Let's Make Robots!

PCB milling


I finally got an usable result trying to mill PCB with my machine. 

I tested using this Eagle PCB layout:











I then generated g-code out of it using the pcb-gcode eagle plugin with the settings below:





























Then I have sent it to the Valkyrie and the result is this:



















Not perfect but usable, it was milled with a broken 0.5 mm drill I have sharpened. I still need to tune things a little,

I milled too deep into the board. Also need to get a proper end mill.

Nevertheless the results are very encouraging even using this setup.

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Your craftsmanship on the Valkyrie is evident from the tolerances on those PCB traces. I am specifically looking at pins 14 and 15 of the L297 and noting that the X-direction, Y-direction, and diagonal traces are all about the same width.  If there were any problems with the machine those fine traces on pins 3-8 and 11-16 would not be uniform.

Comparing it with my Valkyrie-clone, I normally avoid traces of 0.4mm except in the case of absolute necessity, and then I need to keep them aligned to the X-direction since Y-oriented traces have greater tendancy to be broken due to lack of spindle rigidity in the X-direction (traces that go along the Y-direction require X-direction stability on the spindle).  I also notice that the pcb-gcode plugin seems to be a more descriptive version than the version I've been using -- it has pictures and a logo and looks pretty helpful. 

The result looks really good.


I can see with a better cutting bit/depth that you should be able to get to 0.1mm traces -- it looks like the rigidity of the machine is good enough.  To estimate what are reasonable tolerances, I took a look at an LPKF Protomat.  The Protomat* will give you a 4 mil traces minimum (0.10mm), and manufacturer-reported positioning accuracy of 0.00025mm (250 nanometers -- the wavelength of UV-B/UV-C light), so 0.01mm positioning accuracy should be achievable. 

Hopefully a Proxxon IB/E or similar will work out well -- I've heard good things about Proxxon tools and am pretty happy with the Micromot.  I think for milling it might help to have a bit more torque, and the IB/E (or similar) might have a bigger motor for more torque (since the speed offered by the Micromot and the IB/E are the same, I don't know if there is any difference in the spindle motor).

I can't wait to see what Valkyrie 2.1 can do with the right bit!*


LPKF Protomat Series specs: http://www.lpkfusa.com/protomat/s-series.htm
A bit overkill...: LPKF drill/mill bits: http://www.lpkfusa.com/RapidPCB/ToolsAndAccessories/tools.htm
...because the bits are expensive: http://www.lpkfusa.com/Store/ProductDetail.asp?ProductID=131

I'm using the latest version of the plugin found on  http://www.pcbgcode.org/ I think is 3.5.2 or so. It took me a while to understand how it works but it looks like I'm getting somewhere. 

I'm positive I can go even tighter with the tolerances, I just need to calibrate the cutting depth better I used 0.3 mm on this run which proved to be too much. 

Since I'm using halfstepping currently, meaning 76.8 steps/mm, the theoretical resolution would be of 0.013020833333333333333333333333333 per step. 

Rounding it up to a saner value gives a nice round 0.01 mm, add to that some backlash and you still get let's say 0.03 mm which  is still very good.

So I can play a lot with the cutting depth, I think I'll try for 0.25 or even lesser next time.

I got the squareness corrected several times and the table flattened once more ... Also once in a while I'm tightening up the rail bearings because it happens that the machine is hit by my daughter with her walking thingie.   

Now my biggest concern is the Dremel tool, I think is it on it's way to the grave (the lower bearing does strange noises and it looks that the electronic speed control might give up on me), it is definitely not the tool for the job, I should have bought a Proxxon. 

I'll try cleaning it up again, maybe a little oil would help the bearing.