Stir Plate Magnets Different Sizes?

[oljimmy]

Hi all, I'm building my own stirplate and I'm using the RE magnets from an old hard drive. I broke the magnet in half as per instructions but one chunk ended up larger than the other by about 2-3mm:

When I affix these to the computer fan, is the size differential going to be a problem? Or should I try to file the larger one down? Sorry for the newb question.

 

[jtratcliff]

I think you should be alright. For my first stir plate build my broken magnets were very asymmetrically shaped and I had to glue them on cock-eyed to get the fan balanced. Still was able to get a vortex with it.

 

[oljimmy]

Right... I hadn't thought about the fan balance. Are you suggesting that I glue the smaller chunk slightly further away from the center of the fan? To equalize the... uh... (highschoolhighschoolhighschool)... centrifugal force? How did you trial-and-error this?

 

[oljimmy]

Oh! I just thought of the obvious solution. Mark the absolute center of the fan then glue the magnets to it while they're still stuck to the stir bar as pictured. Apply glue to magnets, line the middle of the stir bar up to the center of the fan, glue them on, pull bar off after glue is dried. This should ensure a perfect grip, right?

 

[WrenchBender]

Simple solution is to glue a large steel washer to the fan making sure it's balanced. Then just put the magnets on the washer WITHOUT glue. Easily adjustable and they will stay put without glue. Mine works fine like this.

Dan

 

[jtratcliff]

Simple solution is to glue a large steel washer to the fan making sure it's balanced. Then just put the magnets on the washer WITHOUT glue. Easily adjustable and they will stay put without glue. Mine works fine like this.

Dan

This!