PCB Milling / Routing

I have a Sherline-based 3 axis Mill which I built with hgelp from
this group about 6 months ago. I want to make some small PCBs and
rather than starting using Ferric Chloride, I would like to use my
Mill.

What is the lowdown on PCB Milling or Routing, what can
realistically be done, and what would be the limitations of the
Sherline mill.

I have a feeling that the spindle needs to run very fast (20 K
RPM??), can that be done, if I run at only 3,000 RPM what will the
drawbacks be cutting speed finish etc ??

If anyone has any experience with this I would be interested to know.

Thanx

PeterC