Hillbillysawmiller.
Using single-phase power to run machinery of the size you describe is awfully inefficient. Perhaps you should consider using a primary power source for your 'scragg mill' such as a diesel-engine salvaged from a truck. (What is a scragg mill, by the way?). This would leave the rest of your machinery running wired up as now, with capacity for further future expansion. A diesel engine is a very efficient machine, probably 40% of the fuel energy (diesel-oil contains about 8.3 kilowatt-hours per US gallon), converted to shaft power, and driving the mill direct for a man of your undoubted practical engineering talent would be easier and cheaper than playing about with 100HP of trick motors and risking the CoOp pulling the plug on you. Also with some pipework, you could have up to 130,000 Btu of free heat for the mill/your house plumbed off the engine cooling system. Keep the transmission complete and run off the vehicle propshaft- then you can use the vehicle gearbox to set the optimum speed band. Any diesel engine will have a governor, so a hand operated throttle off the injector pump will give reasonable speed control between mill idling and full load. Now, a road-going truck governor runs at about 10% speed variation, (for driveability reasons), which means the mill will hunt some 10% on/off load. A better engine would be off an agricultural tractor, because the governors on these are set about 6%, with the bonus of a PTO shaft and the hand throttle built in! You could get 4% governing (best) off an air-compressor, water-pump or electrical-generator engine, but the transmission would be more challenging.
regards
English Bob.
