[CAUT] Tuning Pin Questions - tapered pins

[Kendall Ross Bean]

Fred~
 
Yes, one of the things I have heard is that the threads increase the surface
area of the pin in contact with the sides of the hole in the pinblock.
 
Catherine Bielefeldt, in her "Wonders of the Piano" book, offers that bluing
contributes to the holding power of the pins because the oxidizing process
tends to make them "stickier".
 
In my experience, AMSCO pins, in their last years in business, were some of
the worst as far as tolerances. They would vary as much as .005 -on the same
pin! Plus they were often oval in cross-section. Nippon Denro pins were much
better machined, but still varied as much as .002" (or sometimes .003")
within a set, and .001 to .002" sometimes on a given pin. I hear from my
rebuilding friends that Diamond/Klinke pins have very fine tolerances,
within .001 or less. I think oval pins (in cross-section)  bother me the
most, and would probably be the most problemmatic over the long run.
 
Yes I agree that there are many factors involved in how pins hold and for
how long. And some rebuilders are penny-wise when it comes to buying the
most expensive pins, but pound foolish when it comes to pinblocks, either by
not getting good material, or by drilling it carelessly.
 
On the tapered pins - I have restrung a few pianos built around 1880 to 1900
or so that had tapered pins.
 
The pins, when I finally figured out how to measure them- (they seemed to
have a great variation in tolerance, until I realized they were tapered and
I that had not been consistent in where I measured them along the thread)
-were tapered along the entire length of the thread. An 1890 Hemme and Long
upright had I guess what you could call tapered #1/0 pins: they went from
.276 at the top end of the thread to .259 at the bottom, were blued pins,
and were 2 1/4 inches long. One of the things I decided was that putting a
parallel sided pin in a tapered hole was going to cause problems, it would
probably be super tight at the bottom end of the hole and relatively loose
at the top, and as I was restringing using the existing block, (old dry
wood) I hesitated at the thought of possibly splitting the pinblock out at
the bottom of the hole by driving a new oversize pin that would be okay for
the top of the hole but much too large for the bottom. Ultimately I think
what I did was drill the holes out with a parallel sided bit that just fit
the top of the hole (slightly under .276 - it seems even after extracting
the old pins the holes were still a bit smaller than the pins.) Then I used
new # 2 pins or # 3's, whichever felt the best.
 
Yes, you're right, it probably required a good deal of extra effort and
expense to drill tapered holes at the factory, so this was probably one of
the first operations to be eliminated in a cost-cutting effort. Tapered
holes would have had to have been drilled to exactly the right depth for the
tapered pins to fit properly, and I imagine this was not easy to achieve on
a consistent basis. I think that is one of the reasons I ultimately decided
to convert this piano to parallel sided holes and pins.
 
I wonder where Bosendorfer gets their tapered pins. And what technicians do
when they have to replace a Bosie pinblock? Would they have to get a tapered
bit from Bosendorfer? Or would they just convert to parallel sided holes and
pins?
 
~Kendall Ross Bean
 
PianoFinders
www.pianofinders.com <http://www.pianofinders.com/> 
e-mail: kenbean at pianofinders.com
 
Connecting Pianos and People

  _____  

From: Fred Sturm [mailto:fssturm at unm.edu] 
Sent: Monday, July 07, 2008 7:38 PM
To: College and University Technicians
Subject: Re: [CAUT] Tuning Pin Questions


On Jul 7, 2008, at 2:58 PM, Kendall Ross Bean wrote:



 
I would love to see a discussion by parties hopefully much more
knowledgeable than myself, about why these silly pins are the way they are
today.
 


Hi Kendall, 
I don't know how knowledgeable I am on this subject, but I think the answer
to most of your questions can be probably summarized in two words:
aesthetics and salesmanship. A similar example is key bushing cloth, which
we all "know" should be white inside. Maybe at some point there was a reason
(eg, the dye didn't penetrate during the processing - only when the felt was
of sufficient density), but now they go to some trouble to meet the
expectation. It is starting to change: Steinway now has white key bushing
cloth (very recent - probably EU green regulations or PR, as it initiated in
Hamburg). I think the hype about "bluing" is very similar, and done to try
to sell more pins to gullible technicians. That's my own skeptical opinion,
based on what experience I have. But maybe someone else with more varied
experience can tell us why one kind of bluing is better than another, and
why bluing is better than its absence. 
I think that the real difference in tuning pins (available stock - all being
strong enough to stand the torque of being turned while tuning) is
manufacturing tolerances. Are they round within .001"? Are all the pins in a
set within .001" of one another? If so, you've got a good set. The pinblock
will make much more difference: material? number and direction of plies?
glue? drill bit used? control of drilling speed? to name some of many of the
factors that go into determining if pins hold well and turn well.
Threads are for pin removal. They also add to the surface area, so they
impact the friction with the block. Smooth pins work okay in harpsichords. I
don't know if the extra torque of pianos would change that. But I wouldn't
want to experiment, since I want the pins to be removable. "Reverse thread"
is generally accepted as hogwash salesman claim. It is probably a
side-effect of the method of cutting threads, where some filings are laid
down with a direction. I don't think it actually wears out a block, though I
can see where that opinion would come from. I think the amount of cutting
done in a tuning pin hole would be limited rapidly by being clogged by wood
fiber. In any case, I don't think pianos with such pins have a unique
behavior I can identify, though really one would have to follow a piano
through a period of years to come to a conclusion, and I haven't done that
(not with conscious intent, knowing what I had to begin with and observing
to see what happened over time).
Tapered is, I think, a vestige of times when blocks were solid, and drilling
tolerances not that tight. To work really well, you need tapered drill bits
to drill holes with the same taper as the pin. The experience I have with
tapered pins is in harpsichords. A lot of them, the pins aren't truly
tapered, they are cylindrical to the bottom couple centimeters, then that
lowest portion is tapered pretty acutely. Not a very good design in my
experience. They are often hard to remove, and don't really get much tighter
driving them in further. I have only very limited experience with truly
tapered pins, and I don't know if the holes were drilled tapered. In any
case, I don't the the possible gains outweigh the extra expense.

Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu




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