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Threading help

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Is there a formula for figuring out the major diameter of a custom thread? For example: I have a tube that is 1.384 inside diameter and I internal thread it 32 TPI. How do I determine what size to turn the OD of the male part prior to threading it?
 

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You must know the thread form so you should be able to plug the numbers into the standard calculations.
Machinery's Handbook is a handy thing to have laying around ;-)
 
I tried the TM site calculator but its doesnt work out or im doing wrong. I guess if I add the thread depth to the OD it should fit?
 
If you are doing 32 tpi, the thread depth is 0.021 inch. I would start with stock that is 0.042 inch larger than your 1.384 ID.
 
If you haven't already, I would cut the internal thread first and then start with 0.042 oversize and use your tube to check the fit as you get close to the 0.021 thread depth.
 
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