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Electrical cabinet design.

I separated the electrical system into three parts broadly speaking. The first part was the Servo power supply system, providing unregulated 72V DC for the servo controllers.


Second part was the 24V DC control logic for the PLC, limit switches, Emergency stops, spindle and coolant controls etc.†


Third part: 240V AC system (Australian wall socket outlet standard for single phase domestic installations.) This was the main power for the spindle motor, transformer, PLC, DC supply and coolant pump.




Limit switches.

It is very important to have an automatic safety shut down mechanism if for any reason your machine, or the PC controlling it goes crazy. Rotary encoders can fail, electrical spikes can kill electronic circuits, windows based software can do amazing things, but it can also make machine tools do very dangerous things.†


I designed this circuit to interface between the PC and the CNC mill. It uses optical isolators to ensure there is a solid communication link between the PC and CNC mill, but ABSOLUTELY NO ELECTRICAL CONNECTION. This may sound extreme since everything is plugged into the same workshop power system, but in the event of a major electrical malfunction, I want the PC to remain in control irrelevant of the mill. If the PC loses itís mind, the Mill will shut itís self down.


One of the most important design considerations is limit switches. There are many types, and even more ways to set them up. I have embedded inductive proximity switches into the table of my mill so that if the table ever reaches the end of itís travel, the machine will go into ďfaultĒ and disable all servo drives, and tell the PC to stop executing G-Code. Below is a picture of the circuit I produced.

Final inductive proximity switch monitor and optically isolated controls.