MP Toolman wrote:

Shunt wound or permanent magnet DC motors are inherently constant torque
devices because the magnetic field is constant at or below base speed.

Closer to constant speed devices. If the armature and power supply had
zero internal resistance speed would be constant independent of load. A
Variac and a bridge rectifier will do a pretty decent job for a power
feed.

http://www.metalworking.com/dropbox/_1999_retired_files/PWRFEED.TXT

Ted