WO2008150234A1

WO2008150234A1 - Drawer design and assembly method

Info

Publication number: WO2008150234A1
Application number: PCT/SE2008/050668
Authority: WO
Inventors: Rickard Olsson
Original assignee: Rickard Olsson
Priority date: 2007-06-05
Filing date: 2008-06-05
Publication date: 2008-12-11
Also published as: SE533028C2; SE0701355L; EP2166897A1

Abstract

The main object of the invention is to provide a drawer that is possible to efficiently produce in large quantities, which is easy to assemble with as few tools and mounting means (fittings, screws, etc.) as possible, and at the same time reduce the total environmental impact of the produced drawers whilst maintaining sufficient product quality in terms of durability and visual appeal. A drawer according to an embodiment comprises a front piece (1), a left side piece (2), a right side piece (3), a back piece (4) and a bottom (5). The drawer frame comprises the two side pieces (2, 3), the front piece (1) and the back piece (4), and is joined by dovetail joints comprising dovetail protrusions and dovetail grooves.

Description

RICKARD OLSSON

DRAWER DESIGN AND ASSEMBLY METHOD

Technical field

The present invention relates to drawer designs and corresponding assembly methods.

Background art

Nowadays, many furniture designers design drawers to be delivered to the customer in an un-mounted state and then assembled at the site of use. This type of design reduces space requirements throughout the value chain and brings about many advantages.

However, the design must allow for easy assembly of the drawer. Easy assembly is commonly promoted by reducing the number of parts to be assembled and also by reducing the need of tools (screw drivers, hex keys, drills, hammers, staplers etc.). When designing drawers meant to be transported in an un-mounted state the common practice is to divide the design into five main parts, namely: the front piece, the left and right side pieces, the back piece and the bottom. There are numerous known configurations and ways to hold the parts together, all of which incorporate some sort of mounting means (screws, bolts, dowels, nails, staples etc.). Some designs also rely on other parts, such as metal-, rubber- or plastic fittings, to hold the main parts together.

To make the drawer easier to assemble in a correct way the parts often have some sort of guide features like pre-drilled holes, wooden plugs and/or grooves that guide the parts during assembly. Another, often important, aspect when designing such a product is to minimize environmental impact.

Last but not least, said drawer should preferably be visually appealing and thus the front piece should preferably not show any screw heads or fittings and any veneer covered sides should preferably be intact Millions and millions of these drawers are produced and exported worldwide each year, thus production speed and material cost are important factors and limiting for the design of such a drawer. A common material to use for such a drawer is cheap chipboard that has been laminated with a plastic material. This material is produced in a high-speed process and the resulting parts have rather fragile edges and corners, thus making the joints critical for the durability and function of the drawer.

A durable solution for joining drawer parts is proven to be the use of screws in combination with angle bars or other fittings. This however requires quite some thought and skill when assembling the drawer and it is often difficult to locate which screw should be used in what hole and in what order the parts should be assembled. There is also a risk that screws or fittings get lost during assembly of the drawer or earlier in the value chain. The need for tools such as screwdrivers or hex-keys is apparent when assembling drawers according to prior art and sometimes manufacturers deliver those tools with the piece of furniture to be assembled, thus increasing the cost and negative environmental impact of the product.

Disclosure of the invention

An object of the invention is to provide a drawer that may be efficiently produced in large quantities, that is easy to assemble with as few tools and mounting means (fittings, screws, wooden plugs etc.) as possible, and at the same time reduce the total environmental impact of the produced drawers whilst maintaining sufficient product quality in terms of durability and visual appeal.

