Internal Thread Measurements

[WoodBee]

A VFD would be a good way to speed up the return. My lathe is a gear head so I wan't sure if changing speed would lose the indexing between the spindle and the lead screw.

I am not 100% sure, but spindle speed should be set between motor and spindle. Feed is determined between spindle and feedscrew. I think it would work ok. Not sure how fast you can switch though. Does the spindle need to be stopped to change speeds (mine does) ? I think that would limit the practical usability to cutting long threads.
Peter

 

[epanzella]

I am not 100% sure, but spindle speed should be set between motor and spindle. Feed is determined between spindle and feedscrew. I think it would work ok. Not sure how fast you can switch though. Does the spindle need to be stopped to change speeds (mine does) ? I think that would limit the practical usability to cutting long threads.
Peter

Yes, that's right. The spindle speed is the ratio of spindle to motor but as the headstock gears completely surround the output shaft to the gearbox, I wan't sure if the feed gear train would go thru a neutral briefly while shifting the headstock gears. It's been three years since I looked in the headstock. And, yes, the lathe has to be stopped for shifting so it would be slow and not worth the trouble unless the thread was really long and fine.

 

[RJSakowski]

There is one way to cut metric threads on an Imperial lathe without stopping and reversing the lathe. It involves the use of a single point clutch. Basically, since the spindle gear can only engage the lead screw gear train in one angular position the spindle can never be out of sync with the lead screw.

The lead screw still has to be driven back to the start point under power though.

http://www.hobby-machinist.com/threads/threading-at-400-rpm.20196/