Which gives best finish out of the stainless steels?

I need to make a couple of parts on the lathe and wondering whether to use 303 or 304 stainless steel.

The part needs to have a smooth finish so it can be polished well.

It's a fair size lathe so I'm happy using 304.

Thanks.

In my experience freecutting 303 is a joy to use, and it requires real ability not to get a good finish. On the other hand I find 304 to be a real pig.

Andrew

303 is fine. You might find that as with all extruded materials that the skin is a bit dodgy but not much needs turning off to fix that.

There are better grades. If you google StainlessSteelsforMachining_9011_.pdf you should find a run down of many different types by the Nickel Institute

I just looked and it is still about.

John

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I'm with Andrew, prefer 303 every time for a decent finish and it polishes up to mirror easily..

I wanted 303 to carve out a hot cap for a Stirling Engine, The steel merchant only had 316 in the size I wanted, so when I said I'd take it, they gave me a discount of 50% with the words, your going to have a hell of a job with that stuff, hope this is a bit of compensation. Apart from streams of swafe, it machined to a good finish. Definately not free cutting.

Ian S C

Thanks. It's looking like 303.

interesting link, I'll read it later!

I've never had a problem with 316 either, turns beautifully and seems happy with fine cuts. It's only 304 that seems to be a pig.

Andrew

How strange. I've never had any trouble with either 304 or 316. I haven't ever used 303 so no idea. I always get a brilliant finish on either 304 or 316.

Carl.

Like Carl, I have had excellent results with 304. This is just one example

Brian

That is nice Brian. The British Stainless Steel Association give guidelines for machining all types. For the 300 series the main thing is a correct grade of carbide tip, deep enough cuts to prevent work hardening and plentiful lubricant.

Carl.

I wonder if this is a case of all will give a wonderful finish if emery cloth etc is used on it? I assumed a good straight turned finish is required. Just about anything can be polished up.

John

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Edited By John W1 on 15/06/2015 09:15:32

Edited By John W1 on 15/06/2015 09:16:15

One note on these materials.

316 which is commonly referred to as food grade is available in many forms, round, flats, hex etc

303's most common form is rounds and hex, flats are very hard to source.

304 which is the original hardaswitchestits, is also available in many forms but in flat form this now tends to be in sheared plate as opposed to rolled.

Probably to do with stock levels.

So if you want flats then please ask your supplier if it's rolled or sheared and if sheared then add 2mm onto the width to clean up if you want square edges.

Andrew

John W1

This example was a case of hewing out the metal, in this case with a small carbide button tool, and then smoothing the shape with various files before using a worn Scotchbrite pad to finish the job. It was a satisfying piece of freehand turning as well..

I've had equally good results making taper turned furniture knobs in 304 which were then finished with Scotchbrite to leave a satin finish. Good support to the work is I think very important so that flexing is kept to a minimum. Work speed is modest at around 300-400 rpm

Brian.

I went with 303 in the end.

I didn't realise it was a pain to find in odd numbered metric sizes though. Found some at mkmetals eventually!

I'v kept clear of using emery cloth on stainless, the finish is usually good enough off the tool, 90% of the work is done with HSS tools. The hot caps I used to make from solid, first bore out the inside, then Loktite it on a steel mandrel and take the outside down to size. Now days, I use thin walled SS tube, with an end TIG welded in place, might have to go back to the old method, my tame TIGger has been having eye problems.

Ian S C

I did have to make something last week and used a large A2 (304) stainless bolt. It wasn't too bad to cut, although I didn't try and get a mirror finish. I also threaded it (original threads were machined off) with one of those cheap packs of dies that you get in pound shops, no problems. Thread was very good!

I had a hour spare today but unfortunately the stainless 303 hadn't arrived (only ordered it yesterday so not moaning) so I used some 6/4 titanium!

It's not really a mirror finish but it's smooth and shiney!

Did a long pump shaft yesterday in stainless, 50mm in diameter and a couple of foot long.

It had worn quite badly where the seal track ran and so needed building up and turning back to size with a good finish for the seal.

Shaft after welding with 316 wire.

Completed shaft.

This was turned at 1200 rpm feed of 0.07mm per rev and no coolant.

I did take a video of it but You Tube will not upload it although it plays on my computer.

A bit that I missed, 316 is the choice for marine work, prop shafts etc, made lots of fittings for my Brother in law's 50' power cat.

Ian S C