Threading On A Steady Rest Away From The Chuck

[BladesIIB]

Some firsts and/or things I have not done in a long time so really fun customer project. Cutting a 51mm x 1.5mm thread in some strut tubes for a 1989 Buick Reatta. Parts are not available anymore so the customer came up with a modified design that would use the strut from another Buick inside his existing tubes. Just needed them threaded for the nut that goes with the newer Strut.

Used my steady rest, which I almost never use and threaded away from the chuck, which worked awesome for this internal thread to a blind shoulder. Metric thread so I could not disengage the half-nuts. Overall good learning and, cutting away from the chuck allowed me to cut at a decent speed and not have to worry about stopping in a 0.6mm wide groove. Did a practice run in some Aluminum, since these tubes are the part he is no longer able to get so good stress test as well to make sure I did not mess them up. Happy with how they turned out, the customer says he has a few other Reatta owners waiting to see how this turns out so may be some other people looking for a local machinist to help them out with their mods.

 

[Tincamp67]

Thread cutting is always a challenge for me. You make it look easy.

 

[BladesIIB]

Thread cutting is always a challenge for me. You make it look easy.

Thanks. What usually gives you trouble? For me I usually have to take a few extra passes than I expect to. Just take little bits so I don’t go to deep, then spring passes at the same depth to be sure it is getting everything.

 

[Tincamp67]

The fact that I don’t do much of it and then getting set up to do it. i Just putter with small hobby stuff for myself and a few other people on a South Bend 9C. Since the chuck threads on to my lathe, I’ve been hesitant to trying cutting in reverse.

 

[BladesIIB]

The fact that I don’t do much of it and then getting set up to do it. i Just putter with small hobby stuff for myself and a few other people on a South Bend 9C. Since the chuck threads on to my lathe, I’ve been hesitant to trying cutting in reverse.

Yes, that makes sense. I do have to spend some time reading and taking notes before I get on the machine. Verify the depth of the relief groove, depth of thread, plan my passes etc. I recommend grabbing some scrap and just practicing when the finished depth does not matter. Practice cutting the relief groove. Setting your machine for the pitch you want and using the half nuts to practice stopping in the groove. Sometimes I have the most fun and get the most learning when I remove hitting any tolerance from the equation. Builds good skills and confidence in the process for when I do need it to count.

 

[mickri]

I made what I call a "chuck keeper" to keep a chuck from unscrewing when I have to run my lathe in reverse. As long as the threads on the keeper are different from the spindle threads the different threads will work against each other preventing either from unscrewing. The chuck end is sized to be a close fit to the inside of the chuck. The long shaft sticks out the outer end of the spindle. I have posted this numerous times whenever the prospect of a chuck unscrewing rears its ugly head.

 

[Tincamp67]

I’ve practiced on PVC first, then aluminum. Both went well several times, then I tried steel. Not so good. I’ve tried it a few times but have avoided it for a few years now. If somebody needs something that I can do with a tap/die, I’ll tackle that, but I’ve avoided larger projects especially internal threads. Good thing I don’t charge for anything, like BladesIIB, I read, watch videos, just to make sure I don’t screw anything up if I haven’t done it before. Takes me a while.

I may have to build a retaining rod like that.

 

[mickri]

After a lot of practice cutting both internal and external threads on PVC until I had the motor skills down pat I then moved onto steel and didn't have any problems. I use taps and dies for most of the small stuff. 3/8 and smaller. Anything bigger than that and I single point it on the lathe. I use the slowest speed on my lathe, 28 rpm, and take light cuts. A thou or two on the first pass to double check the TPI. Then move up to maybe .005 until I get close. Then a couple of spring passes and finish up with a thou or two if I need to. I always thread towards the headstock. I don't use relief cuts at the end of the thread. I disengage the half nuts and let the tool bit cut a grove. Then do what I need to do to make another pass.

I think that the most important thing is to practice one method until you have it down. For example on internal threads I have the tool bit right side up and cutting on the front side of the hole. This is how I learned how to do it. After reading a bunch of threads posted by people who actually know what they are doing saying that the proper way to cut internal threads is with the tool bit upside down and cutting on the back side of the hole, I tried that and after two passes I was definitely not cutting threads. I was able to save the piece by going back to my usual method.

Get some steel and practice, practice and more practice. If you can cut threads in aluminum, you can cut threads in steel.

 

[BladesIIB]

I’ve practiced on PVC first, then aluminum. Both went well several times, then I tried steel. Not so good. I’ve tried it a few times but have avoided it for a few years now. If somebody needs something that I can do with a tap/die, I’ll tackle that, but I’ve avoided larger projects especially internal threads. Good thing I don’t charge for anything, like BladesIIB, I read, watch videos, just to make sure I don’t screw anything up if I haven’t done it before. Takes me a while.

I may have to build a retaining rod like that.

I agree with @mickri if you can cut threads in aluminum you can cut them in steel. If you are grinding your tooling just be sure it has the relief you need. The PVC and aluminum will be more forgiving on the relief angle if there is not enough where steel could cause more issue. Also, be sure to use a fish tail to get your tooling square to the part. Even if you are not charging, I think a little practice would give you the confidence to not feel like you had to turn any threading project away. Good luck.

 

[mickri]

Mikey's long thread on grinding tools bits can help you out with the angles. The basics are on page 9 IIRC. Well worth the read.

I use an Atlas threading tool for external threads and a threading boring bar for internal threads. They came with my lathe. They are both ground for the proper relief angles. All I have to do is occasionally touch up the top edge with a hone. They both cut nice threads.



I case you are wondering what kind of QCTP I have I made a Norman style QCTP. A fraction of the cost of even the cheaper commercial QCTPs and gave me lots of practice learning how to use my lathe and mill/drill.