Re: [CAD_CAM_EDM_DRO] orange peel on aluminum

Tom,

Ideally you want both available. Sometimes you need cooling more than
lubricating, and the water-based are better at that, plus you can get
more air volume which can help evacuate chips. Case would be some parts
I machined with a .165 wide slot along the edge of a .350 thick plate,
1.4" deep from the edge. The micro-lube did a better job of lubricating,
but at a mere 20 psi, wasn't clearing the chips well enough. Also, if
the aluminum got too hot, it would spread apart, opening the slot and
required a lot of hand labor to squeeze them back in to tolerance.

Regarding orange peel, I just ran into this last night. Had to flycut a
3.5 x 11.5 x 5/8 Al plate. Frankly, I had to hang a tool out way too
far, and sure enough I got orange peel on the finish. This particular
tool had a small corner radius. While this might generally help the
finish, it also increases the length of cutting edge engaged with the
material, which increases cutting forces, which will move a tool hung
out too far. I put a dead sharp corner on the bit (though at a 45 deg
angle to the part surface) and ran at 3000rpm and a fairly low feed
rate. Wonderful finish. BTW, used the SafeTap stick for lube, final pass
was .002 DOC, wiped the lube stick down the length of the part three
places.
Tool corner radius will improve finish only in a rigid setup. If things
are marginal, sharp is better but you have to slow the feed to keep the
finished surface smooth.
And tools must be dead-sharp. I used to think I was pretty good at hand
honing tools until I looked at one under a microscope. Yikes!
I coughed up the bucks recently for a Baldor carbide grinder and it's
one of the best investments in my shop. Lacking this, one would do well
to consider making something along the lines of one of the knife
sharpeners that holds the blade/stone at a fixed angle. All it takes is
ONE slightly off pass with a hone, and you've ruined the edge for really
fine work.

Jon A.