None. Once upon a time, I though the hole contracted as the piece was
warmed, but only because I am not a materials person and didn't really
visualize what would happen. But, someone explained the shape/size of the
control acts just like the piece of metal taken from the hole. As an
example, the diameter of a dime sized piece expands .004 inches from
temperature A to B, if you measure a dime size hole in a plate of the same
material, the hole diameter will expand .004 inches from temperature A to
B.

It also makes sense from a visualization of molecules. In a solid, the
molecules will be fixed at a specific distance from each other at a
specific temperature. As the temperature increase, the vibrate faster and
the distance between molecules increases. Visualize the molecules as a
single layer of marbles touching each other, then take a bunch of marbles
out so that a hole is formed, i.e, there is a ring of touching marbles
around the hole. As the item gets warmer the marbles push away from each
other and thus the hole gets bigger. The marbles around the hole can't
get closer to each other unless the molecules become colder and they can't
squeeze past each other into the hole because the repelling forces won't
let them.

In short, the material doesn't expand in the path of least resistance, it
expands as a whole from the center. Sorta... Try bending a small tube. It
is harder to bend initially than a solid rod because you have to "crimp"
four walls of material versus just the two outside walls of a bar. In a
pulley, the inside ring cannot shrink into itself so the unit expands
outwards and "stretches" the outer portion of the ring rather than
compressing the molecules of the inner ring.

Sorta...
--


Regards,
Joe Agro, Jr.
http://www.autodrill.com
http://www.multi-drill.com
V8013

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