Is there an easy way to cut pipe threads? (taper threads)

[WobblyHand]

If one was to offset the tail stock and thread wouldn't the threads be at an angle rather than symmetric? So they wouldn't be a good match to a proper female thread, right?

Edit: but if we angled the tool, it might be ok?

 

[verbotenwhisky]

That is correct, but the lead screw cannot be used. So you are estimating your thread spacing by hand. Or use the lead screw and adjust thread depth by hand. Either way will be inconsistent.

Turn between centers with the tailstock offset or a dead-center offset.

 

[verbotenwhisky]

If one was to offset the tail stock and thread wouldn't the threads be at an angle rather than symmetric? So they wouldn't be a good match to a proper female thread, right?

Edit: but if we angled the tool, it might be ok?

Correct, you would need to rotate your tool post, I think one would be hard pressed to get all the angles required correct.

 

[MikeWi]

Oi. TPI, of course! I hang my head in shame.

 

[WobblyHand]

Correct, you would need to rotate your tool post, I think one would be hard pressed to get all the angles required correct.

I know it wouldn't be right the first time... Not so sure about the 5th time. By then, I'd be ready to drink a fifth.

 

[Tony Wells]

Your tailstock offset method would only work with relatively short pieces. At 1:16 the offset would be more than your travel in just a few inches of length, so it would be a non-starter for pieces say, 6" long. Close/allthread nipples maybe but not anything long. And yes, the threading tool would need to be canted to match the taper angle. Thread flank angles are specified against a reference perpendicular to the part axis.

 

[WobblyHand]

So if I'm thinking about this correctly, for NPT, which has a taper of 3/4"/ft = 0.0625"/", the cant angle of the tool is 0.0625 * 180/pi? Or 3.581 degrees? Or is the cant correction 1/2 that, at 1.791 degrees?

NPT threads are short. 1/2" NPT is only ~0.53" long. 1" NPT thread length is about 0.78" long. https://www.engineersedge.com/hardware/taper-pipe-threads.htm

 

[B Mann]

So if I'm thinking about this correctly, for NPT, which has a taper of 3/4"/ft = 0.0625"/", the cant angle of the tool is 0.0625 * 180/pi? Or 3.581 degrees? Or is the cant correction 1/2 that, at 1.791 degrees?

NPT threads are short. 1/2" NPT is only ~0.53" long. 1" NPT thread length is about 0.78" long.

Correct, just under 2 degrees. I always though it was closer to 5... But was just guessing. The exact is posted somewhere above in this thread.

Correct on the thread length, but have to take in consideration the total length of the pipe (or part) that would be mounted between centers.

 

[B Mann]

Strange... This just popped up on a recommended tube video. He was cutting BSP threads with a tool bit like this. The bit looks different than a hand threader die.

 

[Stick-man]

Strange... This just popped up on a recommended tube video. He was cutting BSP threads with a tool bit like this. The bit looks different than a hand threader die.
View attachment 573940

That's like the pic I posted. I will try to attempt this tomorrow if I get time.