CA2365174C

CA2365174C - Locking system for mechanical joining of floorboards and method for production thereof

Info

Publication number: CA2365174C
Application number: CA002365174A
Authority: CA
Inventors: Darko Pervan
Original assignee: Valinge Aluminium AB
Current assignee: Valinge Innovation AB
Priority date: 2000-01-24
Filing date: 2001-01-24
Publication date: 2006-11-28
Anticipated expiration: 2021-01-24
Also published as: NO20023444L; NZ519322A; US20100275546A1; BR0108038B1; EP1600578B1; US6898913B2; ES2241834T3; EP2006467A3; DK2006467T3; US7779596B2; PT1250503E; US20050034404A1; EP2275619B1; DE60111922T2; JP4762473B2; EP1250503A1; ATE299547T1; PT2006467E; DK1600578T3; SE0000200D0

Abstract

The invention relates to a locking system for mechanical joining of floorboards (1, 1') which have a body (30), a lower balancing layer (34) and an upper surface layer (32). A strip (6) is integrally formed with the body (30) of the floorboard (1) and extends under an adjoining floorboard (1'). T he strip (6) has a locking element (8), which engages a locking groove (14) in the underside of the adjoining floorboard (1') and forms a horizontal joint. A tongue (38) and a tongue groove (36) form a vertical joint between upper and lower plane-parallel contact surfaces (43, 45) and are designed in such mann er that the lower contact surfaces (45) are on a level between the upper side o f the locking element (8) and a plane containing the underside (3) of the floorboard. The invention also relates to a floorboard having such a locking system, a floor made of such floorboards, as well as a method for making suc h a locking system.

