Jim,

Visibility and convenience. I've tried the methods other posters
suggested and use the angle block and plywood for larger boxes but for
the small one you have a 2X4 spacer in the box should be enough. You
need to see that the wood doesn't touch the lower corner of the box
when you tighten the vise, and it's easier to add a C-clamp or 2 for
extra stiffness near the cut when you can see the upper edge of the
wooden block.

Got it - thanks.

I generally saw/nibble/plasma a large opening in the chassis and make a
separate bolt-on control panel out of 0.062 aluminum. Flat panels are
MUCH easier to fabricate. Make sure the wired panel will pass through
the hole.

That's an interesting idea, especially for a future D-shell problem that
will hopefully surface. There I would be making several units with
multiple ports. As that design evolves, I will have a better idea of
how many different types of holes will be required, and that will help
me decide whether punches make financial and political sense.

With your .062 panels, could I reasonably expect to drill and bolt
several of them to mill at one time? What I have in mind is to drill
holes and bolt to maintain alignment, and then clamp the stack over
plywood or something, probably moving clamps around (add one then remove
another to make way for the endmill/bit) as work progresses.

Then I guess there is a question about whether the alignment holes
can/should be the mounting holes. Confused by what I mean? That makes
two of us With the understanding that I am trying to maintain
precision largely for practice, I am not sure I would be able to drill
the holes add the bolts w/o losing the setup[*]. If a first set of
alignment holes are drilled in margin to be removed later, then I could
stack, drill, bolt, clamp, and then mill a clean edge, drill mounting
holes, and mill the ports/slots. Clamps come off, more bolts in the
mounting holes, remove the bolts in the scrap, clamp, dial the clean
edge to re-align and then clean up the other three edges. If the panels
are small enough, they might be squared up in the vice using the clean
edge as a starting point.
[*] it might be possible with enough relief in/under the plywood
support, which could have corners removed or something to make room for
fingers or a wrench to hold a nut underneath the stack.

Am I making this too complicated? Better ideas are welcome.

Bill