In article ,
says...
This is the best advice.
Use eye protection someone else said and is the only thing I can add.

"jim rozen" wrote in message
...
In article , Ryan says...

I have a task which requires boring four 4" holes in .750 plate aluminum,

Holesaw. Get the best bi-metal blade you can, mount it up
in a bridgeport, and use WD-40 for the cutting fluid.
Retract feed frequently to blow out chips.

Someone else already mentioned this in another post, but
it's worth stressing, particularly on alum plate this
thick. Drill a 1/4" hole or two on the hole saw's cut line.
It will turn the frustration of constantly clearing the
sludge of tooth clogging chips into a walk in the park.
While you're cutting the hole, you'll find a little pile of
chips on the machine table under each small hole, rather
than clogging the hole saw kerf and teeth.

Ned Simmons