I have been revising the wiring diagram, adding information on the selected 24V supply and some notes. I’m sure it’s not finished yet but I’ll attach what I have so far to help with the following discussion.
Here are some PDF file links for reference.
Microstepping
https://motion.schneider-electric.com/technology-blog/stepper-motor-basics-half-and-micro-stepping/TB6600 stepper driver manual
https://forum.arduino.cc/index.php?action=dlattach;topic=558523.0;attach=266385I added notes with suggested starting values for stepper current and microstepping. After the machine is running we can change them to your final settings.
I chose times 4 microstepping to improve the smoothness of the stepping. This decreases the mm/step and increases the steps per second rate from MACH 3 by the same factor. If the higher rate is problem we will have to reduce it.
A more careful reading of the manual revealed my assumption about the ENA input was incorrect. In fact powering that input
turns off current to the motor! I think it would be more correct to call it a disable input.
One of the connection options shown is to not connect anything to the ENA terminals. This would leave the current on at all times. The disadvantage of this is that the motor would consume about 40 watts of power in standby. However once the machine is zeroed you wouldn’t want to turn off the current. Doing that would result in the motors pulling to the nearest full step position. Unless you spend a lot of time with the machine powered and idle not using the ENA inputs makes sense.
By the way, this explains why overloading the BOB enable outputs is not a problem. No current is taken from the BOB when the motors are in use. If there is a failure it would be the inability to turn off the current.
I realized a quirk of the BOB board makes it possible to use an E-STOP switch with only one NC contact. The 24V supply powers the opto couplers for the inputs. Turning off the 24V has the same effect as opening the normally closed E-STOP switch. With this method the BOB’s E-STOP input would be wired directly to GND.