Summary

Just another magnetic stir plate using a 12VDC fan, with allowances for a speed-controlling regulator. Has new changes as V2.
New: added feet for #8 screws.
Video of early test:
https://youtu.be/LTQn-agubDQ
The unconnected gizmo in the short video is a voltage regulator which I later attached to use as a speed controller.

Try this out with my stir bar. Or don't; a real stir bar is best and they can be had for cheap.

Instructions

NEW
Changes added. In-line description changes in bold.
Uses an 80mmx20mm 12V fan. I made room in the case and mounting holes in the lid for a specific DC/DC converter with mounting holes/potentiometer layout like this one
I used 1.25", #8-32 machine screws; my print (.3mm, 2 layers, 100% fill) was close enough I had to screw them in (they went in easily), but I still used nuts. The screws protruding underneath double as feet. The top is mounted with 5x #2x3/8" flat-top screws. The regulator board can be mounted with #4 or #2 screws.
I tested it with just a +12VDC supply, no regulator, and it creates a vortex that reaches the bottom in under 3 seconds. The stirrer was just a couple of magnets hot-glued together with about 1 diameter spacing between them.
TO BE DONE:

ADDED:
Moved power inlet hole to end of electronics compartment; it was blocked by a screwdown.
Thickened lid and reinforced.
Added ventilation to electronics compartment.
Added mounting hole for 6mm shaft potentiometer knob, with knockout.
Added feet for #8 screws.

The BrewStir. It's a magnetic stir plate for homebrew.