Karl Townsend wrote:

I now have four metal mangling machines that need the venerable ISA slot to
operate... These computers are not available new anymore and the new parts
route is about gone too.

I'm settling around one motherboard, CPU, memory, video card combination.
Makes it much easier to maintain. I can do an entire computer swap in
minutes if trouble happens. Or test one component at a time in a spare test
computer.

lets say I'd like to run these machines another 20 years. How many spares am
I likely to need? I'd like to buy them up now. (Note: I don't think I need
to do hard and floppy drives yet - still a lot of these around)

Karl

I'd suggest you take a closer look at Mach3 as well as the couple
external pulse generator modules that work with it which eliminate the
need for parallel ports as well. As you see you're already having
difficulty maintaining a system that requires ISA slots, better to
prepare for a newer setup that will work with more modern components.
Remember that Mach3 is free in code limited trial mode (~1000 lines
IIRC) so you can very easily try it out. It is also very reasonably
priced in full mode (~$150/unlimited for non commercial and
~$150/machine for commercial).