Thanks for that explanation, glad I have learned something new today, I assume (again) that the higher resolution of ballscrew would not be so important to a large woodworking cnc router as compared to the accuracy required of a cnc mill. I would hate to think what 2x 3mtr ballscrews would cost, I take it a support system to prevent screw whip would add to that cost as well I know that double pinion anti backlash and larger steppers would add to the cost of R&P (that's what I have on my machine) but do not have a clue as to what the price difference would be. I know my machine is accurate enough for the type of work I do even fairly detailed relief carving but I suspect the precision would be insufficient if I were to attempt cutting or milling to tight engineering tolerances. Thanks again oh wise one for your enlightenment. :-) :-) My inquisitive mind a satiated lol.