A drawer according to an embodiment, as shown in the drawings, comprises a front piece, a left side piece, a right side piece, a back piece and a bottom. The bottom has a front edge, a left edge, a right edge, and a back edge. A drawer frame is formed by the two side pieces, the front piece and the back piece. The drawer frame parts are joined by means of dovetail, or similarly shaped, grooves and protrusions. The grooves and protrusions may be formed all the way across any part, from one edge or end to the opposite edge or end, or partly across any part in order to provide joining means and, if desired, a stop to guide the parts relatively each other during assembly in a direction along the groove to an end position. Another reason for only providing a groove partly across a surface would be not to machine any surface coated or veneer covered sides where the groove would become visible in an operating position of the drawer. The dovetail protrusions and grooves may be formed with one or more bulges and/or dents in order to provide additional fastening features between the parts. In an embodiment, one or more of the parts of the drawer frame is/are produced from a chipboard material and one or more mounting means is/are inserted in one or more grooves in one or more of the parts of the drawer frame to support the bottom. The use of a cheap chipboard material makes it possible to reduce the material costs. Further, the increased support given by the mounting means makes is possible to use a cheaper, thinner and less stiff drawer bottom, typically made of Masonite®, thus allowing for a less expensive drawer to be produced. Each edge of the drawer bottom may be supported in one or more grooves in one or more of the frame parts or in a space between the bottom side of the left and right side pieces and a left and a right side rail. The rails, if any, are usually Z-shaped with 90° angles, made of pressed steel plate and designed to fit with corresponding fittings that protrude from left and right inner side walls of the piece of furniture in which the drawer is to be mounted. The side rails, if any, are usually positioned to the left and right of the drawer frame, respectively and comprising features that protrude under the bottom side of the side piece at a distance from the bottom side of the side pieces, the distance being almost equal to the thickness of the drawer bottom.

One aspect further relates to a method of assembling a drawer without using any tools. Depending on which embodiment of the drawer that has been chosen, the assembly method varies.

According to an aspect the drawer is assembled in the following order. First, the two side pieces are slid into/onto each dovetail groove/protrusion on the front piece respectively. Then the back piece is slid onto the side pieces to form a drawer frame. Then, the side rails are to be mounted if they have not already been pre-mounted to the side pieces. Then the bottom is slid into the space formed between two side rails and the side pieces so that the front edge of the bottom enters one or more grooves in the front piece. Then one or more fittings are positioned along the back edge of the bottom so that it/they is/are supported by the side rails or by the drawer frame.

According to another aspect the drawer is assembled in the following order. First, the two side pieces are slid into/onto the left and right dovetail grooves/protrusions on the front piece respectively. Then the bottom is slid into the grooves provided in the side pieces, so that the front edge of the bottom enters as far into the one or more grooves in the front piece as possible. Then the middle of the front edge of the bottom is pressed upwards, over the one or more heels or protrusions, whereupon the bottom is slid even further into the front piece until there is enough free space at the back edge of the bottom for the back piece to be slid fully onto the side pieces. Then the back piece is slid onto the side pieces to complete a drawer frame, whereby the bottom is slid back as long into one or more grooves in the back piece as possible. Then, if there is a need of side rails, the rails may be mounted if they have not already been pre-mounted to the side pieces.

According to yet another aspect the drawer is assembled in the following order. First, the drawer frame is assembled; this is usually done by first sliding the two side pieces into/onto the left and right dovetail grooves/protrusions on the front piece respectively. Then, the back piece is slid into/onto the grooves/protrusions of the side pieces. If the drawer bottom is wider than the distance between the side pieces in an operating position of the drawer, then, if there is a need of side rails, make sure that the rails are not mounted to the side pieces yet. In this embodiment, the front and back edges of the bottom are supported in one or more grooves in the front and back piece respectively. In order to easily fit the bottom, its front or back edge should first be positioned in its supporting groove in the front/back piece respectively. When this is done, the other edge of the bottom is to be inserted in its one or more supporting grooves. This is commonly done by first bending the bottom, and then inserting the other edge slightly into the one ore more supporting grooves, and finally releasing the bottom, whereby it straightens out to be well supported in the back and front piece respectively. Then, if there is a need of side rails and the rails are not yet mounted, the rails may be mounted, whereby they support the left and right edges of the bottom, respectively.

When assembling a drawer according to an embodiment with a method according to an aspect the objects of the invention are attained.

Brief description of the drawings An embodiment will be described in further detail below under reference to the accompanying drawings, in which:

Fig IA is a perspective view of a drawer according to an embodiment;

Fig IB is an exploded perspective view of a drawer according to an embodiment; Figs 2A and 2B are top views of two different embodiments of a dovetail joint according to an embodiment;

Fig 3 shows a perspective view of an unassembled first embodiment of a joint between the front piece and the right side piece; Fig 4A through D shows different stages of the assembly of a drawer according to an embodiment;

Fig 5 is a front perspective view of an embodiment of the dovetail joints of the back piece;

Fig 6 is a front perspective view of an embodiment of the back piece provided with a groove;

Fig 7 is a perspective view of an embodiment of the left and right side pieces, each provided with a groove;

Figs 8, 9 and 10 are perspective views of the front piece according to an embodiment showing two alternative embodiments of a groove in the front piece that is provided with a heel or protrusion.

