ahhhh today was intensely frustrating

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set out to mill one PCB. Spent five hours on that then gave up because the damn pcb stock was just too distorted and nonplanar.

Found and fixed a very tricky problem on my oled display board using the hardest SMD rework I have done to date. Was very happy, proud and excited to see the panel in the case, so I made a small adjustment to the display location on the board and somehow managed to break my (only) display in the process.

I know in the bigger scheme of things I'm doing great, but these smaller setbacks are SO HARD to suck up man.

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haven't been making keys for two weeks because opening the mold and seeing some with no feet bc air bubbles or finding another crack in the mold. just. sucks.

At the same time I feel like I'm so close it's not worth to make a new mold, try a different way of compressing it or another solution to the air bubble problem

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should've maybe CWd this with "venting", sorry

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@s_ol what material are the keys made of? could bubbles be moved to a safe zone with vibration while the material is still liquid?

@voxel
These prototypes are made of epoxy, see process docs here: fabacademy.org/2020/labs/opend

I've tried vacuum, but it barely made any difference, I'm not sure if vibration would be any better. This only started to become a problem as I fiddled more with other parts of the process (how to get the keys out of the mold after), before that I only ever had small bubbles on the inside. Think I just have to go back a few steps.

@voxel
The page above doesn't really document all of the things I've tried after the first two keys, I'll have to update that eventually - there was a lot of lessons learned, and I'm not done either.

Also, I'm in talks to get real keys made using injection molding at some point, so I don't *have* to figure out a perfect workflow ;)

@s_ol Bummer, that sounds frustrating. =(

I’m curious though. What’s your process for milling PCBs? That’s something I’ve been wanting to learn how to do.

@cuchaz
I design in KiCAD, then plot as DXF. Tried a bunch of different CAM tools:

- mods ("fabmodules", this one takes PNGs not vector): ok for simple stuff but hard to control details on bigger jobs
- Fusion: cant update DXF once imported, chokes on mid to large size PCBs
- flatcam: just terrible UX, I couldn't figure it out at all
- VCarve Pro: pretty decent

@cuchaz
The main problem is that PCBs aren't flat and our CNC mill doesn't have a Z-sensor that can be read from the PC.
The real way to go is to (automatedly) probe the PCB in a hundred different places to build a heightmap and then use that to skew the toolpath.

Without that the only way to do boards bigger than 5-10cm in any dimension is a lot of luck and splitting up the file into smaller sectors and zeroing them independently, which is a lot of manual work the CAM tools aren't made for.

@s_ol Wow, thanks for sharing all that info. That sounds like a pretty complicated workflow. Any suggestions for mills that can compensate for z variations? Luckily the boards I want to make are tiny (maybe a few cm across), so maybe I can live with the height issues?

@cuchaz
You're welcome. I don't really know about CNC models, I only have experience with what we have in the fablab here. If you search for "PCB CNC Milling" on youtube etc. you will find some guides that might point you in the right direction for finding some though.

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