Cutting Threads with a Die on a mini

J

jschmidling

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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.

www.ebay.com

Master Mechanic Hex Die Various Sizes 1/2 1/4 1/8 3/8 3/16 5/16 7/16 | eBay

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Any ideas?

JackLATHE.JPG
 
jschmidling said:
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.

www.ebay.com

Master Mechanic Hex Die Various Sizes 1/2 1/4 1/8 3/8 3/16 5/16 7/16 | eBay

Find many great new & used options and get the best deals for Master Mechanic Hex Die Various Sizes 1/2 1/4 1/8 3/8 3/16 5/16 7/16 at the best online prices at eBay! Free shipping for many products!
www.ebay.com

Any ideas?

JackView attachment 299636
Click to expand...
Try this. I made it for myself and it works great.
 
I just added a pin that fits into the side of the die housing wich rides on the cross slide for slipping purposes when you can not hold tight enough if you know what I mean. Just plase a piece of wood between bed and pin.
 
I know people do it, but are those die made to cut full depth threads or to clean or finish threads already there?
 
Full depth,but I must say that the coarser the threads the more difficult it would get. I only use it for finer threads. When I do coarse threads, I pre-cut it with the lathe and if I do have a die for that size, I would finish it with the die.
 
I've found that anything bigger than about 3/8" will slip in a lathe chuck when using a die. If you must use a die on a large thread, at least screw cut the thread until nearly finished and then run the die.
 
Your die might well be a big part of the problem. Note that it's a "full circle" type. These are generally used for repairing/restoring existing threads. New threads are generally cut with a die that has an adjustable gap in the periphery.
Whatever kind of die you use, you can probably get an easier start by putting a bevel on the end of the workpiece. Assuming strength is not too critical, you could also reduce the diameter of the workpiece slightly. This will reduce the force needed to cut the threads. Your plan to start the die on the workpiece, then move it to a bench vise and use a regular diestock, is also good. The first few threads will at least start the die perpendicular to the part.
Do you have a good cutting fluid?
 
I've die cut threads in 1/2" in 4130 steel and 6061 T6 aluminum on my mini lathe. I turn the stock down to .498" first. If it is exactly the size of the die it creates a lot of extra pressure. I made an adapter to use an 8" hand wheel to turn the spindle by hand. It uses a bicycle type wedge to lock into the spindle bore. Perhaps the aluminum rod you used is too large in diameter and that caused the problem? Also if the stock slips in the chuck I wrap a piece of brown paper bag around the stock before chucking it. That seems to give more grip.

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Roy
 
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Hex dies are generally not made to cut threads from scratch, they are for cleaning up threads on damaged parts, they are called "hex rethreading dies". Circular OD dies are designed to cut original threads. Also sometimes it makes it a lot easier to use a die if the thread is nearly finished with a single point tool, then the die is used to do the final finishing, this results in a thread that does not wobble as when a hand die does not start truly, or can develop a wobble as the thread proceeds.
 
Are you starting the die from the correct side? Try turning the die around in your holder and trying again.
 
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