cutting internal threads to a shoulder

[curmudgeon]

I want to cut internal threads to a shoulder using my Grizzly G0602 10x22. They'll be at least 1 1/8", maybe 1 1/4" diameter and almost 1/2" deep

Joe makes it look easy -

But, he also says don't try cutting in reverse on a lathe with a screw on chuck.

My lathe has a screw on chuck with a locking device to prevent the chuck from threading off when used in reverse.

Is it safe to cut internal threads in reverse on my lathe when the chuck lock is installed?

For this project it doesn't matter if I cut left hand or right hand threads, but I haven't started the project to install tumbler gears yet so I can't thread left-to-right with the spindle spinning forward.

Are there better ways to cut internal threads to a shoulder (better than Joe? impossible...)

As an alternative, would it be reasonable to add a microswitch to a carriage stop to kill the motor as the tool approaches the shoulder? Without a brake, the spindle and carriage would coast to a stop - if I set it to stop at the right spot with no load it should stop a bit short of crashing when loaded.

Along the same idea, are there carriage stops that can reliably disengage the half-nut at a set position? I'm thinking of a physical linkage, not a switch with actuator.

Please share your wise ideas, and help me avoid folly.

 

[TorontoBuilder]

Our old Craftex lathe had the same locking tabs.

If they're installed properly and torqued then you can reverse thread as indicated. Reverse threading is the only way I am comfortable threading

 

[curmudgeon]

Our old Craftex lathe had the same locking tabs.

If they're installed properly and torqued then you can reverse thread as indicated. Reverse threading is the only way I am comfortable threading

excellent - thank you, time to start grinding some HSS

 

[TorontoBuilder]

excellent - thank you, time to start grinding some HSS

One word of advice... or rather two words. Make a few of those chuck lock retention clamps because replacements are very hard to find.

 

[YotaBota]

More advice - buy a couple of PVC size adapters to practice on. They're cheap and if you make a mistake not likely to hurt anything but the plastic. It doesn't really matter if the PVC isn't the right size, they're just to get your technique down.

After that if the size is correct then you have spindle thread protector. This was on my SM9.

 

[Larry_C9]

I have learned a lot by watching Joe's videos. I really like the thread cutting with an upside down tool bit and running the lathe in reverse.

 

[Susquatch]

As an alternative, would it be reasonable to add a microswitch to a carriage stop to kill the motor as the tool approaches the shoulder? Without a brake, the spindle and carriage would coast to a stop - if I set it to stop at the right spot with no load it should stop a bit short of crashing when loaded.

Along the same idea, are there carriage stops that can reliably disengage the half-nut at a set position? I'm thinking of a physical linkage, not a switch with actuator.

Frankly, I don't like either of these ideas. They are great thoughts, but if they fail the result is REALLY UGLY.

I'd much prefer a good thread lock over that risk.

Have you considered @Tecnico 's crank? Or even just use a chuck key?

 

[TorontoBuilder]

Frankly, I don't like either of these ideas. They are great thoughts, but if they fail the result is REALLY UGLY.

I'd much prefer a good thread lock over that risk.

Have you considered @Tecnico 's crank? Or even just use a chuck key?

cranks... why not just get a treadle powered lathe

I had my eye on a taiwanese 1440 lathe that had carriage stop system that was very reliable... it would have been great for threading but I'd not try to make a stop or microswitch unless I had VFD and foolproof braking

 

[DPittman]

Along the same idea, are there carriage stops that can reliably disengage the half-nut at a set position? I'm thinking of a physical linkage, not a switch with actuator.

Well it might be a bit more involved than what you are looking for but I always wanted to make one of these for my lathe. However I am now thinking an electronic lead screw might be a better solution. But this clutch mechanism looks more fun to build.

Lathe Screw Cutting Clutch

talented designer (Graham Meek) http://modelengineeringwebsite.com/Meek_screwcutting_clutch.html implementation example

canadianhobbymetalworkers.com

 

[Susquatch]

cranks... why not just get a treadle powered lathe

LOL, ya why not!

I'm gunna do this just for the control. I really don't care how crude it might seem.

I'm also shooting for a low speed VFD which would also eliminate the problem.

But I'm not worried personally. I have a d1-5 chuck mount so I can run in reverse to my hearts content.

 

[TorontoBuilder]

LOL, ya why not!

I'm gunna do this just for the control. I really don't care how crude it might seem.

I'm also shooting for a low speed VFD which would also eliminate the problem.

But I'm not worried personally. I have a d1-5 chuck mount so I can run in reverse to my hearts content.

I miss the old old days when I didn't have arthritis

 

[curmudgeon]

Frankly, I don't like either of these ideas. They are great thoughts, but if they fail the result is REALLY UGLY.

I'd much prefer a good thread lock over that risk.

Have you considered @Tecnico 's crank? Or even just use a chuck key?

@Tecnico 's crank, https://canadianhobbymetalworkers.com/threads/tecnicos-shop-window.7257/#post-108244, is a good trick to have in the bag. However, I was hoping not to have to revert to that trick for this job.

It sounds like the factory chuck lock will safely retain the chuck when turning in reverse.

 

[Susquatch]

However, I was hoping not to have to revert to that trick for this job.

I've done a lot of tapping using chuck keys to turn the chuck. Never thought to single point thread that way till I read about @Tecnico's lever.

 

[curmudgeon]

Well it might be a bit more involved than what you are looking for but I always wanted to make one of these for my lathe. However I am now thinking an electronic lead screw might be a better solution. But this clutch mechanism looks more fun to build.

Lathe Screw Cutting Clutch

talented designer (Graham Meek) http://modelengineeringwebsite.com/Meek_screwcutting_clutch.html implementation example

canadianhobbymetalworkers.com

wow - that is very cool!

 

[thestelster]

Post in thread 'Tips of the Trade' https://canadianhobbymetalworkers.com/threads/tips-of-the-trade.4574/post-100613

 

[Susquatch]

Post in thread 'Tips of the Trade'

I re-read your thread. I remember I liked many aspects but...... There is no way in hell I could hit your precision. Even at 70 RPM, that is a no go for me. I need around a 10th of an inch relief in there to do that. I'm just too old and too slow. The poop shoot pucker factor would cause premature incontinancy and my wife would have me locked up.

That's one of the main reasons I want lower speed in my lathe (7 rpm = 1/10th of the pucker factor). So it's that or the spindle crank. For now, I'll keep threading in reverse.

That said, the indicator holder is in process. Maybe with time and practice I can improve.

 

[Susquatch]

It sounds like the factory chuck lock will safely retain the chuck when turning in reverse.

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

 

[thestelster]

That's one of the main reasons I want lower speed in my lathe (7 rpm = 1/10th of the pucker factor). So it's that or the spindle crank. For now

Well, when you do get the VFD set up, put a potentiometer to vary the speed on the fly close by.

Saying that, if you need to quickly drop your speed with the pot, you might need a braking resistor if you're using a big chuck.

 

[curmudgeon]

Post in thread 'Tips of the Trade' https://canadianhobbymetalworkers.com/threads/tips-of-the-trade.4574/post-100613

excellent post - thank you for the reminder

Before you start your first pass, do you use your threading tool to cut a full depth relief at the bottom end of the threads, or do the the threads just run out near the bottom +/- how well you hit your mark?

It's time to do some practicing.

 

[thestelster]

excellent post - thank you for the reminder

Before you start your first pass, do you use your threading tool to cut a full depth relief at the bottom end of the threads, or do the the threads just run out near the bottom +/- how well you hit your mark?

It's time to do some practicing.

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.