, August 28, 2001 12:05 AM
Subject: Re: Hammer Boring Angle


>
> 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
> >
>