to sand the surface of an item uniformly smooth , a sanding machine is used with sanding tools in the form of sanding rollers which are rotated as well as turned in the same plane , and which at the same time are also moved in a different direction from the direction in which the item is conveyed , whereby during the working stroke the sanding elements on the sanding rollers will sand at all possible contact angles in relation to the item . to move the sanding rollers , the apparatus comprises a motor - driven crank arm , in sliding engagement with a carriage supports the sanding rollers , and drives the carriage on rails which extend in a circle about the machine . this achieves a stable and robust construction which also gives the sanding rollers an expedient movement characteristic , which compensates for the predominantly longitudinal sanding movements to which the items are exposed in the outer areas .