Sounds like you are doing everything right. Mine come out well and all I have is a cheap small Harbor Freight lathe. I even did two of those BME twin 23.6cc engines on this lathe, machining the cranks, prop hubs, everything. They run so smooth you can set a drink on top of the airplane and run it through the rpm ranges and it barely jiggles the liquid...

Maybe get your center bore, taper, and threads done, then install the blank on the crankshaft and finish machining it into a prop hub with it mounted to the crank??

AV8TOR