Description

LOCKING SYSTEM FOR MECHANICAL JOINING OF FLOORBOARDS
AND METHOD FOR PRODUCTION THEREOF
Technical Field The invention generally relates to the field of mechanical locking of floorboards. The invention relates to an improved locking system for mechanical locking of floorboards, a floorboard provided with such an improved locking system, a flooring made of such mechanically joined floorboards, and a method for making such floor-boards. The invention generally relates to an improvement of a locking system of the type described and shown in WO 94/26999 and WO 99/66151.
More specifically, the invention relates to a lock-ing system for mechanical joining of floorboards of the type having a body and preferably a surface layer on the upper side of the body and a balancing layer on the rear side of the body, said locking system comprising: (i) for horizontal joining of a first and a second joint edge portion of a first and a second floorboard respectively at a vertical joint plane, on the one hand a locking groove which is formed in the underside of said second board and extends parallel with and at a distance from said vertical joint plane at said second joint edge and, on the other hand, 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 projects towards a plane con-taining the upper side of said first floorboard and which has a locking surface for coaction with said locking groove, and (ii) for vertical joining of the first and second joint edge, on the one hand a tongue which at least partly projects and extends from the joint plane and, on the other hand, 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 comprise surface portions in said tongue groove and said tongue.
Field of Application of the Invention The present invention is particularly suitable for mechanical joining of thin floating floorboards made up of an upper surface layer, an intermediate fibreboard body and a lower balancing layer, such as laminate floor-ing and veneer flooring with a fibreboard body. There-fore, the following description of the state of the art, problems associated with known systems, and the objects and features of the invention will, as a non-restricting example, focus on this field of application and, in par-ticular, on rectangular floorboards with dimensions of about 1.2 m * 0.2 m and a thickness of about 7-10 mm, intended to be mechanically joined at the long side as well as the short side.
Background of the Invention Thin laminate flooring and wood veneer flooring are usually composed of a body consisting of a 6-9 mm fibre-board, a 0.20-0.8 mm thick upper surface layer and a 0.1-0.6 mm thick lower balancing layer. The surface layer provides appearance and durability to the floorboards.
The body provides stability and the balancing layer keeps the board level when the relative humidity (RH) varies during the year. The RH can vary between 15% and 90%.
Conventional floorboards of the type are usually joined by means of glued tongue-and-groove joints (i.e. joints involving a tongue on a floorboard and a tongue groove on an adjoining floorboard) at the long and short sides.
When laying the floor, the boards are brought together horizontally, whereby a projecting tongue along the joint edge of a first board is introduced into a tongue groove along the joint edge of the second adjoining board. The same method is used at the long side as well as the short side. The tongue and the tongue groove are designed for such horizontal joining only and with special regard to how glue pockets and gluing surfaces should be designed to enable the_tongue to be efficiently glued within the tongue groove.- The tongue-and-groove joint presents coasting upper and lower contact surfaces that position the boards vertically in order to ensure a level surface of the finished floor.
In addition to such conventional floors, which are connected by means of glued tongue-and-groove joints, floorboards have recently been developed which are instead mechanically joined and which do not require the use of glue. This type of mechanical joint system is hereinafter referredto as a "strip-lock system", since the most characteristic component of this system is a projecting strip which supports a locking element.
WO 94/26999 and W088/66151 (owner Valinge Alumi-nium AB) disclose a strip-lock system for joining build-ing panels, particularly floorboards: This locking system allows the boards to be locked mechanically at right angles to as well as parallel with the principal plane of the boards at the Long side as wel'1 as at the short side.
Methods for making such floorboards are disclosed in EP 0958441 and EP 0958442 (owner Valinge Aluminium AB).
The basic principles of the design and the installation' of the floorboards, as well as the methods for_making the same, as described in the four above-mentioned documents are usable for the present invention as well.
In order to facilitate the understanding and ' " description of the present invention, as well as the comprehension of the problems underlying the invention, a brief description of the basic design and function of the known floorboards according to the above-mentioned W0 94/26999 and W0 99/66151 will be given below with reference to Figs 1-3 in the accompanying drawings. Where applicable, the following description of the prior art also applies to the embodiments of the present invention described below.
Figs 3a and 3b are thus a top view and a bottom view respectively of a known floorboard 1. The board 1 is rec-tangular with a top side 2, an underside 3, two opposite long sides 4a, 4b forming joint edge portions and two opposite short sides 5a, 5b forming joint edge portions.
Without the use of the glue, both the long sides 4a, 4b and the short sides 5a, 5b can be joined mechanically in a direction D2 in Fig. lc, so that they join in a joint plane F (marked in Fig. 2c). For this purpose, the board 1 has a flat strip 6, mounted at the factory, pro-jecting horizontally from its one long side 4a, which strip extends throughout the length of the long side 4a and which is made of flexible, resilient sheet aluminium.
The strip 6 can be fixed mechanically according to the embodiment shown; or by means of glue, or in some other way. Other strip materials can be used, such as sheets of other metals, as well as aluminium or plastic sections.
Alternatively, the strip 6 may be made in one piece with the board 1, for example by suitable working of the body of the board 1. The present invention is usable for floorboards in which the strip is integrally formed with the body and solves special problems appearing in such floorboards and the making thereof. The body of the floorboard need not be, but is preferably, made of a uni-form material. However, the strip 6 is always integrated with the board 1, i.e. it is never mounted on the board 1 in connection with the laying of the floor but it is mounted or formed at the factory. The width of the strip 6 can be about 30 mm and its thickness about 0.5 mm. A
similar, but shorter strip 6' is provided along one short side 5a of the board 1. The part of the strip 6 project-ing from the joint plane F is formed with a locking ele-ment 8 extended throughout the length of the strip 6.
The locking element 8 has an operative locking surface 10 facing the joint plane F and having a height of e.g.
0.5 mm. When the floor is being laid, this locking sur-face 10 coacts with a locking groove 14 formed in the underside 3 of the joint edge portion 4b of the opposite 5 long side of an adjoining board 1'. The short side strip 6' is provided with a corresponding locking element 8', and the joint edge portion 5b of the opposite short side has a corresponding locking groove 14'. The edge of the locking grooves 14, 14' facing away from the joint plane F forms an operative locking surface 10' for coaction with the operative locking surface 10 of the locking element.
Moreover, for mechanical joining of both long sides and short sides also in the vertical direction (direction D1 in Fig. lc) the board is formed with a laterally open recess 16 along one long side (joint edge portion 4a) and one short side (joint edge portion 5a). At the bottom, the recess 16 is~defined by the respective strips 6, 6'.
At the opposite edge portions 4b and 5b there is an upper recess 18 defining a locking tongue 20 coacting with the recess 16 (see Fig. 2a).
Figs la-lc show how two long sides 4a, 4b of two such boards 1, 1' on an underlay 12 can be joined toge-ther by means of downward angling. Figs 2a-2c show how the short sides 5a, 5b of the boards 1, 1' can be joined together by snap action. The long sides 4a, 4b can be joined together by means of both methods, while the short sides 5a, 5b - when the first row has been laid - are normally joined together subsequent to joining together the long sides 4a, 4b and by means of snap action only.
When a new board 1' and a previously installed board 1 are to be joined together along their long sides 4a, 4b as shown in Figs la-lc, the long side 4b of the new board 1' is pressed against the long side 4a of the previous board 1 as shown in Fig. 1a, so that the locking tongue 20 is introduced into the recess 16. The board 1' is then angled downwards towards the subfloor 12 according to Fig. lb. In this connection, the locking tongue 20 enters the recess 16 completely, while the locking element 8 of the strip 6 enters the locking groove 14. During this downward angling the upper part 9 of the locking element 8 can be operative and provide guiding of the new board 1' towards the previously installed board 1. In the join-ed position as shown in Fig. lc, the boards 1, 1' are locked in both the direction D1 and the direction D2 along their long sides 4a, 4b, but the boards 1, 1' can be mutually displaced in the longitudinal direction of the joint along the long sides 4a, 4b.
Figs 2a-2c show how the short sides 5a and 5b of the boards 1, 1' can be mechanically joined in the direction D1 as well as the direction D2 by moving the new board 1' towards the previously installed board 1 essentially horizontally. Specifically, this can be carried out sub-sequent to joining the long side of the new board 1' to a previously installed board 1 in an adjoining row by means of the method according to Figs la-lc. In the first step in Fig. 2a, bevelled surfaces adjacent to the recess 16 and the locking tongue 20 respectively cooperate such that the strip 6' is forced to move downwards as a direct result of the bringing together of the short sides 5a, 5b. During the final bringing together of the short sides, the strip 6' snaps up when the locking element 8' enters the locking groove 14', so that the operative locking surfaces 10, 10' of the locking element 8' and of the locking groove 14' will engage each other.
By repeating the steps shown in Figs la-c and 2a-c, the whole floor can be laid without the use of glue and along all joint edges. Known floorboards of the above-mentioned type are thus mechanically joined usually by first angling them downwards on the long side, and when the long side has been secured, snapping the short sides together by means of horizontal displacement of the new board 1' along the long side of the previously installed board 1. The boards 1, 1' can be taken up in the reverse order of laying without causing any damage to the joint, and be laid again. These laying principles are also applicable to the present invention.
For optimal function, subsequent to being joined together, the boards should be capable of assuming a position along their long sides in which a small play can exist between the operative locking surface 10 of the locking element and the operative locking surface 10' of the locking groove 14. Reference is made to WO 94/26999 for a more detailed description of this play.
In addition to what is known from the above-mention-ed patent specifications, a licensee of Valinge Aluminium AB, Norske Skog Flooring AS, Norway (NSF), introduced a laminated floor with mechanical joining according to WO 94/26999 in January 1996 in connection with the Domotex trade fair in Hannover, Germany. This laminated floor, which is marketed under the trademark Alloc°, is 7.2 mm thick and has a 0.6-mm aluminium strip 6 which is mechanically attached on the tongue side. The operative locking surface 10 of the locking element 8 has an incli-nation (hereinafter termed locking angle) of about 80°
to the plane of the board. The vertical connection is designed as a modified tongue-and-groove joint, the term "modified" referring to the possibility of bringing the tongue groove and tongue together by way of angling.
WO 97/47834 (owner Unilin Beeher B.V., the Nether-lands) describes a strip-lock system which has a fibre-board strip and is essentially based on the above known principles. In the corresponding product, "Uniclic~", which this owner began marketing in the latter part of 1997, one seeks to achieve biasing of the boards. This results in high friction and makes it difficult to angle the boards together and to displace them. The document shows several embodiments of the locking system. The "Uniclic~" product is shown in section in Fig. 4b.
Other known locking systems for mechanical joining of board materials are described in, for example, GB-A-2,256,023 showing unilateral mechanical joining for pro-viding an expansion joint in a wood panel for outdoor use, and in US-A-4,426,820 (shown in Fig. 4d) which con-cerns a mechanical locking system for plastic sports floors, which floor is intentionally designed in such manner that neither displacement of the floorboards along each other nor locking of the short sides of the floor-boards by snap action is allowed.
In the autumn of 1998, NSF introduced a 7.2-mm laminated floor with a strip-lock system which comprises a fibreboard strip and is manufactured according to WO
94/26999 and WO 99/66151. This laminated floor is market-ed under the trademark "Fiboloc°" and has the cross-section illustrated in Fig 4a.
In January 1999, Kronotex GmbH, Germany, introduced a 7.8 mm thick laminated floor with a strip lock under the trademark "Isilock°". A cross-section of the joint edge portion of this system is shown in Fig. 4c. Also in this floor, the strip is composed of fibreboard and a balancing layer.
During 1999, the mechanical joint system has obtained a strong position on the world market, and some twenty manufacturers have shown, in January 2000, diffe-rent types of systems which essentially are variants of Fiboloc~, Uniclic~ and Isilock~.
Summary of the Invention Although the floor according to WO 94/26999 and WO
99/66151 and the floor sold under the trademark Fiboloc°
exhibit major advantages in comparison with traditional, glued floors, further improvements are desirable mainly in thin floor structures.
The joint system consists of three parts. An upper part P1 which takes up the load on the floor surface in the joint. An intermediate part P2 that is necessary for forming the vertical joint in the Dl direction in the form of tongue and tongue groove. A lower part P3 which is necessary for forming the horizontal lock in the D2 direction with strip and locking element.
In thin floorboards, it is difficult to provide, with prior-art technique, a joint system which at the same time has a sufficiently high and stable upper part, a thick, strong and rigid tongue and a sufficiently thick strip with a high locking element. Nor does a joint sys-tem according to Fig. 4d, i.e. according to US 4,426,820, solve the problem since a tongue groove with upper and lower contact surfaces which are parallel with the upper side of the floorboard or the floor plane, cannot be manufactured using the milling tools which are normally used when making floorboards. The rest of the joint geo-metry in the design according to Fig. 4d cannot be manu-factured by working a wood-based board since all surfaces abut each other closely, which does not provide space for manufacturing tolerances. Moreover, strip and locking elements are dimensioned in a manner that requires consi-derable modifications of the joint edge portion that is to be formed with a locking groove.
At present there are no known products or methods which afford satisfactory solutions to problems that are related to thin floorboards with mechanical joint sys-tems. It has been necessary to choose compromises which (i) either result in a thin tongue and sufficient mate-rial thickness in the joint edge portion above the corre-sponding tongue groove in spite of plane-parallel contact surfaces or (ii) use upper and lower contact surfaces angled to each other and downwardly extending projections and corresponding recesses in the tongue and the tongue groove respectively of adjoining floorboards or (iii) result in a thin and mechanically weak locking strip with a locking element of a small height.
Therefore an object of the present invention is to obviate this and other drawbacks of prior art. Another object of the invention is to provide a locking system, a floorboard, and a method for making a floorboard having such a locking system, in which it is at the same time possible to obtain (i) a stable joint with tongue and tongue groove, (ii) a stable portion of material above the tongue 5 groove, (iii) a strip and a locking element, which have high strength and good function.
To achieve these criteria simultaneously, it is necessary to take the conditions into consideration 10 which are present in the manufacture of floorboards with mechanical locking systems. The problems arise mainly when laminate-type thin floorboards are involved, but the problems exist in all types of thin floorboards.
The three contradictory criteria will be discussed sepa-rately in the following.
(i) Tongue-and-Groove Joint If the floor is thin there is not sufficient mate-rial for making a tongue groove and a tongue of suffi-cient thickness for the intended properties to be obtain-ed. The thin tongue will be sensitive to laying damage, and the strength of the floor in the vertical direction will be insufficient. If one tries to improve the proper-ties by making the contact surfaces between tongue and tongue groove oblique instead of parallel with the upper side of the floorboard, the working tools must during working be kept extremely accurately positioned both ver-tically and horizontally relative to the floorboard that is being made. This means that the manufacture will be significantly more difficult, and that it will be dif-ficult to obtain optimal and accurate fitting between tongue and tongue groove. The tolerances in manufacture must be such that a fitting of a few hundredths of a millimetre is obtained since otherwise it will be dif-ficult or impossible to displace the floorboards parallel with the joint edge in connection with the laying of the floorboards.

