Missed steps is normally caused by overpowering the stepper motor. Microstepping is to be avoided if at all possible. It is a torque robber. It could be that you just have too much mass to move with too small a motor. How big is the machine? What kind of linear bearings? What system for converting rotary motion of stepper to linear? Normally it is not the computer but it could be noise in the conductors. You say that you are running a laptop. That is specifically warned against in Mach3 documentation. Are you using a USB smooth stepper? Home If you are using a usb to parallel converter for printers that could be a problem as they usually are not buffered.