Seeing a lot of 1725 RPM motors on mid-century jointers and planers — my 1956 Delta 6-inch hits about 4,800 RPM at the head with a 7-in to 2.5-in pulley pair. Trivia for the maintenance nerds: was that choice driven purely by 60 Hz 4-pole motor availability, or by keeping knife tip speed and bearing temperature/grease shear in a safe zone for longer service intervals?