Broken Tuning Pins

[Carl Root]

Ron Nossaman wrote:

(snip)
> pin parts with a sort of tearing feeling because it's not hard enough steel
> to snap, but rather twists off like a wood screw, or grade 1 bolt that you
> over torque. I'll bet everyone knows *that* feeling well.   

I torqued off a 3/8" bolt within the past year.  . . . . a personal
record.  

> I don't see how it
> is possible for the tip to not contact all four corners of the flats at
> once, unless either the tip, or the flats, aren't uniformly symmetrical. It
> seems to me that you would have to pull on the hammer in a direction
> significantly off the rotational plane to do what you are describing. 

That's right.  That's what happens when the tip sits too high on the pin
and the fit is loose enough to allow contact at an angle.  The amount of
slop (lost motion?) in the tip/pin fit is important.  Most of us use a
#3 tip on a #2 pin in part to minimize the possibility of torquing the
pin before the tip is properly seated, but that also allows for a loose
fit.  Think of telescoping tubing.  In a tight fit, the scenario I'm
describing would not be possible, but if there is a fair amount of play,
you can easily contact the top of one side and the bottom of the other
as one piece approaches the other.  

There's another element that could enter into this . . . slippage.  If
your technique causes the tip to slip up off the pin as you apply
torque, you would get the kind of bending force I've described.

The
> flats on the pin would tend to automatically square the tip up when torque
> is applied, and it would be pretty tough to counteract that tendency. Isn't
> that the reason they are made that way, to maximize the contact area between
> the pin and the tip and minimize the damage to the pin? A tip that is the
> wrong size, poorly made, or badly applied to the pin, will chew up the
> corners of the flats pretty quickly, but it chews up all four sides, or
> corners, at once. In any case, a broken pin happens so seldom that I would
> think it would take a lot of lifetimes of empirical evidence in normal field
> work to make a compelling case for poorly seated tips breaking pins. How
> about all those cheapest and most poorly made of all possible tuning
> hammers, with the, if possible, even more cheaply and poorly made tips, in
> the hands of all the band teachers, newbie tooners, preachers, and random
> hobbyists skulking about under the lids of helpless pianos? From what I've
> seen of the low end hardware out there, it doesn't seem to be possible to
> properly seat some of those tips on any known tuning pin under any
> conceivable set of circumstances. Shouldn't we see more (any) second hand
> tuning pin breaks from their tuning attempts, under the circumstances?

I tuned a piano a year ago last summer with a long #2 tip.  (I was
hundreds of miles from my own tuning kit).  The fit was not what I was
accustomed to, but no pins were broken because I was careful to seat the
tip as far down as possible, although many times th etip did not seem to
bottom out.  I was careful not to allow any slippage as described above,
and the pins were not too tight.  Let's not forget that the latter is
still the most important factor.  The vast majority of pianos out there
do not have sufficiently high torque to allow for the possibility of
broken pins no matter what fit and technique are applied, but not
because of the pin tightness itself.  It's because the tuner does not
have to get to the point where a serious yank on the hammer would be
sufficient to break rather than turn the pin.

> Realistically, I doubt that they replace all those broken pins, leaving no
> visible evidence that they had been there (except for the chewed up pin
> corners) between service by tuners who have never had a pin break. There is
> one particular tuner that I follow occasionally. In every one of the pianos
> I find with his name inside, there are a number of obviously bent tuning
> pins. I don't know if he ever breaks one, but he didn't break the bent ones
> (or they would have been replaced by straight ones), and if a sloppily
> seated tip is contributory to bending pins (the better to break them), then
> it ought to leave plenty of obvious evidence of impending doom before any
> breakage problems become evident.

This raises an interesting question.  What kinds of torque, tip fit, and
technique are required to bend a pin, but still not break it?  I wonder
if there's a correlation between the force vector and the alignment of
the becket hole. 

. . . . . but not enough to lose any sleep over it, though.

Carl