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RELATED APPLICATION(S) 
       [0001]    The application is a continuation of International Patent Application No. PCT/CA2008/001206 filed on Jun. 27, 2008, which claims benefit of Canadian Patent Application No. 2,623,707 filed on Mar. 7, 2008, which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The application relates generally to hardwood floorboard assemblies and, more particularly, to a new hardwood flooring tongue and groove arrangement. 
       BACKGROUND ART 
       [0003]    In the hardwood floor industry, two main types of hardwood floor are found on the market, 1) solid wood and 2) engineered wood composed of superposed layers of wood. Solid hardwood floorboards are manufactured pre-finished or unfinished. In the pre-finished hardwood floor, the sanding and varnishing process is done at the factory by opposition to the unfinished flooring where the sanding and varnishing are executed on-site after installation of the hardwood flooring. 
         [0004]    The manufacturing process of pre-finished hardwood floor includes varnishing and/or staining steps on assembled floorboard sections of typically 4 feet wide. These sections allow effective use of sanding techniques prior to or concomitant with the varnishing and/or staining steps. There is a need for the manufacturers, to have a tight assembly of the tongue and groove joint between each adjoining floor hoards to prevent the same from becoming disassembled from one another during the sanding and varnishing process. 
         [0005]    During the varnishing process, the floorboards can be assembled and disassembled 2 to 3 times prior to its final packaging. The manufacturers also traditionally packed the floorboards in 4 layers of 3 or 4 wide assembled floorboard panels. There is thus also a need for facilitating the separation of the floor boards into layers of 3 or 4 assembled floorboard panels without damaging the tongue and groove joint. 
         [0006]    The requirement of having a tight assembly of the tongue and groove joint during the sanding operation is a major inconvenient for floorboards installers who need to disassemble the floorboard packages before the installation. If excessive force is used to separate the floorboards, especially those who were exposed to humidity, by applying excessive force, it may cause permanent damage to the tongue and groove joint and/or result in an increase of disassembling time and efforts for the installers. 
         [0007]    None of the traditional floorboards are designed to provide a solid board assembly to prevent disengagement of the individual floor boards during the factory sanding process while still providing for easy disassembly of the pre-finished floorboards into floorboard sections of 3 or 4 floorboard panels prior to packaging and/or into individual floor boards prior the installation. If prior-art tongue and groove designs were made to ease detachment of floorboards, they could not insure a tight assembly during the manufacturing or installation. 
         [0008]    There is thus a need to provide floorboards with tight assembly of the tongue and groove joint for the manufacturing process while remaining easy to detach at the time of installing the hardwood flooring. 
       SUMMARY 
       [0009]    In view of the foregoing, it would be desirable to provide a tightly assembled tongue and groove joint to prevent individual floorboards from being disassembled during factory sanding and varnishing operations while providing for relatively easy manual separation of the boards by the contractor at the time of installation. 
         [0010]    Those contradictory requirements can be met for a tongue-and-groove design that provides a firm grip and a tight assembly of floorboards to insure quality of processing at varnishing, while allowing ease of disassembling by a simple rotational or pivotal movement of the floorboards to ease the work of the installer without modifying the traditional way of installation. 
         [0011]    According to a general aspect, there is thus provided a floorboard assembly comprising: at least first and second hardwood floor boards adapted to be mounted in a side-by-side coplanar relationship, the first floor board having a tongue extending longitudinally along a first side thereof, the second floor board having a groove extending longitudinally along a second side thereof, the groove having a width defined between a top lip and a bottom lip, the tongue being received in a tight fit manner in the groove to provide frictional resistance against translational separation of the first and second floor boards in a common plane thereof, a top surface of the tongue being in frictional engagement with an undersurface of the top lip of the groove from a top outermost contact point to a top innermost contact point, a bottom surface of the tongue being in frictional engagement with a top surface of the bottom lip of the groove from a bottom outermost contact point to a bottom innermost contact point, the top outermost contact point and the bottom innermost contact point defining a first diagonal, the top innermost contact point and the bottom outermost contact point defining a second diagonal, one of said first and second diagonals having a length sufficiently greater than the width of the groove to substantially lock the first and second floor boards against relative pivotal movement in one of an upward or a downward direction associated with said one of said first and second diagonals, and a clearance provided between the tongue and the groove, the clearance reducing the length of the other one of said first and second diagonals to approximate the width of the groove to permit an angular withdrawal of the tongue from the groove by manually pivoting the first and second boards toward each other in the other one of said upward and downward directions. 
