View Full Version : Lathe cutters

10-22-2007, 05:38 PM
For general purpose cutting of anything I might find in my garage (wood, plastic, aluminum, mild steel, cast iron, head bolts), am I going to notice a difference between M2 HSS and 5%, 8% or 10% cobalt? Or, are the cobalts worth the extra money for something that I'd use 95% of the time?

Would a 6" bench grinder, pliers, a wheel dresser, and a cup of water suffice for 1/2" square stock? Are any special wheels are required for grinding the M2 or any of the cobalts?

10-22-2007, 05:50 PM
You probably won't notice a whole lot of difference. M2 is fine for general-purpose use.

Personally, I use Cleveland Mo-Max cobalt. I find that it's somewhat more durable than M2. It does cost more than M2, but since any toolbit you get will last you basically "forever" and you won't need more than half a dozen assorted shapes total, I think the incremental cost is worth it. Your mileage may vary....

To grind HSS you want a good grinding wheel. Maybe some of the other guys can give some recommendations. I use silicon carbide "green grit" wheels, which is officially the wrong wheel to use for HSS, but I like the way it cuts. It tends to wear pretty fast and generate a lot of grit, comparatively speaking, but it cuts well and tends to run cool.

10-22-2007, 06:01 PM
Over the few years I've been doing this now, I have developed a preference for the cobalt cutters. Last time I stocked up with blanks I got all 10%. They are more resilient than M2m and seem to hold an edge better in the face of increased heat. I've also been cheating and getting 3/8" bits rather than 1/2". Slightly cheaper and ALOT less time at the grinder--just use 1/8" shims.

10-22-2007, 06:18 PM
I would agree that M2 is generally more than adequate for the type of stuff you are turning (except maybe the head bolts). If you are turning aluminum and brass you might find that the tools will stay sharp for quite a while.

As far as using 1/2" stock, you can save yourself some sharpening time by using 3/8" or even smaller stock. You can take off quite a bit of metal using a 3/8" tool.

10-22-2007, 06:20 PM
I heard, from this site, that hard wheels were generally for soft steels and soft wheels were generally for hard steels.

My bench grinder has an aluminum oxide 60 grit on one side and a silicon carbide 60 or 80 grit on the other, i can't remember. Anyway, i would rough out the shape on the aluminum oxide wheel and sharpen stuff with the silcon carbide. It does disenegrate faster but it keeps the bit your sharpening cooler so your less likely to loose your temper.

10-22-2007, 07:09 PM
Last time I stocked up with blanks I got all 10%. They are more resilient than M2m and seem to hold an edge better in the face of increased heat.

M42 (which is 8% cobalt) has higher red hardness, and higher wear resistance than M2, but for turning medium or low carbon steels, I don't see a heck of a lot of difference.

By the way, where did you find 10% cobalt? Is that a propriety alloy?

10-22-2007, 07:15 PM
Good thought about using something smaller than 1/2" toolbits. Unless you have a lathe a lot bigger than I expect you do, 1/4" toolbits are probably more than big enough. They're cheaper, and easier to grind. Make up a few toolholders out of 1/2" square stock with a notch in them to take the 1/4" toolbits, if your toolholder can't handle 1/4" toolbits directly.

10-22-2007, 07:21 PM
10% cobalt at J&L:


10-23-2007, 03:19 PM
10% cobalt at J&L:


Ah, that's a Chinese tool blank. I've had really bad luck with the Indian and Chinese high-speed steel, either cutters or lathe tool blanks. What would concern me more is that they don't claim it's M7 or M42, just that it's 10% cobalt. M-42 is the highest concentration of Cobalt in an ISO tool standard (short of something like Stellite), and M42 has 8% cobalt.

Western tool blanks from CPM, Mo-Max, etc are not much more money, but have much higher quality metallurgy.