Running a threaded spindle lathe in reverse to cut heavy threads in a blind hole.

[pestilence]

I now have a plan. I was watching some YouTube videos by a fellow who calls himself doubleboost. In this video at 2:52, he briefly shows an adapter plate he made to mount his lathe accessories on a rotary table.

www.youtube.com/watch?v=8SV7lDiSXto&t=2m52s

The video is about him making an er32 chuck for his boxford lathe and he uses the adapter as a thread gauge to be sure his chuck thread is correct. Since I have a rotary table too, I will first make the same adapter plate for my own rotary table. That will give me both a useful tool, a thread gauge I have to have anyway, and some experience cutting the outside version of the same thread I need to cut on the inside.

If I can't cut that outside thread, THEN it's time to start worrying about doing the inside one, not now

 

[Hawkeye]

Yes. John (Doubleboost) has done quite a few videos on a lot of projects and topics. He's always finding ways to improve his video setup. A good source.

 

[OldMachinist]

I just finished cutting a 2-1/4"-4.5 TPI internal thread in a adapter to mount my lathe spindle tooling on a Brown and Sharpe dividing head. I have a 16" South Bend lathe with a threaded spindle and I've never worried about spinning the chuck off while internal threading using the spindle in reverse method.

 

[roy_tate]

Its too hard to predict the failure case but often, the leadscrew has a roll pin that is designed to snap. ...
Ray

Thank you so much for this comment! I bought an abused lathe and am fixing problems on it. I just realized that my lead screw roll pin was replaced with a small machine screw jammed in it's place, taking away one of my safety measures. I'd rather snap a pin than bust something much bigger!

Roy Tate