straight plunges into the material with a mill can work (using a 1/8 mill to
make a 1/8 hole), but you need to have a mill designed for it. Many mills do not
actually have a cutting surface in the center and so do not work well for a
straight plunge.
But this requires support from the CAM software, some do not do drilling
operations, some do. If the CAM doesn’t do drilling operations, it won’t matter
if it’s a mill or a drill in the machine.
As a best practice, it’s a good idea to use a small drill/mill to make a hole
and then use a larger one to enlarge it rather than trying to plunge a large
mill or drill directly down.
Even drill bits don’t cut the exact center well (if you think about it, you will
realize the bit isn’t moving very much at the dead center, so it can’t cut
well), but they are all designed to survive this.
David Lang