Ebay 3020 desktop CNC router

I bought one of these 3 axis CNC routers via ebay. My goal is to make my own PCB's with it. Well, yeah; that's my goal. But in the 9 months I've owned it I've not yet been able to get a satisfactory piece of work from it. As is usual with most things from China via Ebay, the documentation was non-existant. I got most of my information from other frustrated owners on various mailing lists and message boards. 

Sales picture from ebay

My first issue was that it needed a PC with a parallel port. Having a "legacy free" PC was going to cause problems. As it turned out that problem solved itself. I'm a Linux user. Having done some research on how to use this thing with Linux I discovered that there is an entire Linux CNC project dedicated to these sorts of machines. Because the timing demands of the router are pretty specific Linux CNC requires its own PC hardware. I was able to find a suitable PC in the junk pile that would run the router "properly".

I say "properly" as the supplied controller (the thing in the black box) was pretty lacking in its features. Not only that but when I tried to use the demonstration CNC projects supplied with the Linux software the router became intermitant. Investigation of the controller box revealed that the enclosed circuit board was not grounded at all!! It relied on a single screw thread poking through a mounting hole. Unfortunately the screw head was covered in paint. A wire brush fixed the paint problem and a few other ground cables added here and there brought the lighted power switch into operation. Great, now it would route the demonstration piece.

Rear panel of the controller

Take a look at the back of the controller. Can you see that blanking cover? What is that for? Well, closer examination of the circuit board revealed 4 axis abilities as well as limit switches and a few other features not normally available by default. Do you see that coaxial connector next to the parallel port (click the picture to enlarge it)? At first I thought it was to supply DC power instead of using the built in mains PSU. Good job I didn't try connecting anything to it as it turned out to be the Z axis probe input (used to detect if the router bit has contacted the work piece).

Inside of the controller. Note linear PSU and 2 control boards

Spindle control not connected to anything

Whilst poking around the board I noted a few other things that were useful. As supplied the controller requires manual control of the motor spindle that drives the actual router bit itself. One presses a switch to start the motor and then winds a knob to adjust the bit rotation speed. What a load of crap!!. Why can't the PC turn the spindle off and on and adjust the speed as needed? Turns out that the PC can do these things if only the jumpers on the circuit board were set correctly!! The vacant white connector at the top of the right hand picture controls the bit speed.  Control of the bit spindle was achieved by cross connecting the PWM-OUT on the below board to this connector. The picture also shows the bad grounding issues I dealt with. Here we see that the mounting holes are painted over thus insulating the ground path.

Limit and bit spindle outputs not connected to anything

That brings us back to the limit switches. There's a header on the board that allows for limits on 3 axis. I found a 4 pin CB microphone connectors in my junk box and wired it into the limit header on the circuit board. I still need to install the actual switches on the router itself as they are missing too but unlike the controller circuit board there is no provision for adding these. I bought a few of these switches via ebay and I think I'll try and make a mounting bracket with my new 3D printer. Alternatively I could make the brackets with the router itself?

Limit switches brought to the back of the control box

A-axis output just below the left white connector

So now we have to connect the router to the PC by way of the printer port. My chosen software needed me to create a machine profile so that it would know how to drive the router. This meant having to map the pin functions from the controller to the PC. The below is what I came up with.

Since starting on this journey I have run across some other websites that have also found the same issues as I have. This one is by far the most detailed.