EP1689568A1

EP1689568A1 - Method of strengthening a wood piece

Info

Publication number: EP1689568A1
Application number: EP04799903A
Authority: EP
Inventors: Tatsuya Suzuki
Original assignee: Olympus Corp
Current assignee: Olympus Corp
Priority date: 2003-11-26
Filing date: 2004-11-25
Publication date: 2006-08-16
Also published as: US20050229533A1; WO2005051619A1; CN1886240A; JP2005153364A

Abstract

This method of strengthening a wood piece comprises the steps of: superimposing the wood piece (1) upon a metallic reinforcing member (2) ; and compressing the wood piece and the reinforcing member, so that the wood piece and the reinforcing member are integrated.

Description

DESCRIPTION

METHOD OF STRENGTHENING A WOOD PIECE

TECHNICAL FIELD The present invention relates to a method of strengthening a wood piece by which, for example, a covering member for an industrial product may be obtained. Priority is claimed on Japanese Patent Application No. 2003-396343, filed November 26, 2003, the content of which is incorporated herein by reference.

BACKGROUND ART With a covering member for a device which is intended to be operated by a user while being held in his hand, such as a camera, a portable telephone, an IC recorder, a PDA, a remote control for a household electronic product, or the like, in consideration of the mechanical aspect such as formability, solidity and corrosion resistance, and in consideration of the design aspect such as quality of appearance and designability, and from the point of view of the demands made by industrial mass production, it is normal for such a covering member to be made generally of a material which is suitable for mass production, like a synthetic resin such as ABS, polycarbonate, acryl or the like or a light metal such as aluminum, stainless steel, titanium, magnesium or the like. A material such as a synthetic resin or a light metal is subject to the deficiency that, it may not be satisfactorily gripped by the human hand, since it does not absorb moisture. On the other hand, a natural material such as wood or bamboo or the like is endowed with an excellent feeling which appeals to the human sense of touch, since it is excellent at absorbing moisture and is easily gripped in the hand. In the Japanese Examined Patent Application, Second Publication No, H07-2326, there is disclosed a technique in which, with the objective of strengthening a wooden material, first this wooden material is softened by placing it in an atmosphere of steam at high temperature and high pressure, and thereafter this wooden material is compressed mechanically under the same atmospheric conditions. Furthermore, in the Japanese Unexamined Patent Application, First Publication No, HI 1-226915, there is disclosed a technique in which, with the objective of forming a smooth ornamental pattern upon the surface of a wooden material, a cross-grained wooden member is softened with heat, and then its surface is smoothed by pressing. However, natural materials such as those described above are hardly used at all as materials for industrial products, since they are low in strength and are unsuitable for mass production because their durability and their workability are poor. The present invention has been conceived in the light of the above described situation, and its objective is to provide a method of strengthening a wood piece, so that the wood piece is endowed with high strength of an order such that it can be taken advantage of as a material for an industrial product, and also so that the wood piece is excellent in durability and workability, and is suitable as a material for mass production.

