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

On Jul 13, 3:53*pm, "Michael Koblic" wrote:
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

I don't see any at all.

jsw

On Mon, 13 Jul 2009 12:53:20 -0700, "Michael Koblic"
wrote:

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%?
=========
The additional cobalt makes the tools more heat resistant, i.e.
you can run faster with a heavier chip load for a longer time.

The benefit to the typical home shop machinist is minimal as
their lathes generally lack the speed and power [and the
operators lack the gumption/need] to fully utilize the additional
heat resistance.

A secondary factor is that as the amount of cobalt increases, the
tool gets more brittle and prone to chipping. This can be a
problem on the typical home shop or hobby lathe where rigidity is
marginal due to wear and/or design.

Cobalt is also harder to grind on the typical home shop grinding
wheel, and there are some indications that plain HSS gives a
better finish to many materials.

Unless you are having a wear-out problem with your tools, 5 or
10% cobalt will be of little benefit, and you may well replace a
wear-out problem with a chipping or breakage problem, as well as
finding the tools harder to grind.

Only way to know for sure how these will perform in your shop is
to buy a one or two 5% and 10% tools and give them a try.


Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

"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

It depends on why you want Cobalt to begin with. I never run fast and hard
enough to need Cobalt, and it's a bitch to grind.

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

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

Jim Wilkins wrote:
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

I find I can drill S.S. with the cobalt and it usually doesn't slip & go
dull & harde n the S.S. jjw