Thanks for the replys I have tried the scotch yoke with pwm, and the mechanism was reasonable but couldn't cope with the rebound wave as it was stalling the motor. I wasn't strong enough to do it without stalling, and it was a seriously geared motor. I have a cnc and run mach3, the uc300eth was an upgrade for my setup and allows me to do a tidy setup, and run the hybrid stepper through the Bob. Quite impressed with the hybrid stepper and motor Nema 34.8Nm HSS86 getting 4500 rpm before it stalls. 2005 ballscrew with machined split nut made out of UHMWPE as chlorine won't affect it. Still see if it works if not I will have to try something else. More interested in Gcode options to drive it, as fast and smooth with cycles atm.