In article et,
Bill Schwab wrote:

Would you try to clamp it to the mill, or would you make jigs for the
drilling? If the latter, any suggestions? Would you worry just about
guiding a punch, or would you try to make something to guide the drill
bit itself? I am assuming that any jig would be held in place with
bolts running through holes in waste areas - the fans will make that
easy to do.

For "a few" (I see no indication how many you are making - 1 - 100,
1000, 10,000....), I'd probably just lay out the holes with a scribe and
punch them (did a lot of one-off electronics enclosures in my lab work),
then drill on the punch mark. This is more than adequately precise for
fan mounting (BTDT) with a careful hand and a good drill press. If
you're talking hundreds, jigs are probably in order. If you get to
really high volume, some sort of punch press to stamp them out might be
justified, or (for more flexibility if the parts ever change much) a CNC
mill with a larger table.

The boring old bimetallic hole saw is less likely to bite you than the
fly cutter for making the big fan hole, and again, is more than
adequately precise, and probably faster.

A simple aluminum or phenolic block jig could guide either the punch
(for purists) or the drill (if making only a hundred or so), or could be
upgraded with proper drill bushings for purists and/or higher production
needs. Mild steel also works, just a bit harder to make, depends on the
amount of use it's going to get, and what you have handy for stock.

Mounting it on the mill you have sounds like a pain, and overly precise
for the job at hand (ie, takes much more time fussing than is needed to
do the job adequately, thus, wastes money). Only reason to alter that
thinking is if this is a one-off hobby project and you want to spend
time playing with your mill...

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