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Threading tools

G

garageguy

Super User
Premium Member
I did some more threading today( 3/8-24) and am real unhappy with the results. I was using a brazed carbide tool and that may be the problem. What are you guys using to single point threads, HSS ? The partial profile carbide inserts look good but I can't run fast and am afraid they would give the same results. The thread I cut looked ragged and seemed like a poor profile. Should I be using HSS ?
 
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HSS will usually be sharper and give a better finish than carbide. As you mentioned, slow speed is problematic with carbide.
I do have a carbide insert tool that I like (Mesa Tool) but it's hard to beat hss for slow threading.
 
140mower said:
I'm probably going to be the odd duck here (not for the first time), but I love external threading on the lathe. Hss, carefully ground and stoned, set to center and lots of cutting fluid has never failed to put a smile on my face.....
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Other than the threads, what is the finish like? Some steels just don't cut nicely!
 
I use these tools for threading and grooving. Clean cuts in every material except phosphor bronze.
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For the most part, the harder the steel, the better the thread looks. Try some 4140 or 4340, that should give a nice crisp thread. Some of the lesser grades are hard to get a finish out of no matter what you do.
 
I should have added that I was working with 7/16 cold rolled steel, cutting a short 3/8 thread to a shoulder. A die would not cut up to the shoulder and the thread was only about .500 long. I don't have any HSS ground for threading but will get some ready for next time. @Arbutus , are those inserts carbide?
 
Certain drops of CRS can be plain ratty I find. I have some 1018 that I save for sh*t work, I don't know what it is with the stuff. It always needs post-finishing. Yet I have some 1018 from a different supplier, not great but not horrible.
12L14 free machining steel will make you look like a champ without doing anything special & its very common to source. About as strong but not recommended to weld. Personally I get about the same results between HSS & cheapo carbide threading inserts. And I have violated the SFM recommendations of carbide running at my lowest speed without blowing anything up. But I never got along with brazed carbide threading tools for some reason, had the typical edge chipping problems with high frequency that gives them a bad rap. HSS is the most forgiving & you may never decide to change.

This is an AliExpress holder/insert. I think the toolholder was like $10 & 10 pack of 3-edge inserts was $35 (they vary by size/coating etc.).
 

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140mower said:
I'm probably going to be the odd duck here (not for the first time), but I love external threading on the lathe. Hss, carefully ground and stoned, set to center and lots of cutting fluid has never failed to put a smile on my face.....
Click to expand...

You are not alone @140mower . QUACK QUACK. I love threading too. I even like changing gears to do it.

@garageguy - Almost all my threading has been using HSS. I have the Mesa Carbide and I like it, but the tips do like to chip - prolly cuz I go too slow.

Harder steels finish better. But in my humble opinion, the key to a really nice thread in softer metals is to use the 29.5 degree method with a SUPER SHARP tool - as sharp as you can make it. Grind it and then lap it till it will shave the fur on your arm. Yes, it will dull easily, but your threads will be beautiful.

I have it in my mind to improve my plunge threading skill level, but for now I still like 29.5.

Oh yes, and make sure your tool is on center with minimum stick out. Choke up on the part too. Too much part and tool stick out are hard on finishes.
 
@garageguy - here are some old threads on threading. Lots of great stuff in there by lots of members

Thread 'Threading - 29.5/30 vs 90' https://canadianhobbymetalworkers.com/threads/threading-29-5-30-vs-90.5411/

Thread 'What are you guys using for lathe threading tools?' https://canadianhobbymetalworkers.c...ou-guys-using-for-lathe-threading-tools.4553/

Post in thread 'Piston V.S. Wedge AXA QCTPs Question..' https://canadianhobbymetalworkers.com/threads/piston-v-s-wedge-axa-qctps-question.4122/post-54946

Thread 'Please school me on internal threading, tool holders, inserts, HSS etc.' https://canadianhobbymetalworkers.c...-threading-tool-holders-inserts-hss-etc.3471/
 
Well, after thinking about this for a while I am leaning towards the CRS as the culprit. In the past I have threaded spindles and axles and have never had such pathetic looking threads. And that was with the same tooling. This was the first time threading CRS and probably the worst example I have ever produced. I think PeterT nailed it. @Susquatch ,I will check the threads you linked and go from there. Thanks everybody for your thoughts and comments!
 
@kstrauss The finish looked like the metal was being torn off instead of sliced. very rough surface finish even after spring cuts. I am running as slow as possible, 80rpm I believe.
 
garageguy said:
@kstrauss The finish looked like the metal was being torn off instead of sliced. very rough surface finish even after spring cuts. I am running as slow as possible, 80rpm I believe.
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It's useful to watch some videos that @PeterT posted a while back.

I can't seem to find them. Maybe Peter or @YYCHM can help.

Basically, torn off or gouged off is a pretty good description of what usually happens. I suspect maybe the advantage of carbide is to smoosh (burnish or press) everything back together smoothly after the carnage. But if we find that video, you will begin to wonder how you ever managed to get a good finish on anything. Then again, if you ever look at what lives on your own skin you will wonder how you managed to live long enough to wonder about it.

The magic is in controlling that God awful process such that the result is still a good finish to the human eye.
 
I’m with Mower, about 95% of my external threading is single point. I like going full depth to the end and then ramping out (I’m qwerky, it is my own little signature thing - I like the look) - can’t get that with a die. With single point you can fit the thread if you want, and I get a nice surface finish.

I don’t know why you are not getting a nice finish, the suggestions posted above are good, and basically describe what I do. The brazed carbide tooling should work fine (I used it for several years). I like the Mesa tool, which is very similar to the Nicole offer. It is true the tip pops off easily, but I have a good arrangement for retouching the edge (generally sharpen it up to 3 times). I also use the partial profile and full profile lay down inserts (3 little points), carbide - gives a very nice finish. I like the ~29 degree on the compound, I don’t think the number matters much, just slightly steeper than 30 degrees. Staight in threading is fine, lots of people seem to make this a hill to die on - not a big deal either way IMO.

Speed? It is good to go faster than the typical threading speed, but slow isn’t a problem. I do most of my threading on a small English machine and it allows speed change on the fly - I start out ~100rpm and as I approach the end of the thread (ie a shoulder or the ramp out), then I reduce the spindle speed to 30rpm. The results are great. One could do the same thing if they had a VFD drive (speed change while threading).

Threading is another of those competencies that improves as you work at it. Keep trying, you’ll get it.
 
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