DISCLOSURE OF THE INVENTION As a means for solving the above described problems, there are proposed methods of strengthening a wood piece as described in the following. That is to say, the method of strengthening a wood piece of the present invention, comprising the steps of: superimposing the wood piece upon a metallic reinforcing member; and compressing the wood piece and the reinforcing member, so that the wood piece and the reinforcing member are integrated. In the present invention as described above, by compressing the wood piece and integrating the reinforcing member into the wood piece, a greater strength is obtained than if the wood piece were solely to be compressed. Moreover, the workability of the wood piece which has been strengthened with this reinforcing member is also enhanced by the reinforcing member being plastically deformed. In the above method of strengthening a wood piece of the present invention, a direction along which the reinforcing member extends and a direction of the grain of the wood piece may cross one another. Cracking of the wood piece can easily occur when shear forces from upward and downward act on the wood piece at the locations separated in the direction which crosses its grain. Thus, with the present invention as described above, by providing the reinforcing member in a direction which crosses the grain of the wood piece, it becomes difficult for cracking of the wood piece to occur, even if a shear force of the above described type acts upon it. In the above method of strengthening a wood piece of the present invention, the reinforcing member may be made in the form of a grating or a net. In the present invention as described above, the surface rigidity of the wood piece is enhanced, since, by forming the reinforcing member in the form of a grating or of a net, the wood piece is reinforced over the entire surface upon which the reinforcing member is laid. In the above method of strengthening a wood piece of the present invention, a step of forming a carbonized layer upon the surface of the wood piece where the reinforcing member may be provided. In the present invention as described above, by forming a carbonized layer upon the surface of the wood piece to which the reinforcing member has been provided, the beneficial result is attained that this carbonized layer, which exhibits high electrical conductivity, can serve as a shield against electromagnetic fields. In the above method of strengthening a wood piece of the present invention, the reinforcing member may be quenched. In the present invention as described above, by performing quenching upon the metallic reinforcing member, it is possible to anticipate enhancement of its strength due to metal hardening. In the method of strengthening a wood piece of the present invention, comprising the steps of: making a high density portion of the wood piece thin, and a low density portion of the wood piece thick; and compressing the wood piece having the high density portion and the low density portion. In the present invention as described above, an almost uniform strength is obtained throughout the entire mass of the wood piece, after compression due to an uniform density of the whole wood piece, since the portion of the wood piece for which, the density before compression was high is made to be thin, while the portion of the wood piece for which, the density before compression was low is made to be thick. In the method of strengthening a wood piece of the present invention, comprising the steps of: making a portion of the wood piece at which high strength must be ensured thicker than a surrounding portion thereof; and compressing the wood piece having the portion at which the high strength must be ensured. In the present invention as described above, by forming the portion of the wood piece for which high strength is to be ensured to be thicker than the surrounding portion thereof, it is possible to obtain a higher strength in this portion after compression, because its density becomes higher than that of the surrounding portion. In the method of strengthening a wood piece of the present invention, comprising the steps of: adhering another wood piece to a portion of the wood piece at which high strength must be ensured; and compressing the wood piece to which the another wood piece has been adhered. In the present invention as described above, by adhering the second wood piece to the portion of the first wood piece for which high strength is to be ensured, it is possible to obtain a higher strength in this portion after compression, because its density becomes higher than that of the surrounding portion. In the above method of strengthening a wood piece of the present invention, the direction of the grain of the wood piece and the direction of the grain of the another wood piece may be different. In the present invention as described above, it is possible to obtain a yet higher strength by making the direction of the grain of the first and the second pieces of wood to be different, , since these two pieces of wood mutually compensate one another for the strength in the directions where, individually, each of them is weak. In the method of strengthening a wood piece of the present invention, comprising the steps of: disposing a reinforcing member which is harder than the wood piece on a portion of the wood piece at which the high strength must be ensured; and compressing the wood piece and the reinforcing member, so that the wood piece and the reinforcing member are integrated. In the present invention as described above, by providing the other member which is made from a substance which is harder than the wood piece at the portion of the wood piece for which high strength is to be ensured, it is possible to obtain a high strength at this portion of the wood piece where this other member which is harder than the wood piece is provided as a reinforcement. According to the present invention, it is possible to endow the wood piece with high strength of an order such that it can be taken advantage of as a material for an industrial product, and also with excellent durability and workability, so that it is suitable as a material for mass production. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a figure for explanation of the first preferred embodiment of the present invention, and is a perspective view showing a wood piece which is to be strengthened, and several rod shaped members made of metal, which is the reinforcing member. FIG. 2 through FIG.5 are explanatory figures showing certain situations during the process of strengthening the wood piece. FIG. 6 is a perspective view showing a wood piece which has been compressed and strengthened with reinforcing member. FIG. 7 is a figure showing a variant example of this preferred embodiment of the present invention, and is a perspective view showing a wood piece which utilizes a net made of metal as a reinforcing member. FIG. 8 is a figure for explanation of the second preferred embodiment of the present invention, and is a cross sectional view showing a wood piece which is to be compressed, and upper and lower molds for compressing the wood piece. FIG.9 is a figure for explanation of the second preferred embodiment of the present invention, and is a cross sectional view showing the situation where a wood piece has been compressed by the upper and lower molds. FIG. 10 is a cross sectional view showing a wood piece which has been compressed and strengthened with reinforcing material. FIG. 11 is a figure for explanation of the third preferred embodiment of the present invention, and is a cross sectional view showing a wood piece which has been integrated into reinforcing member and upon whose surface a carbonized layer has been formed. FIG. 12 is a figure for explanation of the fourth preferred embodiment of the present invention, and is a cross sectional view showing a wood piece whose thickness has been made to vary according to the density of its grain. FIG.13 is a figure for explanation of the fourth preferred embodiment of the present invention, and is a cross sectional view showing the wood piece when it has been compressed and strengthened. FIG. 14 is a figure for explanation of the fifth preferred embodiment of the present invention, and is a cross sectional view showing a wood piece of which a portion for which high strength must be ensured has been made thicker than its surroundings. FIG.15 is a figure for explanation of the fifth preferred embodiment of the present invention, and is a cross sectional view showing the wood piece strengthened by compressing the wood piece which includes a portion made thicker than its surroundings. FIG. 16 is a figure for explanation of the sixth preferred embodiment of the present invention, and is a cross sectional view showing a wood piece to which, at a portion for which high strength must be ensured, another wedge of wood has been adhered. FIG.17 is a figure for explanation of the sixth preferred embodiment of the present invention, and is a cross sectional view showing the wood piece when it has been compressed and strengthened. FIG. 18 is a figure for explanation of the seventh preferred embodiment of the present invention, and is a perspective view showing a separate member which is adhered to a portion of a wood piece for which high strength must be ensured. FIG. 19 is a cross sectional view showing a wood piece to which another member has been adhered at a portion for which high strength must be ensured. FIG. 20 is a cross sectional view showing the wood piece which has been strengthened by this another member.

