Creating a tapered thread using a 3D Printer is very much akin to single-point cutting a thread on a Centre Lathe. I trust I am not the only one left with such memories .

Currently I am attempting to create an M27 tapered plug using the standard BSPT format including the standard taper of 1°47' (1.788°). There is something, however, Uncle Google is reluctant to reveal. Wikipedia, that fund of general knowledge, remains silent. I even opened my 22nd Edition of Machinery's Handbook for the first time in years. (Who remembers Machinery's Handbook?) All to no avail!

As I understand it a BSPT Male Thread, at the pipe end, is undersized in comparison to the equivalent BSPP Female thread. I cannot find out how much undersized it should be. Such a specification will define the number of turns of thread before the minor diameter of the thread equals the OD of the pipe (ending the thread cut) which in turn defines the number of turns of thread involved.

Would someone please help with a specification of the thread undersize. A reference to appropriate documentation would be appreciated.

If working from the undersize is not the correct way to define the thread, please relieve my ignorance and tells me how the job is done.

Thanks

----------------------------------------
Artificial Intelligence is no match for Natural Stupidity