Harold:
In your earlier comments on carbide bits you mentioned "Stellite" bits as
being preferable to carbides and HSS. I looked through my bit bins and
found 6, full length, 1/2" Stellite bits with a tool only on one end. I
also noticed that many of my bits were Cobolt, with various designations.
In the past, I never really paid attention to the bits, other than to select
carbides for really hard stuff and cast iron. Now that I find that I have
a goodly variety of all types, some guidance on their usage and
advantages/disadvantages of each would be appreciated.

1. Am I correct in assuming that one grinds stellite bits on a regular stone
and not on a green stone? Seems to work okay and grinds at about the same
rate as HSS bits.

2. Cobolt vs ordinary HSS. What does Cobolt provide other than bigger
cuts, higher temperatures, faster feeds, slower wear, etc. Other than cost,
are there any reason why one would not prefer Cobolt over HSS?

3. Stellite vs. HSS /Cobolt. Advantages, disadvantages, preferred metals
to use on, contra-indications, special problems and issues.

4. Stellite vs. carbides. You said earlier that Stellite would take to
interrupted cuts better than carbides. How about ease of getting a good
finish, lower pressures, etc. Any other advantages or disadvantages of
each.

5. Any special issue, for a given metal to be cut with respect to rake,
relief, etc? for each:: HSS, Cobolt, Stellite, carbide.

Any other sage bits on bits that you might want to put into the book
I've asked you to write?

Boris


-------------------------------------
Boris Beizer Ph.D. Seminars and Consulting
1232 Glenbrook Road on Software Testing and
Huntingdon Valley, PA 19006 Quality Assurance

TEL: 215-572-5580
FAX: 215-886-0144
Email bsquare "at" sprintmail.com

------------------------------------------

"Boris Beizer" wrote in message
ink.net...
Harold:
In your earlier comments on carbide bits you mentioned "Stellite" bits as
being preferable to carbides and HSS. I looked through my bit bins and
found 6, full length, 1/2" Stellite bits with a tool only on one end. I
also noticed that many of my bits were Cobolt, with various designations.
In the past, I never really paid attention to the bits, other than to
select
carbides for really hard stuff and cast iron. Now that I find that I
have
a goodly variety of all types, some guidance on their usage and
advantages/disadvantages of each would be appreciated.

1. Am I correct in assuming that one grinds stellite bits on a regular
stone
and not on a green stone? Seems to work okay and grinds at about the same
rate as HSS bits.

Yes, the use of aluminum oxide for Stellite is the proper choice. Green
wheels are very softly bonded, formulated specifically for grinding
carbides, which are much harder than Stellite. The grade 98M2 Haynes
Stellite toolbits I have are 62 Rc., no harder than the typical HSS toolbit.

The carbide wheels are green so you can identify them at a glance. The
typical silicon carbide wheel is black, but bonded way too hard for grinding
carbide, glazing quickly. The soft bonding continually presents sharp grain
to the carbide to facilitate rapid (?) grinding. (Personally, I don't like
the green wheels, so I rarely use one. I prefer to use wet diamond).
No need to discuss the health issues of using green wheels, which would
become a serious consideration if they were used for grinding Stellite or
HSS. Grinding on softer materials accelerates wheel wear, creating all the
more dust.


2. Cobolt vs ordinary HSS. What does Cobolt provide other than bigger
cuts, higher temperatures, faster feeds, slower wear, etc. Other than
cost,
are there any reason why one would not prefer Cobolt over HSS?

Not in my opinion. The addition of cobalt to HSS increases the temperature
range of the tooling, so it's money well spent, especially if you run your
machines on the
edge, as I used to do. Cobalt bits do grind somewhat slower, but it's
hardly an issue.


3. Stellite vs. HSS /Cobolt. Advantages, disadvantages, preferred metals
to use on, contra-indications, special problems and issues.

Where it really shines is machining materials that seem to have a high
friction coefficient (stainless), or abrade (chrome moly, for example) your
cutting tools such that you'd experience tip failure. Stellite toolbits
are not harder than typical HSS (, but retain their toughness up to a red
heat, very unlike most tool steels. It would be my opinion that using
Stellite for aluminum would be a waste of resources, so I'd likely not do
so. There would be no benefit over using HSS.


4. Stellite vs. carbides. You said earlier that Stellite would take to
interrupted cuts better than carbides. How about ease of getting a good
finish, lower pressures, etc. Any other advantages or disadvantages of
each.

It's entirely possible that my opinion is no longer valid. I'm basing my
statement on the quality of carbide when I was still actively machining,
which was more than 20 years ago. Carbides in general have improved, so I
may not be right now, at least where interrupted cuts are concerned.

