The Gorton 2-28 milling machine that I put in my shop recently, works
great, with one exception: its power feed for the X axis is not
working.

The way it is supposed to work is via a DC motor, controlled by a
simple DC drive. The DC motor has a field winding.

The problem is that the motor does not run.

The DC drive does supply voltage to both F1-F2 and A1-A2. I interpret
those as field and motor windings. F2 and A2 are connected together
and voltage between that point and F1 or A1 is 50 volts.

I opened the motor up. When opened, I tested voltage between brushes
and found out that there is 0 volts between brushes, or brushes and
armature.

How can I interpret this finding and what is the usual cause of such
behaviour.

The motor was really dirty inside, I washed it in a parts washer, but
have not yet reassembled, since I could not find the problem.

Thanks