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

[Terry Farrell]

Any piano action designers out there? Hmmmmm?  (Del?)

I'm rebuilding an 1967 Steinway square grand without the benefit of the original hammers. I bought a new set of hammers for it, but the boring done on them appears incorrect. I will be boring a new set.

I'm not sure what the proper term may be, but for clarity and reference purposes I will be using the term "hammer diameter axis". By hammer diameter axis, I am referring to one of three axes of the hammer: strike point to tail (height); thickness (self-explanatory - about 9 mm thick); and diameter (shoulder to shoulder) - so the hammer diameter length will vary from maybe 1-1/2" in the bass to about 1/2" in the high treble. I hope that is clear.

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.

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.

Assuming I am thinking clearly here, what kind of maximum bias toward parallel with shank from parallel with strings is appropriate? I realize you can't go too far because you want the hammer contact point to be close to a line at the apex of the hammer, but how far is too far (assuming the hammer doesn't end up hitting something else)?

Thanks!!!

Terry Farrell