tuning pins

[Ron Nossaman]

Willum & list:

>Mr Barlett & Steve
>

>>3. Regarding the pins specially cut with a burr to the thread, so that
>>they will turn easier one way than the other, or something like that: has
>>anyone reason to suspect that they might harm the pinblock, i.e., by
>>abrading it over repeated tunings?
>>
>
>It would harm the pin block if the tunings were far and few between and the
>pins had to be turned a lot each time. In my opinion, pins are not turned
>that much during a "normal" tuning to cause the pin block enough wear to
>cause any problems.
>

Sorry guys, I have to disagree. I will state that the following is entirely
my opinion, based on emperical observation and what I (think I) know about
physics in general and pianos in particular. This, hopefully, will obviate
the need to insert apologetic disclaimers after each observation. Ready?

For years now, sales folk dealing in pianos using rolled (pressed?) thread
tuning pins have kept a cut thread pin around to demo to customers. The demo
consisted of wrapping a bit of cloth around the pin and letting the customer
turn it both ways. It turns easily one way, but not the other because of the
rough threads. The sales pitch consisted of explaining how the resulting
grinding action in the piano would destroy the block after a few tunings.
This is nonsense! The Audobon bird call (so-called) consists of a tapered
metal (pewter, I think) plug in a chunk of maple. The plug is smooth and
chirps when turned in the maple. Sound familiar? That's the same thing a
smooth threaded pin does in a dense pinblock (crack-pop-jump). This is a
high friction coeficient situation where the static friction is considerably
higher than the sliding friction. The pin grips like grim death until you
break it loose, then it slides suddenly like it's on ice, only to lock down
again when the sliding friction overcomes pin torque.  The cut thread pin is
driven in tight, just like the smooth thread pin except, when it's turned
the first time, the threads fill up with dust scraped from the side of the
hole in the block. This will lower the pin torque somewhat by the end of the
first tuning. That's why you drill the hole undersize in the first place,
no? After that initial tuning, the block suffers NO FURTHER DAMAGE from
repeated tunings because the "teeth" are already filled with wood dust which
has NO PLACE TO GO to free the teeth to chew up more wood. The trapped dust
lowers the coeficient of friction between the pin and the block making
static friction closer to sliding friction. With similar static torque
readings between the two types of pins, the sliding torque reading will be
lower on the smooth thread pin. When you torque a tuning pin, the top of the
pin moves in the block before the bottom does. As this movement progresses
down the pin and reaches the bottom, the entire pin is twisted before the
bottom moves in the block. If the sliding resistance is less than the torque
necessary to turn the pin beyond the static resistance, the pin jumps as the
torque is released and the bottom catches up with the top. The cut thread
pin isn't skating a smooth surface in a glazed hole so the sliding friction
more nearly matches the torque in the pin when the bottom breaks loose and
it turns smoothly. There it is, Uncle Ron's theory of tunpinnitus jumpus.

That's how I see it. Comments? (be kind <G>)


 Ron Nossaman