The chip load per tooth in milling steel with hss is only a few thousands,
so if the hole is off center by just a few or the hole is on center but
oversized (mill will then be pushed to one side by the set screw) a multi
flute mill will not mill with all flutes.(not the end of the world if you
don't need max mill life, speed or accuracy of size).
If you are using a single flute mill like an indexable one then it isn't as
important.
Having the hole dead center is probaly first concern, if oversize you may be
able to wrap the endmill in shim stock but this can be a pain especially if
you don't have shim stock.

"jt" wrote in message
...

"Gary Coffman" wrote in message
...
On Mon, 1 Dec 2003 11:51:51 -0400, "jt"
wrote:
Or could I just plunge a 3/8 endmill into a 23/64 hole?

Don't do that. It'll be oversize. Bore it or ream it.


That's what I thunk, but thanks for confirming...