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

"Michael Koblic" wrote in message
...
I see lathe toolbits made of M-2 HSS, 5% cobalt and 10% cobalt. The prices
seem to increase nearly exponentially for equivalent sizes.
How much incremental benefit is there from adding 5% cobalt to steel? How
much from increasing this to 10%?

--
Michael Koblic
Campbell River, BC