This invention regards a method of machining fibreboards . More particularly, it regards a method of machining fibreboards in which one section of the fibreboard is turned around after the board has been cut into at least two sections , for subsequent machining, e . g . milling of a tongue and groove along the longitudinal lateral edges of the board sections . The method is particularly appropriate for the machining of panel boards that , when mounted; cover a surface in a room.

When machining fibreboards , which are often decorated on one side, it is common, for production related reasons , to produce relatively large boards that are typically cut into two equally sized board halves in the course of the subsequent machining .

After cutting, the board halves are moved through a machine in which a groove and a tongue, respectively, are milled into at least two opposite lateral edges of each board half .

In prior art , a fibreboard is often cut longitudinally, whereupon a first board half is first transported to a machine for milling of a tongue and groove, whereupon, following a lateral displacement , the second board half follows the first board half to the same machine .

With this method of machining, the groove of e . g . the first board half will be on the side of the first board half that formed the outside edge of the original full board, while the tongue of the first board half will be on the side of the first board half that , prior to halving, was contiguous to the second board half .

Likewise, the groove of the second board half will be on the side of the second board half that , prior to halving, was adjacent to the first board half , while the tongue of the second board half will be on the side of the second board half that formed the outer lateral edge of the original full fibreboard.

Thus when mounted, after joining the tongue and groove, the fibreboards are assembled as they were in the original full fibreboard.

It has proven difficult to achieve a uniform content of moisture in a fibreboard. Typically the moisture content is higher in the middle section of a fibreboard than along its lateral edges . A certain equalizing of this moisture content must be expected after the fibreboard has been mounted. A reduction in moisture causes shrinkage/contraction, and it is known for fibreboard halves to pull apart slightly as they dry out . People in the trade know this phenomenon as "curving" . The problem is made worse by board halves produced

according to prior art drawing in opposite directions after being mounted. Exaggerating a little, one may say that the fibreboard halves form arches with paired concave and convex, respectively, sides facing each other .

The obj ect of the invention is to remedy or reduce at least one of the drawbacks of prior art .

The obj ect is achieved in accordance with the invention, by the features specified in the description below and in the following Claims .

According to the invention this problem of shrinkage is solved by allowing the fibreboards on e . g . a wall to contract in the same direction . Thus the concave side of a fibreboard section is mounted to the convex side of an adj acent fibreboard section . Typically these fibreboard sections constitute a fibreboard half .

The method means that the groove of each fibreboard section must be located on the side of the original fibreboard which formed the outside lateral edge, alternatively on the side of the one fibreboard section that was located adjacent to the second fibreboard section, and that the tongue of the fibreboard section must be on the opposite side .

By so doing the groove of one fibreboard section will be milled in a relatively dry area of the fibreboard section, and it will be coupled to a tongue milled in a relatively moist area of the other fibreboard section .

When the fibreboards dry they will draw in the same

direction, thus achieving approximately the same curvature . Thus the fibreboard sections will pull apart only slightly.

When machining a fibreboard where the fibreboard, which may have a non-uniform moisture content , is cut into at least two fibreboard sections , and where the fibreboard is then provided with complementary orientation determining means of j oining along at least two of its lateral edges , a first type of orientation determining j oining means is provided on a relatively dry lateral edge, while a second type of orientation determining j oining means is provided on a relatively moist lateral edge .

The term orientation determining joining means implies a joining means that prevents the fibreboard sections from being assembled in just any orientation relative each other .

The method is implemented quite simply by at least one of the fibreboard sections being turned around prior to being provided with orientation determining j oining means .

A typical orientation determining joining means is a tongue and a groove on opposite lateral edges .

In what follows is described a non-limiting exemplary embodiment of a preferred embodiment illustrated in the accompanying drawings , in which:

Fig . 1 is a principle drawing of a mounting of fibreboard halves produced according to prior art , where the curving due to dehydration is greatly exaggerated;

Fig . 2 is a principle drawing of a mounting of fibreboard halves produced according to the invention, where the curving due to dehydration is greatly exaggerated;

Fig . 3 is a principle drawing on a slightly smaller scale, showing a fibreboard being cut into two fibreboard halves ;

Fig. 4 is a principle drawing showing the fibreboard of figure 3 after cutting, where a first fibreboard half is being transported to subsequent machining, while a second fibreboard half is being rotated through 180 degrees in the plane of the board;

Fig . 5 shows the second fibreboard half , after having been rotated through 180 degrees , as it follows the first fibreboard half to the subsequent machining; and

Fig . 6 is an end view of the fibreboard halves , on a larger scale .

In the drawings , reference number 1 denotes a clean-cut fibreboard with a middle section 2 , a first longitudinal lateral edge 4 , a second longitudinal lateral edge 6 , a first transverse edge 8 and a second transverse edge 10 , see figure 3.

The moisture content of the fibreboard 1 is higher in the middle section 2 than at the outer edges 4 , 6 , 8 and 10.

After the fibreboard has been cut longitudinally into a first fibreboard half 12 and a second fibreboard half 14 by e . g . a saw blade 16 , the first fibreboard half comprises the first longitudinal lateral edge 4 and an opposite third longitudinal lateral edge 18. The second fibreboard half 14 comprises the second longitudinal lateral edge 6 and an opposite fourth longitudinal lateral edge 20. The third longitudinal lateral edge 18 and the fourth longitudinal lateral edge 20 were created when the fibreboard 1 was cut through the middle section 2 of the fibreboard 1.

It is to be expected that the fibreboard halves 12 and 14 will contract more along their respective third and fourth longitudinal lateral edges 18 , 20 than along their respective first and second longitudinal lateral edges 4 , 6.

After the splitting, the first fibreboard half 12 is moved longitudinally to a following machine in which the first fibreboard half 12 receives a groove 22 in its relatively moist third longitudinal lateral edge 18 and a tongue 24 in its relatively dry first longitudinal lateral edge 4 , in a manner that is known per se.

The tongue 24 and groove 22 constitute a first type of orientation determining joining means and a second type of orientation determining j oining means , respectively.

The second fibreboard half 14 is then rotated through 180 degrees in the plane of the board, and so is turned around before following the first fibreboard half 12 to the machine (not shown) .

The second fibreboard half 14 receives a groove 22 in its

relatively moist fourth lateral edge 20 and a tongue 24 in its relatively dry second lateral edge 6 , in the same way as the first fibreboard half 12.

Thus upon mounting, see Figure 2 , the relatively moist third longitudinal lateral edge 18 of the first fibreboard half 12 , with the groove 22 , is a complementary match to the relatively dry second longitudinal lateral edge 6 of the second fibreboard half 14 , which edge is provided with a tongue 24. Likewise , the relatively moist fourth longitudinal lateral edge 20 of the second fibreboard half is a complementary match to the relatively dry first longitudinal lateral edge 4 of another first fibreboard half 12 etc .

When the moisture content of the fibreboard halves 12 , 14 evens out after mounting, the fibreboard halves 12 , 14 will draw in the same direction, thereby preventing cracks from occurring between the respective longitudinal lateral edges 4 , 6 , 18 and 20.