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Old 08-23-2010, 05:54 PM   #1
ekjohns
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May 2009
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I am building some stir plates and have read about people using different sizes and kinds of stir bars. So far what I have read is that 1" stir bar seems to work better than any other size. I have also read that the ones with the ring in the center make alot of noise and easily get tossed. Finally I have read that someone used an egg stir bar (shaped like a football) and it worked better than anything including the 1" standard stir bar. Assuming the magnet is from a HD, what have people found to be the best?

 
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Old 08-23-2010, 06:26 PM   #2
Catt22
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I've built quite a few stir plates for myself and my brewing friends over the past couple of years. I don't use the HD magnets as I have found them to be difficult to position and balance. I use store bought rare earth magnets. IMO, a 2" (51mm) stir bar works the best of all that I have tried, and I've experimented with quite a few different types. I've found that the larger 2" bars do a better job of stirring at relatively low rpms. I also like the stir bars with the center pivot ring. The ring reduces friction between the bar and the flask making it start more easily and less prone to stalling. A stir plate with well balanced, aligned and spaced magnets should run quietly and seldom, if ever, throw the bar when operated at a reasonable rpm rate. I have not tried the oval (football) shaped stir bars, but one of my friends uses one and likes it a lot. I've also used the barbell shaped stir bars and they work well, but they are generally pretty big and require more power to turn. I like to use the barbell stir bar with a one gallon glass jug with a slightly domed bottom. I've also found that it is best to match the position of the magnets a specific stir bar size for optimum performance. You can check your stir plate for balance by running it full speed without the flask or stir bar. Any vibration you can feel should be minimal. Strong vibrations indicate poor balance of the magnet(s).

 
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Old 08-23-2010, 07:46 PM   #3
Zamial
 
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I agree with cat. The stir bars come in disposable and reusable varieties. I chose the reusable and it was the hex/oct shape with the ring in the center. I had a 1 inch flat and a 2 inch stir bar with pivot ring and I liked the pivot ring style much better but that is because it works and seems to get thrown less often.

I think that there will be some noise no matter what, mine is actually pretty audible. Which I like because I can tell if the bar gets thrown just by the sound. Most of the noise I get is from the air slamming into the bar. (I have convinced SWMBO that it is a relaxing noise, like a zen fountain.)

I can not comment about the HD magnets as I went and got 2 square neodymium magnets from the science and hobby store. (the same place I got the flask and stir bars) This was after I tried to glue 4 smaller magnets to the washer. 2>4. 4 was a PITA that failed BAD.

I also will add that the position of the magnets plays a HUGE roll in the stability of the stir bar. You do not want them to close or to far apart as that will cause the bar to get "thrown" easily. It took quite a bit of "fiddling" with things to get it right but it works great!

Good luck!
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Old 08-23-2010, 07:58 PM   #4
chuckjaxfl
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Feb 2010
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Quote:
Originally Posted by ekjohns View Post
the ones with the ring in the center make alot of noise and easily get tossed
I use one of these, 1". Just shove it into a 1" piece of beer line. Much less noise.

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Old 10-21-2015, 12:49 PM   #5
dude_brewery
 
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Dec 2014
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Quote:
Originally Posted by ekjohns View Post
I am building some stir plates and have read about people using different sizes and kinds of stir bars. So far what I have read is that 1" stir bar seems to work better than any other size. I have also read that the ones with the ring in the center make alot of noise and easily get tossed. Finally I have read that someone used an egg stir bar (shaped like a football) and it worked better than anything including the 1" standard stir bar. Assuming the magnet is from a HD, what have people found to be the best?
Either the egg, or a stir bar with a central pivot ring should work better than a plain stir bar. The plain ones have a lot more surface friction than those pivoting on a central point, and so they tend to get thrown as soon as you approach higher rpms.

Another thing to look out for is the material of your stir bar. Some stir bars are just iron coated in teflon. Others will actually have a NdFeB core that is coated in teflon. This makes a huge difference in the magnetic coupling with your stir plates magnets. I've tested iron stir bars against NdFeB ones, and where the iron kicks out of rotation at a small dimple, the NdFeB will stay in rotation and create a vortex reaching all the way down to the base of my flask.
Personally, I use a 1.25" NdFeB stir bar, hexagonal profile with a pivot ring.

*Edit* My bad, I realize I am replying to this years after the fact. Sorry to stir up old threads. Somehow it popped up in the forefront of my forums, and I had 2cents to throw in.
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Old 10-22-2015, 02:58 AM   #6
twisted-brew
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Mar 2014
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I've found the smooth pill type wok best. I had an octagonal with pivot ring that would spinoff axis at high speeds. The least hydro drag the better.

 
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