Stirplate questions

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oooFishy

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I'm putting together a bare bones stirplate, and am wondering how strong the magnets need to be- 3lbs of force, 20, 100?
People have suggested rare earth magnets, but they are not all the same strength.

Also, why is a special manufactured stirbar needed- in other words, why wouldn't any small metal object suffice?

Thanks.
 

homebrewer_99

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Any size RE magnet should work. There's really no friction when the stirbar is spinning on the ring.

Get a couple stirbars. Don't use metal...trust me, I tried it...it'll only oxidize (turn black) before the starters done.

My frst stirbar ran all wacky...I wore the spinning ring off of it and it would not stay center.

They do sell stirbars with replaceable rings.
 

Scimmia

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Those ones at Radio Shack are tiny, I'm not at all surprised they won't work. If anyone wants to find some locally, try a hobby store, like Hobby Lobby.
 

BrewBeemer

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What's wrong with using a cow magnet, they are chrome plated
and availabe in different sizes. Place the rare earth magnet on the
motor.....=o&o>.....
 

DIY Brewing Company

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The rating of the rare earth magnet is not the problem with the radio shack ones. It is the size of the magnet. I would never use anything that small. It will be spinning so fast that the magnetic field is to small to make a difference.
You can always put an o-ring on the piece of metal to keep it from spinning on the bottom and it shouldn't burn but it would be cheaper in the long run to get a stir bar.
 

GNBrews

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You want to use a commercial stir bar because they are chemically inert and won't harbor bacteria. The rusting of metal is often as much of a biological (bacterial) process as it is chemical.
 

germanskyy

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I got my Rare Earth Metal magnets from YesBuy.net Free shipping and very cheap. I glued a SS washer to my fan and the magnets hold just fine on there when it's spinning.
 

rabidgerbil

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I got my magnets from Rockler Woodworking and they work fantastic. As to stir bars, definitely get the real thing, but DON'T get one with the ring, they wobble and make a ton of noise compared to one like this.

If you know anyone that is a teacher, you can have them order from Carolina Biological Supply for you, and they have great rates on flasks, stir bars, etc. My brother in law is a junior high science teacher, and ordered my stuff for me.
 

aekdbbop

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I am having some problems with my stirplate..

I am using a mini stir bar.. and without the flask it spins fine, but once in the flask, it is thrown almost immediately..

anything I can do?
 

HenryHill

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Advertised here (HBT), I saved the link, but haven't bought from them...

http://www.rare-earth-magnets.com/index.htm

Quote:
Originally Posted by GNBrews
The rusting of metal is often as much of a biological (bacterial) process as it is chemical.

Sort of a 'rust is electricity' statement....

To me it's just....rust.... ;)
 

rabidgerbil

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aekdbbop said:
I am having some problems with my stirplate..

I am using a mini stir bar.. and without the flask it spins fine, but once in the flask, it is thrown almost immediately..

anything I can do?
Is this a home built one?
I think that just about everyone of us that built one has some small issue with this when we first built the plate. You need to find the sweet spot for your magnets. You may need to increase or decrease the distance that your flask is from the magnets. I found that I also had to do a second tweeking to deal with the resistance of liquid being in the flask. First try, bar on top of plate, worked great. Second try, bar in flask, had to tweek. Third try, flask with water in it, had to tweek again. After that last time, it has run great, and I have not had any more problems.

I know for mine, I had to move the flask farther away from the magnets, but I have read on here that some had to move it closer, so you will just have to run some tests and see what works for you.
 

aekdbbop

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I think that my problem could be that I put the magnet on the outside our the fan spoke hub, instead of the center of it.. think that could be it? yeah its homemade too
*edit* yeah i am pretty sure that has to be it now that i think about it.. crap
 

HenryHill

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FWIW:

We machine small forging dies (H-13, fully hardened) for titanium and other exotic metal forgings, for medical, aeronautic and aerospace customers, on large electro-magnets mounted on the mill tables. We even use risers to get some of the workpieces above the magnet for through the part drilling/etc.

In practice, the magnetic field is STRONGER above the magnet, on the risers, than it is on the surface of the magnet. Weird, but true.

To try and pictorial-ise; envision the earth's magnetic field from those wispy memories of school, and notice that they extend upward from the earth's surface, THEN curve and come back to earth. They don't lay horizontal just above the surface...

Shape and strength of the magnets and geometry of the magnetic field you make all contribute to the characteristics of the stir bar above it. People are doing it differently and trying to reconcile how they are not achieving the same results as others.
 
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