With a static phase converter, zero current in the third leg is normal
(after the brief starting interval) when you are running a 3 phase machine
on single phase current. The third leg is only intergized for starting.

But in this case I have two motors in parallel. The big 1.5HP grinder
motor and the little 1/2 HP blower. The big grinder motor is pretty
much unloaded and the the blower motor which is always loaded because
it is moving lots of air. I expected to see some current in the third
leg but I don't see any.

chuck