Here's yet another Raspberry Pi case! This one is a little different. There are several requirements I made for myself and this hit (almost) all of them:

1. No hardware required—everything should snap together, no screws/nuts required
2. Modular—can print 1, 2, 3 or more and stack them together
3. Open for airflow—I prioritized air flow and cooling over a completely hard shell
4. Fits most HATs—each module is 30mm tall which should be enough room for most common HATs
5. Quick to print—most printers should be able to print any one part in less than 2 hours
6. No supports when printing—like most people I prefer not having to print supports and then remove them later (often leaving behind ugly evidence of where the supports were). I was almost able to achieve this, although you'll see from the images that 2 tiny supports are required where the fan mount pegs are (but they break off cleanly)
7. Can mount a fan when stacked—in the 4 Pi configuration there is a special base and cap print that includes mounting pegs for a 120mm fan

Coming off of a Prusa MK3S all mounting pegs are press fit and don't require any additional shaping/sanding/filing for a good fit. Your results may vary. The pegs that hold the Pi are pretty fragile because they're so small. You may want to take one corner of your Pi and twist the mounting hole on and off of each of the pegs a couple of times to break them in a little bit. If you don't do this, and If you need to pull your Pi off the mounts later, you should try and hold the top of the peg down with a small screwdriver while pulling up on the Pi, otherwise you might snap the peg right off.

Configurations

Here's a guide for how many of each part to print depending on how many Pis you have.

Single Pi

That's it!

Multiple Pi

Where X is however many Pis you have.

4 Pi Cluster with Fan

This is the configuration I designed this case for in the first place. You put the fan_base at the bottom, three more bases on top and then finish off with the fan_cap. A standard 120mm PC case fan should fit on the protruding pegs at the top and bottom.

See the images for the recommended support structures when printing fan_base and fan_cap.

Prusa

I3 MK3S

No

Yes

0.15mm

Any

Only supports needed are for the horizontal pegs on the fan_cap and fan_base.