On Apr 23, 6:38 pm, Andy wrote:
I need to cut many 3 in. and 6 in. holes in 1 inch MDF.

My first thought is a router on a trammel - basically make a long
skinny router sub-base out of 1/4" hardboard or something like that.
Sink a little finish nail at the appropriate distance from the bit,
and into your workpiece, plunge and spin (slowly). It would be much
easier on the router if you cut pretty close with a jigsaw first.

goes to 10K rpm) I am not sure what type of bit to use.
It would have to be bearing guided. Any input would be welcome

A bearing would work with a template, but so would a template guide
bushing if that's easier for you. Or a larger round template, and
just use the edge of your stock sub-base as a guide (note - this might
not be as accurate as a bearing or bushing).
Good luck,
Andy

The guide bushing sounds good . Can you rec. a bit to use with that
Thanks