Cutting Threads with a Die on a mini

[jschmidling]

Here is a link to a photo of the difference between thread cutting die and a rethreading die post #5:
https://www.practicalmachinist.com/vb/general/my-die-cutter-rethreader-331563/

Don't quite see what you are referring to but perhaps you can tell me what I have from a picture of my die.

js

 

[Downunder Bob]

After successfully cutting a 1/2-20 thread on aluminum, I decided that it just isn't worth the trouble for the things I have in mind. So I ordered a 1/2-20 die but had to wait till it arrived before I could order a stock to fit it.

As usual, patience lost and I made the wonderful tool shown in the pic out of a pipe fitting and a piece of aluminum bar. It fits into the tail stock chuck of course. I figured that I could at least get a good start on a thread and probably have to grip the tool with a wrench to finish it.

I never intended to run the motor but just rock the chuck back and forth as I did with my South Bend.

Well, it's a total failure. It never occurred to me that the chuck on the lathe could not hold the bar while applying the force needed to thread with a die.

I took it out and clamped it in a very large bench vice and it held but the force to cut seems absurd and this is just aluminum. Obviously, the hand held die stock I ordered isn't going to solve the problem.

The only thing that occurs to me at this point is "Chinese Junk". It's packaged and name branded but no clue of the type of steel but it shouldn't make much difference on aluminum.

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Any ideas?

JackView attachment 299636

That die as you call it, actually looks like a die nut. If so it is not meant fro cutting a new thread, but is meant for cleaning up a damged thread or finish an already roughly cut thread.

You will find that a proper die will have a split in one side and can be adjusted for a tight or loose fit, always adjust for a loose fit for first pass and then tighten up to finish. They are almost always circular and require a special stock to operate it in. The stock has 3 screws for adjusting the depth of cut.

Also if you look at both sides of the die you will see that one side has a long slow lead in, the other has a rather sudden lead in. Normally you would start by using the long slow lead in, and only use the other side if you need to finish up against a shoulder.

A proper die should cut aluminum very easily.

Happy threading.

 

[royesses]

Don't quite see what you are referring to but perhaps you can tell me what I have from a picture of my die.

js


View attachment 299751

Js, that die looks like a standard threading die. Maybe because the photo is kind of dark it looks like it is not sharpened properly. I have round and hex dies that are for threading and also have a rethreading tap die set. Many of them are imports from various countries. They all cut aluminum very easily. I think you might have a defective die. The rethreading dies just force the existing thread back into shape and don't cut at all. Yours looks like a combination of a rethreader and cutter. Maybe you can borrow a known good die from a friend? Just to try out. Even 6061 T6 aluminum cuts easily with my dies in the chuck of my mini lathe. As Downunder Bob said maybe it is a die nut.

Roy

 

[RobertB]

That die looks to have relief angle from the leading edge (could just be angle of picture though), hence it would be a thread cutting die. That said, I think the problem is that it is just a very cheap, poorly made die and is not very sharp. I think a quality die, such as Morse, Greenfield etc. would solve your problem. Also 3 times as much cutting oil as you think it needs. Threading with taps or dies requires LOTS of the proper cutting oil for the material being cut

 

[Flyinfool]

I did a quick drawing of a thread repairing die vs thread cutting die. I drew this exaggerated to help illustrate the point.
The one on the left is the repairing and the one on the right is the cutting.

 

[jschmidling]

I did a quick drawing of a thread repairing die vs thread cutting die. I drew this exaggerated to help illustrate the point.
The one on the left is the repairing and the one on the right is the cutting.View attachment 299765

Thanks for taking the trouble with the drawings. Looks like I have TCD but is probably a junker.

I guess I made a bad assumption about the value of a known brand, i.e. "True Value". Meaningless gibberish these days.

js

 

[Flyinfool]

I have never had good results from any threading tool of the "True Value" brand.

 

[grotto]

I've found using blunt or low quality dies is almost useless. A few times I've had similar results to what you've described, and using a different (sharp) die has solved the problem.
Some low cost dies don’t even seem to work when new, but I've plenty of really old quality ones which still cut great.
I tend to stick with recognised brands, but they're pretty expensive if you're buying them new.
I did get some Chinese ones which are really good, much to my surprise. Wish I'd bought more.