(ii) Material Portion above the Tonaue Groove In a mechanical locking system glue is not used to keep tongue and tongue groove together in the laid floor.
At a low relative humidity the surface layer of the floorboards shrinks, and the material portion that is located above the tongue groove and consequently has no balancing layer on its underside, can in consequence be bent upwards if this material portion is thin. Upwards bending of this material portion may result in a verti-cal displacement between the surface layers of adjoin-ing floorboards in the area of the joint and causes an increased risk of wear and damage to the joint edge. To reduce the risk of upwards bending, it is therefore necessary to strive to obtain as thick a material por-tion as possible above the tongue groove. With known geometric designs of locking systems for mechanical join-ing of floorboards, it is then necessary to reduce the thickness of the tongue and tongue groove in the vertical direction of the floorboard if at the same time efficient manufacture with high and exact tolerances is to be car-ried out. A reduced thickness of tongue and tongue groove, however, results in, inter alia, the drawbacks that the strength of the joint perpendicular to the plane of the laid floor is reduced and that the risk of damage caused during laying increases.
(iii) Strip and Locking Element The strip and the locking element are formed in the lower portion of the floorboard. If the total thickness of a thin floorboard is to be retained and at the same time a thick material portion above the locking groove is desirable, and locking element and strip are to be formed merely in that part of the floorboard which is positioned below the tongue groove, the possibilities of providing a strip having a locking element with a sufficiently high locking surface and upper guiding part will be restricted in an undesirable manner. The strip closest to the joint plane and the lower part of the tongue groove can be too thick and rigid and this makes the locking by snap action by backwards bending of the strip difficult. If at the same time the material thickness of the strip is reduced and a large part of the lower contact surface is retained in the tongue groove, this results on the other hand in a risk that the floorboard will be damaged while being laid or subsequently removed.
A problem that is also to be taken into considera-tion in the manufacture of floorboards, in which the com-ponents of the locking system - tongue/tongue groove and strip with a locking element engaging a locking groove -are to be made by working the edge portions of a board-shaped starting material, is that it must be possible to guide the tools in an easy way and position them correct-ly and with an extremely high degree of accuracy in rela-tion to the board-shaped starting material. Guiding of a chip-removing tool in more than one direction means restrictions in the manufacture and also causes a great risk of reduced manufacturing tolerances and, thus, a poorer function of the finished floorboards.
To sum up, there is a great need for providing a locking system which takes the above-mentioned require-ments, problems and desiderata into consideration to a greater extent than prior art. The invention aims at satisfying this need.
These and other objects of the invention are achiev-ed by a locking system, a floorboard, a floor and a manu-facturing method having the features stated in the inde-pendent claims. The dependent claims define particularly preferred embodiments of the invention.
The invention is based on a first understanding that the identified problems must essentially be solved with a locking system where the lower contact surface of the tongue groove is displaced downwards and past the upper part of the locking element.
The invention is also based on a second understand-ing which is related to the manufacturing technique, viz.