Detailed description of embodiments

Fig IA and B shows a drawer according to an embodiment. The drawer is shown as consisting of a drawer frame and a bottom 5, the frame comprising a front piece 1 , left and right side pieces 2, 3 and a back piece 4. The frame parts are provided with dovetail joints and are designed to easily be joined without tools.

A dovetail joint in this generally relates to a joint as exemplified in Figs 2A and B but it should be realized by the person skilled in the art that the size, angle and shape of the surfaces that make up the joint could be altered within the scope of the invention.

The left side of the drawer is considered to be to your left if you stand in front of the drawer in its operating position, facing the drawer front 1.

Apart from the drawer frame and the bottom 5, a drawer according to an embodiment may be designed for use with a left and a right side rail 6, 7 for interaction with a furniture body in which the drawer is to be used. The design and function of the side rails 6, 7 varies from producer to producer but the general idea is to use the side rails 6, 7 to provide a durable mechanism that makes it easy to slide the drawer in and out. The side rails 6, 7 can also be used to provide the drawer with a self closure mechanism and/or a mechanism that slows the drawer down during closing of the drawer, before it hits its fully closed position. The side rails can be provided with features 10 such as a plurality of lips, or one or more flanges, that protrude from the rest of the rails 6, 7, under the drawer bottom 5, thus making it possible to support the drawer bottom 5 using the side rails 6, 7. The side rails 6, 7, may also be shaped to allow room for other fittings, screws and/or a back rail 8, to be positioned at least partly under the drawer bottom 5 to support it. The other fittings, if any, being supported either by the side rails 6, 7 or by additional screws, fittings, grooves etc. provided in/on one or more parts of the drawer frame, such as the side walls 2,3 or the back piece 4. The fittings could be one or more rails, and the rails could be made of either metal or wood. A wooden rail would typically have the form of a flat strip or list of Masonite® or plywood. Such a fitting has the advantage that it may be mounted by simply inserting it in one or more grooves without any need of tools. The side pieces 2,3 may be distributed to the end consumer with the left and right side rails 6,7, if any, pre-mounted to the side pieces 2,3 in order to simplify assembly and bring down the number of loose components to be distributed, thus a drawer design according to an embodiment has to enable assembly of the drawer without a need of removing the side rails 6, 7.

The bottom 5 according to an embodiment is normally a square shape Masonite® board with four "edges", namely: a front edge 15, a left edge 16 a right edge 17 and a back edge 18. The thickness, width and length of the bottom 5 is adapted to fit with the dimensions of the rest of the drawer and is usually about 3 x 340 x 445 mm. When the bottom 5 "fits" it is supposed to be wide enough and long enough not to be able to slide about relatively the drawer frame, in an operating position of the drawer. If the bottom is supposed to be positioned into the drawer frame from above, the width of the bottom has to be equal to, or slightly less than, the width between the left and right side pieces, respectively. The thickness of the bottom is preferably chosen as thin as possible in order to reduce the material cost of the drawer whilst maintaining enough stability for the bottom to withstand typical loads.

The side pieces 2,3, according to a first embodiment, have a length of about 440 mm, a height of about 155 mm and a width of about 12 mm and could be made of laminated chipboard. From a production economy point of view, it is desirable to choose a drawer design where the side pieces 2, 3 and the back piece 4 have the same cross section, thus making it possible to mass produce the same material for the two side pieces 2, 3 and the back piece 4 and then cut off parts of correct length for the back piece 4 and the side pieces 2, 3 respectively.

According to an embodiment the back piece 4 and the side pieces 2, 3 have the same cross section and material. The front piece 1 could also have the same cross section and material, but normally the front piece 1 would be made of chipboard with a relatively expensive and visually appealing surface such as veneer or shiny plastic. The front piece 1 normally also has a thicker and higher cross section than the other parts of the drawer frame.

