cutting internal threads to a shoulder

[curmudgeon]

I generally will put a relief groove 0.002"-0.003" deeper than depth of thread at the shoulder for either internal or external threads with a grooving tool. But, if I need a full length thread without a relief cut, I'm ok with that. I just find it looks better with the relief cut, and reduces that pucker factor that @Susquatch mentioned.

I tend to do the chamfer after the thread is cut on an external thread, and before on internal thread (no particular reason though), using the same threading insert that I used to do the threads.

I run the lathe at around 50rpm when threading, and using the dial indicator on my carriage stop, I will hit my mark within 0.005". And usually before, almost never after.

thanks for the details - very helpful for me

At 50 RPM, your approach sounds much more practical. With a minimum speed of 150 RPM and reflexes slower than those of a @Susquatch, @Tecnico 's spindle crank handle might work better for me.

 

[thestelster]

thanks for the details - very helpful for me

At 50 RPM, your approach sounds much more practical. With a minimum speed of 150 RPM and reflexes slower than those of a @Susquatch, @Tecnico 's spindle crank handle might work better for me.

I just tried at 150 rpm, set at 24tpi, and I was still within 0.005", but for sure more pucker! Just have to practice, practice, practice. Also, the finer threads, the slower the carriage moves, so less pucker.

You know, that's one of the greatest advantages of the VFD!!

 

[johnnielsen]

Having the threading tool mounted on a dead stop slide helps cure the butt pucker blues.

 

[jcdammeyer]

Having the threading tool mounted on a dead stop slide helps cure the butt pucker blues.

What is a dead stop slide? I don't understand from the photos... Guess I need more than 1000 words?

 

[DavidR8]

Having the threading tool mounted on a dead stop slide helps cure the butt pucker blues.

Is that like a metal leash?

 

[johnnielsen]

Yes.

 

[johnnielsen]

What is a dead stop slide? I don't understand from the photos... Guess I need more than 1000 words?

The threading tool is mounted on an auxiliary slide held in the tool post on the cross slide. When the threading tool approaches a shoulder, the threading tool stops advancing toward the shoulder while the carriage keeps traversing. The threading tool stays clear because the auxiliary slide retreats due to being restrained by the shaft secured to the lathe bed as seen in the pictures.

 

[jcdammeyer]

The threading tool is mounted on an auxiliary slide held in the tool post on the cross slide. When the threading tool approaches a shoulder, the threading tool stops advancing toward the shoulder while the cross carriage keeps traversing. The threading tool stays clear because the auxiliary slide retreats due to being restrained by the shaft secured to the lathe bed as seen in the pictures.

What prevents it from stopping while threading? Looked for videos but can't find any under that sort of subject.

 

[curmudgeon]

The threading tool is mounted on an auxiliary slide held in the tool post on the cross slide. When the threading tool approaches a shoulder, the threading tool stops advancing toward the shoulder while the cross carriage keeps traversing. The threading tool stays clear because the auxiliary slide retreats due to being restrained by the shaft secured to the lathe bed as seen in the pictures.

ah cool - I see it now

Is there some sort of internal latch that holds the threading tool holder to the post until the end stop triggers release?

 

[curmudgeon]

Any report yet on how well it held? Also, can you post a close up of that lock?

I have not attempted the threads yet. It's been 49 years since I threaded on a lathe, so another few days of catastrophizing won't hurt. And, I need to find a scrap bike to upcycle the crankset into a lathe spindle hand crank.

For practice today, I used a dial indicator with magnet back as a visual guide for when to pull the half-nut lever while power feeding. It went much better than I expected.

Here's a close up of one of the two locks:

And, here's a pic of it installed, locking the chuck back plate to the spindle:

 

[Susquatch]

Having the threading tool mounted on a dead stop slide helps cure the butt pucker blues.

I'm stuck on 2000 words just like @jcdammeyer. (funny way to say it). Prolly need 8000 more words.

I think I get the principle, but I don't see it in the photos. Might be my incorrect idea of the principle getting in the way.

Feeling kind of dumb right now.......

 

[Susquatch]

And, here's a pic of it installed, locking the chuck back plate to the spindle:

Curious arrangement. Makes me think too much.

Is that OEM?

Does the lock press the chuck sideways at all?

Does the screw touch the spindle thread underneath the chuck plate?

Does the groove weaken the spindle? I'm guessing not cuz the spindle thread isn't any bigger than the groove.

