This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Procure a strip of sheet metal, 6 in. long, 1 in. wide, or as wide as the armature core is long, and 3/32 in. thick. Bend this into a U-shape, as shown, and file each end similar to the barb on a fishhook. Drill two holes for a bolt to pass through the sheet-metal ends. Fasten a screw or bolt in the center of the bend, to be used for gripping in a chuck or polishing head. Core segments can be quickly wound with this device. - Contributed by Geo. B. Schulz, Austin, Illinois.