BEST MODES FOR CARRYING OUT THE INVENTION The first preferred embodiment of the present invention will now be explained with reference to FIG. 1 through FIG. 7. In FIG. 1, there are shown a wood piece 1 which is to be strengthened, and several rod shaped members(reinforcing member) 2 made of metal, which are for strengthening the wood piece 1. This wood piece 1 is formed in a rectangular plate shape of approximately even thickness, and it is cut so that its grain faces in its lengthwise direction. And the rod shaped members 2 are shaped as rods which are triangular in cross section, are divided into several sections of substantially equal dimensions to the width of the wood piece 1. It should be understood that, as the type for the wood piece 1, there may be suggested, for example, Japanese cypress, paulownia, teak, mahogany, cedar, pine, cherry, bamboo or the like. Furthermore it is possible to utilize, not only proper wood, but also a wooden substance like a material made by compressing waste wood chips or wood sawdust or the like. Next, the various processes involved in reinforcing the wood piece 1 will be explained with reference to FIG. 2 through FIG.5. First, as shown in FIG. 2, the wood piece 1 is put into a steam atmosphere at high temperature and pressure. The wood piece 1 absorbs an excess water component by being thus placed in a steam atmosphere at high temperature and pressure, and accordingly softens. Next, as shown in FIG. 3, still in a high temperature high pressure steam atmosphere the same as the one described above, the rod shaped members are disposed inside the lower mold A in parallel with one another and with equal spaces being left between them, and the wood piece 1 is laid over these rod shaped members 2 so that its widthwise direction agrees with the lengthwise direction of the rod shaped members 2. Each of the rod shaped members 2 thus comes to be disposed in a direction which is across the grain of the wood piece 1. Next, as shown in FIG. 4, the upper mold B is shifted so as to be fitted into the interior of the lower mold A, so that the wood piece 1 is compressed between the upper and lower molds A and B, and this state is maintained for a predetermined time period. The rod shaped members 2 are pressed into the wood piece 1 which has been sandwiched between the upper and lower molds