Fig 2A shows an embodiment of a joint between the back piece 4 and either of the side pieces 2, 3. This joint is accomplished by providing a dovetail protrusion in either of the parts and a matching dovetail groove in the other part. By choosing a certain parting plane angle 9 it is possible to achieve a joint where the left and right outer corners of the drawer, close to the back piece 4, are coincident with both of a corner of the back piece 4, and a corner of the left and right side piece 2, 3 respectively. If the parts have some sort of surface material or coating, such as veneer, paint or plastic, choosing this angle will render only the surface material or coating of the side pieces 2, 3 and the back piece 4 visible when the drawer is assembled. If the pieces would be coated or have a surface material different from the inner material and another angle would be chosen, the inner material of either the back piece 4 or the side pieces 2, 3 would be visible, possibly lowering the visual appeal of the drawer.

Fig 2B shows an embodiment of a joint between the back piece 4 and either of the side pieces 2, 3. This joint is accomplished by providing a dovetail protrusion in either of the parts and a matching dovetail groove in the other part. By choosing a parting plane angle 9 that is perpendicular to one of the side pieces 2, 3 or the back piece 4, and providing a dovetail groove in the inner side surface of the other piece at a distance from the end of the inner side surface of the other part, a joint is created that exposes the end of the part comprising the groove. The groove of the joint is preferably provided in either of the side pieces 2, 3, since that exposes the end material of either of the side pieces 2, 3 at the back of the drawer, where it normally cannot be seen from a user's point of view, rather than exposing the end material of the back piece 4 towards the left or right side of the drawer. When this embodiment is used, the bottom dimensions have to be adjusted accordingly. Fig 3 shows a perspective view of an unassembled embodiment of a joint between the front piece 1 and the right side piece 3, being similar to the joint between the front piece 1 and the left side piece 2. When assembled, the parts will be perpendicular to each other. This joint is accomplished by providing a dovetail protrusion in either of the parts and a matching dovetail groove in the other part. For a joint between these two pieces the groove is preferably provided on the inside of the front piece and the protrusion on the end of either side piece. By providing a groove that stretches from one edge or end to the opposite edge or end of the front piece 1 , or only partly across the front piece 1 , the surface and/or edge or end otherwise to be machined can be kept intact, thus preserving any present veneer at the upper side of the front piece, thereby preserving the visual appeal of the front piece and providing a fix stop so that the front piece will not be able to slide past its preferred position. This type of stop mechanism stops the protrusion of one part from sliding past a stop provided in the groove of the other part and it should be understood that this type of stop could be used for any other dovetail joint in the drawer too if desirable.

Fig 4A, B, C and D shows different stages of the assembly of a drawer according to an embodiment. In this embodiment the bottom 5 is inserted, and supported, in a space formed between the side rails 6, 7 and the side pieces 2, 3 so that a front edge 15 of the bottom 5 enters the one or more grooves 11 in the front piece. Thereby the front edge 15 of the bottom 5 is supported in the one or more grooves 11 in the front piece 1.

Fig 4A shows the two side pieces 2, 3 attached to the front piece 1 and the side rails 6, 7 attached to the side pieces 2, 3. Fig 4B shows what the drawer frame looks like with the back piece 4 fully slid in position.

Fig 4C shows the drawer bottom 5 fully slid in position. Fig 4D shows the fully assembled drawer with the back edge 18 of the bottom supported by a back rail 8 supported by the side rails 6, 7. Fig 5 shows an embodiment of a dovetail protrusion provided with a bulge 13. Any of the dovetail joints in the drawer could be provided with bulges 13 and/or dents in order to enhance the grip between the two parts in a controlled manner. A bulge 13 on a protrusion of such a joint is shown in Fig 5. In a preferred embodiment of a bulge 13 according to an embodiment the bulge 13 is considered to be a certain part of the length of a dovetail protrusion, which part has been given a wider cross section than the rest of the protrusion. The cross section of the protrusion in an embodiment according to an embodiment has three sides of which two are symmetric about a plane that is perpendicular to the parting plane 9. The protrusion's third side is parallel to the parting plane 9 and is wider than the distance between the two other sides measured in the parting plane 9. The dimension of the groove, in which any of the protrusions is supposed to be fitted, is designed to fit with each protrusion respectively.

Fig 6 shows an embodiment of a groove in the lower part of the back piece 4. In this embodiment the groove is provided for supporting the back edge 18 of the drawer bottom 5 without the need of a back rail 8. In this embodiment the left and right side edges 16, 17 of the bottom 5 are supported either by side rails 6, 7 or in grooves in the side pieces 2, 3 or a combination of one or more rails and one or more grooves.

