View Full Version : Stronger cutting bits

11-29-2004, 05:09 PM
Hi -
I have a new lathe and been doing great with cutting aluminum and some soft steels. Now I picked up some stainless steel round stocks. This is extremely hard for the bits I have.

What bits do I need to order for cutting really hard round stocks of stainless steel on my lathe?

Links would be appreciated. Many thanks!

11-29-2004, 05:19 PM
Cobalt!! 40 SFM or so. The cobalt bits will have much greater impact resistantce if being used manually or in a cnc that is not very ridged. I dont really bother with carbide for steel for the most part except for high speed finishing operations at 100 FPM and 20-30k RPM.. Aluminum I use carbide 90% of the time.

11-29-2004, 05:33 PM
Thanks for the reply, you don't by chance have a direct link to the Cobalt bits? (where I can purchase them)

Thanks again!

11-29-2004, 07:02 PM
I can say where you would find them in the UK. I believe you could get them from any tooling store or from an industrial supply house. Cobalt bits are actually High speed steel with a cobalt additive. I use OSG almost exclusivley as that is what my tooling guy carries. I also use them almost explicitly in titanium, unless I am running a tricordial path or using insert cutters. BW are you using this in a cnc or a hand mill, Lathe?

11-29-2004, 07:08 PM
Thanks for the reply -
My mill is CNC but my Lathe is not.

I think the brand is a Sieg??? Not sure if I spelled it right. But the model of the lathe is a C6. Bought it from Arc Euro Trade. The lathe bits I bought from them are not strong enough for stainless steel. Great for aluminum and other things. But stainless is to hard.

Where do you buy yours from? I am in the UK myself. Do you have a phone number and a point of contact I can call? Also are the titanium bits expensive and are they hard to shape on a grinder?

Thanks again!

11-30-2004, 03:39 AM
I use Mo Max cobalt M42 from Cleveland. Go a pack or 12 blanks of Ebay. Great stuff.

11-30-2004, 05:16 PM
One of the "tricks" when turning stainless is to maintain what may seem to be a rather aggressive feed. Stainless can work harden, meaning if you try and shave or do some wee cuts, the steel will harden, the bit then rub, hardening it more, and making the problem worse. Cobalt is good stuff, but with technique (and depending on the SS alloy) good ol' HSS will do fine as well, but it won't hold an edge as well is Co. HTH


11-30-2004, 11:47 PM
If you can rig up flood coolant, it will surely help your tools a great deal. The top rake and side rake angle of your tool's top surface can be more acute than you'd think. Stainless isn't hard, it's just that the chip won't flow. A negative rake tool, or one with low rake angles causes the chip to pile up on the tool, instead of flowing away.

Stainless is a poor conductor of heat, too, so this tends to concentrate the heat at the tool tip, and is why cobalt is a good choice.

But, flood coolant will make the most extreme difference in tool life.

12-01-2004, 01:25 AM
For my lather work (non cnc) (powermatic geared engine lathe), my surface speed for 316 stainless is right around 175 or so (not sure how acurate the speed is.). I use carbide sandivk insert cutters and tian coated inserts. I use my own little flood coolant setup which is a light oil for steels and regular coolant from my cnc for aluminum work. The flood coolant is just a bucket hooked to a small 12v pump. I also use this on my band saw and lower the voltage via a rehostat to control the flow.

I have purchased a set of these lathe tools and am very happy for the price.


They use the tnmg or tnma inserts from various manufactures. Just make sure the screw is tight :)... If you cant get them to ship to you let me know and I will ship them for you. I ship (from) the UK often for my sierra parts.. Have any of those laying around :) cossie stuff rocks lol.. Hope that helps you out a little.


12-01-2004, 06:27 AM
Thanks for the replies - not sure what cossie stuff is to be honest.

12-06-2004, 12:18 PM
I just want to reinforce what the Swede said.
It is very important to keep the feedrate high and the heat low; once your part work hardens it is scrap (unless you want to grind or EDM it).

12-06-2004, 03:56 PM
Why keep feed rates high and what do you mean by high?

12-06-2004, 09:04 PM
You might want to use carbide tool bit, if you are cutting tougher & harder materials, like stainless, or alloy steel. For a small lathe [home shop] I would get 1/2" square, Kennametal brazed bits, left hand tool.[should be able to get in U.K.]

12-06-2004, 11:17 PM
It takes the right coating on carbide, or stainless will stick to it. This happens rapidly, in the phenomenon known as "built-up edge". The metal welds to the tool, then breaks away repeatedly. It tends to pull little pieces of the tool with it. In particular, you get notching of the carbide tool at the depth of cut mark.

This doesn't happen so often using HSS or HSScobalt tools, and they actually work quite well if flood cooled. The truly sharp edges of HSS tools cause less work hardening effects than typical honed carbide inserts. Did I mention that they have to be kept cool? ;)

The only "work hardening" I've experienced on stainless is while drilling and, if the drill fails while in the cnc on automatic, it just keeps on pressing it down anyways, attempting to fuse it to the part. THAT makes a hard spot :D

12-07-2004, 12:00 AM
I should have mentioned it, to make it work 100%, you have to grind a nice positive chip breaker on the tool, that way, you ensure a nice flow of the material, I do it all the time and it works like a charm .

12-07-2004, 02:36 AM
I should have mentioned that with regard to carbide as has been said a netral or positve rack is a must and that is why I use ticn coated inserts vs tican inserts for this very reason (my lathe has a max spindle speed of about 2500 rpm). I fyou use a negative rack liek you would for a hhs or a hss cobalt bit (many differnt grades of hss) they can take the shock or the long stingy chip assosiacted with the negative rake. If you grind your own bits ( I dont unless necessary) it is much easier to use the correct insert cutter as you know it will be sharp vs your hand ground bit that may or may not have the proper trailing edge for clearance etc. It is crazy how many variables can be had with different cutters. I personally have never been to realize some of the feedrates my cnc is capable of vs spindle speed / RPM as the macine will not move fast enough!! 40k soindles is onlu good on certain applications.