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Left hand thread ?

alan speyrer

Stainless
Joined
Feb 15, 2009
Location
Shallowater
Hey guys, i am needing to cut a left hand 7/16"-20tpi with my south bend 10k lathe. I have cut right hand threads many times, never left hand threads, so i am asking what is the proper way to cut left hand threads on a south bend lathe. I have a threading dial.
when i cut right hand threads i like to cut from the chuck to the tailstock with the lathe in reverse. So i would like to cut left hand threads the same way if possible.

thanks
 
L/H thread

Alan
The only reason that your lathe was in reverse was so that you COULD cut from chuck towards Tailstock, presumably with the tool in a rear toolpost .(Or upside down in the front toolpost)
So to cut a L/H thread start from the chuck but with the lathe spindle in forward direction and the tool in the front toolpost . .

Davycrocket
 
If the lathe spindle is in the forward direction, then it should cut threads from the tailstock toward the chuck. I dont understand.

Alan
The only reason that your lathe was in reverse was so that you COULD cut from chuck towards Tailstock, presumably with the tool in a rear toolpost .(Or upside down in the front toolpost)
So to cut a L/H thread start from the chuck but with the lathe spindle in forward direction and the tool in the front toolpost . .

Davycrocket
 
Alan
Doesn't your lathe have reverse/ tumbler gears to allow you to make the leadscrew turn in either direction regardless of the direction of turning of the main spindle ?
This is what they look like on my lathe . Leadscrew rotation is reversed using the lever with the round black Knob ( Not the spindle lock knob towards the top/rear of the spindle )!!

Just checked on lathes

On your lathe it's the lever sticking out where the end cover joins the headstock. You should be able to put the leadscrew into forward , neutral or reverse
Davycrocket
 

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when i cut right hand threads i like to cut from the chuck to the tailstock with the lathe in reverse. So i would like to cut left hand threads the same way if possible.

thanks

The lathe spindle will be turning forward as normal operation. The lead screw will be turning toward the tailstock (bottom hole on the for/rev lever). The compound will be swiveled with the handle toward the chuck at 29.5 degrees and cut away. The carriage will be in (netrual center hole) Use the half nut lever to cut. Just watch your fingers if moving close to the chuck...Bob
 








 
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