The debate over rack-and-pinion vs. ball screw as the mechanical drive component in a CNC Router has been a contentious issue for decades. CNT uses both systems on all of our machines, based on which is best-suited for a particular axis or application.
Ball screws are best known for being very smooth and virtually friction-free. Their shortcomings include the need for precision alignment, contamination susceptibility, and the need for increased diameter and weight associated with length (span) to prevent whip or vibration. This, in turn, requires more gearing or larger motors to compensate for the weight and need to maintain rapid positioning speeds. CNT has been installing ball screws for over 20 years and has no difficulty with the alignment procedures involved in machine assembly. We provide wipers and air/oil pressurization on the nut to prevent contamination. We also limit the length and diameter to allow the best balance without sacrificing speed or performance.
Rack-and-pinion drives are best known for being rigid and not limited by length. When mounted properly, they provide years of use with minimal wear and are virtually impervious to dust and debris. Rack-and-pinion’s shortcomings include lower efficiency (due to higher friction), backlash caused by poor engagement of the pinion, and vibration caused by tooth profile. CNT uses 30-degree helical gear rack with a custom semi-topping profile to create ultra-smooth, low-friction movement with more teeth in mesh for power. Our unique pinion engagement system, combined with mapping software, delivers zero backlash and positional accuracy of ±.002″ throughout the entire travel distance of the rack.
Perhaps the best way to impress on you the rack-and-pinion vs. ball screw question is to look at CNC machines costing $100,000 to $300,000. You’ll notice that most of these machines use both mechanical drives on the same machine, just like CNT Motion.