After making willoucom's Arduino Spinner and printing his case there were a few things I thought could be improved so I redesigned the entire case from scratch with a much more solid feel, screwed in bottom with space for heat set inserts, a recessed spot for the spinner dial to more neatly integrate into the case and a (not perfect) mounting solution for the Arduino.

The arduino mount isn't perfect and it might vary based on where you get yours from I guess, but it should clip in and not be too loose. I've also added a hole underneath where you can run a zip-tie or something to really lock it into place.

You'll need four M3 heatset inserts and another four M3 screws, the holes themselves are quite deep so it should accomodate several different lengths.

Print instructions(I use a Bambu P1S, so I can only speak from this perspective):

The bottom and spinner dial print without supports.

I printed the main body of the case with supports on the recessed spot on the top where the rotary encoder sits. I printed it in ESUN PLA+ and the supports were quite tricky to remove since it's such a small space, but it was much easier to remove with other PLA, the ESUN PLA+ is quite tough which I assume is why, so your milage may vary. Ideally you'd probably want to print it with a PETG interlayer. It doesn't matter however that it ends up a bit ugly in this spot since the spinner dial will cover it anyway. It shouldn't need any supports in any other spots and my printer had no problem bridging the other gaps.

Orientation:

Spinner dial - Flat side with hole down
Bottom - Flat side down
Body - Top down

I have attached my somewhat messy Fusion files if you want to make any changes.

Arduino Spinner project by willoucom: https://github.com/willoucom/Arduino_ArcadeSpinner

Original case that inspired my redesign: https://www.printables.com/model/483522-arduino-arcade-spinner