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Threading without the end groove

Posted: Thu Mar 22, 2018 3:48 pm
by tornitore45
Threading toward the shoulder and consistently stopping at the same place is not for the timid.
Threading away from the shoulder requires the infeed to be at zero rpm, or so I surmise.

What are best practices for both directions?
I know, Harold made an Auger with about 1.5 TPI, but even assuming I was ever that quick with my hand-eyes coordination 72 years have slowed down both my eyes and my hands.

Re: Threading without the end groove

Posted: Thu Mar 22, 2018 8:55 pm
by Bill Shields
threading to a non-groove termination (shoulder or not) is not for the faint of heart since it requires that you retract the tool at the same rate each time....a task best left to a controller.

Having a groove at the termination (shoulder or not) is very doable, but you need to go slow on the RPM and be QUICK with the disengaging lever.

If you run in reverse, you will need a 'starting groove' to place the tool to depth before engaging the lead-screw...you cannot plunge a threading tool into the work at zero speed.

It just takes practice and being 72 or 22...it is the same problem....just more challenging at advanced years.

Re: Threading without the end groove

Posted: Thu Mar 22, 2018 9:41 pm
by John Hasler
Perhaps one could make a starting hole with a drill bit or better yet a 60 degree end mill. Maybe I'll try it someday.

Re: Threading without the end groove

Posted: Fri Mar 23, 2018 1:44 am
by Harold_V
A starting hole, or other ideas less than a radial relief (groove) are not really a good idea, and even a relief may not be acceptable if one is working from a print and it isn't included in the design.

Cutting threads to a shoulder is nothing more than a discipline. It can be mastered by almost anyone, assuming they wish to accomplish the task. Even folks with dyslexia (I am gifted with that cursed thing--shows up readily when I type) can master the task.

Starting a thread from a stationary spindle could be asking for problems. All lash should be eliminated from the drivetrain when the spindle is energized. Starting with a hole or other location critical relieved area would do nothing but slow one down. I see it much like using insert carbide tooling to avoid the learning curve of grinding HSS toolbits.

The best possible advice I can offer for this task is to just do it. Do it until it's comfortable. To avoid problems with pulling out too late, machine plastic---and slow the spindle until it's comfortable. As your skill increases, increase spindle speed until it's reasonable. If you pull out too late with plastic, you won't trash your machine. PVC pipe is cheap and machines nicely. Use some of that. Doesn't matter what thread you chase---do it for practice. The coarser the pitch, the faster you must react. If you start out with a fine pitch, eventually go coarser, so you don't get lulled to sleep with a slow moving carriage, which could make it hard when there's a demand for a fast lead.

When creating a right hand external thread, do these things.

Set your compound @ 5:00. I like 29°, while the book says 29° 30'. Feed with the compound, not the cross slide. The last couple thou can be taken with the cross slide if your tool is very sharp and you wish to improve the finish of the thread. Passes should be very light, however. Otherwise there's considerable interference with chip flow.
Coordinate the cross slide and compound rest so your 0 spot on the dial of the cross slide resides at the mark when the handle is @ 10:00. That makes it VERY easy to retract the tool at the appropriate time, always with the same downward motion. It should become a habit, so you do it without thinking.
Make sure your tool is on center.
Make sure there's enough clearance on the right hand side of the tool to achieve full depth without bumping the shoulder. I grind my threading tools offset, for that reason.
Practice pulling out and kicking out the half nuts in one, smooth motion, at the exact time needed. Do it until it comes natural.

H

Re: Threading without the end groove

Posted: Fri Mar 23, 2018 1:56 am
by Harold_V
Bill Shields wrote:
Thu Mar 22, 2018 8:55 pm
threading to a non-groove termination (shoulder or not) is not for the faint of heart since it requires that you retract the tool at the same rate each time....a task best left to a controller.
Heh!
When I was trained, there was no such luxury. I expect precious few home shops have it, either. Best thing to do is to learn to cut threads the hard way, which is by doing it until it's comfortable.

Worked for me! :lol:

H

Re: Threading without the end groove

Posted: Fri Mar 23, 2018 2:07 am
by wlw-19958
Hi There,

Maybe something like this would work:

Quick Retracting Toolpost

Good Luck!
-Blue Chips-
Webb

Re: Threading without the end groove

Posted: Fri Mar 23, 2018 10:24 am
by NP317
My two favorite lathes for cutting threads are:
1) Hardinge lathe, with the quick-retract lever on the compound slide;
2) CNC lathes that cuts threads impossibly fast and correctly, every time.

I've used both, andI have neither in my home shop...
~RN

Re: Threading without the end groove

Posted: Fri Mar 23, 2018 8:53 pm
by mcostello
On another forum, Forrest Addy (I believe) talked about Someone threading torpedo tubes or caps and had to stop the thread within about .005. I have a dial indicator set up for a stop and it's not all that hard. Especially if I was making the big money on big money parts. You can get a feel for it and anticipate things. This is assuming a reasonably slow speed for the size.

Re: Threading without the end groove

Posted: Fri Mar 23, 2018 10:49 pm
by TimTheGrim
Back when I worked at a technical ceramics company, we had to make threaded core pins for TIG nozzle molds. The end of the external thread on the mold pin was the lead of the internal nozzle thread. The molded part had to unscrew from the pin without damaging the still soft ceramic. It had to be a perfect thread end.
We made a carbide threading tool for a Themac tool post grinder and hand fed the lathe up to the micrometer bed stop using the chuck keys to turn a 4-Jaw chuck. We would not disengage the half nuts, back off the slide and power the lathe back to start point. Adjust cross slide and repeat until done. The core pins were already heat treated to 58 RC and this method produced very nice threads that were then polished to an almost mirror finish. Time consuming yes, but in ‘75 we didn’t have CNC and only made $4.25/hr.
I still have a tool somewhere. If I can find it, I’ll post a pic.

Re: Threading without the end groove

Posted: Sat Mar 24, 2018 2:10 pm
by Magicniner
TimTheGrim wrote:
Fri Mar 23, 2018 10:49 pm
We made a carbide threading tool for a Themac tool post grinder and hand fed the lathe up to the micrometer bed stop using the chuck keys to turn a 4-Jaw chuck.
Thread milling on a lathe in the 70s! Cool! I've only just started playing with that :D
Harold_V wrote:
Fri Mar 23, 2018 1:44 am
Starting a thread from a stationary spindle could be asking for problems.
I use Iscar MGCH 08 and MGCH 06 bars with threading inserts and have threaded from the bottom of blind holes out doing just that where a starting groove wasn't acceptable, no chipped tips yet ;-)
Regards,
Nick

Re: Threading without the end groove

Posted: Sat Mar 24, 2018 2:38 pm
by tornitore45
It just occur to me, some time ago, I made 60* 4 tooth cutter ~1" dia to mill the V groves for a prop washer. I can use that to mill a thread IF I can mount it rigid enough in the flexible spindle or the pneumatic spindle. I used that cutter today to scribe marks for a dial.

Re: Threading without the end groove

Posted: Sat Mar 24, 2018 3:39 pm
by Dave_C
Make sure there's enough clearance on the right hand side of the tool to achieve full depth without bumping the shoulder. I grind my threading tools offset, for that reason.
Harold, did you mean right side? If I am threading toward the chuck I'd want my tool offset with the tip more toward the chuck. So does that mean more clearance on the right or on the left? I may be misunderstanding your explanation of clearance as well so forgive me if I am reading this wrong.

Dave C.