Threading to a shoulder

[earlgo]

This is my preferred method. It prevents running into the shoulder and leaves a nice clean exit. Tool on the side away from the operator and the spindle is turning clockwise. The only bad thing is that the tool pressure is away from the headstock, but it works every time. These are 7/8-14UNF threads and checked with a thread pitch micrometer.

Reverse threading

--earlgo

[SteveHGraham]

Metric shoulder or imperial?

[Harold_V]

Nice setup! I took note that you selected the proper compound attitude (tool MUST be fed in the same direction of carriage travel).

Early in my apprenticeship I did a lot of single point threading, virtually all of it to either a shoulder, or to a prescribed length, so I mastered the art of "pulling out" at the correct interval. Takes a little concentration, but once learned, threading to a shoulder isn't very intimidating. Even as I've aged, the skill seems to be intact, even though it's practiced very little these days. That I reaffirmed just a couple days ago when I generated an internal 18 pitch thread up to a shoulder (in this case, the shoulder was imperial, not metric, Steve!)

Harold

[mcostello]

On another forum a poster said They used to do a 5 start very fast pitch plug for the plug (? ) that closes and locks a torpedo tube. Stop held to .005 or close to that.

[Harold_V]

Doesn't surprise me a bit. Not that I could do it, as I likely couldn't, but I worked briefly with a guy who wasn't all that great on the machines, but could single point threads at an alarming spindle speed and pull out without issue. There was no way I'd have tried threading at the speeds he chose, although I didn't run slowly---unless compared to him.

Key to success is getting a rhythm going, and anticipating the cut's end. Some folks do it better than others.

Alternately, a guy could invest in a Cazeneuve lathe like Patio owns. While the feature it has may not be unique, it isn't common. It allows for threading to a stop. Do that on most machines and you pay by destroying the machine. A very nice feature when you must thread to specific lengths.

Harold

[GlennW]

Be warned that not all lathes are suited to thread to a shoulder as Harold is describing.

I have two lathes, and my larger lathe, a 14x40, is an absolute breeze to thread on and I regularly thread to shoulders and give it no second thought.

My other lathe is a 12 bench late and there is no way in hell I would ever thread to a shoulder on that one. The problem there is that the half nuts at times simply will not disengage if there is the slightest load on them. I think I just about lifted the machine up one time trying to disengage them just before the crash...and it's single phase with no spindle brake, so all you can do is watch at that point, as you can't even stop the spindle. I ended up having to do as "earlgo" does. (which is actually threading away from a shoulder )

The bottom line is if you have a smaller machine, get to now it well before you go charging toward a shoulder with your favorite threading tool. Make a lot of passes on something that you can thread off of and try disengaging at a designated point. That way if it goes bad, you won't be crashing into something. About nine times out of ten my smaller lathe half nuts would disengage properly, but that one time that they wouldn't was a real hair raiser...

[earlgo]

This is indeed threading 'away' from a shoulder as Glenn pointed out.
At the CSTrades in the 70's we were taught to leave the half nuts engaged and stop the spindle when approaching a shoulder and then turn the spindle by hand to approach the shoulder. Seemed slow to me, and it cut the surface speed down a bit. After I got the Atlas and made the tool holder, I found I could thread as shown and it has helped a lot. No shoulder crashes to date and since the d.o.c. is relatively small, there is no issue with cutting pressure toward the tailstock.
--earlgo

[Magicniner]

I thread away from shoulders and out of blind holes, running carbide at the correct speeds and feeds to a shoulder or into a blind hole can get exciting real fast.

[NP317]

I really miss having access to the Southwestern Industries CNC 14-40 lathe I acquired for the Univ. of Washington student shop.
Cutting single-point threads was amazing to watch: Especially multi-start threads running at terrifying speeds! Threads done accurately and quickly. So simple to program and set up. And interior threads were the cat's meow. No crashing of the tool.

I couldn't afford such a CNC machine for my personal new shop, but I can dream and remember.
At least my new manual 14-40 lathe has high rigidity and accuracy, and is pleasing to operate. I'm happy to have it.
~RN

[SteveHGraham]

I think I just about lifted the machine up one time trying to disengage them just before the crash...and it's single phase with no spindle brake, so all you can do is watch at that point, as you can't even stop the spindle.

I'm starting to understand why you enjoy my shop mishaps so much.

[GlennW]

I think I just about lifted the machine up one time trying to disengage them just before the crash...and it's single phase with no spindle brake, so all you can do is watch at that point, as you can't even stop the spindle.

I'm starting to understand why you enjoy my shop mishaps so much.

Exactly!

[Harold_V]

I'm in lock-step with Glenn in regards to half nuts that won't disengage. Make damned sure yours will when under light load, as nothing good will come from hitting a shoulder if they won't release. I've read accounts of horrible destruction when the crash occurred.

Harold