Avon 3000 Mill retrofit

I see you already answered my question. That motor is powered by two contactors fwd/rev. Good enough. It also shows a spindle speed sensor with two wires. Is that perhaps some proximity sensor?

I can see possibly configuring that with hal and/or a custom hal component by using mesa card outputs to trigger the two contactors (via relays, probably).

Normally it will only need to switch once when he selects a different speed. Google: "cvt mill belt drive"

I do like your thinking!
I have been toying with putting an encoder on the spindle. (I have some spindle encoders that was salvaged off Mori-Seiki lathes in a box somewhere) Using the index marker on those should give an accurate rev counter for the MESA and HAL implementation. I would also have a solid encoder for the spindle, should I want to venture into rigid tapping...:thinking

For the record, don't repeat the mistake I made a while back. I mounted the encoder inside the belt drive housing to some shaft driven by gearbelt. If I remember right I used a hal mux switch to select encoder scale according to backgear position. It all worked pretty good, but foiled all attempts at tapping because the encoder was not at a 1:1 ratio to the spindle. I think the big problem was index changed with each spindle revolution.

I figure it would have worked better to drive the encoder at a 1:1 ratio with the actual spindle.

Valuable advice NWE, I will keep this in mind going forward.

I made some progress today. Hooked up all limit switches and the "E-stop out" output.It functions, but I have trouble measuring the output using a multimeter and I suspect it need to be pulled up (using the 7i77D with sinking outputs.
I did manage to run the Default LinuxCNC logo engraving Gcode without the belts connected, and it was good to see the motors doing their thing at LinuxCNC;s command.
Another observation: If I actuate a limit (+vector or -vector, not the overtravel), the control trips the estop circuit, instead of just holding feed in that direction. is this correct?
I am trying to get as far as possible using PNCConf as HAL is still foreign to me.
Next would be to get the rest of the E-stop (including overtravel) circuit connected and tested before I hook up the belts.
Homing on this machine used to involve looking for the -vector switches (could be +Vector on Z) and reversing direction off the limit until the index marker is found. Can this be set up using PNCConf as well?