Help with internal threads for 5c collet holder

I am making a 5c collet holder. I am at the point that I want to thread the holder for the collets. One set of instructions say to bore the hole 1.175 and thread 20 tpi to a pitch diameter of 1.205. Another article says to bore the hole 1.191 and thread 20 tpi till collet spins on freely. This is quite a bit difference between the two. Anybody know which is correct?

Reply to
jim n judy
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Come on, you're a machinist, right? Do just a little shop math. Thirty seconds of trigonometry and a few button pushes on a calculator and you will know the minimum bore (for 100% thread depth) and then from there you can figure out how much slop you want. One thing you might think about is the actual thread shape on your collets - are they full sharp, or are they slightly flatted at the crests?


Reply to
Grant Erwin

Measure the od of your collet and subtract .0541, this will give you your hole size .

To find id thread height mutiply lead x .54127 to find od thread height mutiply lead x .61343

A 5c collet has a 1.250 x 20 thread

1/20 = .05 lead .05 x .54127=.02706 .02706 x 2 =.0541 1.250 -.054 =1.196 hole size
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Reply to

Thanks Tim. Your numbers confirm my own. Also thanks for the link to collets - very informative.

Reply to
jim n judy

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