How To Cut A Left-handed Thread On An Atlas 10f Lathe

louosten

louosten

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Gentlemen;

I need to make a 3/4 x 8 Acme left handed nut for a project I'm working on. The Atlas 10F has a threaded spindle which normally prevents working in reverse rotation without some sort of stop on the chuck. I don't have a collet set...am I out of luck, or is there another way, besides trying to obtain a hand tap ($108) and performing the deed manually? Thanks for comments in advance.
 
Can you put the tool in upside down and cut it on the back, feeding left to right?
 
louosten said:
Gentlemen;

I need to make a 3/4 x 8 Acme left handed nut for a project I'm working on. The Atlas 10F has a threaded spindle which normally prevents working in reverse rotation without some sort of stop on the chuck. I don't have a collet set...am I out of luck, or is there another way, besides trying to obtain a hand tap ($108) and performing the deed manually? Thanks for comments in advance.
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Assuming that you have the reversing shuttle on your lathe or other means to reverse the direction of the lead screw rotation, you would cut the thread with the spindle in forward rotation and feed from left to right.

If you can't reverse the direction of the lead screw rotation, you can't cut a left hand thread.
 
Simple on my lathe. Thread normal rotation with the carriage making the cut as it travels away from the chuck.
I'm not familiar with your lathe but if carriage travel direction is switchable it is that simple.
Many a new operator has made a beautiful left thread when wanting a right thread that way.
That's never happened to me...nope never done that...not once...ok ok I did it once.
 
Depending upon the change gear mechanism, you may be able to fix an intermediate gear between your compound gear (10-101-16A in the parts list) and the change gears which would reverse the direction of the lead screw rotation. The number of teeth doesn't matter as long as it will fit in the space.
 
I cut left hands on my 10f a few times. The chuck never came loose. As mentioned thread for left to right, just remember to grind the tool properly for the thread you are making.
 
For those of you who aren't familiar with an Atlas 10F, it has a FWD-OFF-REV gear box connected directly to the lead screw if it does not have a QCGB. If it does have a QCGB, then it has tumbler type FWD-OFF-REV for driving the change gears.

Lou,

You will either have to get a left-hand Acme threading insert (if you have that type of boring bar) or you will have to grind the bar for left-hand rather than right-hand threads. The cutting edge and front clearance angle remain the same as for right-hand internal threads. But side clearance will be ground on the tailstock side of the cutter tooth instead of the normal (for right-hand threads) headstock side. The compound angle (29.5 deg.(correction - 14.5 deg) toward the headstock) will be the same as for cutting external right hand threads. And of course the power feed will be in Reverse and each cutting pass will begin with the cutter passed completely through the nut.
 
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