Lawnmower blade balancer

Balance your lawnmower blades using this simple tool. Additional parts required are two standard 608zz skateboard bearings, two #4 x 1/2" screws, two 12.5x5 mm rare earth magnets and a M8x80 hex cap bolt. There are multiple blade holders published with this thing. One fits John Deere (splined) mower blades, and the other is for blades with the standard 16 mm (5/8 inch) sized hole. The SketchUp file is included for making your own blade holder.

example magnets: http://www.kjmagnetics.com/proddetail.asp?prod=D84

HUB: Prepare two 608 bearings so that they spin as freely as possible. I remove the shields and wash the bearing in solvent to remove the original grease. The thick grease slows the bearing down. Press the two cleaned bearings into opposite ends of the hub. Lightly oil the bearings with a few drops of thin machine oil. The bearings should turn smoothly and with minimal effort.
HOLDER: (1) Press the two magnets into the blade holder such that the magnets are flush