As I near the end of the build, it was time to fabricate the MPCNC wiring harness.
To keep everything simple and modular, I decided to use terminal strips to join the wiring from the Mostly Printed CNC machine to the Arduino controller. These terminal strips are made of plastic with metal screw inserts. They are available on eBay for about US sixty cents each. Various sizes are available, depending on the diameter of the wire you are using.
Each terminal strip supports twelve connections. I am using two of these strips. The lower strip is for stepper motor connections. Each stepper motor has four wires. The upper strip is for end-stop connections.
I 3D printed a small base to attach the terminal strips, so I could mount the MPCNC wiring harness on the wall beside the machine. The mounting holes in the terminal strip are very small in diameter – about 2 millimeters. This necessitated using M2 screws. I sized the thickness of the plastic mount to accommodate the length of the M2 screws that I had on hand, namely 12 mm. As you can see in the inset photo upper right, I was able to design hex shaped nut holder into the plastic base. Amazingly, the design resulted in a perfect fit.
MPCNC Wiring Harness – Selecting the cables to use
Most of the cabling in my MPCNC wiring harness is 22 gauge, which is the minimum required for the current that will power the stepper motors. The cable that I selected was Belden 8273. This is four conductor stranded shielded cable. There are two pairs of wires each inside a sheath. Each wire is a different color.
Since the end stop wiring carries very little current, I switched to 26 gauge telephone cable for the run from the terminal strip to the microcontroller. Again, the cable has four wires and each is color coded.
As a final note, one of the advantages of pre-fabricating a wiring harness is that you can test all of the connections in the workshop, before making the final attachments to the machine and microcontroller.