Flat Belt Driven De-magnetizer?

[M.B. Naegle]

Trying to find it again, but in one of my old turn-of-the-century machinist books there was a section talking about grinding, and there's a drawing showing a demagnetizer on a work bench, one of the classic boxes with the two plates on top, but it had a small flat-belt pulley on the side connected to the overhead works. How would that work, and do any still exist? It looked purpose built and not like a generator connected to a demag box.

 

[jmkasunich]

Just guessing here, but maybe it drives a couple of spinning magnets. Demagnetizers work by alternately magnetizing the part north then south then north, a little less each time as you pull the part away or drag it across the top of the unit. Spinning magnets would do the same, only slower (the electrical version alternates 60 times per second, belt drive is probably slower).