Stainless 316 - Yikes!

Cutting 316 is a matter of experience. First, a light weight machine doesn't work well. Second, 316 is sticky, you need lots of relief to ease dragging. Third, you should use a slow speed and a high feed. Fourth, the tool nose should be 2 feed revolutions wide. High speed steel with cobalt 5% or more works very well. Carbide tools induce a lot of drag. If you must use carbide, use a negative holder to increase relief. The use of a HSS tool will not contaminate the weld. The use of a coolant also helps, but use an oil, not the water soluble type. You want to use something that lowers the chip friction. Even diesel fuel works well applied by brush. Steve

You didn't mention the grade of carbide you used. Machining stainless is ultra critical regards insert life. If you used a C5 or similar grade, you screwed up big time. C2 is highly recommended for stainless (Carboloy

883, for example, is a great choice).

You'll have better luck with tougher grades of stainless if you allow the machine to take a lighter feed and use considerable positive rake, but even that's a delicate balance. It's often a recipe for tool failure, too. For the most part, anything but 303 is a bitch, and nothing makes it much better. Negative rake works fine if you have the power to pull the cut, but if you don't stop at the right point, the usual result is a broken insert.

Harold

Unless you are either facing to the center, or cutting a taper or profile, you should give the tool greater relief by setting it .005 to .010 from center. For turning and facing set the tool below center. For boring set the tool above center. The rule is - Turn below, bore above.

This is your clue that the rough finish has something to do with the cutting tool geometry. Perhaps you have a smaller nose radius on the HSS tool which is reducing the cutting force. Are you getting any vibration or ringing?

304 welds fine, as easy as 316. It is 303 that is not recommended. As a side note- it is 303 that cuts with a very rough finish as though the material was tearing. It almost sounds like you are cutting 303 instead of 316. It is carbide that causes corrosion from being embedded in the surface. Passivation will remove the carbide particles.

I've read what the others have written, and I cannot specifically comment on stainless.

However, hand feeding an indexable tool sounds like a bad idea unless the tool is specifically made for low horse machines (sharp). What's the horsepower of your lathe? Heavy feed usually means heavier than you can reasonably push with your hand, especially at a reliable rate. I can't imagine getting my hands in line with a cut at the correct feed and speed to get many indexable cutters to work correctly. (500+ SFPM, feed at .010"+/rev in mild steel).

YMMV.

Regards,

Robin

I don't have much (hardly any) experience turning stainless, but I wanted to make some small parts out of 1/2" round 316 a while ago. Using a 12x20 Chinese machine and hand ground HSS cutting tools with a significant top rake angles worked well. The best finish I achieved was using lanolin for cutting lube. I got 2 ounce (weight) tubes of it from Enco for about $5 each.

The parts also needed to be knurled and drilled and tapped 3/8-24 and #6-32, and Lenox Pro Tool Lube was used for these operations. The parts turned out well and there weren't any cutting tool failures. My metalworking tasks are for enjoyment, not for production schedules.

WB ...........

316 is just plain nasty to work. High chromium, keep the speeds low, treat it like a hardened steel. Don't let the cut stop once it's started, you might not get it started again. Feeds, depending on how you're holding your tongue, and the way the tool is sharpened can work from very light to heavy. If you can get away with heavy, so much the better. No light cuts, that .005" finish cut will only eat the tip off your tool, leave at least .010" per side. Lube, I use plain old thread cutting oil, high sulfur, the boss uses another, he swears by his, I swear my mine. Rough finish, in my case, has always been chip scarring, use more top rake. HSS works as well as anything, and allows more freedom with angles. Keep the tool sharp, I use the diamond wheel to just polish the edge, seems to help. Sometimes, not always, grinding to a sharp point, then break the point .015" to .020" helps, more depends on the tool angles. 316 isn't fun to work.

What sort of carbide bits? The best are uncoated bits designed for non ferrous applications which have much sharper edges than most others. I can get a good finish with light cuts on anything from aluminium to stainless steel engine valves with those.