FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a dowel, to an assembly comprising two parts connected by a dowel and to a method of connecting two parts.

In many construction industries, wooden objects are prepared by making a connection between two or more wooden parts (or panels), for example in the construction of houses, housing interiors and furniture. In making a connection, use is often made of a glue and/or a dowel. In this context, a dowel is commonly known as a peg that is present at the interface of two panels, wherein one end of the peg is present in a hole of one panel, and the other end in a hole of the other panel. A dowel serves to align two panels and to truly attach one panel to the other.

In many applications, a dowel is equipped with a particular surface structure so as to enhance the friction of the dowel with the surface of the hole of a panel. It is for example known to provide the surface of a dowel with a groove along the dowel's circumference, or with some protrusions on its surface. When a dowel is primarily used as an alignment means and secondly as a connection means, the friction that is achieved with such conventional surfaces may be sufficient. Also, in many instances it can be circumvented that the connection is truly challenged during production and/or use, i.e. it can be circumvented that a high force is applied that can pull the two panels apart.

In other instances, however, it is required that a very strong connection is present between two panels, wherein the connection heavily relies on the presence of the dowel. This may occur when a glue is used that requires a long time for curing or drying (or when a glue is not used at all) while loading of the connection cannot be circumvented. For example, when a constructed product such as a door-frame of a window-frame has to be coated in a paint shop, it is usually hanging freely on a minimal number of attachments during transport, painting and drying. It has been experienced that conventional dowels are not suitable for achieving such a strong connection between two panels, especially not when an uncured or unhardened (non-water based) glue is present since that even acts as a lubricant so that the connection becomes even weaker. Thus, the low friction of a dowel with the inside of a hole in a panel is an obstacle that needs to be overcome, in particular when a glue is present that is not yet hardened or dried, more in particular when such glue is a non-water based glue.

It is therefore an objective of the present invention to provide a dowel that is capable of making a stronger connection to a wooden panel than known dowels can do, i.e. the force required for releasing the dowel is higher. Preferably, in doing so, the force required for inserting the dowel is not increased correspondingly. It is in particular an objective to provide a dowel that has a higer friction with the surface of a hole of a panel upon inserting it into the hole than upon releasing it from the hole.

SUMMARY OF THE INVENTION

It has now surprisingly been found that one or more of these objectives can be reached by providing the dowel with particular surface properties.

Accordingly, the present invention relates to a dowel for connecting two parts, comprising

an elongate member (2) of an essentially cylindrical shape having

1 ) a first end (3-1 );

2) a second end (3-2);

3) a longitudinal axis (5) extending from the first end (3-1 ) to the second end (3-2);

4) a center point (6) located halfway the longitudinal axis (5);

5) a length (7) which is defined as the distance between the first end (3- 1 ) and the second end (3-2);

6) a diameter (8); and

7) a circumference (9); a plurality of protrusions (10) extending from a first surface part (1 1 -1 ) of the elongate member's surface, which first surface part (1 1 -1 ) is defined as the surface that is present between a first circumferential line (12-1 ) and a second circumferential line (12-2) on the elongate member's surface, wherein the distance between the first circumferential line (12-1 ) and the second circumferential line (12-2), measured in the direction of the longitudinal axis (5) of the elongate member (2), is not shorter than the diameter (8) of the elongate member (2); the protrusions (10) having

1 ) a base (10a), which is the side of the protrusions (1 0) that is adjacent to the surface of the elongate member (2);

2) a summit (10b), which is a point on the surface of the protrusions (10) that is most remote from the base (10a);

3) a height (10c), which is the shortest distance between the summit

(10b) and the base (10a);

characterized in that

1 ) the summits (10b) of the protrusions (10) on the first surface part (1 1 -1 ) are separated by at least a distance that is the smaller of 1 ) 5% of the circumference (9) of the elongate member (2); and 2) the largest dimension of the base (10a), measured along the circumference of the elongate member (2), of the protrusions (10);