Positive rake carbide (as I know it) isn't very good at roughing, not
serious roughing. The diminished tip angle tends to chip away. The
increased tensile strength of Stellite tends to get around that problem,
especially with a well designed chip breaker.

My experience with finishes dictates that you tend to get better results
with positive rake than negative rake, plus it's easier to hold size with
positive rake. Cutting pressures are drastically reduced with positive
rake, but for finishing there are some outstanding carbide grades available
today, very unlike my early days in the shop.

The beauty of Stellite is tools can be easily fashioned for particular
applications without specialized machinery. Nothing more than a steady hand
and a pedestal grinder is needed. Stellite is very good for the guy that
tends to hand grind HSS tools instead of rely on inserts. Needless to say,
those that run CNC machines would not benefit at all.

Early in my career, when Stellite was readily available, we'd use it with
brazed carbide tools, so we could maintain spindle speeds when going from
tool to tool. An excellent example was parting. By parting with Stellite,
one could turn with carbide, then part at the same spindle speeds. There
were no parting tools available that would fit in our setups, so we
typically hand ground them.


5. Any special issue, for a given metal to be cut with respect to rake,
relief, etc? for each:: HSS, Cobolt, Stellite, carbide.

Only on an individual basis. I've violated the rules on many occasions
with excellent results, typically when the rules didn't work. I think if I
was to comment on offhand tool grinding, I'd concentrate on incorporating
chip breakers with positive rake. I rarely grind rake without a chip
breaker. I don't like the way turning tools perform without them. Still,
what I do and how I do it relates to the job at hand. It's very difficult
to make blanket statements. So far as HSS, cobalt & Stellite are
concerned, I tend to grind them with similar relief angles. Again, each
application dictates.

Regards relief angles, you get a gut feeling what will work, and what won't.
My (carbide) grinder is not calibrated such I can set specific angles
without the use of a protractor. I never rely on one and get excellent
results.

Any other sage bits on bits that you might want to put into the
book
I've asked you to write?

Chuckle!

Only that when you are having trouble, it often pays to venture outside the
rules. I tend to analyze the problem at hand and them make decisions.
It's hard to know what to do without experience.

In a way, this is much like playing a musical instrument. You get there
only one way. By practice. You can read about it endlessly, but until you
get your hands dirty, you don't learn much. It's the experiences you have
that build your base from which you make decisions. It's nearly impossible
to pass that on to others. Sorry I'm not more help.

Harold

"Harold and Susan Vordos" wrote in message
...

"Boris Beizer" wrote in message
ink.net...
Harold:

Any other sage bits on bits that you might want to put into the
book
I've asked you to write?

Sorry I'm not more help.

Thank you. It would be more helpful if you could come out here and give me
a hands on lesson.

Boris

--

-------------------------------------
Boris Beizer Ph.D. Seminars and Consulting
1232 Glenbrook Road on Software Testing and
Huntingdon Valley, PA 19006 Quality Assurance

TEL: 215-572-5580
FAX: 215-886-0144
Email bsquare "at" sprintmail.com

------------------------------------------

2. Cobolt vs ordinary HSS. What does Cobolt provide other than bigger

Cobalt will hold an edge longer. When turning tough material like 4140
I choose Mo-Max cobalt toolbits. I remember trying a chinese import
toolbit and it would dull quickly. MO-max cobalt kepts on cutting.

I use just about any toolbit for aluminum and brass. Name brands seem
to stay sharp longer but I have never done any testing. I use whatever
is handy.


3. Stellite vs. HSS /Cobolt. Advantages, disadvantages, preferred metals
to use on, contra-indications, special problems and issues.

Can't buy Stellite, so I buy Tantung, which I believe is similar.

I tend to use Tantung for heavy roughing cuts. Tantung wants to
run 100-300sfpm and really removes the metal. I switch to a sharp
regular or cobalt HSS bit for finish cuts.

5. Any special issue, for a given metal to be cut with respect to rake,
relief, etc? for each:: HSS, Cobolt, Stellite, carbide.

I was told to grind Tantung toolbits with angles suggested for carbide
(which are less than the angles for HSS) because I was having problems
with the toolbits chipping. However I think my problem may have been
caused by using too slow of a speed and too much feed.

chuck

I love Tantung/Stellite. The best example of it's use is when I had to
turn a 5" cast iron backplate on the Jet920, which turns a little too
fast - regular HSS toolbits would just burn up (literally) when
turning the OD of the backplate. I switched to Tantung and finished
the job quickly.