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SirLesPatterson
03-04-2016, 12:35 PM
Awhile back I crashed my 12x24 lathe while trying to make a spindle copy out of aluminum. I didn't disengage in time, I was quite discouraged when that happened. I'm intrigued by the concept of threading from left to right with the tool upside down but I'm concerned about my chuck unscrewing from the spindle. It's a 13x40 lathe if that is relevant and the work diameter is about 1.5" 20TPI. The materials are 'mild' steel, 4130, and 304 stainless. I could use some input on this, thanks.

Royldean
03-04-2016, 12:58 PM
But if you put the tool upside down and thread on the backside of the hole, you can run the lathe in forward and still thread left to right? It's funny how I can't visualize this without my lathe in front of me....

But maybe now that I think about it, you'll get a reverse thread....

Jaakko Fagerlund
03-04-2016, 02:06 PM
But if you put the tool upside down and thread on the backside of the hole, you can run the lathe in forward and still thread left to right? It's funny how I can't visualize this without my lathe in front of me....

But maybe now that I think about it, you'll get a reverse thread....
You would get a left handed thread. Easy way to visualise is the to think of the spindle as a large screw that tries to screw-in or screw out that tool, then think which way the tool moves if spindle is turned the way the tool would need.

Forestgnome
03-04-2016, 02:51 PM
I do it fairly regular. I prefer to do it in a collet, but sometimes need to use the chuck. Sure wish I have a different chuck mount. I would say the saftey of it depends on the diameter of the work and the type of thread. I probably wouldn't do an Acme or large diameter. I do 3/4" on down and haven't had a problem. I put an extra snug on the chuck first to make sure.

Willy
03-04-2016, 03:14 PM
Are you sure that your lathe's chuck mount uses a threaded screw mount chuck?
The reason I ask is that most lathes in the 13x40 size range do not have a threaded spindle.

old mart
03-04-2016, 04:27 PM
Is it possible to have the workpiece longer so the end of the threading could run into a length turned down smaller than the thread core? Then part off the excess, it will give you more time avoid piling up. The minimum speed possible helps, I am lucky to have 30rpm now, but before I got the backgear working properly, I used to thread with the power off using a handle in the headstock spindle.

SirLesPatterson
03-04-2016, 04:32 PM
Are you sure that your lathe's chuck mount uses a threaded screw mount chuck?
The reason I ask is that most lathes in the 13x40 size range do not have a threaded spindle.

Yeah, it's an old Jet 1340 belt drive. Definitely a threaded spindle. The through hole is 1-17/32" so the 1-1/2" pipe will go through and chuck up nice.

I do have a 5C collet closer for it too, I'll have to look and see if I have one of those collets for big stuff. Then I would have to make some sort of plug for the other end of the tube to interface it to the tailstock center. The chuck would be so much easier but I'll look into the collet thing as it sounds safer. Thanks.

SirLesPatterson
03-04-2016, 04:34 PM
Is it possible to have the workpiece longer so the end of the threading could run into a length turned down smaller than the thread core? Then part off the excess, it will give you more time avoid piling up. The minimum speed possible helps, I am lucky to have 30rpm now, but before I got the backgear working properly, I used to thread with the power off using a handle in the headstock spindle.

That's a neat idea - I will look into this. Thanks.

Richard P Wilson
03-04-2016, 04:38 PM
Just machine in a groove, about 1/4" wide, down to thread root diameter, at the left hand end of the thread, just before the register. No problem with the tool crashing then. If you want to have the tool at the back, threading from left to right, then I think you have to have the tool the right way up, and run the lathe in reverse. Problem with this is that if you've got a thread-on chuck, there's a danger it will unscrew during the procedure. An un-necessary complication IMHO. Stick to doing it the right way round with a runout groove.

SirLesPatterson
03-04-2016, 05:37 PM
Just machine in a groove, about 1/4" wide, down to thread root diameter, at the left hand end of the thread, just before the register. No problem with the tool crashing then. If you want to have the tool at the back, threading from left to right, then I think you have to have the tool the right way up, and run the lathe in reverse. Problem with this is that if you've got a thread-on chuck, there's a danger it will unscrew during the procedure. An un-necessary complication IMHO. Stick to doing it the right way round with a runout groove.

That's my normal technique but I don't want a large runout groove on these parts and I'm nervous I'll screw up again. That first crash has me on edge I guess.

danlb
03-04-2016, 11:44 PM
My lathe has a a screw on chuck, so it features a small clamp that tightens with a screw to ensure the chuck can't spin off. The clamp locks into a groove on the spindle. You could probably make something similar by simply drilling a hole for a dog nose set screw. A witness mark on the spindle + backplate will let you check that the spindle has not moved.


Dan

Chris Evans
03-05-2016, 03:46 AM
What is your lathes lowest RPM ? My 14 x 40 only goes down to 82 RPM and I get nervous on bigger pitches you have to be quick to drop out. I may look into altering the drive pulley set up to go lower speed.

Richard P Wilson
03-05-2016, 06:32 AM
That's my normal technique but I don't want a large runout groove on these parts and I'm nervous I'll screw up again. That first crash has me on edge I guess.

