Re: Facing small-ish rounds


"Kirk Gordon" <kg1@xxxxxxxxxxxxxxx> wrote in message
news:4A4588BB.7050001@xxxxxxxxxxxxxxxxxx
Proctologically Violated©® wrote:
Awl --

I built a "riser box" upon which sits a cheapie collet chuck, so's I can
face/drill/tap the ends of longish rod in a vmc, instead of a manual
lathe -- theoretically up to about 21" long (!!!), but right now I'm
doing about 12.5" long, 5/8- 1" dia.

This enables me to face rods to a fairly exact length, which is important
in this app, AND get in pretty quick drill/tapping, otherwise laborious
on a manual lathe.

Yeah, it's only 1 pc at a time (but so would a manual lathe!), but I have
a fixture planned that would do *tablefuls* of these, if shit pans out --
mebbe 50-100 per load.

Inyway,

Using a 3" face mill ( sandvik, 6 sq inserts) on 1" round, I know that
with the face mill clear of the material, I can take a cut, and stop
while the 1" round is *under/within* the diam of the face mill -- iow, no
wasted travel.

The Q is: can I lower in Z while the material is within the face mill
underside, and cut coming back out, or should I just come out, lower Z,
and cut coming back in? Note that no cutting occurs while lowering in Z.

It seems, from the sound of things, I can't take an aggressive cut while
coming back out clear of the material, but is it permissible at all? I
don't want to screw up/chip any inserts. Oh, 6061 aluminum, as always.

I figger I might as well get some cutting bang for my moving buck, whilst
coming back out.

Now, speaking of cutting *whilst moving in Z*, can you do this with an
insert face mill? Initially generating a kind of odd trepan.


Unless your square inserts are set at 45 degrees of lead angle, the
inside-out cut will be much different than a normal cut. If you have,
say, 5 degrees of lead at the outside cutting edge, then you'll have 85
degrees on the inside. (Or 10/80, or 15/75, or whatever.) That means
thinning the chips to the extreme. Chatter is almost guaranteed. There
won't be any such thing as a proper feedrate. Workable depths of cut
won't be enough to make the plan worthwhile. And the lifting (Z axis)
force from of cutting at extreme lead angles could easily make your plans
for exact lengths could go completely to hell.

Even if you're using a 45 degree lead cutter, the inside-out cuts will
be making chips on the wrong sides of the inserts, where they'll want to
smear and squish themselves behind the inserts, into places they don't
belong. That could loosen the inserts, wreck the seats, or ruin the
cutter body.

Other than that, it ought to work just fine.

Or, you could experiment with cutting depths and feedrates till you get
maximum metal removal from the smallest possible number of normal cuts,
and then pass completely over the part with only the very last cut,
letting the tail edges of the inserts give you a free finish pass as the
inserts just dust the part, removing only the little bit of deflection and
tool pressure that were left over from the last rough cut. How well this
works (the free finish pass) will depend on the rigidity of your setup,
and how much your bars want to lean away from the cutting forces. But
you'll have that problem in spades with the inside out stuff, too.

Yeah, to all who pointed out the vicissitudes of this technique, the sound
of the cut reflects as much -- just dudn't sound normal.

I was taking, like, a .020 cut on the way back, but I think I'll even
dispense with this. I though maybe I'd be using a part of the insert not
normally used, getting a li'l more bang for my insert buck, but the sound is
just too shitty....

And then, when I make a mistake, and *reverse* the .1 cut with the .02 cut,
I'm sure I'll pay dearly.....

--

Mr. PV'd

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Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
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KG




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