Steel calibration drums (rollers) are the premise for a uniform surface during the calibrating process. In contrast to rubber rollers the steel rollers avoid the so-called "washed-out" effects when processing soft woods. The calibrating machines from Heesemann are equipped with rollers at an optimized diameter ensuring a good stock removal through a wide opening of the sanding belt. The precise guiding of the workpiece is ensured by press-on lips in front of and behind every roller sanding unit. In order to guarantee a very calm running of the rollers they are balanced very precisely. The exact thickness measuring of the machine is realized through precise and solid worm gears. In order to get the correct final thickness of the workpieces when using different sanding papers with corresponding grits and therefore paper thicknesses it is possible to integrate a mechanical sanding belt grit compensation device. The adjustment of several calibrating sanding units to each other is realized from the terminal by means of numerically controlled positioning drives. The following fine sanding process can be realized with cross- and longitudinal sanding units each with segmented pressure beams.