A quick build of a gentle nail polish "stirrer" using a microwave oven turntable motor, some tube, enclosure, fuse and lead...

I was 3D printing these (pictured) butterflies from Thingiverse (https://www.thingiverse.com/thing:178830) and decided to do some custom designs. I "borrowed" some nail-polish/varnish from my partner. She told me I had to roll the bottle in my hands for a few minutes and not to shake the bottle, as it will introduce bubbles. I looked on eBay for something to do the job, but all I found were shakers!

I had just pulled some parts out of our defunct microwave oven and noticed the turntable motor ran at 5/6 revolutions per minute - perfect!

Step 1: Plan A:

I needed to make a barrel to glue to the plastic fitting (that the glass plate previously sat on) that attaches to the motor, so I modelled one up in Fusion360 (not shown).

The print was going to take quite a few hours and I wanted this to be finished in 2-3 hours, so I looked around and found a hard (harder than usual) cardboard tube from an Aluminium-foil dispenser...

Step 2: Plan B:

I modified my 3D model to become an adaptor for a short piece of this tube, used Repetier with Slic3r Prusa Edition model slicer and began printing the adaptor.

Meanwhile, I cut and finished (sanded the rough cut end) a short piece of the tube, "dug-up" a 3-pin mains power plug with cable, an enclosure, fuse and fuse holder. The enclosure had sloped/angled sides, which would allow the tube to angle slightly upwards (as shown) when placed on one of these sides.

Next I drilled out appropriate holes to mount the motor and its shaft. Then I mounted the motor to the enclosure.

WARNING: Mains wiring ahoy! Do not perform mains wiring if you don't knowwhat you are doing. Don't thinkyou know what you are doing, PLEASE! Perhaps, a very low (less than 50) Volt motor and appropriate power source could be used instead.

The power lead had a cable relief that fitted in a square hole (you could use a cable gland to retain your cable from pulling out and electrocuting someone), so I drilled a hole near the base of the enclosure (where the lid met the rest of the enclosure) and filed it with a square file till the cable relief fit snugly.

The cable outer insulation was striped approx. 100 mm and the inner insulation was striped off the conductors by approx. 15 mm. I placed some heatshink over one wire (Active (Live) or Neutral (Return)) and soldered the wire to the fuse holder. The heatshink was then shrunk over the join. A terminal block, insulated wire joiner or "blue-point" could be used to make the connections.

The other wire (Active (Live) or Neutral (Return)) was done similarly, but it was soldered to the motor. Another two pieces of heatshrink were used to insulate the joins of a short (50 mm) piece of mains rated insulated wire, joining the remaining motor wire to the remaining end of the fuse holder. A 0.5 A (500 mA) 250 VAC was inserted into the fuse holder.

The ground wire was striped and an eyelet terminal was crimped onto it. One of the motor's mounting bolts was removed and reinstalled passing through the eyelet terminal. I guess the ground wire may be soldered directly to the motor (if possible) or the exposed bolt heads could be insulated with silicon to prevent the slightest possibility of electrocution.

Step 3:

By this stage the 3D print was complete, so I glued the barrel to the printed adaptor and glued the adaptor to the plastic (glass plate) adaptor that was part of the microwave oven.

I drilled a hole through the motor shaft and original adaptor, and used some "stiff-ish" wire to stop the barrel assembly from separating from the enclosure assembly. This step is not really required, due to the side wall angle of the enclosure (and gravity) preventing the barrel assembly from falling off in use. Allowing the barrel assembly to be readily removed from the enclosure assembly, allows the whole unit to be packed smaller when not in use!