Never had those drives although a friend  did. 
You can easily make up your own line receiver, only thing you need is the line receiver chip and a bit of vero board and some wires, I think one I have used in the past was AM26C32-EP

Hood

So things are coming along.  Panel is just about wired.  Haven't settled on a new spindle drive yet but figure I can play with X,Y and Z before worrying about spindle and tool changer.
Now to setting up software.

Mach 3 or Mach 4??

I'm familiar with Mach 3 so probably leaning that way.  Thoughts?

Personally, I would always stick with familiarity

I got the x,y,z and spindle going yesterday.  I used Demo version of Mach 3 for now.

Was able to get about 500 inches/minute which is smoking fast.  I turned everything back to 300 in/min just because 500 will scare the heck out of you.

Gonna get the spindle gearing setup correctly today in high gear.  Then I will start working on the gear change.  This is where I'm hoping you guys can help.  

Have some issues with home and limits.  Homing is perfect.  But if i jog onto a limit, it is issueing an estop and disabling everything.  Have to turn on emulate for that switch in order to jog off.  Cslabs has a smart limits setting that seems to do nothing.  I'll get it figured.  Writing first script for gear change.

I have figured out how to get the requested speed and I get the idea of slowing down to change gears.  Issue I have is how to catch a simple S200 entered into mdi.  Thats not a M03 command that I can edit in the m3 script.
  Idea would be we are running 2500 rpm on pulley one.  Threshold for gear change is 900.  A S500 shows up in mdi or in gcode program.  How do I catch that.

My new panel

I have figured out how to get the requested speed and I get the idea of slowing down to change gears.  Issue I have is how to catch a simple S200 entered into mdi.  Thats not a M03 command that I can edit in the m3 script.
  Idea would be we are running 2500 rpm on pulley one.  Threshold for gear change is 900.  A S500 shows up in mdi or in gcode program.  How do I catch that.

Have a play with SpindleSpeed.m1s macro - might do it

Got the gear change working just fine.  First VB code I ever wrote.  But now I have a problem that is Mach related.

If I am running or was running in low gear at 500rpm and stop the spindle with M5.  My current pulley is Number 2
I now enter M3 S2500 (my threshold for gear change is 999rpm.

Mach looks at my pulley 2 max rpm and figures out it is too high.  It throws a warning and reset my speed command to the max in the pulley setting.  Then it calls M3 macro.

So the problem is, I have the code in the M3 macro to look at requested speed (Mach just changed it) and decide if gear change is needed.  Also, as part of that macro, we set the new pulley to number 1.

I can't just change the pulley max rpm as that is directly tied to the analog out that runs the drive.  Right now, at all speeds in any gear, I'm within .5%.

Is there a way to tell Mach to ignore max speed?  Or is there a place it puts the original request that I could go get?

The issue is that when it finally shifts gears, runs the spindle up- I'm stuck at the low gear maximum.  That ain't cool at all.  Easy way to break a tool when I requested 4000rpm and in runs into the material at 1300rpm with only a note at the bottom of the screen. Hoping there is something in there to fix this.

I think the number one question is

Did they throw the data away (the original speed request) or can it be plucked from somewhere?

As Dave has mentioned, the spindlespeed.m1s macro is where you want to be looking at the selected rpm and deciding on the gear.
Hood