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X-Y steps seem wrong

Hi there. I’ve been trying, without success, to rout a PCB using the Boxzy CNC head. Because the unit has a height difference of about 2.5mm from front to back I first routed a pocket in the sacrificial material and mounted the PCB material in that pocket. I was hoping for a near perfect flat/level surface to rout out the PCB tracks. After repeated failures I looked at the result with a microscope and noticed that the tracks are wavy and the square pads are nowhere near square.

My questions are, is there a way to calibrate this to make square things square and what’s up with the wavy tracks?  Here is a picture of the routed PCB compared to what it should look like.  (Hmm… I have the PCB material taped down securely but I will look into this.)

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I just secured the PCB material down with 4 screws, one at each corner. It couldn't move while routing. The problem remains. Any suggestions on how to fix/calibrate?

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What if you started smaller lines first

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Not sure what you mean. I think I was able to fix the issue of the square pads not being square though. I adjusted the number of steps per mm on the X axis and it seems to have fixed that part. I'm routing a sample board now and will check it when it's done. Thanks for your input.

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Hi Paul,

It’s hard to tell exact scale from your image, but It looks like your traces are extremely small, and you are trying to make a compact smd pcb. When milling a pcb, you want to design your traces as thick as possible. The mechanical removal of material (as opposed to etching) is fast and simple, but it does have some drawbacks.

What you are seeing is likely from run out in the collet and endmill, as well as hysteresis from backlash in the bearings. While these results can be improved some using a very high precision collet and run-out rated and balanced endmill, as well as careful calibration of the tightening and placement of the collet and endmill in reference to each other, it will alwasy remain to one degree or another. The best way to handle it is to design larger traces and separate components as much as possible.

If you absolutely need this exact design and scale, you can get the results your looking for by masking the PCB in black, and laser etching the mask in preparation for acid etching. This is the only cost and time effective method I know of to get the results you're looking for with a reasonable amount of time and effort.

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Well, this is a disappointing answer. I have used other machines to do exactly this with success. When that old machine died I saw an opportunity to upgrade. The specs for Boxzy indicated it could do 10 thou spacings easy enough. I think you have a point about the collet and I will look into that. From my picture I can clearly see that the X and Y step sizes are not equal. I'll try to adjust that first. This seems to be an unexplored topic here so I do appreciate the suggestions but acid etching is not an acceptable path. I will post here if I have success.

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Just make sure you use a precision collet, rather than an adapter. The adapters makes things a lot worse, where the precison collet improves things. http://m.elairecorp.com/site/makitaroute...

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Paul will be eternally grateful.
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