A and B, so that the sharp angle portions of the triangular shape are stuck into the lower surface of the wood piece 1. Finally, as shown in FIG. 5, when the high temperature high pressure steam atmosphere is released and the wood piece 1 is taken out from between the upper and lower molds A and B, the wood piece 1 is formed in the shape of the internal space which is defined when the molds A and B are fitted together, and the rod shaped members 2 are integrated into the wood piece 1 which has thus been formed, in the state of being embedded in the lower surface of the wood piece 1. The wood piece 1 which has been strengthened in the above described manner takes the form as shown in FIG. 6. With this wood piece 1, a greater strength is obtained than in the case of a wood piece that has simply been compressed, since the rod shaped members 2 have been integrated into it by compression. Furthermore, with this wood piece 1 which has been strengthened with the rod shaped members 2, the workability is also enhanced, because the rod shaped members 2 are able to be plastically deformed. Yet further, by arranging the rod shaped members 2 so as to cross the grain of the wood piece 1, it becomes difficult for splitting of the wood piece 1 to occur, even if shearing force acts on it in a vertical direction. FIG. 7 shows a variant example of this first preferred embodiment. A net 3 made of metal is used as the reinforcing member in this wood piece 1. This net 3 is made of a plurality of metal wires 3a which extend in two directions which are almost mutually perpendicular, and, with respect to the wood piece 1, these metal wires 3a that extend in each direction are arranged so as to cross the grain of the wood piece 1, respectively. Since, with this wood piece 1 which utilizes the net 3 made of metal as its reinforcing member, the net 3 reinforces the wood piece 1 over a whole surface which is formed as a sheet, accordingly the surface rigidity of the wood piece 1 is enhanced. It should be understood that the same beneficial results would also be obtained from a grating formed by metal punching or the like, instead of the net 3 made of metal. In this preferred embodiment of the present invention, it may be contemplated enhancing the strength by hardening of the metal, by quenching the metallic rod shaped members 2 or the net 3. Next, the second preferred embodiment of the present invention will be explained with reference to FIG. 8 through FIG. 10. It should be understood that to structural elements which are the same as in the above described first preferred embodiments and which have already been explained, the same reference symbols are appended, and their explanation will be curtailed. The wood piece 1 of this second preferred embodiment is not simply shaped as a flat plate, but rather is in a box shape, as shown in FIG. 8. Before it is strengthened, this wood piece 1 is processed by cutting off portions from a block shaped wood, so that it consists of a bottom portion la which is connected by smooth curved surfaces to side wall portions lb. The grain of this wood piece 1 extends in the lengthwise direction of the bottom portion la, and, at the periphery of wall portions lb, it faces in the thickness direction of the wall portions lb. Next, the various processes involved in strengthening of the wood piece 1 will be explained. First, the wood piece 1 is put into a steam atmosphere at high temperature and pressure. The wood piece 1 absorbs an excess water component by being thus placed in a steam atmosphere at high temperature and pressure, and accordingly softens. Next, as shown in FIG. 8, still in the same high temperature high pressure steam atmosphere as the one described above, the wood piece 1 is placed into the lower mold A, and the net 3 made of metal is placed upon the inner bottom portion of the wood piece 1. The net 3 is curved beforehand so as to agree with the shape of the wood piece 1. Here, the relationship between the shape of the lower surface of the wood piece 1 (its outer aspect) and the shape of the lower mold A, and the relationship between the shape of the upper surface of the wood piece 1 (its inner aspect) and the shape of the upper mold B will be explained. As described above, smooth curved surfaces extend from the bottom portion la of the wood piece 1 to its wall portion lb when the radius of curvature of the curved surface of the lower surface of the wood piece 1 (its outer aspect) is termed Ro, the radius of curvature of the curved surface of the upper surface of the wood piece 1 (its inner aspect) is termed Ri, the radius of curvature of the curved surface of the lower mold A which contacts the curved surface of radius of curvature Ro upon the wood piece 1 is termed RA, and the radius of curvature of the curved surface of the upper mold B which contacts the curved surface of radius of curvature Ri upon the wood piece 1 is termed RB, then the relationships Ro>RA and Ri>RB hold between these values. Next, as shown in FIG. 9, the upper mold B is shifted so as to be fitted into the interior of the lower mold A, so that the wood piece 1 is compressed between the upper and lower molds A and B, and this state is maintained for a predetermined time period. The net 3 is pressed into the upper surface of the wood piece 1 which has been sandwiched between the upper and lower molds A and B, and furthermore compression force is applied to the bottom portion la and the wall portion lb of the wood piece 1, so that it is compressed to be of thickness from about 1/2 to about 1/3 of its original. At this time since, due to the above described relationship between the radii of curvature, at the wall portion lb, the compression force does not act in the direction of the grain of the wood, but rather, on the outside, a frictional force in the upward direction acts so as to shear the outer aspect of the wall portion lb in the upward direction, while, on the inside, a frictional force in the downward direction acts so as to shear the inner aspect of the wall portion lb in the downward direction, accordingly the grain of the wall portion lb, which originally was oriented in a horizontal direction, is deformed so as to be bent in the vertical direction. Finally, when the high temperature high pressure steam atmosphere is released and the wood piece 1 is taken out from between the upper and lower molds A and B, the wood piece 1 is formed in the shape of the internal space which is defined when the molds A and B are fitted together, and the net 3 is integrated into the upper surface of the wood piece 1 which has thus been formed, in the state of being embedded in the upper surface of the wood piece 1. After having thus been compressed, the bottom portion la and the wall portion lb of the wood piece 1 are of almost the same thickness as one another. The wood piece 1 which has been strengthened in the above described manner takes the form as shown in FIG. 10. With this wood piece 1, in addition to the fact that a high strength is imparted by integrating the net 3 which is made of metal into it by compression, also, since the grain of the wall portion lb is bent around into the vertical direction which contributes" to the strength of the wall portion lb, accordingly it is possible to enhance the strength of the wall portion lb up to the same level as that of the other portions of the wood piece 1. Next, the third preferred embodiment of the present invention will be explained with reference to FIG. 11. It should be understood that to structural elements which are the same as in the above described preferred embodiments and which have already been explained, the same reference symbols are appended, and their explanation will be curtailed. With the wood piece 1 of this preferred embodiment, after it has been strengthened by the process