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

1. Floorboards provided with a locking system for mechanical joining of said floorboards, said floorboards having a body, said locking system comprising:

for horizontal joining of a first and a second joint edge portion of a first and a second of said floorboards, respectively, at a vertical joint plane, a locking groove formed in the underside of said second board and extending parallel with and at a distance from said vertical joint plane at said second joint edge and a strip integrally formed with the body of said first board, which strip at said first joint edge projects from said vertical joint plane and supports a locking element, which locking element projects towards a plane containing the upper side of said first floorboard and which locking element has a locking surface for coaction with said locking groove, and

for vertical joining of the first and second joint edge, a tongue which at least partly projects and extends from the vertical joint plane and a tongue groove adapted to coact with said tongue, the tongue groove having an upper groove part, a lower groove part, and inner groove part, and a groove opening at the vertical joint plane, the tongue groove extending horizontally between the vertical joint plane and the inner groove part,

the first and second floorboards within their joint edge portions for the vertical joining having coacting upper and coacting lower contact surfaces, of which at least the upper contact surfaces comprise surface portions in said tongue groove and said tongue, wherein the upper and lower contact surfaces are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of the floorboards,

the locking element comprises an upper edge which is closest to a plane containing the upper side of the floorboards, the upper edge being located in a horizontal plane which is positioned between the upper groove part and the lower groove part, and

the thickness of the strip is varied.

2. The floorboards as claimed in claim 1 , wherein the strip has a portion closer to the locking element and a portion farther from the locking element, wherein the strip is thinner in the portion closer to the locking element than in the portion farther from the locking element.

3. The floorboards as claimed in claim 1 , wherein, when the first and second floorboards are mechanically assembled, there is a recess between the upper part of strip and the adjacent panel edge.

4. The floorboards as claimed in claim 1 , wherein the portions of the floorboard between the lower contact surface and the locking groove have a thickness which is equal to or less than the distance between the lower contact surface and the upper side of the floorboard.

5. The floorboards as claimed in claim 1 , wherein the portion of the strip between the lower contact surface and the upper edge of the locking element has a thickness which is equal to or less than the distance between the lower contact surface and the underside of the floorboard.

6. The floorboards as claimed in claim 1 , wherein the tongue and the tongue groove are arranged eccentrically in the thickness direction of the floorboards and placed closer to the underside than to the upper side of the floorboards.

7. The floorboards as claimed in claim 1 , wherein the locking element has an operative locking surface for coaction, for horizontal joining, with a corresponding operative locking surface of the locking groove, and that said operative locking surfaces are inclined at an angle which is lower than 90°, measured relative to a plane containing the underside of the floorboard.

8. The floorboards as claimed in claim 1 , wherein the locking element has an operative locking surface for coaction, for horizontal joining, with a corresponding operative locking surface of the locking groove, and that said operative locking surfaces are inclined at an angle which is 55-85°, measured relative to a plane containing the underside of the floorboard.

9. The floorboards as claimed in claim 1 , wherein the tongue groove has an inner boundary surface and the tongue has an outer end, wherein the inner boundary surface of the tongue groove in the first floorboard is positioned further away from the vertical joint plane than the outer end of the tongue of the second floorboard when the first and second floorboards are mechanically assembled.

10. The floorboards as claimed in claim 1 , wherein the locking groove has an inner surface and the locking element has an outer surface, wherein, seen perpendicular to the joint plane, the inner surface of the locking groove extends further away from the vertical joint plane than the outer surface of the locking element when the first and second floorboards are mechanically assembled.

11. The floorboards as claimed in claim 1 , wherein the locking groove has a bottom wall, wherein there is a gap between the upper edge of the locking element and the bottom wall of the locking groove.

12. The floorboards as claimed in claim 1 , wherein there is a gap between a side of the locking element furthest away from the vertical joint plane and an edge of the locking groove furthest away from the vertical joint plane.

13. The floorboards as claimed in claim 1 , wherein the first and second floorboards are structurally identical.

14. The floorboards as claimed in claim 1 , wherein said floorboards are mechanically joinable with adjoining floorboards along all its four sides by means of said locking system.

15. The floorboards claimed in claim 1 , wherein the floorboards have a surface layer on the upper side of the body and a balancing layer on the rear side of the body.

