The best model I found for the 3.5" Adafruit touchscreen I'll be using is by designer Tronnic. It mounts to the lower-left aluminum extrusion on the Ender 3, resulting in a symmetrical addition that looks like it came from the factory.
Download the model from Thingiverse and print the following:
|1||2_1_Ender3_Touchscreen_Pi_Back_40mm_Fan.stl or 2_Ender3_Touchscreen_Pi_Back.stl*|
* If you decide to add a fan to your enclosure, I recommend printing the 40mm fan back. Otherwise, print the blank back.
Raspberry Pi 4
If you're using the Raspberry Pi 4 for OctoPrint, be sure to print this remix as well.
For the main holder base/bracket, I recommend printing at least 50% infill. If you're using Cura, I recommend the "Gyroid" infill pattern. I printed with 15% "Cubic" infill originally, and the weight from the Pi and fan caused slight sagging.
If you like perfect symmetry, I recommend you also print this separate screen surround to border the original Ender 3 screen.
Insert the Pi into the case and ensure there's a snug fit.
If your touchscreen came with 4 small perforated tabs on the corner, you may need to snap them off with a pair of pliers to make the screen fit in your case—I already did this before taking this photo.
Using this 40mm USB fan is optional but recommended. It's only $10, so I decided to do it just to ensure I always get the highest quality prints possible. Using the included screws, mount the fan so that it sucks air away from the Pi (blowing out the back). Cover the screws with Kapton tape to prevent shorts.
If you printed the optional screen surround for the original screen, mount it around the original Ender 3 using a bit of hot glue or foam tape. This makes things look a bit nicer and adds additional symmetry!
Your Ender 3 now has an awesome touchscreen that you can use to control your printer.
Next, update your Ender 3 firmware. Many Ender 3s shipped with unsafe, outdated firmware that lacks thermal runaway protection; thermal runaway is a leading cause of 3D printer fires. Updating your firmware only takes a few minutes and is an important safety upgrade!