that the tongue groove must be designed in such manner that it can be manufactured rationally and with extremely high precision using large milling tools which are normally used in floor manufacture and which, during their displacement relative to the joint edge portions of the floorboard that is to be made, need be guided in one direction only to provide the parallel contact surfaces while the tool is displaced along the joint edge portion of the floorboard material (or alternatively the joint edge portion is displaced relative to the tool). In known designs of the joint edge portions, such working requires in most cases guiding in two directions while at the same time a relative displacement of tool and floorboard material takes place.
According to a first aspect of the invention, there is provided a locking system for mechanical joining of floorboards having a body and a balancing layer on the rear side of the body, said locking system comprising: for horizontal joining of a first and a second joint edge portion of a first and a second floorboard respectively at a vertical joint plane, on the one hand a locking groove which is 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, on the other hand, 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 projects towards a plane containing the upper side of said first floorboard and which has a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge, on the one hand a tongue which at least partly projects and extends from the joint plane and, on the other hand, 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 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 lower contact surfaces, if multiple, are co-planer, and the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned below the upper contact surface and above the lower contact surfaces but closer to the lower contact surfaces than to the upper contact surfaces.
According to another aspect of the invention, a new manufacturing method for making strip and tongue groove is provided. According to conventional methods, the tongue groove is always made by means of a single tool. The tongue groove according to the invention is made by means of two tools in two steps where the lower part of the tongue groove and its lower contact surface are made by means of one tool and the upper part of the tongue groove and its upper contact surface are made by means of another tool. The method according to the invention comprises the steps 1) of forming part of the strip, part of the lower part of the tongue groove and the lower contact surface by means of an angled milling tool operating at an angle <90° to the horizontal plane of the floorboard and the strip, and 2) forming the upper part of the tongue groove and the upper contact surface by means of a separate horizontally operating tool.
According to another aspect of the invention, there is provided a method for making floorboards with a 14a locking system for mechanical joining of two adjoining floorboards, in which method the floorboards, by chip-removing working, are formed with a locking system, which for horizontal joining of a first and a second joint edge of a first and a second floorboard at a vertical joint plane, comprises on the one hand 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, on the other hand, a strip formed integrally with the body of said first board and at said first joint edge projecting from said vertical joint plane and supporting a locking element, which projects towards a plane containing the upper side of said first floorboard and having a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge of the first and second floorboards, comprises on the one hand a tongue which projects from said second joint edge and the upper part of which extends from said vertical joint plane and, on the other hand, a tongue groove intended for coaction with said tongue, said first and second floorboards having cooperating upper and cooperating lower contact surfaces which are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of said floorboards, of which at least the upper contact surfaces comprise surface portions in said tongue groove and said tongue, in which method the chip-removing working is carried out by chip-removing milling or grinding tools being brought into chip-removing contact with parts of said first and second joint edges of the floorboard for forming said locking groove, said strip, said locking element, said tongue, said tongue groove and said upper and lower contact surfaces, wherein parts of said tongue groove and at least parts of the lower contact surface are formed by means of a chip-removing tool, whose chip-removing 14b surface portions are brought into removing contact with the first joint portion and are directed obliquely inwards and past said joint plane, the upper contact surface and parts of the tongue groove are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing engagement with the first joint portion in a plane which is essentially parallel with a plane containing the upper side of the floorboard, the lower contact surfaces, if multiple, are formed co-planer, such that an upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned below the upper contact surface and above the lower contact surfaces, but closer to the lower contact surfaces than to the upper contact surfaces.
According to a further aspect of the invention, there is provided a flooring system comprising a plurality of mechanically joinable floorboards, each having a body and preferably a surface layer on the upper side of the body and a balancing layer on the rear side of the body, said floorboards comprising: for horizontal joining of a first and a second joint edge portion of a first and a second floorboard respectively at a vertical joint plane, on the one hand a locking groove which is 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, on the other hand, a strip formed in one piece 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 projects towards a plane containing the upper side of said first floorboard and which has a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge, 14c on the one hand a tongue which at least partly projects and extends from the joint plane and, on the other hand, 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 comprise surface portions in said tongue groove and said tongue, whereby the upper and lower contact surfaces are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of the floorboards, and the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned between the upper and the lower contact surfaces but closer to the lower than to the upper contact surface wherein the lower contact surface comprises surface portions in said tongue groove and on said tongue.
According to yet another aspect of the invention, there is provided a method for making floorboards with a locking system for mechanical joining of two adjoining floorboards, each having a body and preferably a surface layer on the upper side of the body and a balancing layer on the rear side of the body, in which method the floorboards, by chip-removing working, are formed with a locking system, which for horizontal joining of a first and a second joint edge of a first and a second floorboard at a vertical joint plane, comprises on the one hand 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, on the other hand, a strip formed in one piece with the body of said first board and at said first joint edge projecting from said vertical joint plane and supporting a locking element, which projects 14d towards a plane containing the upper side of said first floorboard and having a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge of the first and second floorboards, comprises on the one hand a tongue which projects from said second joint edge and the upper part of which extends from said vertical joint plane and, on the other hand, a tongue groove intended for coaction with said tongue, said first and second floorboards having cooperating upper and cooperating lower contact surfaces which are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of said floorboards, of which at least the upper contact surface comprise surface portions in said tongue groove and said tongue, in which method the chip-removing working is carried out by chip-removing milling or grinding tools being brought into chip-removing contact with parts of said first and second joint edges of the floorboard for forming said locking groove, said strip, said locking element, said tongue, said tongue groove and said upper and lower contact surfaces, wherein parts of said tongue groove and at least parts of the lower contact surface are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing contact with the first joint portion and are directed obliquely inwards and past said joint plane, such that the lower contact surface comprises a surface portion in said tongue groove and on said tongue, and wherein the upper contact surface and parts of the tongue groove are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing engagement with the first joint portion in a plane which is essentially parallel with a plane containing the upper side of the floorboard, such that the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the 14e floorboards, is located in a horizontal plane, which is positioned between the upper and the lower contact surfaces but closer to the lower than to the upper contact surface.
Brief Description of the Drawings Figs la-c show in three stages a downward angling method for mechanical joining of long sides of floorboards according to WO 94/26999.
Figs 2a-c show in three stages a snap-action method for mechanical joining of short sides of floorboards according to WO 94/26999.
Figs 3a-b are a top plan view and a bottom view respectively of a floorboard according to WO 94/26999.

Fig. 4 shows three strip-lock systems available on the market with an integrated strip of fibre-board and a balancing layer, and a strip lock system according to US 4,426,820.
5 Fig. 5 shows a strip lock for joining of long sides of floorboards, where the different parts of the joint system are made in three levels P1, P2 and P3 as shown and described in 4V0 99/66151.
10 Fig. 6 shows parts of two joined floorboards which have been formed with a locking system accord-ing to the present invention.
Figs 7 + 8 illustrate an example of a manufacturing method according to the invention for manu-15 facturing a floorboard with a locking system according to the invention.
Figs 9a-d show variants of a floorboard and a locking system according to the present invention.
Describtion of Preferred Embodiments Prior to the description of preferred embodiments, with reference to Fig. 5, a detailed explanation will first be given of the most important parts in a strip lock system.
The cross-sections shown in Fig. 5 are hypothetical, not published cross-sections, but they are fairly similar to the locking system of the known floorboard "Fiboloc~"
and to the locking system according to WO 99/66151.
Accordingly, Fig. 5 does not represent the invention.
Parts corresponding to those in the previous Figures are in most cases provided with the same reference numerals.
The construction, function and material composition of the basic components of the boards in Fig. 5 are essen-tially the same as in embodiments of the present inven-tion, and consequently, where applicable, the following description of Fig. 5 also applies to the subsequently described embodiments of the invention.

In the embodiment shown, the boards 1, 1' in Fig. 5 are rectangular with opposite long sides 4a, 4b and oppo-site short sides 5a, 5b. Fig. 5 shows a vertical cross-section of a part of a long side 4a of the board 1, as well as a part of a long side 4b of an adjoining board 1'. The bodies of the boards 1 can be composed of a fibreboard body 30, which supports a surface layer 32 on its front side and a balancing layer 34 on its rear side (underside). A strip 6 is formed from the body and balancing layer of the floorboard and supports a locking element 8. Therefore the strip 6 and the locking element 8 in a way constitute an extension of the lower part of the tongue groove 36 of the floorboard 1. The locking element 8 formed on the strip 6 has an operative locking surface 10 which cooperates with an operative locking surface 10' in a locking groove 14 in the opposite joint edge 4b of the adjoining board 1'. By the engagement between the operative locking surfaces 10, 10' a horizon-tal locking of the boards 1, 1' transversely of the joint edge (direction D2) is obtained. The operative locking surface 10 of the locking element 8 and the operative locking surface 10' of the locking groove form a lock-ing angle A with a plane parallel with the upper side of the floorboards. This locking angle is <90°, preferably 55-85°. The upper part of the locking element has a guiding part 9 which, when angled inwards, guides the floorboard to the correct position. The locking element and the strip have a relative height P3.
To form a vertical lock in the D1 direction, the joint edge portion 4a has a laterally open tongue groove 36 and the opposite joint edge portion 4b has a lateral-ly projecting tongue 38 which in the joined position is received in the tongue groove 36. The upper contact sur-faces 43 and the lower contact surfaces 45 of the locking system are also plane and parallel with the plane of the floorboard.

