Abstract:
Boards of lumber or the like which exhibit defects such as knots or knotholes are repaired by cutting a bore through the board at the site of the defect and by filling the bore with a plug of conforming shape. The width of the bore changes at a first location along its axis and undergoes a reverse change at another location in order to interlock the plug with the board. The plug may be formed by filling the bore with hardenable mastic or by fitting conforming pieces of wood or the like into opposite ends of the bore, the pieces being abutted and secured together by adhesive. The interlocking configuration of the bore and plug assures that the plug cannot be ejected from the board.

Description:
TECHNICAL FIELD 
     The invention relates to the correction of defects in lumber or other boards of structural material. More particularly the invention relates to boards in which knotholes or other defects are removed and replaced with filler material and to a method for correcting such defects. 
     BACKGROUND OF THE INVENTION 
     Boards of lumber produced at a sawmill or the like may exhibit defects which adversely affect the quality of the material and which may make it unsuitable for intended uses. Knot free boards are desirable for some purposes. Knots make it difficult to prepare a smooth finish on the surface of a board, may bleed pitch and have a tendency to loosen and drop out after a period of time. In other cases where knots are acceptable, there may be loose knots, split knots or knotholes which downgrade the quality of the lumber. Other forms of localized defect can also be present such as decayed areas, pitch pockets, impact damage or excavations made by birds or insects. 
     Such defects in boards of lumber or the like can be repaired and the quality of the lumber upgraded by cutting a bore through the board to remove the defective region and then filling the resulting opening with a filler material which may be a hardenable mastic or a plug formed of the same wood as the board that is secured in place with adhesive. The techniques heretofore used for repairing defects in this manner do not provide optimum results. The plug of filler material is held in place in the opening in the original wood solely by adhesives and thus the plug can be loosened and ejected by impacts or other forces. 
     Prior board defect repairs also tend to require complicated installation operations such as the forming of openings in the wood and fabrication of conforming plugs that each have a convoluted shape for resisting twisting of the emplaced plug and for providing a greater area for application of adhesive. One prior process requires the complication of providing threads at the opening in the board and also on the plug so that a threaded engagement, reinforced by adhesive, can be effected. A threaded plug is not inherently locked into the wood and can be worked loose if subjected to sufficient torsional force. 
     A board repair which is more positively resistant to loss of plugs from openings in the original wood or the like would be highly advantageous. 
     The present invention is directed to overcoming one or more of the problems discussed above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a repaired board of lumber or the like has a bore in the original material of the board that extends between opposite surfaces of the board. The bore is at a region where a defect in the board has been removed in the course of cutting the bore and the bore is filled with a plug of filler material. The width of the bore and plug changes at a first location along the length of the bore and undergoes a reversed change another location along the length of the bore thereby interlocking the plug with the board. 
     In another aspect of the invention, the plug is formed of hardened mastic material. In still another aspect, the plug is formed of blocks of solid material fitted into opposite ends of the bore and adhered together with adhesive. 
     In a further aspect, the invention provides a method for repairing a defect in a board of lumber or like material. Steps in the method include cutting a bore through the board to remove the defective portion and forming the bore to have a transverse dimension which increases at a first location along the axis of the bore and which decreases at another location along the axis of the bore. A plug is formed in the bore that fills the bore and which has end surfaces that are coplanar with the opposite surfaces of the bore. 
     The invention enables the correction of localized defects in boards of lumber or other structural material by cutting out the defective area and filling the resulting passage with a plug in a manner which leaves the plug securely interlocked into the original material of the board. The repair does not constitute a weak spot in the board as the plug cannot be dislodged by impact forces or pressures of magnitudes that can be sustained by other portions of the board. The board repair does not require overly complicated operations and, in many of its preferred forms, does not require specialized tools. 
     The invention may be further understood by reference to the following description of preferred embodiments and by reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view of a piece of lumber undergoing correction of a localized defect. 
     FIG. 2 is a section view of another piece of lumber showing a series of defect repairs of different possible configurations. 
     FIG. 3 is a section view of still another board illustrating additional possible configurations for the repair. 
     FIG. 4 is a partially exploded section view of a board showing another form of the defect repair. 
     FIG. 5 is another section view of a board illustrating another embodiment of the invention. 
     FIG. 6 is a view of the surface of the board region shown in FIG. 5 taken along line 6--6 thereof. 
     FIG. 7 is a section view of a portion of still another board depicting another embodiment of the defect repair. 
     FIG. 8 is a view of the surface of a board repaired in accordance with still another embodiment of the invention. 
     FIG. 9 is a section view taken along line 9--9 of FIG. 8. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1 of the drawings, the invention provides for the upgrading of boards 11 of wood or other similar structural material by providing for removal of localized defects such as knots 12 and restoration of the board in the region of the removed material. It should be recognized that the invention may be used to repair other forms of local defect and may be applied to structural materials other than lumber, fiberboard being one example. 
     A bore 13 is drilled or otherwise cut through the board 11 at the location of a defect which is to be corrected, the bore being of sufficient diameter to remove any defective wood at the site. The bore 13 is formed to have a non-linear configuration which exhibits a change of diameter or transverse dimension at a first location 14 along the axis of the bore and which undergoes a reversed Change of diameter or transverse dimension at a second location 16 along the axis of the bore. 