         [0012]    According to a further general aspect, there is provided a pre-finished floorboard assembly comprising at least first and second solid wood floor boards, the first floor board having a tongue extending longitudinally along a first side thereof, the second floor board having a groove extending longitudinally along a second side thereof, the groove having a width defined between a top lip and a bottom lip, the tongue being insertable in frictional engagement in the groove to counteract pull-apart forces exerted on the first and second floor boards during factory sanding and varnishing operations, and at least one play provided between the tongue and the groove at one of a tip portion of the tongue and an outermost portion of the top and bottom lips of the groove, the play being configured to allow the tongue to be angularly withdrawn from the groove by manually pivoting the first and second floor boards towards one another in only one of an upward and a downward direction. 
         [0013]    The term “floor board” should not be strictly construed to the preliminary meaning of the word and is intended to broadly refer to any floor planks, floor strips and the like used in the fabrication of a hardwood flooring. 
         [0014]    Floor boards can be made from different hardwood essence, such as pin, oak, maple, wild cherry, cherry, birch and walnut. It is understood that the present invention is not limited to only those commonly available wood species. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Reference will now be made to the accompanying drawings in which: 
           [0016]      FIG. 1  is a cross-sectional view of a prior art hardwood floorboard assembly illustrating a tongue-and-groove interconnection between two adjacent solid wood planks; 
           [0017]      FIG. 2  is a cross-sectional view of a hardwood floorboard assembly illustrating a lip clearance angle of a tongue and groove joint between two adjoining floor boards in accordance with an embodiment of the present invention; 
           [0018]      FIG. 3  is a cross-sectional view of a floorboard assembly illustrating another possible way of providing a lip clearance angle for enabling pivotal disassembly of two adjoining floor boards; 
           [0019]      FIG. 4  is a cross-sectional view of the floor boards shown in  FIG. 3  but illustrated in an unassembled state in order to illustrate some of the geometrical characteristics of the tongue-and-groove joint; 
           [0020]      FIGS. 5   a  to  5   c  are cross-sectional views illustrating in sequence the pivotal disengagement of the floor boards shown in  FIG. 3 ; 
           [0021]      FIGS. 6   a  and  6   b  are cross-sectional views illustrating the retaining action between the floor boards of  FIG. 3  when subject to downward bending forces as well as the retaining action when subject to pull apart forces exerted in the plane of the floor boards; 
           [0022]      FIGS. 7   a  to  7   c  illustrate various ways of providing the lip clearance angle required to permit withdrawal of the tongue from the groove in response to a relative pivotal movement of the floor boards; and 
           [0023]      FIG. 8  is a cross-sectional view of a downwardly pivotally separable floor board assembly in accordance with a further embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]      FIG. 1  shows a prior art tongue and groove joint of the type used to interconnect solid wood boards in a coplanar relationship to form hardwood flooring. More particularly,  FIG. 1  shows first and second adjoining floor boards  10  and  12 . Each floor board panel  10 ,  12  has a tongue  14  extending axially along a first longitudinal side thereof and a groove  16  extending axially along an opposite longitudinal side thereof for receiving the tongue  14  of an adjacent floor board, as is well know in the art. As shown in  FIG. 1 , the tongue  14  of the first floor board  10  is frictionally engaged in the groove  16  of the second floor board  12  in order to maintain the first and second floor boards  10  and  12  in a coplanar side-by-side relationship. The tongue  14  has parallel top and bottom surfaces  18  and  20  which are respectively in frictional engagement with the top and bottom lips  22  and  24  of groove  16 . As can be appreciated from  FIG. 1 , the top outermost contact point A, between the tongue top surface  18  and the groove top lip  22 , and the diagonally opposed bottom innermost contact point B, between the tongue bottom surface  20  and the groove bottom lip  24 , cooperate to lock the first and second floor boards  10  and  12  against relative upward pivotal movement, as depicted by arrows R 1 . The length of line AB is too great as compared to the width of the groove  16  (i.e. the distance between the top and bottom lips  22  and  24 ) to permit any upward pivotal or tilting movement of the tongue  14  in the groove  16 . Likewise, the top innermost contact point C, between the tongue top surface  18  and the groove top lip  22 , and the diagonally opposed bottom outermost contact point D, between the tongue bottom surface  20  and the groove bottom lip  24 , cooperate to lock the first and second floor boards  10  and  12  against relative downward pivotal movement, as depicted by arrows R 2 . Again, the length of line CD is significantly greater than the width of the groove  16 , thereby preventing downward pivotal movement of the tongue  14  in the groove  16  and that even for soft wood species exhibiting relatively high level of compressibility. The difference between the length of lines AB and CD and the width of the groove  16  is simply too important to allow any upward or downward pivotal movement of the tongue  14  in the groove  16 . By analogy, it would be like trying to fit a 6 feet long vertical beam between 5 feet spaced-apart top and bottom beams. 
