In article ,
"Harold and Susan Vordos" wrote:

[...]

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.

In a sense, once you understand the geometry, it's all closely related.
Threading offers some challenges beyond normal turning because of the rapid
advance of the tool with coarse threads, so your side clearances have to be
modified. I gather you'll get to that eventually. I didn't realize your
class was not an introductory to machining, so I may have spoken out of
turn. Lets keep a watch and see what you're taught. Also, try to keep
in mind I'm an old school machinist, with absolutely no hands on with CNC
machinery. Many of the things that I hold dear and spelled success for me
may very well not be being taught now. However, for the guy with a manual
machine at home, knowing the things I learned spell total freedom.

I for one am deeply interested in learning the old-fashioned
(requiring intelligence) way of doing things. Even if I never do it
that way I usually notice my quality of work improving as a side-effect
of simply knowing more.

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.

I'm afraid you have me at a disadvantage. Kenneth McDuff? Doesn't ring
a bell.

Serial killer who prowled around Waco, TX a couple decades ago.
Executed in the late '90s, IIRC. Don't mess with Texas.

[...brevity...]

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.

While I'd be a fool to say I know why, my guess is that the insert you're
using isn't doing the cutting, but the built up edge is. The cut would be
ragged and change according to the amount of buildup present, which would
likely be constantly changing to some degree, affecting the diameter. The
finish would show exactly that, being a torn and ragged surface instead of a
shiny one.

There's nothing like a sharp tool when you're machining aluminum. It's
perfectly willing to machine freely and leave a decent finish, providing you
do your part and supply the proper tool and lubrication. Grade of
aluminum makes a difference too, as does the condition. Soft aluminum is a
bitch.. 7075, 6061 and 2024, all in an artificially aged condition,
(T-6, T651, T351, etc.) are all great to work with. Some grades are not
considered machining grades and cut poorly.

Class was again today. We had a test and a substitute, so it took
some smooth talking to get some machine time. Unfortunately, the good
mandrel was our teacher's private property and got locked in his box.
For good reason, too. Apparently someone threaded the shop's mandrel.
So, didn't get to mess with the flywheel, but I did make a cutter and
mess with some scrap aluminum. Wow, a whole lot better! For one, the
piece never got hot. Aluminum just flew right off even if I jammed the
cutter in. I didn't exactly mean to do that, but it turned out well
enough.
I didn't make a chip breaker, though. Even without it no matter what
I did I couldn't get strings. Depending on how much I cut I either just
scores of tiny flakes or sometimes little curls. Probably because my
tool is pointed and has no "nose" to it.
Rather than measure everything out and go for exact grinding I just
eyeballed it this first time around. I was also operating under the
assumption I could get the bit as hot as I could stand holding without
doing any damage. Got some blue and brown on it, but otherwise looks as
much like http://www.sherline.com/images/grndfg10.gif as I could
remember at the time. I intended to round off the sharp corner, but
wound up hosing that and had to grind the end of the tool back until I
had a point again. Using it like that I could rough out a piece in a
big hurry and just turn the feed way down for a final pass and get a
smooth finish the diameter I intend. Is there a trick to rounding that
corner, or is it just something to practice until I don't hose it?
Also, that lathe still had the two carbide holders sitting on it, but
this week they both have built up edges.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/