[CAUT] Tuning Pin Questions - The truth about reverse thread pins.

[Kendall Ross Bean]

Cy~
 
Thanks for your kind words, and your observations on tuning pins.
 
Yes I often wondered if the reverse threads weren't just a side-effect of
the way they cut the threads, that some salesman who happened to have a silk
handkerchief discovered by accident. Apparently the ratcheting effect is
quite apparent in silk; more dubious is the effect in laminated maple or
beech.
 
I'm presently unstringing a Yamaha C3 from around 1977 and noticed that
Yamaha used plated pins with plated threads. (i.e.The middle pin in the
picture I enclosed in my initial post on this thread about Tuning Pins).
David Porritt responded to my inquiry (on the pianotech archives) and
revealed that a new set of Genuine Yamaha pins he had gotten within the last
year or so was the same type as I just pulled out of the '77 C3: Plated pins
with plated threads.
 
I decided to do a little experiment. I took the old pins I had pulled from
the '77 C3 I am restringing and tried turning them in a handkerchief. I'm
not sure the handkerchief was silk, as a matter of fact I'm pretty sure it
wasn't, just cotton or linen, but it had very fine threads, just like silk.
Here's what I discovered:
 
The threads on the plated pins I had pulled form the C3, (with the plated
threads) turned just as easily one way or the other in the handkerchief. I
also had a new plated thread pin I had gotten as part of a demo kit from a
piano company. I tried this pin as well. Same result as above. 
 
However~
 
A new Denro pin (Blued) showed the reverse thread effect. It would turn in
the clockwise (winding up, tightening the string) direction, but not the
other. The effect was very pronounced. It literally would not turn in the
reverse direction, but grabbed the handkerchief
 
A new Denro (nickel/blued) pin showed the same effect. It also would turn in
the clockwise direction, but not the other. (In the handkerchief, that is)
 
I decided to try some used pins in the handkerchief, pins I had pulled out
of pianos I was restringing. From what I could tell, pins that had been in a
pinblock and in service for years demonstrated little or none of the
"reverse thread" effect. I then pulled some newer Denro pins out of some
pinblock samples I did a few years ago. (They had been driven in, and turned
several times each way to try and duplicate what I could expect in the way
of torque after driving and chipping and tuning the piano.) They too,
demonstrated little or none of the effect when placed in the handkerchief. I
did notice, however, that rusty pins were much harder to turn in the
handkerchief, either way!
 
Okay, this is all fine for handkerchiefs. But as we all know, tuning pins
are not driven into handkerchiefs.
 
I have some pinblock samples in the shop into which I had driven many test
pins. These are relatively new Denro pins, and relatively new pinblock
material (it hasn't been more than a few years since I did the tests. Since
there is no string under tension on these pins to muck up the readings, I
figured it should be fairly objective. Using a torque wrench on a sample of
the standard garden variety Wisconsin rock maple medium laminate (rotary
cut) pinblock material you can get from Schaff or Pianotek, I noted no
differences in torque in either direction (these were the blued Denro pins.)
This seemed to indicate that the reverse thread effect may work well in
handkerchiefs, but not in rock maple. I also had a chunk of Bolduc quarter
sawn 5 ply pinblock into which I had driven Denro nickel-blued pins. Perhaps
because this material actually presents much more consistent end grain to
the pin, (unlike the somewhat amorphous rotary cut material) I noted a
slight differential in the torque, it was maybe 5 to 10 lbs higher in the
reverse direction (or say maybe 100 inch lbs in the clockwise direction and
105 to 110 in the counterclockwise (on some pins) but I couldn't get it to
consistently do this on all the pins, so I concluded that if there is a
reverse torque effect, it is very slight by the time you get the pins into
the pinblock and have turned them a few times.
 
Someone of course will no doubt have to submit this to much more rigorous
and controlled testing to conclusively be able to say that the reverse
thread claim is just so much marketing hot air, but I am convinced that,
outside of brand new pins with virgin, freshly cut threads pins in
handkerchiefs, there isn't much, if any, substance to it. It seems, as Fred
Sturm stated, there is some byproduct of the thread cutting process where
some fine burrs or projections are created on the surface of the threads
that have some kind of rachet-like or velcro-like bias to it (perhaps like
the hooked or burnished edge on a cabinet scraper), but it also seems the
process of pounding the pin into a hard rock maple block and turning it a
few times removes most, if not all, of this surface condition.
 
Also, if there really were anything to it, why would Yamaha plate the
threads on the pins they use in their pianos, effectively neutralizing any
reverse thread effect? (I have also noticed that pins I removed from a Kawai
grand a few years ago for restringing also had plated threads, -they looked
just like the Yamaha pins.) 
 
~Kendall Ross Bean
 
PianoFinders
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