Using ( Helical ) angled teeth on the rack and pinion help to increase accuracy. The machine will also run smoother compaired to standard gearing. We use Helical rack and pinion on our Laser and its accurate to 0.1mm. You will need a tensioning device to keep the pinion correctly set into mesh with the rack, too tight causes additional wear and tear and extra load on the drive system and too slack causes backlash. As with all drive systems they need to be kept clean and lubricated. I normally use a dry lub to prevent stuff sticking to the rack or pinion which would then be ground into the teeth preventing them from meshing correctly.

Regards

Ian