         [0025]    Accordingly, the only way of disassembling the floor boards  10  and  12  without breaking the tongue  14  or the lips  22 ,  24  of the groove  16  is to pull apart the boards  10  and  12  by applying withdrawal forces in the plane of the boards  10  and  12  in a direction opposite to a direction of insertion of the tongue  14  in the groove  16 , as depicted by arrows P 1  and P 2 . The top and bottom frictional surfaces respectively defined between: 1) top contact points A and C and  2 ) bottom contact points D and B, provide resistance against the linear withdrawal of the tongue  14  from the groove  16 . It can be appreciated that the distance between top contact points A and C is equal to the distance between bottom contact points D and B. The tighter the fit between the tongue  14  and the groove  16 , the greater the forces P 1  and P 2  must be to separate the floor boards  10  and  12 . A tight fit is particularly desirable where the floor boards are to be pre-finished (factory finished). If a loose fit is provided, the boards run the risk of becoming disengaged from one another during the sanding and varnishing procedures, thereby resulting in poor quality finish. However, once on-site, it is desirable for the boards to be easily separable to facilitate the installation thereof. The above tongue and groove joint arrangement with planar disengagement of the boards does not meet the above contradictory needs. Therefore, compromises had heretofore to be made between a good quality finish and easy installation. 
         [0026]    Turning to  FIG. 2 , there is shown an embodiment of a new tongue and groove joint which still provides resistance against coplanar disengagement of the floor boards  10  and  12  while allowing easy separation of the floor boards  10  and  12  by a simple upward pivotal action. As will be seen hereinafter, the tongue and groove joint has been modified to permit an upward pivoting or tilting movement of the tongue  14  in the groove  16 , thereby allowing easy withdrawal of the tongue  14  from the groove  16 . 
         [0027]    It can be appreciated from  FIG. 2 , that the length of diagonal line AB can be shortened, for instance, by displacing the top outermost contact point A inwardly towards the bottom of the groove  16  (towards the right hand side on  FIG. 2 ). By doing so, line AB is pivoted about the innermost bottom point B to a position closer to the vertical, thereby resulting in a shortening of the line AB to a dimension which is closer to the width of the groove B. When the length of line AB is sufficiently close to the width dimension of the groove  16 , it becomes possible to disengage the floor boards  10  and  12  by simply pivoting the boards  10  and  12  towards each other in an upward direction, as illustrated in  FIGS. 5   a  to  5   c . The angle θ between line AB and the vertical is herein referred to as a lip clearance angle. The lip clearance angle θ can be generally defined as the angle which permits pivotal disengagement of the floor boards  10  and  12  in one of the upward or downward direction, while still providing sufficient contact surfaces between the tongue  14  and the groove  16  to counteract planar pulling-apart of the floor boards during factory sanding/varnishing operations. 