In the joined position according to Fig. 5, the two juxtaposed upper joint edge portions 41 and 42 of the boards 1, 1' define a vertical joint plane F. The tongue groove has a relative height P2 and the material portion above the upper contact surface 43 of the tongue groove has a relative height P1 up to the upper side 32 of the floorboard. The material portion of the floorboard below the tongue groove has a relative height P3. Also the height of the locking element 8 corresponds to approxi-mately the height P3. The thickness of the floorboard therefore is T = Pl + P2 + P3.
Fig. 6 shows an example of an embodiment according to the invention, which differs from the embodiment in Fig. 5 by the tongue 38 and the tongue groove 36 being displaced downwards in the floorboard so that they are eccentrically positioned. Moreover, the thickness of the tongue 38 (and, thus, the tongue groove 36) has been increased while at the same time the relative height of the locking element 8 has been retained at approximately P3. Both the tongue 38 and the material portion above the tongue groove 36 are therefore significantly more rigid and stronger while at the same time the floor thickness T, the outer part of the strip 6 and the locking element 8 are unchanged. In the invention, the lower contact surface 45 has been displaced outwards to be positioned essentially outside the tongue groove 36 and outside the joint plane F on the upper side of the strip 6. By the inclination of the underside 44 of the outer part of the tongue, the tongue 38 will thus engage the lower contact surface at, or just outside, the joint plane F. Moreover, the tongue groove 36 extends further into the floorboard 1 than does the free end of the tongue 38 in the mounted state, so that there is a gap 46 between tongue and tongue groove. This gap 46 facilitates the insertion of the tongue 38 into the tongue groove 36 when being angled inwards similarly to that shown in Fig. la. Moreover, the upper opening edge of the tongue groove 36 at the joint plane F is bevelled at 47, which also facilitates the insertion of the tongue into the tongue groove.
As mentioned, the height of the locking element 8 has been retained essentially unchanged compared with prior art according to WO 99/661151 and "Fiboloc~". This results in the locking effect being retained. The locking angle A of the two cooperating operative locking surfaces 10, 10' is <90° and preferably in the range 55-85°. Most preferably, the locking surfaces 10, 10' extend approxi-mately tangentially to a circular arc which has its cen-tre where the joint plane F passes through the upper side of the floorboard. If the guiding portion 9 of the lock-ing element immediately above the locking surface 10 has been slightly rounded, the guiding of the locking element 8 into the locking groove 14 is facilitated in the down-ward angling of the floorboard 1' similarly to that shown in Fig. lb. Since the locking together of the two adjoin-ing floorboards 1, 1' in the D2 direction is achieved by the engagement between the operative locking surfaces 10, 10', the locking groove 14 can be somewhat wider than the locking element 8, seen transversely of the joint, so that there can be a gap between the outer end of the locking element and the corresponding surface of the locking groove. As a result, the mounting of the floor-boards is facilitated without reducing the locking effect. Moreover, it is preferred to have a gap between the upper side of the locking element 8 and the bottom of the locking groove 14. Therefore the depth of the groove 14 should be at least equal to the height of the locking element 8, but preferably the depth of the groove should be somewhat greater than the height of the locking ele-ment.
According to a particularly preferred embodiment of the invention, the tongue 38 and the tongue groove 36 are to be positioned eccentrically in the thickness direction of the floorboards and placed closer to the underside than to the upper side of the floorboards.

The most preferred according to the invention is that the locking system and the floorboards satisfy the relationship T - (P1 + 0.3 * P2) > P3, where T - thickness of the floorboard, P1 = distance between the upper side 2 of the floorboard and said upper contact surface 43, measured in the thickness direction of the floorboard, P2 = distance between said upper and lower contact sur-faces 43, 45, measured in the thickness direction of the floorboard, and P3 = distance between the upper edge 49 of the locking element 8 closest to the upper side of the floor-board and the underside 3 of the floorboard.
It has been found advantageous from the viewpoint of strength and function if the locking system also satisfies the relationship P2 > P3.
Moreover, it has been found particularly advanta-geous if the relationship P3 > 0.3 * T is satisfied since this results in more reliable connection of adjoining floorboards.
If the relationship P1 > 0.3 * T is satisfied, the best material thickness is obtained in the material por-tion between the tongue groove 36 and the upper side 2 of the floorboard. This reduces the risk of this material portion warping so that the superposed surface coating will no longer be in the same plane as the surface coat-ing of an adjoining floorboard.
To ensure great strength of the tongue 38 it is pre-ferred for the dimensions of the tongue to satisfy the relationship P2 > 0.3 * T.
By forming the cooperating portions of the tongue 38 and the tongue groove 36 in such manner that the inner boundary surfaces of the tongue groove in the first floorboard 1 are positioned further away from the verti-cal joint plane F than the corresponding surfaces of the tongue 38 of the second floorboard 1' when the first and the second floorboards are mechanically assembled, the insertion of the tongue into the tongue groove is facili-tated. At the same time the requirements for exact guid-ing of the chip-removing tools in the plane of the floor-s boards are reduced.
Moreover it is preferred for the locking groove 14, seen perpendicular to the joint plane F, to extend fur-ther away from the vertical joint plane F than do cor-responding portions of the locking element 8, when the 10 first and the second floorboards 1, 1' are mechanically assembled. This design also facilitates laying and taking up of the floorboards.
In a floor which is laid using boards with a locking system according to the present invention, the first and 15 the second floorboards are identically designed. Moreover it is preferred for the floorboards to be mechanically joinable with adjoining floorboards along all four sides by means of a locking system according to the present invention.
20 Figs 7 and 8 describe the manufacturing technique according to the present invention. Like in prior-art technique, chip-removing working is used, in which chip-removing milling or grinding tools are brought into chip-removing contact with parts of said first and second joint edges 4a, 4b of the floorboard on the one hand to form the upper surface portions 41, 42 of the joint edges 4a, 4b so that these are positioned exactly at the cor-rect distance from each other, measured in the width direction of the floorboard, and on the other hand to form the locking groove 14, the strip 6, the locking element 8, the tongue 38, the tongue groove 36 and the upper and lower contact surfaces 43 and 45 respectively.
Like in prior-art technique, the floorboard material is first worked to obtain the correct width and the cor-rest length between the upper surface portions 41, 42 of the joint edges 4a, 4b (5a, 5b respectively).

