"The Dougster" wrote in message
...
A 2- or 4- flute end mill makes a fine trepanning tool on the lathe.

Trepanning of a square blank held on an expaning arbor through a
smallish center hole leaves a square with a round hole, and a disc
with the smallish hole. If what one wants is the disc, trepanning
saves the wear, tear, and irritation of the interrupted cut, and save
turning all those square points into chips.

I am trepanning an octagonal blank into a center disc and outer collar
to hold a thin walled tapered part, soon.

I hold my 5/16 4-flute end mills in the cross slide with a boring bar
adapter, a keyless chuck, straight shank adapter, and a sleeve. I've
trepanned Masonite, acrylic, and polypropylene with this setup.

Align the collinear end teeth radially to the rotation center
carefully so they will cut with correct rake and clearance. Alignment
to the machine axis is less critical, except when cutting steel; the
side flutes will burnish steel and harden it before they start cutting
if they're not precisely aligned. This is a Bad Thing and can ruin the
cutter. I know this will happen even though, as you read above, I
haven't trepanned steel. It's one reason I haven't. In any other
material, misalignment will only result in a little side cutting
action during feeding.

Best,

Doug

But in a lathe the patient's head would have to be spinning. I think it
would be more practical to do this on a Bridgeport or large drill press.