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

[Ron Nossaman]

On 11/2/2012 9:04 AM, Terry Farrell wrote:

> So, it appears that I do have to learn the hard way from scratch what
> they need to be to work. And hence, the question.

I understand, and sympathize.



>> The clearance problems should be worst in the bass and low to mid tenor.
>
> Right. But that's not what's happening because the bass are bored so the
> hammers are parallel with the bass strings (no deviation), but in the
> mid tenor, where the strings are more parallel with the shanks, the
> hammer boring makes the hammers not parallel with the strings, but the
> hammer angles deviate toward being more perpendicular to the shanks than
> the string angles.

The bore distance is longer in the low tenor too, which aggravates 
clearance problems. Geometrically (rather than from extensive experience 
with squares), high angles to the shank makes clearance worse, and lower 
angles should help "some". What those numbers ought to be in relation to 
the strings, hammer width across the shoulders, and shanks, I have no idea.


> I agree wholeheartedly with all that. But I still have the basic
> question:  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)?

Sorry, I don't know. I'd have to whittle and try much like you're doing. 
Any chance you have some spare hammers of about the same size to use as 
sacrificial prospecting victims? Or make some faux hammers from some of 
that spruce you have lying around. I'd do that rather than experiment 
with the real hammers, assuming I'd trash at least a few figuring out 
what definitely didn't work.


> I guess I'm looking for a number, if there is any, that would apply to a
> normal piano action (not a square). I know I will have to use that kind
> of information and see how it might apply to my square grand. I know
> that no one is going to give me a number for the square. But maybe my
> most basic question is this: the existing hammers in the tenor are bored
> so the hammers are about 10 degrees toward perpendicular to the shanks
> from parallel with the respective strings. My common sense tells me this
> is WRONG - plain flat wrong. My common sense tells me hammers should be
> parallel with the strings where clearance allows, or angled slightly
> toward parallel with respective strings to improve clearance. I'm hoping
> that some background on how designers choose hammer boring angles in
> normal pianos will help guide me in my quest to make some intelligent
> decisions on my square.

I've noticed that the string angle to the shank is the deciding factor. 
The higher the angle from parallel to the shank, the less possible it 
becomes to have the hammer bored to be parallel to the string and still 
clear adjacent hammers. Checking an Excel file on bore angles of various 
makes, I see up to about 20° in the bass, and about 15° in the treble. 
But that's without beveling the shoulders of the hammers like in the 
squares. That buys a lot more angle deviation, but I don't have a real 
number. I'd prioritize for clearance first, because I'd like it to at 
least sort of work, and "parallelitivity" to the string second.


> Thanks so much for sharing your thoughts.

Sorry they aren't more specific, but after the first one of these things 
I did back when the earth was young and seemed less arbitrary 
(illusionary, I know now), I was reluctant to ever have anything at all 
to do with another one.
Ron N