How to thread stainless

Remember, which grade of stainless matters. You mentioned 304 and are looking at getting 303. I've done both and didn't do anything real special. On 304 I used import carbide inserts and a holder I got from ebay. On 303 I use HSS that I grind. I can't see HSS chipping on 304 unless you are running way too fast, which you shouldn't be for threading.

I don't use the compound when threading, just straight in. It might help to use it on 304 due to work hardening though. Use plenty of cutting fluid. I find tap magic works pretty well, kool-mist in the sprayer is nice as it keeps temperature down. If you hone the HSS properly, it should help keep the heat down.

For general turning I usually use HSS, but if I want to remove a lot of material quickly carbide is nice. As it's for roughing, I don't really worry about the finish and just let it be a bit rough. My carbide holders are all import stuff, but I do have some brand name inserts that work well with them. Well, they claim to be brand... Hard to say sometimes with ebay, but I'm not willing to pay new prices for my hobby.
 
I was running 65 rpm. It was 304 and they were hss brazed inserts at 60 degree angles. I went in at 30 degrees. They chipped instantly.
 
I would go with a lay down type threading insert holder with Carmex (Iscar) carbide insert. This seems to be the least expensive, you can go to the Carmex website and they list different inserts grades, although I find the BMA works on a wide range of materials. David Best is the go to person for turning 304 stainless, he also put together a book on indexable tooling which goes through all this in great detail. General turning I use CCMT/CCGT 32.51, you can get inserts specifically for stainless, but you need to have your speed, feeds and DOC dialed in aggressively so it does not work harden. 304 is probably the least forgiving, 303 and some of the other SS grades turn much easier.
 
For 303 S/S threading, the HSS tools work fine, just run a little slower than if working with mild steel. The Aloris threading tools work very well and since they are only sharpened on top and have a long length vertically, they have quite a long life. I do all my threading using the compound at half the included thread angle.
 
FTlatheworks said:
I was running 65 rpm. It was 304 and they were hss brazed inserts at 60 degree angles. I went in at 30 degrees. They chipped instantly.
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I can't say that I have ever heard of brazed HSS inserts --- There are either inserts or there are brazed tools which are likely to be a carbide blank brazed to a steel shank, these, as commercially made may not have enough clearance ground on the leading edge for threading purposes.
 
FTlatheworks said:
29 degrees not 30
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29 versus 30 degrees is a matter of taste, I was educated to use 30 degrees, worked in a large shop in my apprenticeship and as a journeyman, and nobody used 29 degrees, and subsequently nobody that I had working in my business used 29 deg. either. It is said that 29 deg. is used to clean up the backside of the thread (the RH flank of the thread) In my observation, the spring passes perform that task well enough.
 
FTlatheworks said:
isnt the ccgt inserts for brass and aluminum?
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Yes, but due to the sharp edge, it works very well for semi-finishing and fine finishing in stainless and steels as well. Downsides are moderate tool life, and chips that won't break. You can get a beautiful finish.
 
benmychree said:
I can't say that I have ever heard of brazed HSS inserts --- There are either inserts or there are brazed tools which are likely to be a carbide blank brazed to a steel shank, these, as commercially made may not have enough clearance ground on the leading edge for threading purposes.
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My mistake, they are steel shank and brazed with a hss 60 degree insert. I don’t think they are of a high quality.
 
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