16. Floorboards provided with a locking system for mechanical joining of said floorboards, said floorboards having a body, said locking system comprising:

for horizontal joining of a first and a second joint edge portion of a first and a second of said floorboards, respectively, at a vertical joint plane, a locking groove formed in the underside of said second board and extending parallel with and at a distance from said vertical joint plane at said second joint edge and a strip integrally formed with the body of said first board, which strip has a thickness that varies, such that the strip has at least two surfaces that are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of the floorboards, such that the strip has an uppermost essentially plane-parallel surface and a lowermost essentially plane-parallel surface, which strip at said first joint edge projects from said vertical joint plane and supports a locking element, which locking element projects towards a plane containing the upper side of said first floorboard and which locking element has a locking surface for coaction with said locking groove, and

for vertical joining of the first and second joint edge, a tongue which at least partly projects and extends from the vertical joint plane and a tongue groove adapted to coact with said tongue,

the first and second floorboards within their joint edge portions for the vertical joining having coacting upper and coacting lower contact surfaces, of which at least the upper contact surfaces comprise surface portions in said tongue groove and said tongue, wherein the upper and lower contact surfaces are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of the floorboards,

the locking element comprises an upper edge which is closest to a plane containing the upper side of the floorboards, the upper edge being located in a horizontal plane which is positioned between the upper contact surface and the uppermost essentially plane-parallel surface.

17. The floorboards as claimed in claim 16 , wherein the strip has a portion closer to the locking element and a portion farther from the locking element, wherein the strip is thinner in the portion closer to the locking element than in the portion farther from the locking element.

18. The floorboards as claimed in claim 16 , wherein, when the first and second floorboards are mechanically assembled, there is a recess between the upper part of strip and the adjacent panel edge.

19. The floorboards as claimed in claim 16 , wherein the portions of the floorboard between the lower contact surface and the locking groove have a thickness which is equal to or less than the distance between the lower contact surface and the upper side of the floorboard.

20. The floorboards as claimed in claim 16 , wherein a portion of the strip between the lower contact surface and the upper edge of the locking element has a thickness which is equal to or less than the distance between the lower contact surface and the underside of the floorboard.

21. The floorboards as claimed in claim 16 , wherein the tongue and the tongue groove are arranged eccentrically in the thickness direction of the floorboards and placed closer to the underside than to the upper side of the floorboards.

22. The floorboards as claimed in claim 16 , wherein the locking element has an operative locking surface for coaction, for horizontal joining, with a corresponding operative locking surface of the locking groove, and that said operative locking surfaces are inclined at an angle which is lower than 90°, measured relative to a plane containing the underside of the floorboard.

23. The floorboards as claimed in claim 16 , wherein the locking element has an operative locking surface for coaction, for horizontal joining, with a corresponding operative locking surface of the locking groove, and that said operative locking surfaces are inclined at an angle which is 55-85°, measured relative to a plane containing the underside of the floorboard.

24. The floorboards as claimed in claim 16 , wherein the tongue groove has an inner boundary surface and the tongue has an outer end, wherein the inner boundary surface of the tongue groove in the first floorboard is positioned further away from the vertical joint plane than the outer end of the tongue of the second floorboard when the first and second floorboards are mechanically assembled.

25. The floorboards as claimed in claim 16 , wherein the locking groove has an inner surface and the locking element has an outer surface, wherein, seen perpendicular to the joint plane, the inner surface of the locking groove extends further away from the vertical joint plane than the outer surface of the locking element when the first and second floorboards are mechanically assembled.

26. The floorboards as claimed in claim 16 , wherein the locking groove has a bottom wall, wherein there is a gap between the upper edge of the locking element and the bottom wall of the locking groove.

27. The floorboards as claimed in claim 16 , wherein there is a gap between a side of the locking element furthest away from the vertical joint plane and an edge of the locking groove furthest away from the vertical joint plane.

28. The floorboards as claimed in claim 16 , wherein the first and second floorboards are structurally identical.

29. The floorboards as claimed in claim 16 , wherein said floorboards are mechanically joinable with adjoining floorboards along all its four sides by means of said locking system.

30. The floorboards claimed in claim 16 , wherein the floorboards have a surface layer on the upper side of the body and a balancing layer on the rear side of the body.