Fig 7 shows left and right grooves 21 , 22 provided in the left and right side piece 2, 3 respectively. These grooves may be provided for supporting the left and right side edges 16, 17 of the bottom 5 respectively.

Figs 8 and 10 show an embodiment of a heel or protrusion 12 in a groove in the front piece 1. The heel or protrusion 12 has the shape of an arc starting and ending at a distance from the left and right side of the front piece 1 respectively. The top of the arc is preferably situated at a mid distance between the left and right side of the front piece 1. The heel or protrusion 12 reaches all the way to the bottom of the groove in the front piece 1 but does not stretch all the way to the inner side of the front piece which faces the inside of the drawer in an operating position. The space in the groove that is between the inner side of the front piece 1 and the heel or protrusion 12 provides support for the front edge 15 of the drawer bottom 5 in and operating position. The distance above the highest point on the arc to the above lying surface in the groove must be enough to make room for the bottom 5 to be slid all the way into the bottom of the groove in the front piece, in a direction from the back piece 4 towards the front piece 1, along grooves in the side pieces 2, 3 for supporting the drawer bottom 5.

Fig 9 shows another embodiment of a heel or protrusion in a groove in the front piece 1. This heel or protrusion 12 is provided in the lowermost part of the groove, closest to the bottom side of the drawer and has the shape of a rectangular parallelepiped. The heel or protrusion 12 stretches from the bottom 5 of the groove and partly out of the groove towards the inner side of the front piece 1. The distance above the heel or protrusion 12 to the above lying surface in the groove must be enough to make room for the bottom 5 to be slid all the way into the bottom of the groove in the front piece, in a direction from the back piece 4 towards the front piece 1, along grooves in the side pieces 2, 3 for supporting the drawer bottom 5. When using a heel or protrusion according to this embodiment extra efforts have to be taken when designing the rest of the drawer in order to make sure that the front edge 15 of the bottom 5 has extra space above the left and right side edges 16, 17, in the part of the grooves in the side pieces 2,3 closest to the front piece 1 , in order for one to be able to lift the front edge 15 of the bottom 5 and slide it above the heel or protrusion 12 all the way into the one or more grooves in the front piece 1. An alternative to providing extra space in the grooves in the side pieces 2, 3 would be to arrange for the front piece to be slidable slightly further downwards, relatively the side pieces, along the dovetail joints holding those parts together, that would make it possible to first slide the front piece downwards, then slide the bottom 5 all the way into the groove in the front piece 1 , above the heel or protrusion 12 without having any extra space in the grooves in the left and right side pieces 2,3 above the left and right edges 16, 17 of the bottom 5.

It should be understood that the choice of material for the drawer bottom 5 and each part of the drawer frame is preferably some sort of wood, but that materials such as plastic or metal could be used to form these parts as well. Modifications are possible within the scope of the appended claims, which cover the general idea of how a drawer according to an embodiment could be designed to be assembled with a minimum need of fittings or tools. The shown embodiments are only to be considered exemplary and not limiting for the design of the drawer.

Claims

1. Drawer wherein the drawer comprises a front piece (1), a left side piece (2), a right side piece (3), a back piece (4) and a bottom (5) with a front edge (15), a left edge (16), a right edge (17), and a back edge (18), characterized in that a drawer frame comprising the two side pieces (2, 3), the front piece (1) and the back piece (4), is joined by dovetail joints comprising dovetail protrusions and dovetail grooves, wherein one or more of the parts of the drawer frame is/are produced from a chipboard material and wherein one or more mounting means (8) is/are inserted in one or more grooves in one or more of the parts of the drawer frame (1 , 2, 3, 4) to support the bottom (5).

2. Drawer according to Claim 1 , further characterized in that the dovetail joints between side piece and back piece are provided in absolute proximity of the two back corners of the drawer.

3. Drawer according to Claim 1 or 2, wherein the mounting means (8) comprises/comprise one or more rails.

4. Drawer according to Claim 3, wherein the rail/rails is/are one or more wooden list/lists.

5. Drawer according to Claim 1-4, wherein one or more dovetail grooves are provided only partly across the part in which they are provided.

6. Drawer according to Claim 1-5, wherein one or more dovetail joints are provided with either one or more bulges (13) and dents that fit with the bulges (13), or provided with only one or more bulges (13).