         [0028]    It has been found that pivotal separation of the floor boards  10  and  12  can be achieved without risking breaking the tongue  14  or the lips  22  and  24  of the groove  16  for lip clearance angles θ up to about 20 degrees. It is understood that this upper limit may vary depending on the level of compressibility of the wood species used to form the floor hoards. For instance, soft wood species, such as pine, may permit slightly greater lip clearance angle. It has also been noticed that the effort required to pivotally separate the floor boards  10  and  12  noticeably increases for clearance angles θ greater than 16 degrees. A 16 degrees lip clearance angle corresponds for instance to a 0.07 inch long top contact line AC for a 0.240 inch groove opening (i.e. distance between top and bottom lips  22  and  24  of the groove  16 ) in the example illustrated in  FIG. 2 . 
         [0029]    It has also been found that if the lip clearance angle θ becomes too small (i.e. the distance between the top outermost and innermost contact point A and C in  FIG. 2 ), the planar retention benefit afforded by the frictional engagement of the tongue  14  in the groove  16  is lost. Such a planar retention lost should be avoided in order to prevent disengagement of the floor boards  10  and  12  during the sanding and varnishing operations. Tests have shown that the floor boards become subject to coplanar separation during factory sanding and varnishing operation for tip clearance angles smaller than about 12 degrees. This corresponds to a 0.05 inch long top contact line AC for a 0.240 inch groove opening. The best results (i.e. easy pivotal separation with good planar retention) have been obtained for a lip clearance angle of about 14 degrees. In  FIG. 2 , this can also be expressed in term of a ratio between the length of the top contact surface (length of line AC) and the width or opening of the groove  16 . A 14 degrees lip clearance angle corresponds to a 1/4 ratio. For instance, for a groove having a 0.240 inch width or opening, line AC would be 0.060 inch long. 
         [0030]    In the embodiment illustrated in  FIG. 2 , the desired lip clearance angle θ is obtained by machining an undercut  26  in the outermost edge portion of the undersurface of the top lip  22  of the groove  16 . As will be seen hereinafter, the undercut  26  may have several configurations. The undercut  26  defines a play P to permit withdrawal of the tongue  14  from the groove  16  via a relative upward pivotal movement of the floor boards  10  and  12 . For instance, a 0.05 inch play P can be used for 0.240 inch groove opening and a 0.06 inch top contact line AC (i.e. 14 degrees lip clearance angle). With such a tongue and groove configuration, the tongue  14  can be tightly received in the groove  16  to provide strong planar retention of the floor boards  10  and  12  while allowing for easy pivotal separation of the floor boards  10  and  12  in the upward direction, as illustrated by arrows R 1 . However, any attempts at separating the floor boards  10  and  12  by means of downward pivotal movement, as represented by arrows R 2 , will be blocked by the contact points C and D. The line CD has not been altered by the modification made in the groove upper lip  22 . As can be appreciated in  FIG. 2 , line CD is significantly longer than line AB and way too long compared to the groove opening to permit any downward pivotal movement of the tongue  14  in the groove  16 . 
         [0031]    Accordingly, the pivotal movement of the tongue  14  in the groove  16  has been unlocked in only one direction (i.e. the upward direction). 
         [0032]    As shown in  FIG. 3 , the desired lip clearance angle θ can also be obtained by machining both the groove top lip  22  and the undersurface  20  of the tip portion of the tongue  14 . According to this embodiment, the position of both the top outermost contact point A and of the bottom innermost contact point B is modified in order to reduce the length of line AB. The embodiment shown in  FIG. 3  essentially differs from the embodiment of  FIG. 2  by the addition of a second undercut  28  in the undersurface  20  of the tip of the tongue  14 . The second undercut  28  displaces the bottom innermost contact point B away from the bottom of the groove  16  that is to the left hand side on  FIG. 3 . By so displacing the bottom innermost contact point B in an outward direction relative to the groove  16 , the top outermost contact point A can be displaced to a lesser extend inwardly toward the bottom of the groove  16 . By comparing  FIGS. 2 and 3 , it can be seen that the undercut  26 ′ ( FIG. 3 ) is not as deep as undercut  26  ( FIG. 2 ). In contrast to the embodiment of  FIG. 2  where only the top contact line AC is shortened, the total length reduction of the contact surfaces between the tongue  14  and the groove  16  is shared by both the top and bottom contact lines AC and DB (in a proportion of for instance 70% on the top contact surface and 30% on the bottom contact surface). According to the embodiment of  FIG. 3 , the resistance against planar separation of the floor boards  10  and  12  is more evenly shared by the top and bottom contact surfaces represented by lines AC and DB (in  FIG. 2  the top contact surface AC is significantly shorter than the bottom contact surface DB). As for the first embodiment, the floor boards  10  and  12  can be easily pivotally disengaged from one another in the upward direction, as indicated by arrows R 1 . Pivotal disengagement or separation is however once again prevented in the downward direction (arrows R 2 ) by the contact points C and D which are not affected by undercuts  26 ′ and  28 . 