Oh, my mistake, I thought you were having a second attempt at the dummy spindle nose.

I think you should be OK with 20TPI at about 80RPM, just watch it like a hawk and whip the cross slide back when the end of the cut is approaching. If you use an HSS tool, its less liable to chipping than carbide if you do misjudge slightly.

cameron
03-05-2016, 08:58 AM
I know you don't want the groove, but if you can cut the thread longer than needed, you can make the first pass long, and each consecutive pass slightly shorter than the previous. Then if you do overrun a bit, the tool runs into an area which is only a few thou larger in diameter. It will give you a bit of a jolt and raise a burr, but it's not a real crash.

QSIMDO
03-05-2016, 09:48 AM
Could you stop the power at 3/4 of the way then turn the final distance by hand?
I remember an article where the gentleman installed a hand crank on the power end of the spindle and did the entire thread without power.

cameron
03-05-2016, 09:55 AM
Could you stop the power at 3/4 of the way then turn the final distance by hand?
I remember an article where the gentleman installed a hand crank on the power end of the spindle and did the entire thread without power.

A hand crank is great for small, fine threads. It quickly turns into hard work as pitch and diameter increase.

Black_Moons
03-05-2016, 09:57 AM
Could you stop the power at 3/4 of the way then turn the final distance by hand?
I remember an article where the gentleman installed a hand crank on the power end of the spindle and did the entire thread without power.

This. As long as your not using carbide you should be able to stop midcut and resume under hand power for the last few turns. if you are using carbide, for some reason the instant the work stops the carbide snaps if its still trying to cut. (Some say backlash/etc in the drive train or some such, I just know it happens from seeing it 1st hand)

Also, some threaded chucks have a 'clamp on' part that clamps them to the spindle after being threaded on, I presume so you can thread/etc in reverse, and so while doing (interrupted) forward cuts, the lathe chuck does not get screwed on so tight that you bust your backgear trying to get it off. (See: Large number of lathes with a couple teeth on the backgear missing.. Yes that is EXACTLY how 90% of them happened)

You could consider trying to make this clampon part if your lathe spindle would allow it.

Edwin Dirnbeck
03-05-2016, 10:55 AM
I have been turning for 66 years. There is NO EXCUSE for a lathe manufacturer to make a lathe that runs in reverse but has no provision to keep a screw on chuck from unscrewing, period end of story.SOOO it is your lathe and your chuck . As you use your lathe more and more you will find many occasions to run your lathe in reverse, It would be well worth your time to design a good way to keep the chuck on. Perhaps a clamp ring that clamps on your spindle and also a dog point set screw that engages the chuck as others have suggested , Good luck Edwin Dirnbeck

Sunset Machine
03-05-2016, 12:17 PM
It's not that big of deal. Next time you're threading, try turning the chuck by hand. I can thread that way, but I can't unscrew the chuck. So why would it come unscrewed unless there's a boo-boo?

Start your tool in the groove, rightside up in back of the work or upside down in front, reverse rotation. Feed towards the tailstock. Little thing like 20 TPI, heck, you can probably use the same threading tool.

Edwin Dirnbeck
03-05-2016, 01:08 PM
It's not that big of deal. Next time you're threading, try turning the chuck by hand. I can thread that way, but I can't unscrew the chuck. So why would it come unscrewed unless there's a boo-boo?

Start your tool in the groove, rightside up in back of the work or upside down in front, reverse rotation. Feed towards the tailstock. Little thing like 20 TPI, heck, you can probably use the same threading tool.

If you are feeding away from the chuck,you don't need a starting or relief groove,just set a carriage stop so that you can start in the same z axis point each time. It is nice to have a relief groove if you are feeding toward the chuck.In the olden days when I was young and dumb BUT FASTER, I could thread toward the chuck without a relief groove. I have cut many thousands of threads toward the chuck with a Hardinge lathe that had the semi auto thread thread stop and best of all cnc lathes that would thread right up to the chuck jaws at 1500 rpm.On my engine lathe I never thread toward the chuck anymore,its to easy to go the other way.Edwin Dirnbeck

old mart
03-05-2016, 01:12 PM
I have cut an 8 tpi thread by hand, it is hard going even at 3 thou extra per pass when you have nearly finished the thread, but entirely possible. I use carbide tips 16 size, I get better results with these for external and internal, in the UK, I can buy single inserts with three edges from APT, there must be an equivalent supplier in the States.

Paul Alciatore
03-05-2016, 02:26 PM
Here is my solution to the problem of threading up to a shoulder:

http://img.photobucket.com/albums/v55/EPAIII/P1010001-1.jpg (http://smg.photobucket.com/user/EPAIII/media/P1010001-1.jpg.html)

I didn't make a stinking, small crank for the spindle: I made a GREAT BIG one. So far, it has allowed me to hand crank any thread I wanted to cut. And I can stop it at any point I want.

QSIMDO
03-05-2016, 04:24 PM
Watch your rotator cuff with that long throw crank!
Maybe you and cameron can get gym memberships to handle a smaller crank. ;)