2) a circumferential surface within the first surface part (1 1 -1 ) that does not contain a protrusion (10) constitutes less than 50% of the surface area of the first surface part (1 1 -1 ), wherein a circumferential surface is defined as the surface that is present between two circumferential lines;

3) the largest dimension of the base (10a), measured along the

circumference of the elongate member (2), of the protrusions (10) on the first surface part (1 1 -1 ) is not more than 20% of the circumference (9) of the elongate member (2); and

4) the number of protrusions (10) on the first surface part (1 1 -1 ) is at least thirty.

For the purpose of the invention, a dowel is a connecting element that is suitable for connecting two parts (such as panels, boards, staves) in such a way that one end is present in a hole of a first part and the other end is present in a hole of a second part. Thus, each end of a dowel allows fixation to a different part.

A dowel of the invention comprises an elongate member of an essentially cylindrical shape, on which protrusions are provided. The characterizing feature of a dowel of the invention comprises the particular spacing, distribution, size and number of the protrusions on the surface of the elongate member. The entire surface of the dowel may be provided with such protrusions. Usually, however, the protrusions are present on a particular part of the dowel. Such part is in particular present in the proximity of an end of the elongate member. In case it is present on only one end, the other end is typically provided with a different means for fixation, for example a screw thread, a cap, or a neck. The protrusions according to the invention may also be present on two or more separate parts of the dowel, for example close to each of the two ends of the elongate member.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings.

Figure 1 shows the elongate member of a dowel according to the invention, equipped with protrusions.

Figure 2 shows an enlargement of one protrusion on the elongate member of a dowel of the invention, wherein the protrusion is a directed barb.

Figures 3-5 show a dowel according to the invention wherein one side of the dowel is equipped with an alternative fixation means.

Figure 6 shows a dowel according to the invention wherein both ends of the dowel are equipped with protrusions.

Figure 7 shows a dowel according to the invention comprising two different types of protrusions.

Figure 8 shows a dowel according to the invention comprising a longitudinal groove.

Figure 9 shows a dowel according to the invention wherein a ring is present around the dowel. Figure 10 shows a dowel according to the invention comprising means for roughening the surface of a hole into which the dowel is inserted.

Figure 1 1 shows a dowel according to the invention wherein the dowel is hooked.

Figure 12 shows yet another dowel according to the invention.

DETAILED DESCRIPTION

A dowel (1 ) of the invention comprises an elongate member (2) of an essentially cylindrical shape. The shape of a hole made by a drill is usually also cylindrically. Thus, the cylindrical shape of the elongate member makes it easy for a hole to receive the dowel, and such shape allows for a uniform contact of the dowel with the surface in the hole.

Figure 1 shows the elongate member (2) of a dowel (1 ) according to the invention. The elongate member (2) has a two ends (3), which are a first end (3-1 ) and a second end (3-2). These ends (3) define the longitudinal axis (5); this axis extends between the first end (3-1 ) and the second end (3-2) and coincides with the longitudinal axis of symmetry of the cylindrical elongate member (2). Halfway between both ends (3) and at the longitudinal axis (5), there is the center point (6) of the elongate member (2). Further, the elongate member (2) has a length (7) that is defined as the distance between both ends (3). Being of a cylindrical shape, the elongate member (2) has a diameter (8) and a circumference (9).

On the elongate member (2) are provided protrusions (10). These can be regarded as separate three-dimensional shapes that are present on the surface of the elongate member (2), wherein a surface of the protrusion (10) is adjacent to and in negative relief with the surface of the elongate member (2). In practice, of course, the protrusions (10) extend from the surface of the elongate member (2), i.e. they rise from the surface. They form one piece with the elongate member (2), are integrated in the structure of the dowel (1 ) and are not separate or detachable entities. Protrusions (10) extend from the curved surface of the elongate member (2) that is present between the first end (3-1 ) and the second end (3-2), i.e. in principle not on the cross- sectional surfaces on either end (3).