According to the invention, the subsequent chip-removing working then takes place, in contrast to prior-art technique, by chip-removing working in two stages with tools which must be guided with high precision in one direction only (in addition to the displacement direction along the floorboard material).
Manufacturing by means of angled tools is a method known per se, but manufacturing of plane-parallel contact surfaces between tongue and tongue groove in combination with a locking element, whose upper side is positioned in a plane above the lower contact surface of the locking system, is not previously known.
In contrast to prior-art technique the tongue groove 36 is thus made in two distinct stages by using two tools Vl, V2. The first chip-removing tool V1 is used to form parts of the tongue groove 38 closest to the underside 3 of the floorboard and at least part of the lower contact surface 45. This tool V1 has chip-removing surface por-tions which are directed obliquely inwards and past the joint plane F. An embodiment of the chip-removing surface portions of this first tool is shown in Fig. 7. In this case, the tool forms the entire lower contact surface 45, the lower parts of the tongue groove 36 which is to be made, and the operative locking surface portion 10 and guiding surface 9 of the locking element 8. As a result, it will be easier to maintain the necessary tolerances since this tool need be positioned with high precision merely as regards cutting depth (determines the position of the lower contact surface 45 in the thickness direc-tion of the floorboard) and in relation to the intended joint plane F. In this embodiment, this tool therefore forms portions of the tongue groove 36 up to the level of the upper side of the locking element 8. The location of the tool in the vertical direction relative to the floorboard is easy to maintain, and if the location per-pendicular to the joint plane F is exactly guided, the operative surface portion 10 of the locking element will be placed exactly at the correct distance from the edge between the joint plane F and the upper side 3 of the floorboard.
The first tool V1 thus forms parts of the tongue groove 36 that is to be made, the strip 6, the lower contact surface 45, the operative locking surface 10 and the guiding part 9 of the locking element 8. Preferably this tool is angled at an angle A to the principal plane of the floorboard, which corresponds to the angle of the locking surface.
It is obvious that this working in the first manu-facturing step can take place in several partial steps, where one of the partial steps is the forming of merely the lower parts of the tongue groove and of the lower contact surface 45 outside the joint plane 5 by means of an angled milling tool. The rest of the strip and the locking element can in a subsequent partial step be form-ed by means of another tool, which can also be angled and inclined correspondingly. The second tool, however, can also be straight and be moved perpendicular downwards in relation to the upper side of the floorboard. Therefore the tool V1 can be divided into two or more partial tools, where the partial tool closest to the joint plane F forms parts of the tongue groove and the entire lower contact surface 45, or parts thereof, while the subse-quent partial tool or tools form the rest of the strip 6 and its locking element 8.
In a second manufacturing step, the rest of the tongue groove 38 and the entire contact surface 43 are formed by means of a chip-removing tool V2, whose chip-removing surface portions (shown in Fig. 8) are moved into chip-removing engagement with the first joint por-tion 4a in a plane which is essentially parallel with a plane containing the upper side 2 of the floorboard. The insertion of this tool V2 thus takes place parallel with the upper side 3 of the floorboard, and the working takes place in levels between the upper side of the locking element 8 and the upper side of the floorboard.
The preferred manufacturing method is most suitable for rotating milling tools, but the joint system can be manufactured in many other ways using a plurality of tools which each operate at different angles and in dif-ferent planes.
By the forming of the tongue groove being divided into two steps and being carried out using two tools, V1 and V2, it has become possible to position the lower con-tact surface 45 at a level below the upper side of the locking element. Moreover, this manufacturing method makes it possible to position the tongue and the tongue groove eccentrically in the floorboard and form the tongue and the tongue groove with a greater thickness in the thickness direction of the floorboard than has been possible up to now in the manufacture of floorboards, in which the strip is integrated with and preferably mono-lithic with the rest of the floorboard. The invention can be used for floorboards where the main portion of the board and the joint edge portions of the board are of the same composition, as well as for floorboards where the joint edge portions are made of another material but are integrated with the board before the chip-removing work-ing to form the different parts of the locking system.
A plurality of variants of the invention are feas-ible. The joint system can be made with a number of dif-ferent joint geometries, where some or all of the above parameters are different, especially when the purpose is to prioritise a certain property over the other proper-ties.
The owner has contemplated and tested a number of variants based on that stated above.
The height of the locking element and the angle of the surfaces can be varied. Nor is it necessary for the locking surface of the locking groove and the locking surface of the locking element to have the same inclina-tion. The thickness of the strip may vary over its width perpendicular to the joint plane F, and in particular the strip can be thinner in the vicinity of the locking ele-ment. Also the thickness of the board between the joint plane F and the locking groove 14 may vary. The vertical and horizontal joint can be made with a play between all surfaces which are not operative in the locking system, so that the friction in connection with displacement parallel with the joint edge is reduced and so that mounting is thus facilitated. The depth of the tongue groove can be made very small, and also with a tongue groove depth of less than 1 mm, sufficient strength can be achieved with a rigid thick tongue.
Figs 9a-d show some examples of other embodiments of the invention. Those parts of the tongue groove and the strip which are positioned below the marked horizontal plane H, are preferably made by means of an angled tool (corresponding to the tool Vl), while those parts of the tongue groove which are positioned above this horizontal plane are made by means of a horizontally operating tool (corresponding to the tool V2).
Fig. 9a shows an embodiment where the lower contact surface 45 is essentially outside the joint plane F and a very small part of the contact surface is inside the joint plane F. Between the tongue 38 and the locking groove 14 there is a recess 50 in the underside of the tongue. This recess serves to reduce the friction between the tongue and the strip 6 when displacing the adjoining floorboards l, 1' along the joint plane F in connection with the laying of the boards.
Fig. 9b shows an embodiment where the lower contact surface 45 is positioned completely outside the joint plane F. For reducing the friction, a recess 51 has in this case been formed in the upper side of the strip 6, while the contact surface 45 of the locking tongue is kept plane. The locking element 8 has been made somewhat lower, which makes the locking system particularly suit-able for joining of short sides by snap action. The recess 51 in the strip 6 also reduces the rigidity of the strip and thus facilitates the joining by snap action.
Fig. 9c shows an embodiment with a centrically posi-5 tinned tongue 38 and a short rigid strip 6 where the lower plane contact surface 45 constitutes the upper side of the strip and is largely positioned outside the joint plane F. Just like in the other embodiments according to the invention, the lower contact surface 45 is positioned 10 in a plane below the upper side of the locking element 8, i.e. below the marked horizontal plane H.
Fig. 9d shows an embodiment with a stable locking system. Locking in the vertical direction (D1 direction) takes place by means of upper and lower contact surfaces 15 43 and 45 respectively, of which the lower extend merely a short distance from the joint plane F. The portions of the strip outside the lower contact surface 45 up to the locking element have been lowered by forming a recess 53 and therefore they do not make contact with the adjoining 20 floorboard 1'. This means a reduction of the friction when displacing adjoining floorboards in the direction of the joint plane F during the laying of the boards. The example according to Fig. 9d also shows that the demands placed on the surface portions of the tongue groove 36 25 furthest away from the joint plane F need not be very high, except that there should be a play 46 between these surface portions and the corresponding surface portions of the tongue 38. The Figure also shows that the working with the tool V2 can be carried out to a greater depth than would result in a straight inclined surface 54 which extends with the same inclination above the horizontal plane H.

Claims

CLAIMS:

1. A locking system for mechanical joining of floorboards having a body and a balancing layer on the rear side of the body, said locking system comprising:
for horizontal joining of a first and a second joint edge portion of a first and a second floorboard respectively at a vertical joint plane, on the one hand a locking groove which is 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, on the other hand, 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 projects towards a plane containing the upper side of said first floorboard and which has a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge, on the one hand a tongue which at least partly projects and extends from the joint plane and, on the other hand, 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 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 lower contact surfaces, if multiple, are co-planar, and the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned below the upper contact surface and above the lower contact surfaces but closer to the lower contact surfaces than to the upper contact surfaces.

2. The locking system as claimed in claim 1 further comprising a surface layer on the upper side of the body.

3. The locking system as claimed in claim 1 or claim 2, 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.

4. The locking system as claimed in any one of claims 1 to 3, wherein the portion of the strip between the lower contact surface and 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.

5. The locking system as claimed in any one of claims 1 to 4, 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.

6. The locking system as claimed in any one of claims 1 to 5, wherein the locking element has an operative locking surface for coaction 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.

7. The locking system as claimed in claim 6 wherein angle is 55° to 85°.

8. The locking system as claimed in any one of claims 1 to 7, wherein the relationship T - (P1 + 0.3 * P2) > P3, where T = thickness of the floorboard, P1 = distance between the upper side of the floorboard and said upper contact surface, measured in the thickness direction of the floorboard, P2 = distance between said upper and lower contact surfaces measured in the thickness direction of the floorboard, and P3 = distance between the upper edge of the locking element closest to the upper side of the floorboard and the underside of the floorboard.

