New milling machine

I had a CNC 3018 PRO machine from Amazon.

• It needed assembling, but I've done that now. It is something to bear in mind if buying one though.
• It is a bit of a "home made" style, with the PCB bolted to the frame, etc.
• The one I got had a bent screw for X axis, which limited the usable space a bit.
• It has a working area 30x18cm.
• I was able connect a Z-axis probe (well, contact to PCB copper clad board).
• It works well, and I used bCNC on my Mac to work it.
• It comes with a controller box, which is not needed really!
• It is surprisingly cheap.

So, especially given the bent screw, I decided to get a replacement, and went for a CNC 3020 from Amazon.

• This is a much more "industrial" unit - proper drag chains and cables. Looks good but costs a bit more.
• Work area (you guessed it) 30x20cm
• Comes pre-built
• Has a boxed controller and power supply, with nice connectors to the machine.

However, it has a challenge or two - the main one is that it works with some very specific software (a pirate copy of which is apparently supplied with it). It has parallel (!) and USB, but the USB only works with that software and only on a windows machine - it does not even appear on a Mac even in a debug log! The software did not look too good anyway! This is a bit of a bugger.

The upgrade

My solution was to upgrade the controller to a TingG controller. This adds a bit to the cost (especially with the customs/VAT and admin charge from US). But was not actually at all hard to do.

The old controller is bolted to a heat sink, and can simply be unscrewed.

The new controller is slightly smaller. I needed to drill/tap an M3 hole in the heat sink for one of the screws so that I could screw it to the heat sink. I also cut an extra hole in the case for the USB connector.

Also, I decided to use the heat sink, which meant something between the new controller board and the heatsink. I got some small copper block / heat sinks and thermal tape - and I used them between the back of the new board and the existing heatsink.

The TinyG is designed to work without the need for a heatsink, but this can not really do any harm.

The connectors on the old board were not the same, though the new board has pads which means I could have changed them. I decided instead to use the screw terminals on the new board, fitting bootlace crimps on the wires. I had to swap the cables to make them fit, and use the motors 2, 3 and 4 as closest to edge of the case. But they all fit!

I also connected the emergency stop to the reset pins. I have not worked out how to connect the spindle drive to the new board yet - that is a challenge for another time. The case has a button and a dial for that which works for now.

I also got a 6 way (plus ground) chassis DIN connector and wired up all 6 end stops (X/Y/Z Min/Max).

This meant various micro switches, and super glue on the actual machine.

And also, the Z-Min I wired to croc clips to allow me to use contact to PCB for homing Z axis.

The TinyG has good documentation, covering setting the current, etc. I was able to set the axis to the right motors, and set the polarity and travel per rotation, etc.

However, the bCNC code I was using did not like the TinyG, and I ended up installing CNC.js which works nicely on my Mac. It does lack the multiple point Z axis levelling of bCNC sadly, but works.

I did have to configure the homing for Z axis a tad as it is designed for a switch from which you back off. For PCB contact you get the exact Z home, and do not need offsets. But this is all well documented.

Slack (backlash)

However, even though it is a really good solid construction and seems to have no play, I found there was an issue with the X axis. It seems to have around 0.1mm slack on it. This means if you move right to a point it is actually around 0.05mm short of it, same if moving left (i.e. is then 0.05mm right of it). Make a row of left and right moves and lines and you see the problem clearly. This test shows it well - centre is left and right moves before each line, but left is all moves from the right (apart from first, bottom left) and right is all moves from the left. Repeatable slack!

Oddly the Y axis is absolutely spot on!

This is not really enough of a problem to cause issues making PCBs, but is annoying so I wanted to fix it.

I checked for anything loose, and also checked the TinyG for any options, but to no avail.

My solution (now updated to the eps2gcode tools) is software to compensate for slack. This seems to work.

Overall I am quite happy with the result.

P.S. Tightening this nut a bit fixed it.



P.P.S. After reading the TinyG docs I am actually running at 4 micro steps not 8, so 1/200th mm spacing, which I think will be more than adequate for anything I am milling. I suspect 1/100th mm would be fine but actually that is a lot more noisy. Now that the backlash is sorted maybe I'll go back to 8.

PCB milling

My first attempt as the RFID reader version of my "scales" system meant a lot of enamelled wire...

It was a tad messy, and time consuming. But worked well.

I decided a small PCB would be a better solution, and the answer for one-off PCBs is, of course, a milling machine.

Nearly 30 years ago I used such a machine when working at Nokia. It was very useful, and expensive. These days you can get a small CNC machine for under £200!

I purchased one from Amazon (duh!).

It took some assembly, to say the least, but plenty of good videos on line.

It has an arduino, which allows moving the head and running code (.nc) files from a micro SD card. It looks like the main machine talks serial / USB, but not got that playing just yet.

Making PCBs

I designed the PCB on inkscape, which is fine for a small PCB like this. The challenge, as always, is a small single sided PCB with minimal links. My first design assumed I could run tracks between the pins on a 0.1" header (which I could do 30 years ago). It seems this is tricky, to say the least. Maybe we can managed 1/20th" pitch devices like an SO8, just, but tracks between 0.1" headers are not so easy.

So I redesigned with "chunky" tracks. This meant one small link. A 1206 0Ω resistor would be ideal, and Amazon prime do them, but out of stock, so a wire will have to do.

In inscape it is easy to make tracks and pads. You then just stroke-to-path, and union the paths and tracks to make an SVG cut path. Of course this cuts on the track edge which makes the tracks smaller. You can make that a path and stroke-to-path again and union first stage, but that is faff. Simpler to design with chunky tracks and pads that almost touch when designing, knowing the cut path will be thicker. If that makes sense. Obvious I needed a layer for drilling, and cutting around the edge of the PCB, and the tracks.

Making GCODE

This is a lot harder than I expected - there seem to be several solutions, and FlatCAM looked promising, but I cannot get to work on my Mac. There is an svg2gcode tool, but did not work well. I ended up just making my own code to convert EPS to GCODE with options for speed and cut depth and so on. The GCODE goes on the SD card, and simple.

Stupid UI

The UI on the arduino is daft - it has a mode to control portion, but then uses all 8 buttons and has no way to escape back to the main menu as far as I can see - so I set origin and have to power cycle to then run the file. Maybe I am being thick.

The result...

Milling

Drilling

Cutting

Ok I cut too deep and cut in to the bed, idiot. I'll either cut less or add a sacrificial layer below.

That worked

Final PCB

It is not that good, but the design with chunky tracks means it works!

And time to try it out for real...

It only bloody works!!!

P.S. I have open sourced the eps2gcode.

P.P.S. Make sure the screws are tight on the screw ends - else you get drunk tracks on your PCBs.

P.P.P.S. bCNC is the tool for sending GCODE to the CNC machine directly - works a treat on a Mac.