[pianotech] Design Hammer Bore Angles; was: Simulated Nose Bolt

[Ron Nossaman]

On 11/2/2012 7:30 AM, Terry Farrell wrote:

> To the best of my knowledge, it seems to me that the hammer boring
> for an American square grand piano (or any piano) should result in
> the diameter axis of each hammer either being parallel to its
> respective string(s), or if not parallel, then purposely angling the
> hammer diameter axis a few degrees toward parallel with the hammer
> shank. Is that correct? Should hammers be bored so that there is
> always some appropriate bias toward the hammer diameter axis being
> more parallel with the hammer shank?
>
> That's what I observe on all vertical and modern grand pianos, and
> makes sense for clearance. I believe the same applies to a square
> grand.

Well, I'm not an action designer, but I'm a fair to middlin' mechanic. 
Look at the difference between the angles of the strings to the shanks 
between modern pianos and that square. You have a whole different world 
there, and nothing you do will make it work like a modern piano, or even 
an intelligently designed mechanism. Compare the old hammers with the 
new and see how the angles match. If they do, they aren't mis-bored. If 
they aren't mis-bored, rejoice that you don't have to learn the hard way 
from scratch what they need to be to work.


>
> On the set I have, the bass hammers are close to parallel with their
> respective bass strings, but starting in the low tenor and going up
> the scale, the hammers start to diverge from being parallel with
> their respective strings, but the deviation from parallel with the
> respective strings is toward the diameter axis of the hammer being
> perpendicular to the hammer shank - not parallel with the hammer
> shank. I'm sure you can easily imagine what kind of hammer clearance
> problems that produces.

The clearance problems should be worst in the bass and low to mid tenor. 
Depending on the bore angle, your choice is between only hitting one 
unison with the hammer, or having them clear one another. Theoretically, 
there is a compromise where each is possible, if you squint just right 
and are good with a sharp knife and sanding paddle.

At the absolute very best, the hammers BARELY clear and BARELY miss 
adjacent unisons. Plan on being there for a while. Except for certain 
pathological cases, aversion therapy works!
Ron N