Using a CD jewel case, some magnets and a 12-volt air compressor, you can build an elaborate Tesla turbine sharpener for pencils you probably don’t even use. Oh, did I mention it could kill you?

Sometimes you absolutely, positively need to know the angle of the cutting edge on a knife. When you do, the best tool for the job is a laser goniometer, and [Felix Immler] shows us three different ...