Glue 2pc 8mm magnets and add a 6200 ball bearing in centrum.
Place these over a 10mm drill and you can balance the lawn mower knife after sharpening.
For lowest friction, clean the ball bearing with alcohol from all grease, and lubricate it with thin sewing oil, .
Fusion 360file included in case you want to change to other magnets sizes/ ball bearings or knife with another center hole.
The author marked this model as their own original creation.