9. The locking system as claimed in claim 8, wherein relationship P2 > P3.

10. The locking system as claimed in claim 8 or 9, wherein the relationship P3 > 0.3 * T.

11. The locking system as claimed in claim 8, 9 or 10;
wherein the relationship P1 > 0.3 * T.

12. The locking system as claimed in any one of claims 8 to 11, wherein the relationship P2 > 0.3 * T.

13. The locking system as claimed in any one of claims 1 to 12, wherein the inner boundary surfaces of the tongue groove in the first floorboard are positioned further away from the vertical joint plane than corresponding surfaces of the tongue of the second floorboard when the first and second floorboards are mechanically assembled.

14. The locking system as claimed in any one of claims 1 to 11, wherein seen perpendicular to the joint plane, the locking groove extends further away from the vertical joint plane than the corresponding portions of the locking element when the first and second floorboards are mechanically assembled.

15. The locking system as claimed in any one of claims 1 to 14, wherein there is a gap between the upper side of the locking element and the bottom of the locking groove.

16. The locking system as claimed in any one of claims 1 to 15, wherein there is a gap between the side of the locking element furthest away from the joint plane and the edge of the locking groove furthest away from the joint plane.

17. The locking system as claimed in any one of claims 1 to 16, wherein the locking element has an operative locking surface for coaction with a corresponding operative locking surface of the locking groove, and that these operative locking surfaces are inclined at such an angle relative to a plane containing the underside of the floorboard that the locking surfaces extend essentially tangentially relative to a circular arc with it centre where the vertical joint plane intersects the upper side of the floorboard, seen in a section perpendicular to said joint plane and perpendicular to the floorboards.

18. The locking system as claimed in any one of claims 1 to 17, wherein the first and second floorboards are identically designed.

19. A floorboard provided with a locking system as claimed in any one of claims 1 to 18.

20. The floorboard as claimed in claim 19, which is mechanically joinable with adjoining boards along all its four sides by means of a locking system as claimed in any one of claims 1 to 18.

21. A floor consisting of floorboards which are mechanically joined by means of a locking system as claimed in any one of claims 1 to 18.

22. A method for making floorboards with a locking system for mechanical joining of two adjoining floorboards, in which method the floorboards, by chip-removing working, are formed with a locking system, which for horizontal joining of a first and a second joint edge of a first and a second floorboard at a vertical joint plane, comprises on the one hand 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, on the other hand, a strip formed integrally with the body of said first board and at said first joint edge projecting from said vertical joint plane and supporting a locking element, which projects towards a plane containing the upper side of said first floorboard and having a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge of the first and second floorboards, comprises on the one hand a tongue which projects from said second joint edge and the upper part of which extends from said vertical joint plane and, on the other hand, a tongue groove intended for coaction with said tongue, said first and second floorboards having cooperating upper and cooperating lower contact surfaces which are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of said floorboards, of which at least the upper contact surfaces comprise surface portions in said tongue groove and said tongue, in which method the chip-removing working is carried out by chip-removing milling or grinding tools being brought into chip-removing contact with parts of said first and second joint edges of the floorboard for forming said locking groove, said strip, said locking element, said tongue, said tongue groove and said upper and lower contact surfaces, wherein parts of said tongue groove and at least parts of the lower contact surface are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing contact with the first joint portion and are directed obliquely inwards and past said joint plane, the upper contact surface and parts of the tongue groove are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing engagement with the first joint portion in a plane which is essentially parallel with a plane containing the upper side of the floorboard, the lower contact surfaces, if multiple, are formed co-planar, such that an upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned below the upper contact surface and above the lower contact surfaces, but closer to the lower contact surfaces than to the upper contact surfaces.

23. The method as claimed in claim 22 wherein the floorboards are of the type having a body.

24. The method as claimed in claim 23 further comprising a surface layer on the upper side of the body and a balancing layer on the rear side of the body.

25. The method as claimed in any one of claims 22 to 24, wherein the chip-removing working is carried out in such manner that portions of the floorboard between the lower contact surface and the locking groove obtains a thickness which is equal to or less than the distance between the lower contact surface and the upper side of the floorboard.

26. The method as claimed in any one of claims 22 to 24, wherein the chip-removing working is carried out in such manner that the tongue and the tongue groove are positioned eccentrically in the thickness direction of the floorboard and closer to the underside than to the upper side of the floorboard.

27. The method as claimed in claim 25 or 26, wherein the chip-removing working is carried out in such manner that the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboard, is positioned between the lower and upper contact surfaces but closer to the lower than to the upper contact surfaces.

28. The method as claimed in claim 27, wherein the chip-removing working is carried out in such manner that the relationship T - (P1 + 0.3 * P2) > P3, is achieved, where T = thickness of the floorboard, P1 = distance between the upper side of the floorboard and said upper contact surface, measured in the thickness direction of the floorboard, P2 = distance between said upper and lower contact surfaces measured in the thickness direction of the floorboard, and P3 = distance between the upper edge of the locking element closest to the upper side of the floorboard and the underside of the floorboard.

29. The method as claimed in claim 28, wherein the chip-removing working is carried out in such a manner that the relationship P2 > P3 is achieved.

30. The method as claimed in claim 28 or 29, wherein the chip-removing working is carried out in such manner that the relationship P3 > 0.3 * T is achieved.

31. The method as claimed in claim 28, 29 or 30, wherein the chip-removing working is carried out in such manner that the relationship P1 > 0.3 * T is achieved.

32. The method as claimed in any one of claims 28 to 31, wherein the chip-removing working is carried out in such manner that the relationship P2 > 0.3 * T is achieved.

33. The method as claimed in any one of claims 22 to 32, wherein the chip-removing working is carried out in such manner that the inner boundary surfaces of the tongue groove in the first floorboard are located further away from the vertical joint plane than the corresponding outer boundary surfaces of the tongue of the second floorboard when the first and second floorboards are mechanically assembled.

34. The method as claimed in any one of claims 22 to 33, wherein this chip-removing working is carried out in such manner that the locking groove, seen perpendicular to the joint plane, extends further away from the vertical joint plane than corresponding portions of the locking element when the first and second floorboards are mechanically assembled.

35. The method as claimed in any one of claims 22 to 34, wherein the chip-removing working is carried out in such manner that the bottom of the locking groove is positioned closer to the upper side of the floorboard than is the upper side of the locking element.

36. The method as claimed in any one of claims 22 to 35, wherein the chip-receiving working is carried out in such manner that the locking element obtains an operative locking surface for coaction with a corresponding operative locking surface of the locking groove, and that these operative locking surfaces will be inclined at such an angle relative to a plane containing the underside of the floorboard that the locking surfaces extend essentially tangentially relative to a circular arc with its centre where the vertical joint plane intersects the upper side of the floorboard, seen in a vertical section perpendicular to said joint plane.

37. A flooring system comprising a plurality of mechanically joinable floorboards, each having a body and preferably a surface layer on the upper side of the body and a balancing layer on the rear side of the body, said floorboards comprising:
for horizontal joining of a first and a second joint edge portion of a first and a second floorboard respectively at a vertical joint plane, on the one hand a locking groove which is 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, on the other hand, a strip formed in one piece 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 projects towards a plane containing the upper side of said first floorboard and which has a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge, on the one hand a tongue which at least partly projects and extends from the joint plane and, on the other hand, 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 comprise surface portions in said tongue groove and said tongue, whereby the upper and lower contact surfaces are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of the floorboards, and the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned between the upper and the lower contact surfaces but closer to the lower than to the upper contact surface wherein the lower contact surface comprises surface portions in said tongue groove and on said tongue.

38. The flooring system as claimed in claim 37, 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.

39. The flooring system as claimed in claim 37 or 38, wherein the portion of the strip between the lower contact surface and 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.

