On 23/01/2021 01:52, Snag wrote:
Â* It's an old motor , 3/4 hp . And it's a universal motor , with a
flat disc commutator and brushes that can be rotated to reverse motor
rotation . I was looking at it today and saw on the tag that it can be
operated on 110 or 220 volts ... Currently it's wired with the
armature and field windings in parallel , I believe that's called
shunt . I was operating it on 110 volts on my lathe (until I got a
smaller unit , this thing is huge) . I have a project that I might use
it on , but I'd like to go 220V . Am I correct in assuming that
hooking the windings in series will convert it to 220 ? Since this
motor is a universal motor , is it speed controllable by varying the
voltage ?

It may not be a universal motor but rather an repulsion motor
https://en.wikipedia.org/wiki/Repulsion_motor , possibly a repulsion
start induction run variant. I have a 1hp one on a compressor and the
commutator segments move once up to speed to take them out of the
circuit and like yours the brush position can be changed to alter the
starting torque and direction.