Centre pinning question - answered?

[David Boyce]

That seems to make a lot of sense Allen.  One might consider too that the 
repeated use could have a buffing or burnishing effect on the surface of the 
old pins at a microscopic level, such as to make them more "slippy". 
Doubtless there are engineering instruments that can measure friction on the 
surface of a rod of small diameter!  Teflon powder, after all, makes 
surfaces more slippy with a microscopically thin molecular layer not 
measurable by a micrometer.

Best,

David.

"I carefully mic'd just the ends of many of the old pins and found them to 
be a half-thousandth smaller (50.5 rather than 51). So my operating theory 
at this point (until someone convinces me I'm wrong) is that indeed (as my 
shop mate - and also Wim Blees in an earlier post - suggested) the pins 
themselves have worn slightly. At first this seems unlikely; but then again, 
after 70+ years of wear, perhaps it's not surprising that some wear would 
take place due to the friction from the bushing cloth turning hundreds of 
thousands of times? "