SLA Printing

This is slightly off-topic, but ultimately technical, so I've not placed it in the something-different section of the site.

Off the back of the MNT Reform stuff, I'd been thinking of buying an SLA printer. Although few parts are 3D printed (trackball assembly, trackball buttons, speaker cover), I'd quite like to be able to produce those parts myself, given they're not metal, and aren't available off-the-shelf like the keycaps, screen, SOM and SSD/Wifi cards.

Here's some notes I've put together for my own reference. But for everyone else, I have an Elegoo Mars Pro, I'm printing with Elegoo's ABS-like red resin, and I'm washing/curing with isopropranol 99.9% in Elegoo's Mercury Plus washing/curing station. I'm quite happy with both, and there's a decent availability of parts like the resin tank and LCD.

Slicing

SLA printers aren't as friendly as FDM printers. For one, the formats used aren't standardised. With FDM, no matter the model of printer, I could expect Cura (LGPLv3) to work without issues. The best parameters could be found from the community, and everyone benefitted with the continued development of Cura.

With SLA, it seems like every printer has a specific slicer to use. In my case, I bought an Elegoo Mars Pro - so the software provided was ‘Chitubox’. This, as you may expect, did not work out of the box on Devuan. This was largely due to my use of Wayland. Fortunately the more recent release fetched from Chitubox directly worked without issue. Although it is still proprietary software, which I'm not happy about.

Chitbux is not Cura. It's not even close in terms of features. But it does work, and it does have enough going for it to make it useful (print configuration, support generation, cost tracking).

Printing

Printing with an SLA printer is less - but more careful - work. Whereas FDM is something you can fiddle with while printing (I'm one to adjust the bed while the first few layers are going down), you can't do that here. Resin is messy stuff, and it's not good to get it anywhere you can't rinse down with isopropanol. Isopropanol is also not stuff you want to have lying about.

Furthermore, much like FDM printing, the process itself gives off fumes. Unlike the sweet smell of melted PLA, cured resin is much less pleasant, and far more chemical. Given the printer came with masks and gloves, I can only assume there is some quantifiable risk in SLA printing.

The preparation of the model for printing isn't too different to FDM. Although SLA printers build downwards rather than upwards, the process is similar enough I haven't managed to ruin too many prints. The only change I found useful was to rotate flat-faced models 10% to reduce surface area on the FEP film. Unlike with FDM where you want a nice flat face to adhere to the bed, doing that on an SLA printer creates a form of suction that will end up with your print stuck to the bottom of the resin tank instead of the (rising) build platform.

Finishing

I haven't tried water-washable resin. My impression is that the results are more brittle, but I could be wrong. Elegoo sell it, so when I run out of isopropanol I'll try it out. The general process for finishing a printed resin part is to remove the build platform, dunk it in 99% isopropanol to get rid of left-over resin, then cure it with a strong UV light for a few minutes.

So far I've found the results good enough to use without further work. But I did play around with clear lacquer, which undoubtedly made for cleaner more professional-looking parts. This could be further improved with some light sanding to blur the layers further.