Hi Mark,  I see no particular reason why someone with good mechanical
skills and access to the right tools shouldn't build a solenoid
operated roll punch, but I would be wary of expecting it to be an easy
route.

If you have one punch per note it's a lot of hardware to fit together
to fairly tight tolerances; if your drill press is a mill-drill with
an x-y table on leadscrews it's do-able but I imagine it would be quite
a time investment, whereas without access to that kind of machine shop
style tooling I think some of the parts would be a huge challenge
because of the number of dimensions that need to be accurate.

I can't see how you could do this with such a high proportion of
off the shelf hardware as a single hole punch.  (Which hardware,
incidentally, also got better at the cheap end in recent years --
has anyone tried this with SBR20 linear bearing rail yet?  It's cheap,
strong and incredibly smooth).

You certainly can get solenoids big enough to punch holes in paper,
but go too big and they start to need pretty chunky and costly
components in the drive circuitry.  This may be a factor behind the
"set and punch" designs you've seen.  Two early questions would be what
are the amperage limits of the driver board you want to use, and how
small a solenoid can you get away with?

I think if I were pursuing this approach I'd start from practical tests
of a single solenoid, choose a size, and work the whole design back
from there both physically (spacing and mounting) and electronically
(power of the driver circuit).  Speaking of size, do you expect to
stagger the punches into several rows to make them fit across the roll
width, and if so, how does that MIDI unit handle the timing?

As for making the punches, that seems like fairly standard toolmaking
to me.  Are you after a flat-sides-with-rounded-ends design or something
else?  If they're not circular I can't see how you avoid the work of
cutting keyways to keep them aligned.  I think I know how I would make
the part, but it depends rather on available tools.  Making the matching
die holes worries me more.

Best,
Lester Hawksby