In article ,
"Harold and Susan Vordos" wrote:

[...]

I'm shaking my head in disbelief as I read you're being taught to use a
negative rake holder with aluminum, however.

It isn't really that we're being taught wrong as much as we're not
being taught about choosing cutting tools. Really, I'm using this class
in somewhat the wrong way--it's designed as a class to tech new kids
where all the knobs are, weed out slackers, and get everyone comfortable
around the equipment. Not so much a general introductory machining
class. Up until now, without knowing much at all about cutting tools
I've been making passable parts--they're just not pretty or fast. So it
would seem that they just chose a bunch of cutters that would survive a
semester of new students at a time and let the teacher cover a wider
range of material. In fact I believe the curriculum has a class
somewhere that's dedicated almost entirely to cutter angles, materials,
shapes, and physics.
Although I see the logic behind this, admittedly, I'd prefer at least
a couple of days on cutting physics. We are all going to make cutters
for threading, but that's not exactly the same thing as making a
generalized cutting tool.
I saw elsewhere in the thread you were starting to wonder about my
teacher's competence. As far as I can tell he's quite skilled and so
far every question I've brought to him has been answered. I figure if I
start using HSS tooling instead of the inserts he'll hang around me and
point out all the important stuff. It's just that this is a basic class
And as a bit of trivia, he's still got Kenneth McDuff's old toolbox.
Apparently, Mr. Sadist took this same class before he got arrested.

[...]

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.

Heh, I know how much of a pain it is to have a wad of razor wire get
snagged by the chuck and spun around at a few hundred RPM!
How would I incorporate a chip breaker into the rake angle? My
wild-assed guess would be to grind a too-shallow rake angle across the
whole top of the tool, then the proper rake angle only about half way
back. That would make a little hump just behind the cutting edge. Any
photos on the web of grinding chip breakers?
And how would I judge the effectiveness of a chipbreaker? Should I
expect to produce a bunch of little uniform chips, or should I just
expect the string to snap off every so often?

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.

Ah, my day-job is diesel equipment buffoonery & repair, so I'm quite
accustomed to the smell. Even kind of like it. (: That's why I can
get it easily--have a (cleaned out) mustard bottle full of it already.
I have no idea what's in the bottles of cutting oil in the machine
shop. Some are quite thick, some are thin, all have different smells,
most are the color of fresh motor oil, some are the color of used, one
looks like gear oil, but doesn't smell like it, and another I swear is
water. Probably some good oil somewhere in that collection.
If I can find some known good cutting oil I'll use that.

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.

Yeah, I did discover that. I found on the mill with the flycutter
around .015" cut will get me exactly what I intend, but less than that
usually cuts too much and more than that cuts too little. Or maybe it
was the other way around--last did anything over there was two weeks
back. Steel on the lathe was always right on once I quit mixing up the
inch and metric dials, but aluminum (oddly enough!) was pretty much
unpredictable -- always somewhere between -1 and +4 thou.

[...]

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

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