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Dumb watchmaker collets question

Weight Driven

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May 24, 2004
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this will seem like a dumb question but over the weekend I picked up a box of collets and am not sure what size they are, either 7mm or 8mm. When I measure the threads they are about 7mm and when I measure the portion that is not threaded, the solid part, it is 8mm. What would be the correct way to measure a collet? Thanks for any help with this.
 

Scott Erholm

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Mar 28, 2009
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For starters, I do not believe there is such a thing as 7mm collet, certainly not a popular size.

The size is determined by the body, so your collets are 8mm.

There's more to it than that, however. There is also the model style, which is most likely either WW (Webster-Whitcomb) or Moseley. Moseley collets may have a conoidal head (curved) and may be longer (40 mm).

Is the head of your collets angled or curved? And what is the length from the end of the thread to the end of the chuck angle? Is there a make stamped on the body?
 

Weight Driven

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May 24, 2004
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thanks for the reply Montana. The heads are curved. Not sure of the length as have not measured yet. I thought they were 8mm but was not 100% sure.
 

Dave B

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Jun 7, 2008
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Page 58 of The Watchmakers' Lathe, by Ward Goodrich has a table showing complete exterior collet dimensions for 56 different collets to fit various lathes.
 

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