Hi . I'm setting up a new to me PRS which is replacing my old unistrut machine that has served me well for 17 years . I must say that I am impressed with the evolution of the shopbot . I am having a bit of trouble though figuring out how to tension the pinions against the gear racks on the X axis . ---How much backlash is acceptable ? --On the old unistrut machine I think the frame flexed enough to allow me to set things up pretty tight