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