Theoretical concerns aside, then how can one tell if a DC motor is
appropriate for use on a lathe?


wrote:
Real DC motors, unless they're horribly inefficient, don't stray too far
from the theoretical -- so you can pretty much calculate the torque vs.
current characteristic from the speed vs. voltage characteristic.

snip
With regard to the original query, because the
manufacturer quotes RPM/supply current, these are clearly series
wound motors possibly intended for wheeled transport.

There is little to choose between them. The higher
speed motor is likely to be slightly smaller and lighter than the
lower speed machine. The lower speed machine is a bit more
efficient and the lower speed and higher torque may be an
advantage.

Neither machine is suitable if the main aim is
constant speed with variable load.

Jim