Figure 2 shows an enlargement of a single protrusion (1 0) extending from the surface of an elongate member (2). The protrusion has a base (10a), a summit (1 Ob) and a height (10c), which will be defined below.

The base (10a) of a protrusion (10) is defined as the surface of the three-dimensional shape {i.e. the protrusion (10)) that is in contact with the surface of the elongate member (2), i.e. it is adjacent thereto. Therefore, this surface is not in contact with an atmosphere. Since the surface of the elongate shape is curved, the base (10a) of a protrusion (10) is also curved.

The summit (10b) of a protrusion (10) is defined as that part of the protrusion that is most remote from the base. The most remote part may be formed by a single point, by a line or by a surface. In case of a line or surface, each point on the line or surface has an equal shortest distance to the base.

The height (10c) of a protrusion is defined as the shortest distance between the summit of the protrusion and the surface of the elongate member. This is measured along the normal of the elongate member's surface that passes through the summit of the protrusion (10).

The protrusion (10) in Figure 2 has a plurality of sides that extend at different angles from the surface of the dowel. These sides are the surfaces (10-1 ), (10-2) and (10-3) that extend from the elongate member.

The protrusions (10) serve to generate friction with the surface of a hole (usually a hole in a panel) into which the dowel (1 ) is introduced. This is accomplished by adjusting the diameter (8) of the dowel (1 ) to the diameter of the hole in such a way that the diameter (8) of the elongate member (2) plus twice the protrusion height (10c) is larger than the diameter of the hole. The diameter (8) of the elongate member (2) is usually not larger than the diameter of the hole. However, in the embodiments wherein the dowel (1 ) comprises a longitudinal groove (17) (as will be further elaborated below), diameter of the elongate member (2) may be larger than that of the hole, since such groove allows compression of the dowel (1 ) in a direction perpendicular to the longitudinal axis (5). Thus, after the introduction of the dowel (1 ) into a hole with the appropriate size, the protrusions (10) are pressed into the surface of the hole and thereby friction is generated that prevents the dowel (1 ) from releasing from the hole. This will be the case in any suitable use of a dowel (1 ) of the invention, no matter whether or not a longitudinal groove is present,

The protrusions (10) may in principle have any shape that is capable of providing the required friction during use. For example, the protrusions have a triangular pyramidal or square pyramidal shape. The base (10a) of such shape is a triangle or a square, respectively; the summit (10b) of such shape is a point, while the interfaces of the surfaces of the pyramid are straight edges. These shapes provide a good friction with the hole.

Protrusions may also have a more complex shape. For example, different sides {i.e. surfaces) of the protrusion may extend at different angles from the surface of the dowel. Figure 2 shows an example of such protrusion. The surfaces (10-1 ) and (10-2) extend steeper from the surface of the elongate member than surface (10-3). With such protrusion, the friction that has to be overcome to move the dowel (1 ) into a hole of a panel is smaller than the friction that has to be overcome to move the dowel (1 ) out of the hole.

For the purpose of the invention, a protrusion having this property is referred to as a directed barb. Thus, a directed barb on a dowel (1 ) has the effect that inserting the dowel (1 ) into a hole requires less force than pulling it out of the hole. Usually, the side of a directed barb that faces the end of the elongate member (2) that is closest to the barb contains a surface under an oblique angle with the surface of the elongate member (2), while the side of a directed barb that faces the center point (6) of the elongate member (2), contains a surface under a steep angle {i.e. an angle steeper than the said oblique angle) with the surface of the elongate member (2).

