Abstract: A grinding apparatus is housed in a casing (24). The grinding machine (3) with its grinding pin (15) is journalled in a rotatable attachment (2) such as to be imparted a rocking motion. The apparatus is carried by a pair of arms (7) which are freely movable in a generally horizontal plane, the one arm (9) being mounted for vertical movement on a stand (6). This vertical movement can be adjusted to produce a balanced effect and to deliver a downwardly acting force, feed pressure. Both the balancing and the feed pressure are achieved with the aid of one single piston-cylinder device (11).