         [0033]    As shown in  FIG. 3 , a third undercut  29  can be defined in the undersurface of the bottom lip  24  along all the extent of the lip in a depth wise direction of the groove  16  (see L 4  in  FIG. 4 ). The third undercut  29  provides added flexibility of the bottom lip  24  to facilitate the insertion and the withdrawal of the tongue  14  in the groove  16 . According to the illustrated embodiment, the third undercut  29  provides a bottom lip thickness reduction of about 0.020 inch to about 0.030. The play created by the third undercut  29  facilitates the insertion of the bottom lip  24  of the groove  16  underneath the tongue  14  after the board  10  has been nailed down to the sub floor structure. The third undercut can also compensate for expansion of the tongue  14  or of the groove lips due to environmental factors such as humidity. The third undercut  29  also contributes to minimise the risk of breaking the groove lips or the tongue when a board has to be removed. 
         [0034]      FIG. 4  shows some of the geometrical details of the embodiment of  FIG. 3 . The length L 1  of the second undercut  28  can represent about 15% to about 30% of the length L 2  of the tongue  14 . The reduction in the tongue thickness T 1  can represent about 5% to about 20% of the total thickness T 2  of the tongue  14 . The transition angle δ defined by the undercut  28  can be about 10 to 50 degrees. 
         [0035]    The length L 3  of the lip undercut  26 ′ can represent 15% to 30% of the length or deepness L 4  of the groove  16 . The play P′ defined by the first undercut  26 ′ can represent 5% to 20% of the width W of the groove  16 . A play P′ of at least 0.020 inch can be made in the undersurface of the upper lip of groove  16  for a 0.240 inch groove width W. The transition angle β defined by the undercut  26 ′ can be about 10 to 50 degrees. 
         [0036]      FIGS. 5   a  and  5   c  illustrate the procedure for pivotally separating the floor boards  10  and  12  shown in  FIGS. 3 and 4 . One has simply to grab the boards  10  and  12  by the sides thereof opposite to their adjoining edges and to exert an upward folding or pivoting action, as represented by arrows R 1 . The width of each floor boards  10  and  12  acts as a lever to facilitate the relative pivotal movement of the floor boards  10  and  12  about an initial point of pivot corresponding to a point of contact  30  between the top upper lip  22  of floor board  12  and the confronting side face of the other floor board  10 . The lip undercut  26 ′ and the tongue undercut  28  provide the required clearance to permit the angular withdrawal movement of the tongue  14  from the groove  16 , thereby allowing for easy separation of the floor boards  10  and  12 , as shown in  FIGS. 5   b  and  5   c.    
         [0037]    However, if downward pivotal efforts are applied on the floor boards  10  and  12  as represented by arrows R 2  in  FIG. 6   a  or if manual pull-apart forces P 1  and P 2  are applied in the plane of the floor boards  10  and  12  as shown in  FIG. 6   b , the tight fit engagement of the tongue  14  in the groove  16  will restrain the board against becoming disengaged from one another, as explained hereinbefore. 
