A means to another barrel theading procedure so that your butt hole don't pucker up.

If your using a 3 or 4 jaw chuck thats threaded onto the headstock you run the risk of it loosing off threading this way! Just something too keep an eye on.
 
This is fairly common practice. Also used to cut left hand threads if all you happen to have is a right hand tool or insert.

But still, lifesaver if you didn't know about it.
 
Only works if you are permitted a runout groove. Some projects allow it and others don't. Some lathes have a tendency to lurch when you engage the halfnut, this can easily break your cutting tool if it lurches into the part. Not a bad practice, but learning how to do it properly is better.
 
50 years ago I was taught how to thread... and at that time the instructor also mentioned the backwards thing... but none of us were interested in the backward method.

I never am in a hurry when threading and using a dial gauge to indicate a 'stop' and slow rpm I never have a problem conventionally...
 
This is the method I've used, no need for split second timing. I wouldn't go back to threading towards the head stock. My chucks aren't threaded, so no worry about them loosening when turning backwards.
 
You don't need to run the tool upside down. At least for the threads that would be used in small arms barrel threading. Run the lathe backwards, but use an internal boring bar on the far side of the workpiece. You can run the lathe faster that way...
 
Probably one of the better tips I ever got, was to put a dab of whiteout or a sharpie mark on the material in the lathe, so you have a visual cue of the rhythm of it going around.

Being a white guy, I gots no rhythm, can't dance, and too fat to fly, but I can usually pull off a pretty nice looking thread up to a shoulder, with a nice ramped out valley on that thread.
 
Many of the barrels I've fitted were for Remington Model 700s. There is a recoil lug sandwiched between the barrel shoulder and the receiver face. I want that part of the shank to be unthreaded, and the recoil lug a nice fit; threads stop short of the barrel shoulder. I do not want a significant relief cut at the end of the threads. What I do is disengage the half nuts at the end of the threaded portion of the shank. This results in a relief cut, V-shaped, the width of a single thread. I suppose that the passes could be to the right, starting in a V cut.
I've never had a problem stopping on cue when threading towards the spindle. Like guntech, I thread at low rpm. Things aren't happening very fast.
 
guntech said:
50 years ago I was taught how to thread... and at that time the instructor also mentioned the backwards thing... but none of us were interested in the backward method.

I never am in a hurry when threading and using a dial gauge to indicate a 'stop' and slow rpm I never have a problem conventionally...
Click to expand...

Neither of my lathes will slow down enough for my taste and reaction time. Threading in reverse is no different than threading forward. The results are the same either way.

I mirrored a device a now deceased friend of mine made up. It runs off a BBQ rotisserie motor attached to a frame that quickly bolts to the frame of the table. It runs a belt that runs a sheave attached to the back of my four jaw chuck. I put the lathe into the proper gear sequence, engage the half nut and use the external drive to run the chuck at 25 rpm. Sloooowww, yes, very but it makes for lovely, smooth threads although I have to make several extra passes with the lower powered external drive.

For some folks that use their lathes a lot the method mentioned by tiriaq and guntech work well. For others, that only thread occasionally, the reverse method will alleviat a lot of their tension. I like my set up because it works for me. As for only working if you're permitted a runout groove, not so. That's what the stop is for. You can run your bit right up against the shoulder if you must but it has to be ground properly.
 
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