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?

jim n judy wrote:

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 size
http://www.cox-internet.com/drspiff/...ts/Collets.htm

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......


Thank You. I have "run the numbers" and I also checked my Handbook BUT
the drawings that came with the casting kit say a bore of 1.175 hence
my dilemma. I just wanted to check with others before turning this
piece.