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?

Help with internal threads for 5c collet holder
 

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

Help with internal threads for 5c collet holder
 

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

Help with internal threads for 5c collet holder
 

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.