I designed a DIY stepper motor power feed for my RF-31 that is about 50% complete at this time. I wanted more capability than the commercial units, and so far I only have spent about $100 on the motor, driver, and pulse generator speed control. I expect the total cost to be about $150. It has loads of torque at low speed, no gearbox, keeps the crank handle, is compact, and has an auto-reverse feature. It uses a limit switch assembly that my DRO read head mounts onto. (DIY TouchDRO is fantastic--best mod ever!)