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CNC Probing

When you are milling PCBs with a CNC having a level surface is extremely important and can be very difficult to achieve. This post describes some of the techniques I used to get a level surface so I could mill PCBs with reasonable quality. Milling a PCB requires cutting away just 0.05mm of copper (or less) from the surface. If you cut too deeply you will damage the cutting tool tip and, due to the arrow shape of the cutting tool, make your isolation cuts too wide - reducing the width of the resulting tracks. If your cut is not deep enough the tracks will not be isolated and your board will hav…

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CNC Updates

It has been a long time since the last post but I certainly haven't been idle in the Lab. Most of my time has been spent working on my larger CNC machine (a CN3020T) including a number of control board redesigns and fine tuning a PCB milling workflow. In my last update I described a simple ATmega328p based board running GRBL. That worked fairly well to control the small linear stepper assemblies I bought on eBay so I decided to use a similar board to control my larger CN3020T machine (which I've been having problems with for a while). To actually drive the stepper motors I bought a set of sing…

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A Simple CNC Machine - Part 3

Another update on my mini-CNC project - progress has been a little slower than I hoped for but I've reached an important milestone now - moving motors! As you can see there are some issues with the precision of the movement - each of those moves is supposed to be 20mm. It doesn't quite make the full 20mm and doesn't return to the same starting point. I'll discuss those issues later in the post but first I would like to talk about the circuit itself. I intended to use the GRBL firmware from the start which requires an ATmega328p with an external 16MHz oscillator. The circuit I used is a basic m…

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A Simple CNC Machine - Part 2

In this second post about my small CNC machine I walk through the process of etching a PCB and building up the controller circuit. The board layout I came up with is shown above - there are more jumper wires than I would have liked and it is not exactly a compact design. Some of these issues are hard to avoid on a single sided board and, truth be told, I didn't spend a lot of time trying to opimise it. My main goal was to fit it on a 75mm x 150mm panel which is the normal size PCB panel I buy. The next step is to make sure the components fit and I haven't made any alignment errors. The image a…

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A Simple CNC Machine - Part 1

I have been trying to get a replacement CNC controller board up and running for a few months now - fighting with LinuxCNC and a cheap Chinese Blue Board controller I bought off eBay. Although I can get it basically operational - enough to cut simple shapes out of MDF but I have been having a lot of problems getting enough accuracy to do anything more significant (and certainly not enough to reliably mill PCBs). If you are building up your own CNC or looking to replace the controller in an existing one I would recommend keeping away from this particular product. After finding that more recent v…

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