which has been explained above with respect to the first preferred embodiment, at its surface where the rod shaped members 2 are provided, a carbonized layer 4 of almost uniform thickness is formed. Although wood is originally a good insulator, it may be converted into a good conductor by being carbonized, and it then exhibits characteristics which are the same as or superior to those of a metal, and moreover this wood piece 1 is extremely effective as a covering member for, for example, an electronic device, since, it becomes a electromagnetic shielding material which is remarkably light in weight, in comparison with a metal. It should be understood that, while this carbonized layer 4 may be formed by burning one side of the wood piece 1, it should also be considered that deformation may occur if only one side of the wood piece 1 is burned, since the portion which has been burned shrinks, so that a dimensional discrepancy arises vis a vis the other side. To address this problem, it is effective to burn one side of the wood piece 1, while drying out the water component which is included in the other side thereof by heating the other side up to the temperature which is required for evaporating the water component, and then both sides of the wood piece 1 shrink together, so that the occurrence of deformation is avoided. Next, the fourth preferred embodiment of the present invention will be explained with reference to FIG. 12 and FIG.13. It should be understood that to structural elements which are the same as in the above described preferred embodiments and which have already been explained, the same reference symbols are appended, and their explanation will be curtailed. With the wood piece 1 of this fourth preferred embodiment, in its state before being compressed, as shown in FIG. 12, a portion which is of high density (denoted by I in the figure) is made to be thin, while a portion which is of low density (denoted by II in the figure) is made to be thick. When a wood piece 1 with such shape is strengthened according to the process which has been explained with reference to the above described first preferred embodiment, the resulting reinforced wood piece 1 comes to be formed in a plate shape of almost uniform thickness as shown in FIG. 13, and the compression ratio of the portion which originally had a high density is lower, while the compression ratio of the portion which originally had a low density is higher, so that, considering the wood piece 1 after compression as a whole, it has an almost uniform strength, since its density after compression is almost uniform. Next, the fifth preferred embodiment of the present invention will be explained with reference to FIG. 14 and FIG.15. It should be understood that to structural elements which are the same as in the above described preferred embodiments and which have already been explained, the same reference symbols are appended, and their explanation will be curtailed. The wood piece 1 of this fifth preferred embodiment is intended to be used as a casing for a piece of electronic equipment, say a camera, and a hole lc is formed through it for, for example, exposing a release button (not shown in the figures). And in the state of this wood piece 1 before it is compressed, as shown in FIG. 14, a portion thereof around the edge or the like of this hole lc (denoted by III in the figure), for which it is required to ensure high strength, is formed to be thicker than portions which surround it. When a wood piece 1 with such shape is strengthened according to the process which has been explained with reference to the above described first preferred embodiment, the resulting reinforced wood piece 1 comes to be formed in a plate shape of almost uniform thickness as shown in FIG. 15, and a relatively high strength is ensured for the portion III which originally was formed thicker than its surroundings, since the compression ratio of this portion III is higher, as compared to the compression ratio of its surroundings. Next, the sixth preferred embodiment of the present invention will be explained with reference to FIG. 16 and FIG. 17. It should be understood that to structural elements which are the same as in the above described preferred embodiments and which have already been explained, the same reference symbols are appended, and their explanation will be curtailed. The wood piece 1 of this sixth preferred embodiment, just like the wood piece 1 of the fifth preferred embodiment, is intended to be used as a casing for a piece of electronic equipment, so that a hole lc is formed through it. And in the state of this wood piece 1 before it is compressed, as shown in FIG. 16, to a portion thereof around the edge or the like of this hole lc (denoted by IV in the figure) for which it is required to ensure high strength, there is adhered another wood piece 5 which is formed in a circular wedge shape. When a wood piece 1 with such structure is strengthened according to the process which has been explained with reference to the above described first preferred embodiment, the resulting reinforced wood piece 1 comes to be formed in a plate shape of almost uniform thickness as shown in FIG. 17, and a relatively high strength is ensured for the portion IV to which the wedge shaped wood piece 5 was adhered before the compression process, since the compression ratio of this portion IV is higher, as compared to the compression ratio of its surroundings. In this sixth preferred embodiment, it is desirable to arrange for the grain of the main wood piece 1 and the grain of the supplementary wood piece 5 to be almost perpendicular to one another. By doing this, it is possible to ensure even higher strength for the resulting product, since these two pieces of wood mutually reinforce one another in their respective directions where they are each weakest. Next, the seventh preferred embodiment of the present invention will be explained with reference to FIG. 18 through FIG. 20. It should be understood that to structural elements which are the same as in the above described preferred embodiments and which have already been explained, the same reference symbols are appended, and their explanation will be curtailed. The wood piece 1 of this seventh preferred embodiment, just like the wood piece 1 of the fifth preferred embodiment, is intended to be used as a casing for a piece of electronic equipment, so that a hole lc is formed through it. And in the state of this wood piece 1 before it is compressed, as shown in FIG. 19, at a portion thereof around the edge or the like of this hole lc (denoted by V in the figure) for which it is required to ensure high strength, there is positioned another member 6 which is made of a substance which is harder than wood (for example, a metal, a ceramic, or a reinforced plastic). The shape of this other member 6 is as shown in FIG. 18, it is formed in a circular ring shape, with its portion around its inner peripheral surface being made the thickest, and with its thickness gradually diminishing towards its outer periphery. When a wood piece 1 with such structure including the other member 6 is strengthened according to the process which has been explained with reference to the above described first preferred embodiment, the resulting reinforced wood piece 1 with the embedded member 6 comes to be formed in a plate shape of almost uniform thickness as shown in FIG. 20, and a relatively high strength is ensured for the portion V into which the other member 6 is embedded, since, along with the portion V being reinforced with the other member 6, also the compression ratio of this portion V against which the other member 6 has been positioned is higher, as compared to the compression ratio of its surroundings. While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.

