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Cutting NPT on a lathe

IronSkull

Plastic
Joined
Dec 6, 2011
Location
Dearborn, MI
Is is possible to cut a 2" pipe thread with a manual lathe with taper attachment? This particular thread it on a casting and the thread needs to end tight into a shoulder. Cant get close enough with a die.
 
A taper attachment is the only easy way on a lathe that i can think of. moving the tailstock over might work but the threading tool needs to be square to the shalf of pipe, not the taper where the threads are cut . if that makes any sense.
 
I have a big axleson lathe that will do 11 1/2 per in. And I understand the set up. Just like cutting straight thread, set the tool 90 to the work, and the cut follows 3/4 over a foot taper. Thats all I needed to know. Thanks
 
60deg single point tool still set up as if cutting a straight thread? 90deg to axis of work and 30deg on compound?

Yes - only set the compound to 29deg, IME it gives a better finish on threads.

If I was working up close to a shoulder or other obstruction I'd reverse the spindle, invert the tool and cut away from danger;)

It works for me on a TA.

FWIW - If it needs to seal ''right'' as in not overun and foul the shoulder etc etc, either get a gauge (warning big $$) or a sample of what has to screw on to it.
 
No prob. do it all the time. Presume you have 11 1/2 tpi on your qcgb. Hope you have a telescoping type taper attachment otherwise you will be feeding thread depth with the compound. Make sure you snug up the gibs, the backlash in the cross slide screw will allow the pressure on the tool to push the cross slide back that amount. Other than that, a piece of cake. Peter
 








 
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