This may seem like a dumb question... has anyone ever tried using a casing that is itself a ferrous (magnetic) material? My mind can't quite parse out whether it would interfere with the attraction between the stir bar and magnets.
The reason I ask is that I have a fried guitar pedal that would make a perfect casing. I'd rather figure out the casing before sourcing the other materials. To be specific, I have one of these:
Mine is made out of a medal box as well and I ended up just cutting out a hole where the magnets spin at because I couldn't find magnets strong enough to go threw the medal and turn the stir bar. You can always try using it and if it doesn't work use a whole saw and cut a circle hole in the top.
Got around to building my stir plate. A standard LM317 build with an on/off switch.
There's an 80mm computer fan which as a piece of 1" schedule 40 PVC hotglued to it with some rare earth magnets on it. I've dremeled out some holes (melted out, really) for the magnets using a cutting wheel and then secured the first magnet with hot glue. The rest stay by themselves. The speed is controlled by an LM317 with a 330 ohm resistor going from OUT to ADJ and a 10k ohm audio taper potentiometer with on/off switch. I can control power on/off and get anywhere from around 3V to 11.5V out to the fan. The power connector is a standard kobiconn 2.1mm barrel jack from Mouser, but the rest of the parts are from Radio Shack. The box is a 6x4x2 project box from Radio Shack as well.
One problem I ran into was putting too many magnets on the fan. With 4 magnets the 1" stir bar would not spin at all. I think the friction of the bar pulled so hard against the device would just prevent the fan from spinning at all. 3 works great, doesn't throw the bar at even the highest speed, and is silent at low speed with a dimple being pulled into the starter.
$1.99 box from Goodwill.
Master switch left over from some idea I had for my boat.
$0.99 12V power supply from Goodwill
Pot bought off Amazon = too much after shipping and handling, but at the time it was the only way I could buy one.
$8 (?) for a 10 pack of rare-earth magnets from Amazon and a fan from a computer I don't use anymore.