Hello,
I think the most informations you can find on the homepage from rchobby.
1. I don’t seem to be able to find any way to interface this into Mach3 other than a straightforward On/Off
You can use the input "VI" for pwm signals from Mach3.
The "REV" input you can use for forward and backward.
2. Looking at the termination panel image I think it looks like I could use a Charge Pump Circuit from the PWM output on Pin but I’m not too sure.
"VI" is for pwm input.
3. Is it possible to control the Motor Speed with Mach3?
Yes with pwm (0 ... 10 V) and "VI".
4. Where does the water bit come into the equation, How does the water circulate?
On top of the spindle are 2 fittings for water input and outlet. The water circulates through the spindle housing (see homepage
http://www.rchobby-net.de/fraese/spindel3/spindel33.htm).
5. Do I need a circulating pump and a cooler setup?
Yes. An other way is to use a large buffertank (10 l) and than you can use the spindle for a hour or so without cooler.
Please have a deeper look in your frequency converter manual. There is the most described.
LazyBee