It has been possible to do rigid tapping for a lot longer than that Sam, as long as you had a servo or stepper on the spindle, no other hardware required. Was it a good way, well not really, you had to use swapaxis() and to be honest I just used the floating holder as it was easier and did a great job.
Regarding tuning in one place, well its all done in Mach, the plugin is in Mach
I presume you have to tune your spindle loop in LinuxCNC?
Now did I need to use the PLC, nope, CSMIO has a load of I/O and lots of expansion capability if required. So why did I use a PLC, well two reasons,
1. I had one sitting doing nothing.
2 I know my way around the direct logic PLCs so its easy. Doing it in Brains and/or VB would take me longer, but it could be done and has been by others.
The ladder in my PLC runs to, I think, 17 pages of A4 when printed out at 60%, lots of I/O on this changer and I wanted lots of interlocks, you can even see one working in one of the vids. The toolchange takes a lot longer to happen simply because I had such a slow accel/decel set for the test and the spindle took so long to drop to 200rpm which is the tool change rpm and the toolchange will not happen until that rpm is seen.
Even if in the future if I decide to go with LinuxCNC (about as likely as you using Mach, but never say never
) then I would still use the PLC, for the simple reason I would not have to learn the ladder logic in Linux. That is assuming LinuxCNC supports Modbus?
One thing I really like about the CSMIO is the capability of using high res encoders, that means very tight control can be kept.
Hood