PCB milling

The new CNC machine is working well, so I thought it worth explaining a bit more on the PCB milling. I am getting pretty good at it now.

Drilling

I 3D printed a support for the PCBs, holding them a couple of mm off the bed. This allows me to drill through the PCB and mill around the outline. Designs on thingiverse.

Milling

I previously mentioned milling bits, and there are lots you can buy from Amazon and the like. However, the best one I have found so far is one from RS components (part 382002). It is not cheap (£40), but don't be fooled - it works, and works, and works. I did manage to finally blunt one after a lot of PCBs, but really it is very good. The small end means it does not snap off easily either.

I am using a 0.5mm drill to make holes, and a 1mm drill to mill around the edges.

Design rules

I am now milling for the finer pitch used by the ESP32-WROOM-32 SoC modules. So I have to be able to mail quite fine tracks with 1.27mm spacing.

What I have found is that, with that bit, the simplest rule is to ensure isolation tracks are at least 1mm apart. This is quite easy, using inkscape, I just set the tracks to 1mm wide and see if any over lap. I have a layer for the parts, a layer for the drilled holes, a layer for the edge mill, and a layer for the isolation tracks. I can then simply save each layer as EPS and convert to an NC G code file.

Faster milling

I also updated my code to take the EPS output from inkscape and make a mill file. It now sorts the lines, and makes paths with a much more optimal routing. On GitHub.

PCB Milling bits

I have been playing with milling PCBs, and the issue is working out what bit to to use for milling PCBs.

The CNC 3018 I got comes with some fine tipped bits, they are cheap, and sharp..,

They are indeed pointy. If you try milling, they break, as they seem to in a slight breeze. They may have uses for wood or something, but for PCB they do not.

Broken bit

Even broken, they have some use, but the width depends on where they broke. And you have to start the cut again once it breaks. Bugger.

Flat end mill

You can get flat end mill bits...

These are not bad, but as you can see, the end is quite long. This is a 0.5mm diameter bit, which is still quite chunky, but it can cut the copper off a board.

The problem is they snap, and do so easily. It is a tad obvious from the design. So not so good.

What they do work really well for is drilling a hole and moving around to make a larger hole. All of the holes I make are done with this 0.5mm bit.

Bigger bit

I also have a 1mm version...

This is something I use for cutting the PCB outline. Works well.

Cutting the board.

What I found works well is a wider bit...

The issue here is depth control. At 45 degrees it means cutting down an extra 0.05mm means an extra 0.1mm width.

The trick is Z axis levelling, which bCNC can do. I added to my CNC 3018...

I initially tried to connect the wires to "Z" on the controller, but missed and was connected to next pins which are "A5", but it seems they worked and "Z" (I assumed Z end stop) did not work. The bCNC code just worked (with "A5"), and did auto levelling. Wow.

End result is I can cut tracks between 0.1" pitch pins!

I have been getting good at single sided designs with no links, but this makes it that bit easier.

P.S. Designs and code on GitHub... @aaisp giving back to open source.

It is funny how old-school lead(+silver) solder is easier to use...

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.