In article ,
"Harold and Susan Vordos" wrote:

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

It's a skinny little 3/8 mandrel and 6" long while my part was only
3/4" long. I had a chatter problem at first (I did kinda like the funky
looking finish, though) but it went away as soon as I limited myself to
passes of .010 or less. Not a problem since I'm only making one wheel
and only needed to shave off about .070 anyway.


That's even worse than I had expected. While I realize that the number of
passes you may have to take isn't of importance at this point, I think you
can understand that if you were engaged in doing this for gain, you'd be out
of business before you got started. Again, you're in a learning phase
right now, so it's important to experience these things so you understand
them.

Holding by other means, you'd have roughed the flywheel within .03"/side,
then taken appropriate finish cuts of equal sizes for consistent tool load.
One to determine size, the balance (2 passes) splitting the remaining
material, half for each pass. That way you can better control diameter when
it's critical. Certainly, the outside of a flywheel isn't, but it's a good
method to learn for when your project demands precision.

We lose 10 points each time we restart a part, but I'm taking the
class to learn--not necessarily to fluff my GPA. I may very well do
another wheel simply for the hell of it.
Either that or when I get to make my own project up after finishing
this one I'll do something with a wheel on it.

How would I check a carbide for its grade? Would it be embossed on
the inset itself, or would I simply have to check the package it came
out of?

Depends on the maker. Some carbide is identified on each piece, but you
can't rely on that. The C2 designation might appear as something else, so
you have to understand carbide markings for it to make sense. For
example, if you're using Carboloy, their C2 grade would be marked 883, and
C5 would most likely be marked 370. Understand that any carbide will cut
any material, but how they hold up is determined by the grade. C2 has
excellent edge hardness, but is brittle and chips easily. Not a problem when
machining aluminum, but when you machine steel, unless you're taking very
light cuts, it tends to chip the edges around the point of contact, the
result of chips acting against the carbide. The point may very well stay
intact and still cut fine, but if you use the tool for a deeper pass than
the previous one, it often breaks because the tool has lost proper
configuration because of edge erosion.

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.

In the old days, (carbide) makers talked about a triangle. If your choice
gave problems, you moved around the triangle. As you gain one feature, you
give up two others. There's usually a balance of the three features that
will provide good tool service and life. I'm not sure they even talk
about that today, it's been years since I last had to worry about carbide
grades. If you can find some old Kennametal data, they used to include
the triangle, and it would help you understand how it works. It's been too
long for me to recall it correctly.

Sounds like bicycle parts: cheap, durable, light--pick two.

What's important here is that your insert hasn't been machining steel before
using it on aluminum, even if it's the right grade. The keen edge will be
gone, and without that you're likely to have problems. Finish often speaks
volumes about the condition of the cutting edge, even when you think
everything is OK. If you're machining 6061-T6, you should expect the
surface to show feed marks, but otherwise cut quite cleanly, with no
fuzziness on the surface, assuming you're using a lubricant. If you get the
slightest signs of fuzziness, the edge is likely experiencing some chip
welding, maybe at the microscopic level. That makes for poor machining and
increased cutting pressure. That works against you when using a mandrel,
especially when you're driving with such a small diameter. Knowing the
size you're using, I'd suggest what you're experiencing is more or less
normal. That's why you try to avoid using mandrels. I also avoid turning
between centers as much as I can. Same problem. Too much chatter and the
cuts demanded can't be accomplished. Soft jaws answer the vast majority of
the problems. It's a little too early for you to worry about them at this
point. Besides, the chuck you're using may not accommodate them. Not all
chucks do.

These inserts get used on any damn thing that finds its way onto the
lathes. Poor things probably had to cut stone at some point. In fact,
I had to put a steel center into the chuck and take a light cut off of
it so the mandrel would run true immediately before I machined the
wheel. So, yeah, it got "steeled" first.
Would the steel or aluminum--not both rule also apply to HSS bits, or
are they OK with it since they can be sharpened?
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.
But that's really nothing compared to the guy who took a .050" pass
using a carbide insert cutter in the mill, but ran it backwards and way
too fast. It took off .050, but as a smear instead of as chips. Ah,
school.

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