repetition/backcheck problem

[Ron Torrella]

On Thu, 20 Aug 1998 A440A@aol.com wrote:

> Ron writes:
> > If you replace
> >the pinblock and the new one it thinner or thicker than the original, you
> >may have changed the string height.  That would throw off the original
> >boring specs.
> 
> Greetings, 
>    Not to mention the entire bearing picture!  
> It is common for the strings to be quite out of parallel witht the keybed,
> especially in the top octave of the grands, as the strings go up from the capo
> bar to the bridge.   	Taking a straight measurement as mentioned above will
> not provide for the hammer to be at 90 degrees to the shank and string at
> contact. Trying to get this relationship as close as possible has led me to
> the following procedure.
>     I find bore distance with  trial hammers marked in various bore distances,
> and checked with a square from the string plane.  The hammers are square to
> the shanks, so the shorter the boring the more acute the angle to a given
> string. 
>  I like for the hammers to be at about 89 degrees. 

You're right....l forgot to mention that.  The 90 degree thing is an
"ideal" number but, more often than not, we're dealing with a moving
target.  Something to add to the mix is the flexibility of the
hammershank....which is more the reason why I tend to aim for a rake angle
of about 89 degrees.

There was a class at Providence that had slo-mo video of an action. Did
anyone happen to attend it? I wonder if it was slow enough to show how
much deflection there is in the shank when the hammer collides with the
string on a very loud blow.

Ron Torrella, RPT
Piano Technician
University of Michigan
School of Music