40. The flooring system as claimed in any one of claims 37 to 39, 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.

41. The flooring system as claimed in any one of claims 37 to 40, wherein the locking element has an operative locking surface for coaction with a corresponding operative locking surface of the locking groove, and wherein said operative locking surfaces are inclined at an angle which is lower than 90°, preferably 55-85°, measured relative to a plane containing the underside of the floorboard.

42. The flooring system as claimed in any one of claims 37 to 41, wherein the relationship T-(P1+0.3*P2) > P3 is achieved, where T = thickness of the floorboard, P1 = distance between the upper side of the floorboard and said upper contact surface, measured in the thickness direction of the floorboard, P2 = distance between said upper and lower contact surfaces measured in the thickness direction of the floorboard, and P3 = distance between the upper edge of the locking element closest to the upper side of the floorboard and the underside of the floorboard.

43. The flooring system as claimed in claim 42, wherein the relationship P2 > P3 is achieved.

44. The flooring system as claimed in claim 42 or 43, wherein the relationship P3 > 0.3*T is achieved.

45. The flooring system as claimed in claim 42, 43 or 44, wherein the relationship P1 > 0.3*T is achieved.

46. The flooring system as claimed in any one of claims 42 to 45, wherein the relationship P2 > 0.3*T is achieved.

47. The flooring system as claimed in any one of claims 37 to 46, wherein the inner boundary surfaces of the tongue groove in the first floorboard are positioned further away from the vertical joint plane than corresponding surfaces of the tongue of the second floorboard when the first and second floorboards are mechanically assembled.

48. The flooring system as claimed in any one of claims 37 to 47, wherein seen perpendicular to the joint plane, the locking groove extends further away from the vertical joint plane than the corresponding portions of the locking element when the first and second floorboards are mechanically assembled.

49. The flooring system as claimed in any one of claims 37 to 48, wherein there is a gap between the upper side of the locking element and the bottom of the locking groove.

50. The flooring system as claimed in any one of claims 37 to 49, wherein there is a gap between the side of the locking element furthest away from the joint plane and the edge of the locking groove furthest away from the joint plane.

51. The flooring system as claimed in any one of claims 37 to 50, wherein the locking element has an operative locking surface for coaction with a corresponding operative locking surface of the locking groove, and wherein these operative locking surfaces are inclined at such an angle relative to a plane containing the underside of the floorboard that the locking surfaces extend essentially tangentially relative to a circular arc with its centre where the vertical joint plane intersects the upper side of the floorboard, seen in a section perpendicular to said joint plane and perpendicular to the floorboards.

52. The flooring system as claimed in any one of claims 37 to 51, wherein the first and second floorboards are identically designed.

53. A floor consisting of mechanically joined floorboards of the flooring system as claimed in any one of claims 37 to 52.

54. A method for making floorboards with a locking system for mechanical joining of two adjoining floorboards, each having a body and preferably a surface layer on the upper side of the body and a balancing layer on the rear side of the body, in which method the floorboards, by chip-removing working, are formed with a locking system, which for horizontal joining of a first and a second joint edge of a first and a second floorboard at a vertical joint plane, comprises on the one hand 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, on the other hand, a strip formed in one piece with the body of said first board and at said first joint edge projecting from said vertical joint plane and supporting a locking element, which projects towards a plane containing the upper side of said first floorboard and having a locking surface for coaction with said locking groove, and for vertical joining of the first and second joint edge of the first and second floorboards, comprises on the one hand a tongue which projects from said second joint edge and the upper part of which extends from said vertical joint plane and, on the other hand, a tongue groove intended for coaction with said tongue, said first and second floorboards having cooperating upper and cooperating lower contact surfaces which are essentially plane-parallel and extend essentially parallel with a plane containing the upper side of said floorboards, of which at least the upper contact surface comprise surface portions in said tongue groove and said tongue, in which method the chip-removing working is carried out by chip-removing milling or grinding tools being brought into chip-removing contact with parts of said first and second joint edges of the floorboard for forming said locking groove, said strip, said locking element, said tongue, said tongue groove and said upper and lower contact surfaces, wherein parts of said tongue groove and at least parts of the lower contact surface are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing contact with the first joint portion and are directed obliquely inwards and past said joint plane, such that the lower contact surface comprises a surface portion in said tongue groove and on said tongue, and wherein the upper contact surface and parts of the tongue groove are formed by means of a chip-removing tool, whose chip-removing surface portions are brought into removing engagement with the first joint portion in a plane which is essentially parallel with a plane containing the upper side of the floorboard, such that the upper edge of the locking element, which upper edge is closest to a plane containing the upper side of the floorboards, is located in a horizontal plane, which is positioned between the upper and the lower contact surfaces but closer to the lower than to the upper contact surface.

55. The method as claimed in claim 54, wherein the chip-removing working is carried out in such manner that portions of the floorboard between the lower contact surface and the locking groove obtains a thickness which is equal to or less than the distance between the lower contact surface and the upper side of the floorboard.

56. The method as claimed in claim 54, wherein the chip-removing working is carried out in such manner that the tongue and the tongue groove are positioned eccentrically in the thickness direction of the floorboard and closer to the underside than to the upper side of the floorboard.

57. The method as claimed in claim 54, wherein the chip-removing working is carried out in such manner that the relationship T-(P1+0.3*P2) > P3, is achieved, where T = thickness of the floorboard, P1 = distance between the upper side of the floorboard and said upper contact surface, measured in the thickness direction of the floorboard, P2 = distance between said upper and lower contact surfaces measured in the thickness direction of the floorboard, and P3 = distance between the upper edge of the locking element closest to the upper side of the floorboard and the underside of the floorboard.

58. The method as claimed in claim 57, wherein the chip-removing working is carried out in such a manner that the relationship P2 > P3 is achieved.

59. The method as claimed in claim 57 or 58, wherein the chip-removing working is carried out in such manner that the relationship P3 > 0.3*T is achieved.

60. The method as claimed in claim 57, 58 or 59, wherein the chip-removing working is carried out in such manner that the relationship P1 > 0.3*T is achieved.

61. The method as claimed in any one of claims 57 to 60, wherein the chip-removing working is carried out in such manner that the relationship P2>0.3*T is achieved.

62. The method as claimed in any one of claims 54 to 61, wherein the chip-removing working is carried out in such manner that the inner boundary surfaces of the tongue groove in the first floorboard are located further away from the vertical joint plane than the corresponding outer boundary surfaces of the tongue of the second floorboard when the first and second floorboards are mechanically assembled.

63. The method as claimed in any one of claims 54 to 62, wherein this chip-removing working is carried out in such manner that the locking groove, seen perpendicular to the joint plane, extends further away from the vertical joint plane than corresponding portions of the locking element when the first and second floorboards are mechanically assembled.

64. The method as claimed in any one of claims 54 to 63, wherein the chip-removing working is carried out in such manner that the bottom of the locking groove is positioned closer to the upper side of the floorboard than is the upper side of the locking element.

65. The method as claimed in any one of claims 54 to 64, wherein the chip-receiving working is carried out in such manner that the locking element obtains an operative locking surface for coaction with a corresponding operative locking surface of the locking groove, and that these operative locking surfaces will be inclined at such an angle relative to a plane containing the underside of the floorboard that the locking surfaces extend essentially tangentially relative to a circular arc with its centre where the vertical joint plane intersects the upper side of the floorboard, seen in a vertical section perpendicular to said joint plane.