Physicist trying to do engineering. Not going well. After advice with 4 axis gantry.

[Neale]

If it helps, here's a rough wiring diagram that would suit a lot of break-out boards and stepper drivers. As JazzCNC says, the Enable signal is sometimes considered optional; if you leave it disconnected then the stepper driver defaults to "Enabled" anyway. The "Pulse" connection is sometimes marked "Step"; again, previous post explains why.

I've just had a quick look at the "manual" for your BOB; not very helpful, is it? However, you should be able to identify step and dir signals for each axis (=stepper driver). Doesn't appear to be an Enable output anyway but I might have misread it. All ground connections (- connections on stepper driver) go to a single common ground terminal on the BOB. The manual then tells you what pin numbers in Mach3 you should configure for each signal (Mach3>Config>Ports and Pins). However, there is still this question about whether you are running on a 32-bit Windows; the parallel port driver will not work on any 64-bit Windows version.