@hman
I just bought a variable speed sewing machine motor from Amazon
Looks like a deal if it really works for your application. But it also sounds like the motor is simply over rated for the application so that it does not get too overloaded. Probably over rated for your application as well. Let us know how this work out. I have recently decided that I want to put a variable (slow) speed wheel grinder together to sharpen my tools. I have a very nice set of grinder wheels on a shaft that I picked up at a garage sale.. just no motor. Maybe this would work ok.
Hairy Experience Story: My wife's very old Singer (>50 years) sewing machine (model 237) motor (smaller than what you purchased, 100 watt, 110V, 7000 rpm) recently died as the foot feed rheostat was partially stuck on and left the motor with current flowing, but no motion. So no back emf..... So the rheostat and motor both get hot. Not knowing it was still on she left the room. Normally she would unplug the machine when finished, but it did not happen this time. Could have cause a house fire as the foot feed also burned up and burned the rug and hardwood floor where it sat. The internal motor wires burnt through and the heating stopped so no house fire! Took us weeks to get the burnt smell of rug, varnish, Bakelite, motor windings etc out of the place!
I replaced the parts with the same model (used ebay for little of nothing). But this destroyed unit also gave me the opportunity to check out how this variable speed worked. Motor had carbon brushes (unlike yours), foot feed rheostat was a pile of carbon disks which as the foot pressure was applied to the spring they were pushed together to lower its resistance. Hence, more pressure, less resistance and so more current through the "rheostat" and motor. However, the rheostat and motor do get hot. (Not a resistance wire wound rheostat with a center contact point as we commonly see today.... which also gets hot if supplying all the power.) At very low foot pressure, so low current, the motor is stalled, but with a little more pressure, and so current, the motor starts up slowly. The speed then is determined by the frictional loads vs the power supplied. Not a modern feed back controller, but works nice for sewing and the operator provides the closure for the control loop! The foot feed housing was molded from Bakelite, while the inside had wires, contacts, levers, springs, carbon disk pile etc. The carbon disk pile was located inside a ceramic tube and a plunger went when down the tube to compress the pile of disks. The designers back then did not have the modern semiconductors we have today, but they were ingenious in their designs and the motor and foot feed seem to have a very long life time!
I doubt that the modern replacement foot feeds for this unit are made the same way as their housing looks metallic rather than like molded Bakelite:
PS. Yes, my wife has an expensive modern sewing machine too, but she prefers her old one! I guess we all like to use our old favorite tools.
Dave L.
