Native34,
Yes, you can setup the spindle with ESS and MACH4, but you will need to add one additional piece of hardware, since the ESS plugin does not have the capability yet. You can add a C41 PWM speed control board from CNC4PC. The board comes with a couple of relays and the ability to sent out a voltage signal 0-10V.
Inside the ESS plugin for MACH4 you configure the following:
Port1-Pin14(output) Spindle Fwd
Port1-Pin16(output) Spindle PWM
Inside of MACH4 configuration under Output Signals
Spindle ON ESS, Spindle PWM
Spindle FWD ESS Spindle FWD
Under MACH4 Spindle you set the RPM range.
This works and click the appropriate relays to turn the spindle forward or reverse.
You will probably need to make minor adjustments on the pot on the C41 board to ensure you are getting the full 10Vs at the highest RPM setting. For example if the spindle is supposed to go 24,000 RPM, then execute M3 S24000 on the MDI line in MACH4 and press cycle start. You should be able to get a reading of 10V. Now change the command to M3 S12000 and you should see the voltage drop to 5V.
You also need to configure the VFD to operate remotely using relays for spindle on/direction and remote analog voltage for speed control. This will get you working and the card is probably $40.
Hope this helps.
Russ