Project: PCB Mill CNC – First Steps

Last time I tried to build a CNC, I didn’t realise how CAM software interacted with the hardware. From research I have found that packages like Mach3 generally communicate with a CNC tool via a parallel/printer port. The protocol is pretty simple: each motor has two direct pin connections – step and direction.

So first things first I need a parallel port. You don’t find these kind of things on modern laptops, so I took a dive back in time to my dad’s old laptop from about 10 years ago. We are talking a 256MB of RAM, 20GB HDD, 1GHz pentium processor, 3.37kg beast.

This is what a parallel port looks like.

This is what a parallel port looks like.

The first step I decided was to check that the parallel port is spouting out the right kind of data. So with the help of a parallel port break-out device (thanks again, dad) I hooked up the PC to my oscilloscope.

What I would expect is a series of pulses on the “step” pins and a constant voltage (until I change direction) on the “direction” pins. Luckily, this is exactly what I got.

The Mach3 interface. Retro but functional.

The Mach3 interface. Retro but functional.

The parallel port breakout device with probes.

The parallel port breakout device with probes.

Oscilloscope reading. Can you make out the tiny pulses?

Oscilloscope reading. Can you make out the tiny pulses?

What this means is that the PC can be connected directly to stepper motor controllers which coincidentally also have a “step” and a “direction” pin and therefore I do not need any kind of intelligence in the form of a microprocessor.

In the end the stepper motor drivers I went for are these albeit from a significantly cheaper distributor:

My choice of stepper motor driver.

My choice of stepper motor driver.

So, next thing I reckon is to wire up one of these drivers and motors and test it out.

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