Homebrew PCBs

Even if it were a perfect circle, a 0.25" plunge (about twice my normal)
on a 12" radius means it's offset by only 2-3 mil.  I think the amount
of slop in the whole system is more than that, esp in the runout of the
bit itself.  A normal plunge would be way less than the runout.

Plus, because there's two beams, at least the dremel is still vertical
as it plunges - it's not itself rotating about a point 12 inches away.

But either way, the results are good - I rarely break drill bits, and
usually when I do it's because of something stupid I did (like drop
them) and not the drill press.