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bernhardkubicek

notes on PCB milling on repraps.

I have been doing PCB milling on normal and DIY CNC machines for now 4 years. Some documentation is available here.
Traumflugs reprap wiki page on pcb milling is here.

From why I think that Ultimaker is not suitable: first, mounting a dremel is difficult (Its also not a good tool for this imho). You could maybe add a rc-model brush motor with a tool fitting underneath. See the MIT Mantis router for that.
However, you would have sidewards wobble due to the long hinge. Also, the belts allow for high-frequent xy oscillations.
Why is that a problem?
Look at this image:
You see that copper flakes exist at the sides of the groves.
compare to this:
The reason for this is: Copper is very soft. The edge of the engraving tool (V shaped cone, with half of it axially cut away) is not infinitely sharp but round. If you move in xy forward, it will rotate 360 until it cuts the next time. If the xy-traveled distance is less than the small but existing radius of the edge, you just squeeze the copper away, as it is so soft. With some luck, it might be cut away the next turn.
However, if you vibrate, this will happen in a way, that some pushed copper will be connected to its normal layer, and hence you will have flakes. The vibration distance for that is very small, less than 0.1mm.
Some people shrug this off, you can sand it or scotch-brite it. But I disagree. If you sand it, the flakes will bend into the groves, and you will get short connections. And cleaning this will require you to take a needle, and clean each grove, after electric contact testing between adjacent islands ( a sweeping stepping over lines on the board with loads of connections is very good for that, i have been there quite often).
So obviously also important, the rotational speed. If you rotate too fast for constant xy-feed rate, you will just push copper away, instead of cutting it, and get flakes. If you rotate too slow, the tip will break off due to excessive sidewards force. I have also seen flakeing in this regime, not sure whats the mechanism there. So for a rotational speed of 15000rpm, 700-1200 mm/min seems good.
Next thing, if the pcb can vibrate in height, you have the problem even worse. Especially with drilling and cutting the dimensino(0.6mm 3mm cutting height in 1.5mm stepdowns) this is very critical. It will break the tool instantly.

Which leads me to the believe, that you cannot reliable mill pcbs with a machine that is driven by belts. Trapazoidal spindles I think are minimum.
And thats also why I started to playfully design a trapezoidal lasercutable pcb mill. Some images of the first axis are here:
http://www.flickr.com/photos/bernhardkubicek/sets/72157629759069867/

Don't be the product, buy the product!

Schweinderl