INDUSTRIAL APPLICABILITY Since this covering member is satisfactory from the point of view of the mechanical aspects such as formability, durability, corrosion resistance, and so on, and also is satisfactory from the point of view of the design aspects such as quality of appearance and designability and so on, accordingly it is very suitable as a covering member for a device which is intended to be operated by a user while being held in his hand, such as a camera, a portable telephone, an IC recorder, a PDA, a remote control of a household product, and the like.

Claims

1. A method of strengthening a wood piece, comprising the steps of: superimposing the wood piece upon a metallic reinforcing member; and compressing the wood piece and the reinforcing member, so that the wood piece and the reinforcing member are integrated.

2. A method of strengthening a wood piece according to claim 1, wherein a direction along which the reinforcing member extends and a direction of the grain of the wood piece cross one another.

3. A method of strengthening a wood piece according to one of claims 1 and 2, wherein the reinforcing member is made in the form of a grating or a net.

4. A method of strengthening a wood piece according to one of claims 1 to 3, further comprising a step of: forming a carbonized layer upon the surface of the wood piece where the reinforcing member is provided.

5. A method of strengthening a wood piece according to one of claims 1 to 4, wherein the reinforcing member is quenched.

6. A method of strengthening a wood piece, comprising the steps of: making a high density portion of the wood piece thin, and a low density portion of the wood piece thick; and compressing the wood piece having the high density portion and the low density portion.

7. A method of strengthening a wood piece, comprising the steps of: making a portion of the wood piece at which high strength must be ensured thicker than a surrounding portion thereof; and compressing the wood piece having the portion at which the high strength must be ensured.

8. A method of strengthening a wood piece, comprising the steps of: adhering another wood piece to a portion of the wood piece at which high strength must be ensured; and compressing the wood piece to which the another wood piece has been adhered.

9. A method of strengthening a wood piece according to claim 8, wherein the direction of the grain of the wood piece and the direction of the grain of the another wood piece are different.

10. A method of strengthening a wood piece, comprising the steps of: disposing a reinforcing member which is harder than the wood piece on a portion of the wood piece at which the high strength must be ensured; and compressing the wood piece and the reinforcing member, so that the wood piece and the reinforcing member are integrated.