Threading math question….

[mac1911]

I have made a few threaded parts on my lathe so far. Although I feel like I went the long way.

Watching videos and reading here and there Im not finding what I am looking for

Lets say im threading a 10mm X 1.50 external thread
Major minor dia of

9.968

8.376

With the compound set at 29.5’
How do or should you even be dialing in the minor dia with the compound dial. To cut 1.592 mm thread depth to reach the minor dia? Or .0626
Im very new to machining and all the math involved.

I just feel like I am missing something for that ahha , thats how its done. ?

 

[mmcmdl]

Regardless of what you dial in , you're after the pitch diameter . Thread wire sets are $15 , invest in a set to save all the hassles .

 

[Stephen S]

Regardless of what you dial in , you're after the pitch diameter . Thread wire sets are $15 , invest in a set to save all the hassles .

I agree on the thread wire set investment.
I have a mid late 1960's Clausing lathe. yes 29.5° is correct.
With that being some imports are different. some call out 60° on the compound.
I found this video un YouTube How To Cut Threads On A Lathe. Mabey worth the time to view it.

 

[RJSakowski]

Roughly, the compound travel will be 1/cos(29.5) X thread depth. I say roughly because you also have to take into account the radius of the cutter tip. This is OK for determining how much to advance the compound but you should stop short and either use the thread wires or use a nut for a test fit. Another way is to blue the part before threading and when the remaining blueing is almost gone start to check for fit or use the thread wires. Thread wires can be tricky until you get the hang of them. There are thread micrometers available that make life easier.

Edit: 1/cos(29.5) =1.149

 

[markba633csi]

Many of us just go by the major diameter and test the fit with a nut
I do, anyhow

 

[Stephen S]

Roughly, the compound travel will be 1/cos(29.5) X thread depth. I say roughly because you also have to take into account the radius of the cutter tip. This is OK for determining how much to advance the compound but you should stop short and either use the thread wires or use a nut for a test fit. Another way is to blue the part before threading and when the remaining blueing is almost gone start to check for fit or use the thread wires. Thread wires can be tricky until you get the hang of them. There are thread micrometers available that make life easier.

Agree. I have and use both.
On the thread wires i have foam type material that I put the wires in to hold them on one side. hold the other side with one hand and the other hand to measure across the wires.

 

[Janderso]

I find my thread wires in my chip pan . They are a bit of a PITA
Since I have 7 fingers, I struggle even more than most trying to use thread wires.
Once I learned how to use these thread mics, I find measuring thread depth much easier. This set covers 0-2” diameter and all the popular threads per inch.

This Shars set was not too bad $$$. The 0-1 is only $61.

 

[Janderso]

Agree. I have and use both.
On the thread wires i have foam type material that I put the wires in to hold them on one side. hold the other side with one hand and the other hand to measure across the wires.

Hmm, haven’t tried the foam method.

 

[markba633csi]

I guess you could stick the wires into a piece of foam while you hold the mic?
Fiddley, no matter how you do it

 

[mmcmdl]

Tape 2 wires together for the bottom . Hold them tight to the thread with your mics , slide the top wire in and measure .