Magnetic lathe chuck, 6 1/2" diameter with switch and flex

This form of chuck, which is essentially a revolving electro-magnet, was used for holding washers, rings. or other articles difficult to chuck, and was specially useful for grinding operations.

The electro-magnetic chuck has the disadvantage that the accidental interruption of current can be dangerous. So with the invention of the permanent magnet chuck in 1 933, it is less commonly used.