Facing small-ish rounds

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.
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Mr. PV'd

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Just dont go too deep. Usually the inserts don't stick out much on the inside. But Iv'e ramped with a flycutter a lot. The problem I ran into was the burr. But the flycutter i used only had like 30 grand depth max inside the inner circle. If I tried to take 25-30 grand the bur would be beyond the cutting edges. So it worked fine when I ramped 15-20 grand. If thats what ya meant?
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Basically, I'm asking if you have a round sticking up at X0Y0, and you bring down a face mill at X0Y0, is it OK to cut from the inside of the face mill on outwards. And, if so, how much, z-wise, relative to a "normal" cut, going from outside the cutter to the inside.
Also, would the feeds/speeds change?
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On Fri, 26 Jun 2009 13:32:31 -0400, "Proctologically Violated"

To a certain extent, yes. It depends of the geometry of the inserts. The square (45 degree angled I presume) inserts you're using are probably the best because of better radial support in both directions. The problem is that if the insert lies above the centerline of the tool, or is tilted to increase the cutting angle, you'll run into (pun intented) clearance problems due to the cutting angle being too small on the inside.
Check the clearance outside/inside with a dial indicator and notice the difference.
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wrote:

I wonder if it pushes the insert away from the corner its in? I bet it does.
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Proctologically Violated wrote:

Why not a smaller endmill to start?
Best, Steve
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Regards,
Steve Saling
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Proctologically Violated wrote:

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.
KG
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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.....
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