Breakout Board Speed Control

You are looking at the wrong side of the problem, BOB is not the part with issues, KBIC is, so you must check and be sure the inputs on the KBIC are galvanically isolated from the rest of the board.
If they are not isolated, ... well i would throw it in the bin, but you can get some kind of isolation probably, or just use a relay to run it at full speed using the relay on the BOB should do, most probably.
This is something you do not play with.

I don't have my KBIC attached. I just wanted to see if I could read a voltage of 7 at 1400rpm from the terminals of the bob before I even attach it to the KBIC. The KBIC is not isolated, but the BoB is supposedly.

tuxcnc wrote:

... but 12-24V is also used to power the home, estop and probe inputs on the opposite side of the board.

So no, BOB is not properly isolated for this case.

tuxcnc wrote:

it is safer to use a separate cheap Chinese PWM->0-10V board and a separate small power supply.

You should really, really take his advice, and be very careful with wiring.

I see what you mean now about it not being properly isolated. I'll buy a cheap board off of amazon. In the mean time though, I just want to make sure I know how to set it up in general. I just want to know why I'm not getting anything out of it when I issue a s command.

I would think something like this would work, right? It has a PC817C, so I figure it is used to optically isolate the two circuits. What has me slightly concerned is that the listing (and many others) don't mention the fact that they are optically isolated (does this mean that it isn't?).

Logthor wrote:

this would work, right? 

Yes, this is a very similar circuit to the one used in BOB and will work identically.
The difference is that the power supply for this circuit should be not used for anything else, that BOB does not provide.
Voltage is a potential difference and is measured between two points.
The same wire, it may be 12V to the second pole of the power supply, but hundreds of volts to machine chassis.