Printing a Pi 5 case that actually breathes (and survives a garage in July)

Hi all! This is the long version of a story that starts with a sad, droopy Pi case (my own (I'm the enclosure lady, I know)).

In July my garage hit 38°C for a week. My Pi 5 lives out there running OctoPrint for the printers, in a case I printed in PLA two years ago. By the end of that week the lid had sagged in the middle like a hammock, and the Pi was throttling every afternoon. So I redesigned it properly, and here's everything I learned.

Material: PLA is not for hot places

• PLA starts going soft around 55-60°C. A Pi under load warms its own case, and a hot garage or a car or a sunny window gets you there quickly. Fine for an indoor desk Pi. Not for anything else.
• PETG is good to about 75-80°C, easy to print, a little stringy. This is what I use now for anything indoors-but-warm.
• ASA handles heat and UV, so it's the one for outdoor stuff (Matt's letterbox, I'm looking at you). It wants an enclosure on the printer and decent ventilation because of the fumes.

My PETG settings

On my printer (0.4 mm nozzle), these have been reliable for a year:

• Nozzle 240°C, bed 80°C
• 0.2 mm layers, 4 walls (walls matter more than infill for a case)
• 25% gyroid infill
• Part cooling fan 30-50%, and off for the first layer
• Glue stick on smooth PEI as a release layer. PETG sticks to smooth PEI so well it can rip chunks out of the sheet (ask my first sheet (RIP))

Screws, not snap fits

The Pi's mounting holes are M2.5 on a 58 × 49 mm rectangle. I put brass M2.5 heat-set inserts into the base with a soldering iron (around 245°C for PETG, a steady push, let it sink by itself, don't force it). The lid is held on with four M2.5 screws.

And here's my soapbox moment (you knew it was coming): print cases with screws, not snap fits you glue shut. The next person (who might be you, in two years, at 11pm) should be able to open it with a screwdriver. Repairability starts with the enclosure.

Airflow: the hexagons had to go

My first redesign had a gorgeous honeycomb lid. Lovely. I tested it before installing it, which I recommend:

sudo apt install stress-ng
stress-ng --cpu 4 --timeout 600 &
watch -n 2 vcgencmd measure_temp

With the official Active Cooler and the honeycomb lid: 74°C after ten minutes in a 31°C garage. The honeycomb looked open but the actual open area right above the fan was tiny, and the side had no exit for the hot air. Version 3 has a plain round opening right over the cooler's fan and long slots along the side where the heatsink fins push air out. Same test: 61°C max. Less pretty. Much happier Pi.

Quick checklist if you're designing your own

1. Material for the hottest place it will ever be, not where you're sitting now
2. Open area directly above the fan, and a clear exit path for the hot air
3. Heat-set inserts and screws
4. Leave access to the USB-C, the HDMI ports, the SD slot and the GPIO header, even if you think you won't need them (you will)
5. Test with stress-ng before you call it done

Happy to share the files if anyone wants them (they're not fancy (but they're open)).