Denny Graham,
I know you are one for exact, documented facts, so my vague recollections might not be worth a hoot, but here goes anyway!
Many moons ago, as the head flunky in charge of nuttin, my job was to check armatures on a growler. As I recall, I would put the naked armature into the big 'V' cradle, turn the machine on, and using a old hacksaw blade, would lightly pass the blade over the armature (not commutator).
You had to rotate the armature several times to check it full circumference. If the armature WAS shorted, the hacksaw blade would be magnetically attracted to the shorted bar, or area.
It seems like there was always a small amount of magnetic attraction, but when shorted, it became very obvious.
This is how I remember it!
Stuart