         [0038]      FIGS. 7   a  and  7   c  illustrate various possible tongue and groove configurations that could be implemented to provide a desired lip clearance angle θ between the tongue and the groove of adjacent floor boards.  FIGS. 7   a  and  7   c  are not intended to constitute an exhaustive representation of all the possible alternatives. A person skilled in the art will understand that various permutations or combinations of the illustrated undercut arrangements can be provided to permit pivotal disengagement of the floor boards, in one of an upward or downward direction while still restraining linear removal of a board tongue from the associated groove of an adjacent board. 
         [0039]    Now referring more particularly to  FIGS. 7   a  to  7   c , it can be seen that the upward pivotal movement can also be unlocked by solely adding one undercut  32 ,  32 ′ or  32 ″ in the undersurface of the tip portion of the tongue  14 . 
         [0040]    Irrespective of their emplacement (on the tongue or the lip of the groove) the undercut can have various profiles. For instance, the undercut can have a stepped profile ( FIG. 7   a ), a slanted or bevel profile ( FIG. 7   b ), or a rounded or arc profile ( FIG. 7   c ). These profiles as well as other suitable profiles could also be applied to the undercut  26  defined in the undersurface of the groove upper lip  22  shown in  FIG. 2 . The person skilled in the art will understand that a wide variety of profiles could be adopted. 
         [0041]      FIG. 8  illustrates one example of a downwardly pivotable tongue and groove arrangement. 
         [0042]    According to this embodiment, the diagonal AB remains unchanged as compared to line AB on  FIG. 1 . The length of line AB is significantly longer than the width of the groove  16  and thus upward pivotal movement, as represented by arrows R 1 , of the tongue  14  in the groove  16  is impossible without breaking the tongue  14  or the lips  22  and  24  of the groove  16 . However, relative downward pivotal movement of the floor boards  10  and  12  as represented by arrows R 2  is rendered possible by the shortening of the contact line CD. In the illustrated example, the shortening is accomplished by means of a slanted undercut  36  on the top of the tip portion of the tongue  14  and a two-step undercut  38  on the outmost portion of the top surface of the bottom lip  24  of the groove  16 . The lip clearance angle θ is defined between line CD and the vertical and like the lip clearance angle for unlocking the upward pivotal movement, it is comprised in range extending from about 12 degrees to about 20 degrees. 
         [0043]    The above described tongue and groove arrangement is advantageous in that it can be “retrofitted” or adapted to any conventional tongue and groove arrangements. Also, it does not necessitate the purchase of any special tooling apart from new cutting knives having a cutting edge profile corresponding to the additional undercuts to be defined in the floorboards. It also facilitates the verification of the planarity between two adjoining boards since the tongue and groove engagement can be made very tight. The above described tongue and groove arrangement also reduces the likelihood that the floorboards being returned to the manufacturer by the installers because the boards are too difficult to separate from one another. It also contributes to improve the quality of the finish of factory finished floor boards by ensuring a greater integrity of the connection between the boards during the sanding and varnishing operations. 
         [0044]    Still further embodiments and modifications of the present invention are available. The scope of the appended claims is not intended to be limited, therefore, only to the specific exemplary embodiments described above.

Summary:
A floorboard assembly comprises first and second solid wood floor boards ( 10 ) and ( 12 ). The first floor board ( 10 ) has a tongue ( 14 ) extending longitudinally along a first side thereof. The second floor board ( 12 ) having a groove ( 16 ) extending longitudinally along a second side thereof. The groove ( 16 ) has a width defined between a top lip ( 22 ) and a bottom lip ( 24 ). The tongue ( 14 ) is insertable in a tight fit manner in the groove ( 16 ) to prevent translational separation of the boards ( 10, 12 ) in a common plane thereof. A clearance ( 26, 26′, 28, 32, 32′, 32″, 36  and  38 ) is provided between the tongue ( 14 ) and the groove ( 16 ) at one of a tip portion of the tongue ( 14 ) and an outermost portion of the top and bottom lips ( 22, 24 ) of the groove ( 16 ). The clearance ( 26, 26′, 28, 32, 32′, 32″, 36  and  38 ) is configured to allow angular withdrawal of the tongue ( 14 ) from the groove ( 16 ) by manually pivoting the first and second floor boards ( 10, 12 ) towards one another in one of an upward and a downward direction.