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Terry,
<p>I am not an engineer, but I consulted one while researching for my patent,
and that's how it was explaiened to me. The problem is that when
you twist or flex the top portion, the bottom portion doesn't twist or
flex as much. If you twist or flex the pin that is 2" in diameter
in the base and .276" in the top portion to the breaking point, it's going
to break at the transition point every time. If your argument were
correct, it would break randomly at any point along the top portion.
Are there any engineers who would care to elaborate? Carl?
<p>Paul
<p>Farrell wrote:
<blockquote TYPE=CITE><style></style>
I'm trying to understand this. Let's
say we have a 0.276 -in. dia. tuning pin that is 2-in. long. Let's
say it has a shear strength of 300 inch-pounds. Meaning of course if you
install the pin in a new Baldwin, put a tuning hammer on it (or a torque
wrench) and try to turn it, when you get to a shear force of 300 inch-pounds,
it will shear into two pieces - leaving one piece in your tuning lever
tip and the other in the block. Now take a similar pin, but make it
6 inches long. Do the same things, and it should shear at 300 inch-pounds
of torque. Length should not matter (you will of course get more twist
with the longer pin before it shears). Now take a 0.286-in.
dia. tuning pin that is 2-in. long. Let's say it has a shear strength of
350 inch-pounds. Do the same things to it and it will shear at a torque
of 350 inch-pounds. Now take a pin with a bottom of 0.286-in. dia.
and a top of 0.276-in. dia. Put it in that same nasty Baldwin block - or
a strong vice - or whatever - just so it doesn't move - at it will shear
at a torque of 300 inch-pounds. Now take a pin with a bottom of 2-in.
dia. and a top of 0.276-in. dia. Put it in that same nasty Baldwin block
- or a strong vice - or whatever - just so it doesn't move - at it will
shear at a torque of 300 inch-pounds. The larger base would act just like
the pinblock with the constant diameter 0.276-in pin in it. They would
both shear at 300 inch-pounds. Or so it would seem to me. Concentrating
shear forces? How does it do that? Terry Farrell <span id=__#Ath#SignaturePos__></span>
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<div style="FONT: 10pt arial">----- Original Message -----</div>
<div
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><b>From:</b>
<a href="mailto:larudee@pacbell.net" title="larudee@pacbell.net">larudee@pacbell.net</a></div>
<div style="FONT: 10pt arial"><b>To:</b> <a href="mailto:pianotech@ptg.org" title="pianotech@ptg.org">pianotech@ptg.org</a></div>
<div style="FONT: 10pt arial"><b>Sent:</b> Sunday, January 27, 2002 11:27
AM</div>
<div style="FONT: 10pt arial"><b>Subject:</b> Re: Tuning Pin Size</div>
Terry,
<p>All of what you mention affects shearing, but the bottom portion also
affects it by concentrating the shear forces at the point where the diameter
changes. In other words, the greater the difference, the more torsion
and flex will end at that point and the less those forces will be distributed
thoughout the pin.
<p>Paul
<p>Farrell wrote:
<blockquote TYPE="CITE"> "The larger the size difference between the
two portions, the greater the risk." Why would that be? I should think
the point at which a pin would shear would depend entirely on the metal
composition (let's assume this is constant), its diameter, and the tightness
of the pin/block fit (torque). As you make any pin size fit tighter in
the block, it will get closer to its shear point. As you make any pin smaller
in diameter, you will move toward a lower shear point. Diameter and torque
- I think that is all. Why would the diameter contrast between the top
and bottom portion affect its shear strength? Is there something about
the machining process? Or do you mean (by the above quote): 'The smaller
the diameter of the top portion of the pin, the greater the risk of shearing'
(because, of course, the smaller diameter pin will have a lower shear strength,
and will shear at a lower pin torque). How would the diameter of the bottom
portion of the pin affect the shear strength? I am assuming that the rebuilder
will drill/ream/whatever the hole to a proper diameter for the diameter
of the pin bottom portion. Terry Farrell <span
id=__#Ath#SignaturePos__></span></blockquote>
</blockquote>
</blockquote>
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