Turning stainless steel

[epicfail48]

Any simple way to tell what you got from the scrap bin, other than try a piece and see how it behaves?

Only trick I know of is the magnet test, if a magnet sticks it's (probably) 400 series stainless, otherwise it's (probably) 300. Most other tests are going to be a bit more involved. You can try welding it, if its non-magnetic and welds clean there's a high chance it's 304

[DR]

There are premium grades of stainless available that machine very well. They come at a price and can be hard to find in small, hobby type quantities. Carpenter Project 70 316 alloy was one we used a lot. Unfortunately Carpenter seems to be trying to get away from small quantity online sales.

The way these easy to machine alloys are formulated is to skew the ingredients that make stainless hard to machine to the low end of the alloy spec. Likewise the things that make stainless easier to machine are skewed to the high side of the alloy spec. The material comes in a fully annealed condition. Cost can be 2 times or more than the cost of off the shelf material, but the cost savings in tooling can actually make the material less expensive in the long run.

Just about every mill that specializes in stainless alloys has their own version of these premium materials, it's just a matter of finding them.

[wierdscience]

Having a good carbide insert that performs well in stainless helps greatly. These can occasionally be found on Ebay for less, but they are worth the money IMO.

https://www.mscdirect.com/product/details/70926365

https://www.mscdirect.com/product/details/91141549

Follow the speeds and feeds suggested by the mfg and even 316 will break a chip. Adding water sol coolant increases insert life, but it's not a hard requirement.

[Mcgyver]

303 and 416 machine like buttah. 304 and 316 not so much. .

this.

to remember, there's a low end little rhyme...304 she's a whore, 303, she's for me.

I don't have to make stuff to anyone's drawings, so it would have to be a good reason to not run a free machining stainless. Sheet & plate, you can't get (or least not easily/commonly) free machining so you deal with it. Run slowly and take a big chip. (reminds me of Teddy R, walk softly and carry a big stick). That will make it easier to avoid dwelling which will miserably and seemingly instantaneously harden the material. use coolant

[R.Bolte.Jr]

Some great advice in this thread.
The only thing I'll add, while it demands respect, don't fear stainless. It can be a very satisfying material to work with. A little practice and you can get great surface finishes that don't require any further treatment to stay nice. Even people who don't know a lot about machining will be impressed with whatever doodad you show them that you made out of stainless. lol

[oxford]

Some great advice in this thread.
The only thing I'll add, while it demands respect, don't fear stainless. It can be a very satisfying material to work with.

This is a very good comment. My experience is only with 304, I worked for an equipment manufacturer for the food industry and we dealt with a lot of it.

It isn’t some mystery metal, learn a few tricks and it isn’t hard to deal with.

I will say normal round bar for the most part comes oversize, out of round, or both unlike cold rolled round bar. If you need to use it for shafting or plan on it working for nominal fits you will need to do some work if you don’t order ground material.

Barstock and angle can be hit/miss as well, keep your expectations of it to be more like hot rolled steel vs cold rolled.

With the above said, I wasn’t involved with material purchasing and who knows what type of grade/finish that place was buying.

[garyhlucas]

I was turning 304 on a SB heavy 10 with a big chip coming off. My said “Our machinist said our lathe couldn’t cut stainless!” I said HE couldn’t cut stainless. Put the back gears in for high torque and low speed and feed fast and deep to get a thick chip and it machines just fine.

For those of you that don’t know, 303 machines easily but cracks if you weld on it. 304 & 316 weld fine.

[MrWhoopee]

I will say normal round bar for the most part comes oversize, out of round, or both unlike cold rolled round bar. If you need to use it for shafting or plan on it working for nominal fits you will need to do some work if you don’t order ground material.

^^^This^^^

Be very careful with standard stainless round bar. It is mechanically straightened and the straightening rolls create a three lobed effect. The shaft will frequently mic on size but is not actually round.
Order 316PSQ or 416PSQ (pump shaft quality) if nominal size is important. It's the stainless equivalent of TGP. 316 for maximum corrosion resistance (acidic environment like tomato processing), 416 for better machinability.

[oxford]

Be very careful with standard stainless round bar. It is mechanically straightened and the straightening rolls create a three lobed effect. The shaft will frequently mic on size but is not actually round.

This is what I have seen, I was going to call it egg shaped and yes, it will read correct with a micrometer.

[polaraligned]

to remember, there's a low end little rhyme...304 she's a whore, 303, she's for me.

Sounds like 304 is the one for me.

[tom_d]

Any simple way to tell what you got from the scrap bin, other than try a piece and see how it behaves?

First thing to do is put a magnet on it. Doesn't tell the whole story, but does narrow it down. If it's sticky it's most likely 400 series. The 300 series stainless is not magnetic.

[garyhlucas]

That triangular shape is called a trochoid, and it is why you can’t measure roundness with a two point instrument like calipers or a micrometer. You need three points. Explaining this to a so called precision machinist got me a week off when he got mad at me. I learned later he had secretly scrapped 3 housings because they weren’t round.

[JRouche]

How hard is ss to turn. Any harder than steel. Never welded or turned any of it. Just wondering.

I love to turn stainless steel, all of the types. Never found one to be difficult. Not all will have a great finish.

All I have turned was very simple./ Machining or drilling? My worst times. JR

[Mcgyver]

Sounds like 304 is the one for me.

lol, then take Doozers advice and just don't dwell

[MrWhoopee]

lol, then take Doozers advice and just don't dwell in the cu*t.

There, fixed that for ya.