Locking system for mechanical joining of floorboards and method for production thereof

A floor board including an upper surface layer, a body layer arranged beneath the upper surface layer, a lower balancing layer, and a mechanical locking system for locking a first edge of the floor board to a second edge of an identical second floor board at a vertical joint plane located at upper joint edge portions perpendicular to a horizontal plane, the mechanical locking system comprising:

• the first edge and the second edge together including a tongue and a groove forming a part of a first mechanical connection for locking the first and second edges to each other in a first direction at right angles to a principal plane of the floor boards, the tongue and groove being formed in the material of the body layer, the tongue having an end configured for insertion into the groove, the end constituting the innermost portion of the tongue that is furthest away from the vertical joint plane, the groove has an upper groove part, a lower groove part, an inner groove part and a groove opening at the vertical joint plane and extends horizontally between the vertical joint plane and the inner groove part;
• and
• a locking device arranged on an underside of the first and the second edges, the locking device forming a second mechanical connection locking the first and the second edges to each other in a second direction parallel to the principal plane and at right angles to the edges,
• wherein the locking device includes a locking groove which extends parallel to and spaced from the second edge, the locking groove being open at the underside of the second edge and including an internal surface,
• wherein the locking device further includes a strip formed from the body layer and the balancing layer extending from the first edge, the strip extending throughout substantially an entire length of the first edge and being provided with a locking element projecting from the strip,
• wherein the strip, the locking element, and the locking groove are configured such that when the second edge is pressed against an upper part of the first edge and is then angled down, the locking element can enter the locking groove,
• wherein the locking element has a locking surface which faces the first edge and is configured so as to contact the internal surface of the locking groove to prevent substantial separation of the joined first and second edges,
• wherein the tongue and the tongue groove have upper contact surfaces,
• wherein an upper edge of the locking element is located in a horizontal plane, which horizontal plane is positioned below the upper contact surfaces of the first mechanical connection and above the lower groove part,
• wherein the tongue and tongue groove are configured such that a gap is provided between the end of the tongue and the inner part of the groove and/or between a lower part of the tongue and the lower groove part.