Threading help

[3strucking]

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?

 

[magicniner]

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 ;-)

 

[Chuck K]

http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx

 

[3strucking]

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?

 

[SubtleHustle]

I found a formula that is supposed to be correct...

Major Diameter= Diameter -(.866603/8/TPIx2)

 

[Cobra]

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.

 

[3strucking]

I am going to try that. seems like the simplest way to do a non standard thread.

 

[Cobra]

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.

 

[3strucking]

thanks for the help