I like AISI 4340 in normalized condition. Machine shops might find it a bit hard to work, but it can cover up design flaws due to its good strength and toughness.
AISI 4130 normalized or prehardened is more common and cheaper and is in many ways nearly as good as 4340. They may try to sell you on free machining (leaded/resulfurized) steel but I would avoid it unless you feel confident in your design. To really answer your question requires looking at the design in detail, which I haven't done. Seth Gary Graunke wrote: > > What material is best for a direct drive coupler? I'm having a coupler made > that connects an A/C driver motor (max RPM 10,000) to a Honda Insight > transmission shaft. The piece will be machined with male spline on the motor > end, and a female spine on the tranmission end. The max torque is 92 ft-lbs. > > Regards, > Gary -- vze3v25q@verizondotnet