I assume the tapered groove acts a bit like a collet taper to increase contact area and friction.

OVERALL, I think its a Cool idea. I like it better than the split collar principle used on other systems.

 

[curmudgeon]

Is that OEM?

Yes, first post includes a copy 'n paste from the manual.

Does the lock press the chuck sideways at all?

Not if installed correctly. The thread on chuck bottoms out on the spindle shoulder. The lock should just act as a retainer making it very hard to thread the chuck off. With sufficient effort, a guerilla could apply enough torque to shear the cap screws or crack the locks.

Does the screw touch the spindle thread underneath the chuck plate?

I don't think so. I replaced the 3-jaw with the 4-jaw before I started using the lathe and did not notice any marks in the spindle. I would be cranky if that steel cap screw touched the spindle.

Does the groove weaken the spindle? I'm guessing not cuz the spindle thread isn't any bigger than the groove.

Agreed, I think it's impact is inconsequential.

I assume the tapered groove acts a bit like a collet taper to increase contact area and friction.

OVERALL, I think its a Cool idea. I like it better than the split collar principle used on other systems.

With a wedge, the design tolerates low accuracy and high variability in locating the screw holes.

I haven't confirmed by testing myself, but I've now seen enough videos of running this lathe in reverse that I think it will work OK.

 

[PeterT]

Having the threading tool mounted on a dead stop slide helps cure the butt pucker blues.

I dont quite get it - what stops the carriage & the rest of the toolpost assembly from carrying on into the chuck?

 

[jcdammeyer]

I dont quite get it - what stops the carriage & the rest of the toolpost assembly from carrying on into the chuck?

The operator. All that mechanism does is prevent the cutting too from going any further and it appears as the carriage goes further to actually pull the cutting part out of the thread. The operator still has to release the half nut or stop the spindle.
So unlike my ELS you can't start a pass and then turn away to the work bench to continue with what you were doing.

 

[johnnielsen]

The operator. All that mechanism does is prevent the cutting too from going any further and it appears as the carriage goes further to actually pull the cutting part out of the thread. The operator still has to release the half nut or stop the spindle.
So unlike my ELS you can't start a pass and then turn away to the work bench to continue with what you were doing.

You got it. It gives you time at the end of the thread cut to stop or reverse the spindle. The tool post mounted slide stops the advancement of the threading tool when the leash ( as R8 phrased it) becomes taut. It's sole purpose is to allow the operator time to disengage, stop or reverse the spindle. When the carriage is rolled back to the thread start position, the thread tool slide returns to it's start position due to the "leash" becoming slack and allowing a spring action to push the threading tool towards the chuck. Now you are ready for another threading pass.

 

[curmudgeon]

You got it. It gives you time at the end of the thread cut to stop or reverse the spindle. The tool post mounted slide stops the advancement of the threading tool when the leash ( as R8 phrased it) becomes taut. It's sole purpose is to allow the operator time to disengage, stop or reverse the spindle. When the carriage is rolled back to the thread start position, the thread tool slide returns to it's start position due to the "leash" becoming slack and allowing a spring action to push the threading tool towards the chuck. Now you are ready for another threading pass.

cool idea - so, no latch to keep the threading tool components engaged with the carriage assembly, just a spring? Would luv to see more details.

 

[Susquatch]

cool idea - so, no latch to keep the threading tool components engaged with the carriage assembly, just a spring? Would luv to see more details.

Me too. I get the idea. It's cool as hell! But I can't seem to see how it gets implimented in the hardware. Feeling pretty dumb to be honest...... LOL

 

[curmudgeon]

Me too. I get the idea. It's cool as hell! But I can't seem to see how it gets implimented in the hardware. Feeling pretty dumb to be honest...... LOL

It looks like there is a component attached to the toolpost that allows the tool holder to slide, and it sounds like a spring retains the sliding tool holder in place until the tether stops it, while the carriage continues under feed. The angle of the slider also pulls the tool holder away from work.

 

[Susquatch]

It looks like there is a component attached to the toolpost that allows the tool holder to slide, and it sounds like a spring retains the sliding tool holder in place until the tether stops it, while the carriage continues under feed. The angle of the slider also pulls the tool holder away from work.

OKaaaaayyyyy, but...... what keeps the tool holder rigid enough to cut nice threads?

Or is this one of those you can have nice threads or you can have low butt pucker but you can't have both?