Building my CNC Router

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Interface Circuit .

Most of the hobby CNC software and stepper controllers use the PC's parallel port to send the signals back and forth. Depending on the software, the parallel port has 10 or more pins we can use to interface with out CNC table. In a stepper motor based table, each axis needs at least 2 pins, one for step direction and the other for step increment. So for a 3 axis machine we really only need 6 pins in out parallel port. We can use other pins to switch relays on and off, say for example spindle motor or coolant pump.

A note about the PC parallel port. There are a few ports on the back of a computer that should never be plugged or unplugged while the computer is running. These include the parallel port, AT or PS2 keyboard/mouse port, and any SCSI ports.

NEVER plug or unplug the parallel port while either the PC or CNC table interface circuits are powered up. Always make sure the PC and CNC electronics are tuned off when you plug or unplug the parallel port, or you will damage your computer. Trust me, I've seen it happen several times, once in a laptop that needed to have the mainboard replaced as a result, very expensive.

Below is the first circuit I put together for my CNC router. The opto couplers are there to protect my Printer Port, see above. The relay is used to switch the router head off and on, and uses a simple MOSFET driver circuit. The MOSFET shown was pulled from a dead computer UPS, UPS's, like most PC hardware, are great for spare parts. At first I used K179 and then KT-5191 stepper drivers ( see next page ), these stepper controllers need a logic high to switch, and this is supplied by the opto isolator outputs.

Later I moved to a microstepper controller for my stepper motors, and these needed a sink input to switch, ie the input needed to be switched to ground, so I had to redesign the opto driver part of the circuit. More information on the microsteppers is on the next page.

To add in the near future....

  • PDF files of the above circuit diagrams to make them easier to print.
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