7. Drawer according to Claim 1-6, wherein the bottom (5) is to be slidably mounted, wherein the front piece (1) is provided with one or more grooves (11) in which the front edge (15) of the bottom (5) is supported, and wherein the left and right edges (16, 17) of the drawer bottom (5) are supported by either a left and a right side rail (6, 7) attached to the drawer frame, or by grooves (21 , 22) provided in the left and right side pieces (2, 3) respectively, or by a combination of one of said rails (6, 7) and one of said grooves (21, 22) on the left and right side piece (2, 3) respectively.

8. Drawer according to Claim 7, wherein a groove (14) is provided in the back piece (4) for supporting the back edge (18) of the bottom (5), wherein the depth of the one or more grooves (11) supporting the front edge (15) is larger than what would be necessary for accommodating the bottom (5) in an operating position of the drawer, and specifically as much larger as the depth that the bottom (5), in an operating position, protrudes into the groove (14) provided in the back piece for supporting the back edge (18) of the bottom.

9. Drawer according to Claim 8, wherein one or more of the grooves (11), supporting the front edge (15) of the bottom (5), are provided with heels or protrusions (12) of such a height and having such a position that the bottom (5), in an operating position, is restrained from moving in a direction further towards the front piece (1), and wherein the one or more grooves supporting the front edge (15) is/are of such a shape and size that the space above the one or more heels or protrusions (12) is large enough for the bottom (5) to be moved into the space.

10. Method of assembling a drawer comprising a front piece (1), a left side piece (2), a right side piece (3), a back piece (4), a bottom (5), and a left and a right side rail (6, 7) attached to the left and right side piece (2, 3) respectively, characterized in that the two side pieces (2, 3) are first slid into/onto the left and right dovetail grooves/protrusions on the front piece (1) respectively, whereupon the back piece (4) is slid onto the side pieces (2, 3) to form a drawer frame, whereupon the bottom (5) is slid into the space formed between the side rails (6, 7) and the side pieces (2, 3) so that the front edge (15) of the bottom (5) enters the one or more grooves (11) in the front piece (1), whereupon a fitting (8) is positioned along the back edge (18) of the bottom so that the fitting (8) is supported by the side rails (6, 7) or the back piece (4).

11. Method of assembling a drawer comprising a front piece (1), a left side piece (2), a right side piece (3), a back piece (4), a bottom (5), and a left and a right side rail (6, 7) attached to the left and right side piece (2, 3) respectively, characterized in that the two side pieces (2, 3) are first slid into/onto the left and right dovetail grooves/protrusions on the front piece (1) respectively, whereby the bottom (5) is slid into the grooves provided in the side pieces (2, 3) so that the front edge (15) of the bottom (5) enters as far into the one or more grooves (11) in the front piece (1) as possible, whereupon the middle of the front edge (15) of the bottom (5) is pressed upwards, over the one or more heels or protrusions (12), whereupon the bottom (5) is slid even further into the front piece (1) until there is enough free space at the back edge (18) of the bottom (5) for the back piece (4) to be slid onto the side pieces (2, 3), whereupon the back piece (4) is slid onto the side pieces (2, 3) to complete a drawer frame, whereby the bottom (5) is slid back as long into the one or more grooves (14) in the back piece (4) as possible. Whereby the rails (6, 7) may be mounted if they have not already been pre-mounted to the left and right side pieces (2, 3) at delivery.

12. Method of assembling a drawer comprising a front piece (1), a left side piece (2), a right side piece (3) a back piece (4), a bottom (5) and a left and a right side rail (6, 7), characterized in that the two side pieces (2, 3) are slid into/onto the left and right dovetail grooves/protrusions on the front piece respectively, whereby the back piece (4) is slid into/onto the grooves/protrusions of the side pieces (2,3), whereby the front or back edge (15, 18) of the bottom (5) is positioned in its supporting groove (11 , 14) in the front/back piece respectively, whereby the other edge (18, 15) of the bottom is inserted in its supporting groove (14, 11) by first bending the bottom (5), then inserting the other edge (18, 15) slightly into the one ore more supporting grooves (11 , 14), and finally releasing the bottom (5), whereby it straightens out to be supported in the back and front piece (4, 1), whereby the left and right side rails (6, 7), if not already mounted to the side pieces (2, 3), are mounted to the left and right side piece (2, 3) respectively.