# Internal Left hand threads



## rdean (Mar 23, 2014)

I have been reading about making internal threads on a lathe in different sections of this forum and it brought to mind a project I did in nylon about a year ago.
I wanted to make a 10TPI internal left hand thread for a project I was working on but my lathe lead screw was not reversible.  I set up my rotary axis on the CNC to cut the threads.  They were not perfect and I didn't have any degree offset but it worked fine for this project.  



I made a collar to fit the spindle carriage with a home made boring bar and the cutting point extending out the bottom.  I wrote a program that wrapped "Y" around "A" and moved the "X" axis +1.000 per revolution of the "A" while "A" was turning in the minus direction. I started with the boring bar all the way into the hole and the cutter just touching the bottom of the hole.  I had no idea how it would turn out so I manually set the depth cut to about 0.010 and ran the program.  At the end of the first pass the the "Z" lifted 0.200 and went back in the hole while the "A" went back to zero.  I manually lowered the "Z" another 0.010 and ran the program again.  I did this several more times until I had the depth of cut I wanted.

Like I said the threads weren't perfect but it worked for this project.
Thanks for looking
Ray


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## Terrywerm (Mar 23, 2014)

Just goes to show ya: There's always more than one way to skin a cat!!   Great thinking and a great way to work around a problem!


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