     In the present example, the foregoing condition is met by forming the bore 13 with an intermediate region 17 of predetermined diameter and by causing the diameter of the bore to become progressively greater towards each surface of the board 11 at a uniformly increasing rate. Such a bore can easily be made with standard tools. The bore 13 may, for example, be initially drilled with a drill bit (not shown) having a diameter corresponding to that of the intermediate region 17 after which both end regions may be enlarged with a standard rotary countersink bit 18. Alternately, the countersink bit 18 may be used alone at each side of the board or other types of cutting tool may be used as will be apparent to those skilled in the art of carpentry. 
     Referring to FIG. 2, the bore 13 is then filled with material which forms a plug 19 that conforms in shape with the bore. The plug 19 may be a filling of mastic which is initially semiliquid but which cures into a hardened state, plastic wood or wood paste being preferred for the purpose as the hardened material then accepts paint or other finishings in the same manner as the other portions of the board. A strip of adhesive coated tape 21 may, if desired, be used to temporarily close the lowermost end of bore 13 during the filling and curing process to provide a smooth end surface on the plug that is co-planar with the adjacent original surface of board 11 and another such strip of tape 22 may be temporarily emplaced over the other end of the bore after the mastic is in place. In the case of finished grades of lumber, the tapes 21 and 22 are abraded away during the final sanding of the board 11 and are removed individually in the case of rough lumber. 
     Retention of the plug 19 in bore 13 is not dependent on the adhesive properties, if any, of the filler material as the configuration of the bore and plug interlocks the plug with the original material of board 11. 
     The bore 13 need not have the specific configuration described above in order to provide the desired interlocking. The additional bore 13a and plug 13a of FIG. 2 is of maximum diameter at the intermediate region 17a and becomes progressively narrower at a uniform rate towards each end of the bore and plug. The further additional bore 13b and plug 19b is of minimum diameter at the intermediate region 17b and becomes progressively broader at a non-uniform rate towards each end of the bore and plug imparting a concave profile to the plug. 
     The bore 13c and plug 19c of FIG. 3 has a maximum width at the intermediate region 17c and becomes progressively narrower towards each end at a non-uniform rate causing the plug to have a convex profile. Bore 13d and plug 19d of FIG. 3 has a midsection 17d with a uniform first diameter and opposite end regions 23 of a uniform but greater diameter. This configuration is reversed in the bore 13e and plug 19e of FIG. 3. Bore 13e and plug 19e have a midsection 17e of a uniform first diameter and end regions 23e which are of a uniform but smaller diameter. Still other configurations are possible which meet the hereinbefore described conditions for interlocking plugs 19 and boards 11. 
     In some instances, the filler material of plug 19 may lack the strength of the original wood. This does not usually cause problems where the bore 13 and plug 19 are relatively small, of the order of one half inch or less for example. In the repair of larger defects, it may sometimes be desirable to form the plug 19 of wood which is preferably similar to the original wood of the board 11. This has the further advantage of providing a repair in which the presence of a plug is less apparent. FIG. 4 depicts the formation of such a repair using a wood plug 19f. 
     The bore 13f may have the configuration hereinbefore described with reference to FIG. 1 except insofar as it is typically of greater diameter. Thus, with reference again to FIG. 4, the bore 13f has a circular midsection 17f of minimum diameter and adjoining opposite end regions 14f and 16f which progressively increase in diameter towards the ends of the bore. 
     Plug 19f is formed of two tapered circular blocks 26 of wood each of which has a configuration conforming to that of the regions 14f and 16f of bore 13f. The smaller diameter surfaces 27 and tapered side surfaces 28 of the blocks are coated with adhesive 29 and the blocks are then fitted into opposite ends of bore 13f. Hardening of adhesive 29 at the now abutted inner surfaces 27 secures the blocks 26 together to form the plug 19f and interlocks the plug with the board 11f. Hardening of the adhesive 29 at the sides surfaces 28 of the blocks 26 further secures the plug 19f in place and also prevents rotation of the plug. 
     The plugs 19a, 19b, 19c, 19d and 19e of FIGS. 2 and 3 can also be formed of adhered pieces of wood in an essentially similar manner although formation of the particular plugs such as 19a, 19c and 19e that have inner regions of greater diameter than the end regions tends to be more complicated as a greater number of preformed pieces are needed in such cases. 
     The regions 14 and 16 where the transverse dimension of the plugs 19 changes need not extend all the way around the periphery the of the plug as in the previously described repairs. For example, with reference to FIG. 5, the bore 13g may be basically cylindrical in shape but have outwardly extending connecting passages 31 at one or more limited locations around the periphery of the midsection of the bore. Filling of the bore 13g with mastic than forms a plug 19g which is interlocked into the board 11g by small tab-like projections 32 which extend into the passages 31. Drilling of the passages 31 is more easily accomplished if the passages are angled relative to the rest of the bore and are aligned along axes which extend out through an end of the bore. Such passages can be drilled simply by advancing a drill bit 33 into the end of the bore 13g along such axes. 
     In the embodiment of FIG. 7, the bore 13h is also essentially of right cylindrical form but has a passage 34 which extends from the midsection, in parallel relationship to the faces of the board 11h, to an end or side edge 36 of the board. The plug 19h can, if desired, be formed by closing the opposite ends of the bore 13h with strips of tape 21h and 22h in the manner previously described and then injecting mastic into the bore through the passage 34. 
     Referring jointly to FIGS. 8 and 9, a largely cylindrical plug 19i may also be interlocked into the board 11i by forming notches 37 in the board around the periphery of each end of the otherwise cylindrical bore 13i. Filling of the bore 13i  with mastic then results in a plug 19i having a series of outwardly extending tabs 38 at each end which effect the interlocking action. 
     Thus many variations and modifications of the invention are possible and it is not intended to limit the invention except as defined in the following claims.