My main Octoprint/Octodash Pi4b has a GeekWorm “armor” case, which does a pretty solid job of passive cooling on its own, but as I've been overhauling my print enclosure, I wanted to rackmount it to de-couple it from the printer, and improve cable management by just having a USB hub tying the printer to the pi/cameras/etc.
There are some existing rackmount solutions, but I also wanted to add a 40mm fan with air channels intended to direct the fan current around the case for additional active cooling, and it seemed like a good design exercise.
The intention is for some of the airflow to route down from the fan across the fins, to the front and out, and for the rest to flow backwards, then curve around to blow out under the case and directly over the motherboard, to exit by the I/O ports and header pins
I haven't used any airflow simulations (in case it wasn't obvious from the super scientific diagram above), but it does keep my CPU temp at or below ~45c during a long ASA print where the enclosure accumulates a fair degree of heat, even though it's near the front door of the enclosure, where airflow might be diminished.
PRINTING
This is designed to press fit snugly against the pi case, so it wouldn't hurt to double-check your dimensional accuracy prior to printing. If you want to test the fitment first, use negative volumes in the slicer to print only a small segment of the object, then try out the alignment to be sure, before you commit to the full print.
For filament: PETG, PLA+, or anything else with properties suitable to your enclosure should work fine.
The one I'm using right now was printed in PETG on a .6mm nozzle with .2mm layer height and no other special settings.
I recommend printing with the object oriented standing up at an angle, with the flattened corner on the build plate, and organic supports everywhere.
I feel like this orientation provides better dimensional strength, looks good, and printed reasonably well, but you could most likely just stand it vertical and print that way if you prefer.
I printed mine laying down flat on the base, which ended up ok, but required a lot of post-processing clean up to get the fitment correct.
POST-PRINTING
Remove supports, then check the ridges inside the print.
If they didn't come out cleanly, just check the fit by pressing each half of the armor case (one at a time, without the Pi) into the print to validate the fitment.
The case should slide in and out cleanly without sticking too much. There should be a clear gap for airflow near the base of the case fins (as shown above). If there are any issues, clean up the print fins as needed, then carry on.
Mount the fan using its mounting screws or zip ties (see below). Make sure to align the power cable properly in the case, so it can be easily connected to the header pins. On my installation, I just ran the cabling along the gap outside of the header pins (shown below) so the excess stays out of view.
Attach the Geekworm case to Pi, then slide it into the print--it should press-fit neatly.
I designed it using measurements I took of the one I have (purchased May, 2020, in case there have been revisions, but I don't see any indication that there have been new versions).
It's rack-mountable using standard rack screws which should slightly self-tap into the print.
Do a gentle test-fit of the screws before mounting the Pi case, etc! It worked perfectly on my print the first time I tried it, and has survived repeated moves as I adjusted the way my enclosure was laid out.
Your mileage may vary depending on dimensional accuracy, print orientation, material, astrological sign, or whatever other factors could affect such a thing.
If the screw fit seems too tight, don't force it; I'd recommend carefully heating up the screw somewhat with a lighter/small torch before screwing it in slowly to ensure that the screws go in without cracking the case mount.
NOTE: if your rails have circular holes instead of rectangular openings, just add a negative volume to the print object in the slicer to remove the stabilizing nubs on the rail side. Negative volumes attach nicely to the object in PrusaSlicer, so you can align it and then rotate into whatever print orientation you'd prefer.
Any Pi-compatible fan with a 40mm footprint should work just fine--I used a Noctua 5V 40x10mm and connected it directly to the power pins on the Pi header.
Fan mounting may work with screws, but I also placed zip tie slots adjacent to the screw holes and used that to mount my fan. If you're going to use zip ties, mount the fan before doing anything else with this print; it's a little bit fidgety to get them routed properly, but likely impossible to do so if the Pi's already in place.
I designed it to align with the existing fan screw holes, so the self-tapping screws that come with the fan should work just fine, but I haven't tried it. If you go this way, do it first and be careful/go slow to minimize risk of breaking the mounts.
Screw mounting holes on the bottom of the Pi/case are all still accessible (but you'll need longer screws, of course).
Pin headers are also all accessible, with the caveat that Pi hats are not going to work without breakouts or ribbon cables, due to the added height and the presence of a fan on top.
MicroSD card slot and all side I/O ports are also accessible with no issues that I've encountered.
This design is compatible with flat ribbon cables, but please be advised…. it is…. unpleasant to attach them with this mount and the case--I used a very thin spudger, a pair of small tweezers, and a copious amount of profane language to get it in place. It works (I uploaded a picture for proof), but I don't advise it.
Seriously. I cannot recommend strongly enough that you avoid ribbon cables altogether, and just use USB cameras instead. They're incredibly easy to set up now with the revised camera stack build of Octoprint, and I'm using 3 that I've connected both directly to the Pi and via a powered hub, with no latency issues.
After all these warnings, it's probably user error on my part and it's actually super easy, barely an inconvenience. \_(ツ)_/ I'm not your supervisor, do what you want :D
