"B.B." u wrote in message
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In article ,
"Harold and Susan Vordos" wrote:

"B.B." u wrote in
message
news
In article ,
"Harold and Susan Vordos" wrote:
snip--

So what does the C2/C5 rating refer to? Grain size? Carbide vs.
"other" content? Is there some sort of system to choose which grade
where, or is it just down to C2 for some stuff, C5 for others, all
other
grades not made anymore?
Searching on google got me a whole lot of marketing, but not much
else.

I've been out of the shop so long that I am no longer knowledgeable
where
carbides are concerned. It's particularly bad considering they've made
great strides with carbide, too, so I can only assume that it may not be
as
critical as it once was. I'm not convinced you'd find many machinists
that really understood the differences in how they're put together,
though.
When you go back to my time in the shop (primarily brazed carbides),
constituents of the carbide were altered to accomplish the performance
required. Carbide went from hard to strong, and from edge wear
resistant
to crater resistant. As you moved from one feature towards another,
you
gained certain qualities, but lost others. It could be that today it's
just not as important. Dunno.

I'll do some more digging on carbides and grades. If I find anything
juicy I'll post it in RCM. Seems like something that would be nice to
know.

Agreed. Very few seem to grasp the significance of choosing the proper
grade. I'd welcome anything you can uncover.


I'm sure it is too. Would an aluminum-cutting setup involve only a
different insert, or also a different insert holder. IIRC, the holders
out there have a negative rake (angles down towards the work, which I
believe is called negative) and a negative side-rake. (down towards the
headstock) Are the rake angles a function of the holders, or are all
holders angles this way, expecting the lip on the edge of the carbide to
determine back/side rake?

There are holders that determine rake angle, such as the negative rake types
you're apparently using, but there are inserts with grinds that can alter
the rake angle to some degree. It's conceivable to have negative rake
holders that have positive rake inserts, but they're usually somewhat timid
in performance. The edges are relatively fragile and easily chipped, so
they're usually used for light cuts only.

I'm shaking my head in disbelief as I read you're being taught to use a
negative rake holder with aluminum, however. You couldn't come up with
any worse combination than you have. Even for roughing, positive rake is a
better choice in aluminum. It requires far less horse power. The material,
being quite soft and low in tensile, machines very easily. There is little
benefit in using negative rake, and it goes from a bad idea to a horrible
one for finishing. Negative rake tools don't cut at the tip, but rely
instead on what is known as a false cutting edge. The cut occurs back of
the tip, where cratering is generated. When you try to take light cuts,
the tip comes into play and isn't up to the task. Long ago, it was
recommended that a slight chamfer (.005") be stoned on the tip to discourage
chipping, prolonging the useful life of the insert. You can imagine how
poorly it would perform when taking a light cut. It's not a good idea to
use negative rake for finishing, not even in steel, although if the cuts are
heavy enough, it works fine. You really should be using positive rake,
and a sharp tool, with no chip welding of any kind.

Positive rake tools generally have a cutting edge on one side of the insert
only, so a triangular insert has only three cutting tips, not six.


Would the steel or aluminum--not both rule also apply to HSS bits,
or
are they OK with it since they can be sharpened?

HSS is not as critical as to how it's applied, but when it is a concern,
one
selects tool steel high in cobalt, which offers tougher conditions at
elevated temperatures. Any HSS will work for aluminum, especially if
you
understand chip breakers and rake angles. You can create tools that will
peel it off faster than you can imagine. Lubrication is very important,
however. It doesn't take much, something as simple as brush application
works fine. Kerosene is the lubricant of choice for aluminum, but almost
anything is better than nothing. I've used Stoddard solvent that isn't
real
clean with great success, but if you'd like things to smell nice,
consider a
small can of WD-40. It appears to be nothing more than solvent with a
little wax dissolved in it, along with a perfume. It works fine for
aluminum.

Rake angles I think I've got a handle on. At least enough to get
started. As I understand it a chip breaker is just a little groove some
ways back from the cutting edge, correct?

Yes, that's correct, but it's a good idea to incorporate a chip breaker as
your rake angle. It takes a little grinding experience to get good at it,
but it really pays benefits. A simple rake angle improves machining
ability, but creates horrible chip problems. When you couple the chip
breaker with the rake angle, all that goes away. If nothing else, you gain
considerable safety, not generating long strings that can wrap around your
spinning object.

It was common practice to have a small can on the machine with an acid
brush
in it. To keep the can from getting blown about by the air hose
(they're
use extensively in production shops, believe it or not) you'd place a
piece
of stock in the bottom. I've always had a can of kerosene and sulfur
based
oil at my lathe and mill.

Is diesel close enough to kerosene to work? I can get a little
container of diesel easy, but kerosene will be a hassle. I'm in texas,
so our diesel is as sulphury as law allows. (:

I own a couple Dodge diesels, and hate the smell of the fuel. I've never
tried it, but I can't imagine it wouldn't work. I used Stoddard in place
of kerosene to get away from the smell, which is similar to diesel. If
you have a (Stoddard) solvent container for cleaning parts, just dip a
little out as needed. I've done that for years. Sulfur is very much a part
of lubricating when machining. One of the best oils for machining steel is
sulfur based cutting oil. The stinky stuff.

I wound up leaving the outside of my flywheel .003" oversize (we
have
a tolerance of .005" over/under) so I could file/sand off the uglyness.
Alas, there is no lubricant. I did try painting my wheel with a
film
of oil for one cut, but it didn't appear to help any, so I didn't mess
with it any more. Got a bit stinky anyhow.
My lathe actually had two carbides sitting at it. One was
undamaged,
but the other had an impressive little heap of metal welded firmly to
the cutting edge.

With the inserts you described, it's no wonder. Once you find chip
welding on an insert, for all practical purposes, it's no longer a good
insert. The welding generally occurs because of tip flaking or
cratering,
with the chips welding into the rough edge or surface. There's usually
no
way in hell it will cut well once that happens.

Good to know. Thanks.

By now you grasp the importance of not using negative rake, hopefully. You
have enough material left to make one good pass and end up with a beautiful
surface. Don't blow it screwing around with the negative rake inserts.
If, by chance, you do, chalk it up to learning. You'll remember the screw up
far better than you would good success. Making mistakes is very much a
part of the learning process, especially on machines. You'll come to realize
that not everything is as it appears. Often you'll dial a cut and the
machine takes more or less than the amount you "requested". A good
machinist knows how to get around that problem. A loser rarely ever
figures it out.

You'll come to realize that not everyone in your class will have the same
dedication to learning as you may have. I took a welding class several
years ago. One of the students was a druggie, and wasn't interested in
the
least in learning anything. He took advantage of circumstances for
reasons
best known to him. Didn't make sense to me, but it apparently did to
him.
Sigh! He finally quit showing up-----

Heh, over in my welding class two weeks back some guy showed up for
the first time since the beginning of the semester. The teacher simply
told him up-front that he hasn't been there, his excuse (broke down
truck) was bull****, and he would do nothing more than waste his and the
teacher's time and a whole bunch of electricity. Kicked him out on the
spot. I like that teacher!

By the time we're old enough to attend such classes, we're expected to
behave as adults. People like him (and the druggie that was in my class)
have a way of disrupting the learning of those that are serious. I like
that teacher, too.

Harold