Patent ID: 7806620

Claim:
A corner joint comprising two frame side members having attachment channels and mitered end portions, and at least one corner piece having two insert parts joined at connecting ends and positioned relative to one another at a predetermined angle, each insert part configured to be received by the mitered end portions of a respective one of the attachment channels of the side members, the attachment channels being confined by an inner wall and an outer wall, wherein a mutual interlocking between the corner piece and the frame side members is carried out by lips defined by a pressed-in material part of the outer wall, which said lips cooperate with notches defined on the corner piece; wherein each insert part includes at least one said notch comprising a triangular shape defined by a first side against which the lip is positioned which is longer than a second side over which a free end of the lip is pressed in; wherein the lips generate a pre-stress in the form of pressure on both frame side members and tension in the corner piece, the material of the lips being compressed from a first length to a second length, which is shorter than the first length; and wherein a compression force has been created in each of the frame side members ends by pushing off both frame side members respectively on the lips; the corner piece comprising inclined parts defining a pressure zone between the lips and a place on the inner wall which is situated deeper in the attachment channels than the lips to provide a pressure between said place and the lips; each insert part being equipped with a resilient member, which resilient members are connected to one another at an angle; and the inclined parts being respectively connected to free ends of the resilient members; wherein a free space or clearance free of material is provided on an outside corner of the corner piece, the free space or clearance extending from the lips to at least the connecting end of the insert parts; wherein the inclined parts create tensile forces in the resilient members, since a pressure in the inclined parts results in a tension in the resilient members; the tensile forces in the resilient members resulting in pressure forces in the outer and inner walls, thus contributing to rigidity and the pre-stress of the corner joint as a whole; wherein the resilient members are positioned generally along and in contact with the inner wall of the respective attachment channel.