On Jul 13, 5:57*pm, "Steve Lusardi" wrote:
Well, I have to disagree with all the responders. I use exclusively cobalt
HSS tooling as a hobbyist. I do not find them hard to grind if you use the
correct wheels. I use both M35 (5%) and M42(8-10%) and again there is a
difference. I have many tool bits that are more than 20 years old and are
still perfectly serviceable. They hold their edge, even with stainless. I
prefer them to carbide because you can grind more relief and not experience
failure and they do not chip like carbide. The extra relief is very
important if you have light machines, because it reduces tool loading
significantly and allows excellent results even with toy machines.
Additionally, they handle intermittent cuts as good as normal HSS. Cobalt
tooling is superior in every way. I not only use cobalt tools on my lathes,
but also almost exclusively on my vertical R8 mill. I do use standard HSS
steel tools on my horizontal mill because of cost though. I cannot think of
many things more discouraging than suffering tool failure on a final cut.
That alone justifies the use of properly ground cobalt tools in my mind.
Although I have cooling on all my machines, I rarely use it because of the
mess it makes. It is far better to go a little slower and use cobalt alloy
tools. As the answer to M35 or M42, you can see a small difference in edge
life, but I find little difference otherwise and if the choice between the
two costs additional money, I usually opt for M35.
Steve

There's nothing there to disagree with, except you compare them to
carbide more than to HSS.

I see a big jump from cheap (Enco) to good (auction) HSS, but not much
more to 5% cobalt. My cobalt drill bits, a low-cost black oxide
numbered stub set from MSC, are significantly more likely to break
than HSS. The yellowish replacements from them have held up better.

When HSS won't cut on the lathe I go right to carbide. There isn't
much difference between HSS dulling on hard cast iron in 20 seconds
and cobalt in 30.

jsw