Threading issues with metal choice

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VTdave

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This could probably be a general question, but since I've got an Atlas lathe, though I'd start here. I'm learning to thread and have had some success. My question has to do with various grades of steel for threading. I'm cutting basic 1/2-20 threads. I started with some 1/2" steel from a local fabricator, and after a few failed attempts, got to where I could somewhat consistently cut threads onto which I could pretty easily screw a nut. I then got a piece of 1/2" steel rod from Tractor Supply, and I haven't been able to create a thread that I can get a nut on for the life of me. To test whether it was my setup or the metal, I tried the identical setup on a piece of 1/2" aluminum, and that worked.

One of the things I noticed about the TS steel is that the cut wasn't very clean--lots of rough spots, burrs. etc. Once I finished the thread, I could get the nut started--about a turn--but it wouldn't go further. So I'm wondering if it's just the quality of the steel, given that I was able to use the same tooling, speed, etc. successfully with the other steel and the aluminum. Or, does it sound like I might be using the wrong tool or speed, etc. with the TS steel? Thanks.
 
Cheap steel, might be good to weld to, (might not, too) otherwise it's not really machinable. Buy quality steel, it's worth it.
 
VTdave said:
This could probably be a general question, but since I've got an Atlas lathe, though I'd start here. I'm learning to thread and have had some success. My question has to do with various grades of steel for threading. I'm cutting basic 1/2-20 threads. I started with some 1/2" steel from a local fabricator, and after a few failed attempts, got to where I could somewhat consistently cut threads onto which I could pretty easily screw a nut. I then got a piece of 1/2" steel rod from Tractor Supply, and I haven't been able to create a thread that I can get a nut on for the life of me. To test whether it was my setup or the metal, I tried the identical setup on a piece of 1/2" aluminum, and that worked.

One of the things I noticed about the TS steel is that the cut wasn't very clean--lots of rough spots, burrs. etc. Once I finished the thread, I could get the nut started--about a turn--but it wouldn't go further. So I'm wondering if it's just the quality of the steel, given that I was able to use the same tooling, speed, etc. successfully with the other steel and the aluminum. Or, does it sound like I might be using the wrong tool or speed, etc. with the TS steel? Thanks.
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steel from the TS and lowes by me is 12L14 up to 3/4 inch. pretty lucky around here.
 
It would have to be labeled. 12L14 would be ideal for the OP's screw cutting practice: the inclusion of a bit of
lead makes it very easy to machine. Ebay is the place to buy small quantities if local suppliers don't have it.
www.ebay.com

12L14 Steel Bar Stock 3/4 in Round x 10" -11.75" in Long (1 PC) | eBay

These are ranging from 10" minimum length up to 11.75" Price Reduced for quick sale.
www.ebay.com
 
TS steel is most likely cold-rolled (C1018) which machines like sh*t at best (but welds nicely) and tends to raise substantial burrs. Did you deburr the thread with a triangular file then hit the crests with a flat file?
 
The crap you can buy at my local hardware place is cold rolled 1018. It is NOT of a consistent diameter - might be 1/2" +/- a few thou - nor is it straight. It turns like typical 1018 - burrs all over the place. So, I agree with MrWhoopee that it is likely the steel and not you.
 
If your thread is tapered then there is a rigidity problem. If you are not doing so already, try supporting the workpiece with a live center in the tailstock. Also try to improve the rigidity of the cutter. If neither is possible, then just keep taking spring cuts until the cutter stops removing metal. Thread cutting oil is helpful - the stuff they sell at the hardware store for cutting pipe threads works well. And yes, the metal aloy makes a huge difference. I use 12L14, 6061 aluminum or brass 360 most often. They make even a novice like me look good.
 
It's the steel, it's not you or the lathe. Garden variety steel tears like crazy sometimes. Use plenty of cutting oil and razor-sharp bits it helps minimize the problem.
The 4xxx series of chrome-moly steels machine very much better but cost a bit more
-Mark
 
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