Homemade stir plate isn't working

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Brett3rThanU

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So I just made a stir plate and bought a 50mm stir bar, however every time after 1-2 revolutions the stir bar just flies off. The magnet appears to be centered on the fan, but when the stir bar lines up, it appears to be not centered. I did some quick reading and it sounds like a lot of people have probs with 50mm stir bar. Is there any other alternative rather than ordering a new one?
 
I have it as close to the magnet as possible, the plexiglass is millimeters away from the magnet so there's no way I can get it closer. It's a variable speed fan so I have it as slow as it'll go and the magnet still throws.

IMG_20120218_091223.jpg
 
Two issues that I had with that exact issue...
I put a spacer between that first magnet and the fan motor, a spacer also cannibalized from the HD...and put the other half of that hardrive magnet on top of the other to increase the mag field strength..
Almost forgot...had to put a potentiometer between the power supply and fan...cannibalized again from a broken toy
 
I have had to glue a metal washer to the fan first, then I stacked up four hdd magnets to get the optimal strength. I can turn a 2 inch stir bar at full speed with this setup. I know it can get frustrating, but this build is a trial and error, just be patient and keep at it.

Z
 
That HD magnet should be enough if it's positioned properly. When using HD magnets, I have had better luck breaking the magnet in half and lining up the two pieces in a straighter line than the curved shape allows. A pair of vise grips with the edge lining up with the halfway point and then another set of pliers works for breaking it in half. Make sure you have the opposite poles on each end. It really is trial and error with the placement--the magnets should stick to the fan on their own temporarily and then when you find the sweet spot super glue it down. A rheostat will help dial down the RPMs but if you have the magnets centered well it should work at full-bore from the start. Good luck!
 
cram said:
That HD magnet should be enough if it's positioned properly. When using HD magnets, I have had better luck breaking the magnet in half and lining up the two pieces in a straighter line than the curved shape allows. A pair of vise grips with the edge lining up with the halfway point and then another set of pliers works for breaking it in half. Make sure you have the opposite poles on each end. It really is trial and error with the placement--the magnets should stick to the fan on their own temporarily and then when you find the sweet spot super glue it down. A rheostat will help dial down the RPMs but if you have the magnets centered well it should work at full-bore from the start. Good luck!
Click to expand...

I had to do the same thing with the rare earth magnets i used. With one it kept throwing the bar. I lined up two and it worked like a champ.
 
i dont think 1 magnet is strong enough unless it is broken and stacked. I spend $6 and went to hobby lobby and got round magnets stacked in 2 groups of 3 and it is so strong I can go from 0 - max with out even a slight flicker with any size stir bar. MORE POWER!
 
so I stacked 2 HD magnets. Glue is drying currently, so I'll update later. I also centered the stir bar rather than the magnets so hopefully that helps.
 

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