I built a stir plate (an "exact" clone of http://www.homebrewtalk.com/f51/my-s...y-build-86252/
). Using a 1' stir bar and a 1L flask on the slowest speed setting the stir bar is thrown . If I increase the speed a little it spins just fine but pulls the vortex all the way to the stir bar which causes it to rattle and major bubbles as the stir bar smacks the tip of the vortex around. A 2" stir bar never gets going as it is thrown after just 2 or 3 revolutions. Just testing with water so far.
I started with a 12V PS and have since reduced to 9V PS.
Do I have too strong a vortex for a starter? Any ideas what else to try to tone down the vortex a tad without throwing the stir bar?