In article , Richard J Kinch
says...

How do you get a clean start to outside threads cut on a lathe?

I like to put a 45 degree chamfer on the end of the part,
*before* I start threading. Best is if the small end of
the chamfer is smaller than the minor dia of the thread
by some small amount.

For most materials, forming the chamfer after the threading
is complete will mung up the lead-in and it will be very tough
getting the female threaded part to start cleanly.

Jim

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