[ANDREW.GROGAN1]

I recently built a stir plate with an old computer fan, a cigar box, and a magnet from the hardware store.  I tried testing it last night and it’s not working.  There is clearly a magnetic field, as the bar sticks to the spot on the box where the magnet is underneath, but when I turn it on, it doesn’t do anything.  The stir bar seems to slide to one side of the stir plate as pictured but I can’t get it centered on the magnet.  I’m wondering is the magnet is maybe too strong or maybe the fan is too slow or too fast.   

Anyone have any thoughts on what I might be doing wrong?

Here is a link to magnets I purchased

http://m.acehardware.com//product/index.jsp?productId=3633664

[Joe Sr.]

Are you sure the fan is spinning? Are you testing it with the stir bar in a flask?  Or right on top of the box?

[ANDREW.GROGAN1]

The fan is spinning.  I tested it with a measuring cup with a similar glass thinness and base.  My flask is in the mail. 

[Joe Sr.]

Dunno.

Could the magnet be flipped?  But then the bar wouldn't stick to the box.

If the fan is too fast, you'll throw the magnet.  If the magnet was too strong, I think it might stop the fan from spinning.  But I don't know for sure.

I've never had an issue with my stir plates.  I used hard drive magnets, which have a different shape.

[mbarnaby]

I would try starting the fan before introducing the flask/stir bar, is sounds like the fan might be struggling to get started.  once run place the flask on top.