If you want to build a PCB Mill, think "light" and "round"
    http://freeandeasy.sourceforge.net Done and working. Very fast and
    suprizingly accurate.

No offense intended, and I wish you luck, but...  That's not "done and
working."  That's a plastic prototype with a stylus sitting where you
need a high speed cutter.  I thought about making my own PCB mill.  I
even had the "polar coordinates will simplify the mechanics" idea.  I
suspect it might work for drilling (and let's face it, drilling is a
major PITA that resist-squirting injets won't solve.)  But I looked at
the existing commercial tables (T-Tech, LPKF) and decided that there
was an awful lot of MECHANICAL engineering in between something like
the prototype pictured on sourceforge and something that would
actually work.  The commercial units have BIG THICK aluminum tables
and weigh ... a lot.  The motors and solenoids that they're using are
nasty-looking.  It's not just a matter of accurately moving a table
under a tool; you have to do that WHILE the tool is pushed into
contact with your work hard enough to have it cut through metal.
Without deforming anything.  Seems to me like it'll be hard...

BillW

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