Patent ID: 7171791

Claim:
A locking system for mechanical joining of floorboards at a joint plane, each of said floorboards having a core; a front side; a rear side; and opposite joint edge portions, the locking system comprising: one of the joint edge portions is formed as a tongue groove which is defined by upper and lower lips and which has a bottom end, and the other of the joint edge portions is formed as a tongue and which includes an upwardly directed portion on an upper surface thereof, wherein the tongue groove, as seen from the joint plane, has an undercut groove, an opening, an inner portion, and an inner locking surface, and at least parts of the lower lip are formed integrally with the core of the floorboard, and the tongue has a locking surface which is formed on the upwardly directed portion to coact with the inner locking surface in the tongue groove of an adjoining floorboard, when two such floorboards are mechanically joined together, so that the front sides of each floorboard are positioned in a same surface plane and meet at the joint plane directed perpendicular thereto, at least a major part of the bottom end of the tongue groove, is positioned further away from the joint plane than is the outer end of the tongue when two such floorboards are mechanically joined together, the inner locking surface of the tongue groove is formed on the upper lip within the undercut portion of the tongue groove for coaction with the corresponding locking surface of the tongue, which locking surface is formed on the upwardly directed portion of the tongue to counteract pulling apart of two mechanically joined boards in a direction perpendicular to the joint plane, the inner locking surface and the locking surface defining a locking plane where said locking surfaces are most inclined relative to the surface plane when two such floorboards are mechanically joined together, that the lower lip has a supporting surface for coaction with a corresponding supporting surface on the tongue at a distance from the bottom end of the undercut groove, said supporting surfaces being intended to coact to counteract a relative displacement of two mechanically joined boards in a direction perpendicular to the surface plane, a second plane is defined as being parallel to the locking plane and being located further away from a point where the surface plane and the joint plane intersect than the locking plane, all parts of the portions of the lower lip which are connected with the core are located on a side of the second plane opposite the point, and the upper and lower lips and the tongue of the joint edge portions are designed to enable disconnection of two mechanically joined floorboards by upward pivoting of one floorboard relative to the other about a pivoting center close to the point of intersection between the surface plane and the joint plane for disconnection of the tongue of one floorboard and the tongue groove of the other floorboard.