A protrusion (10) that is a directed barb is displayed in Figure 2. Surface (10-3) is a surface under an oblique angle with the surface of the elongate member (2), facing an end (3) of the elongate member (2). Surfaces (10-1 ) and (10-2) are surfaces under a steep angle {i.e. an angle steeper than the said oblique angle) with the surface of the elongate member (2), both facing the center point (6) of the elongate member (2). Depending on the type of material in which a barb of the invention is to be inserted, a dowel is selected with a particular height (10c) of the protrusions (10). When the material is hard (such as hardwood), the height (10c) of the protrusions will be smaller than when a softer material is used (such as pine wood or fiber board). Usually, the height of the protrusions is between 1 -25% of the diameter of the elongate member. The height may be 20% or less, 17% or less, 15% or less, 12% or less, 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, 3% or less or 2% or less of the diameter of the elongate member. The height may be 2% or more, 3% or more, 4% or more, 5% or more, 6% or more 8% or more, 10% or more, 12 % or more or 15% or more of the diameter of the elongate member. The height may be in the range of 0.1-3 mm, in particular in the range of 0.2-1 .5 mm.

The protrusions (10) are concentrated on a particular part of the elongate member's surface, which is the first surface part (1 1 -1 ). This surface part is defined as the surface that is present between two (imaginary) circumferential lines (12) on the elongate member's surface. For the purpose of the invention, a circumferential line is a line along the surface of the elongate member that defines a circular cross-section of the elongate member, i.e. the line is a circle that defines a plane that is perpendicular to the longudinal axis. The first surface part is present between a first circumferential line (12-1 ) and a second circumferential line (12-2) on the elongate member's surface. This surface part extends over the entire circumference between the first circumferential line (12-1 ) and the second circumferential line (12-2). For the purpose of the invention, any surface that is enclosed by (and therefore defined by) two circumferential lines is termed a "circumferential surface". Accordingly, any circumferential surface, for example the first surface part, is curved. Cutting the first surface part in the longitudinal direction of the elongate member, followed by unrolling it, in an imaginary way, would yield a flat rectangular surface. Two opposing sides of such rectangle have a length identical to the circumference of the elongate member. The length of the two other opposing sides equals the distance between the first circumferential line (12-1 ) and the second circumferential line (12-2). This distance is always longer than the diameter (8) of the elongate member (2), because otherwise the protrusions (10) cover a too small area for reaching an effective fixation in a hole of a panel.

In a dowel of the invention, there are certain requirements with respect to the particular spacing, distribution, size and number of the protrusions (10) on the first surface part (1 1 -1 ) (which will be elaborated below). A dowel of the invention contains at least one set of protrusions (10) that fulfills those requirements. This set is present on the first surface part (1 1 -1 ). In addition, this set defines the size of the first surface part (1 1 -1 ). This is because the position of the first circumferential line (12-1 ) is defined by the position of that part of the protrusion's base that is most proximate to the first end (3-1 ) of the elongate member (2), while the position of the second circumferential line (12-1 ) is defined by the position of that part of the protrusion's base that is most proximate to the second end (3-2) of the elongate member (2). Thus, the bases of the two protrusions that are most remote from each other, taking only account of the component along the longitudinal axis, define the spacing between the first circumferential line (12- 1 ) and the second circumferential line (12-2). In this way, all the protrusions of the set lie in their entirety on the first surface part.

Besides the protrusions (10) that are present on the first surface part (1 1 -1 ), other protrusions (10) may also be present on another surface part. These protrusions do not necessarily have to be arranged as on the first surface part (1 1 -1 ) as prescribed by the present invention.

In a dowel (1 ) of the invention, the protrusions (10) on the first surface part (1 1 -1 ) have to meet the following requirements.

1 ) The summits (10b) of the protrusions (10) on the first surface part are separated by a distance that is equal to or larger than the smaller of two distances, herein below referred to as Distance 1 and Distance 2.

Distance 1 is at least 5% of the circumference (9) of the elongate member (2);

- Distance 2 is the distance that is equal to or larger than the largest dimension of the base (10a), measured along the circumference of the elongate member (2), of the protrusions (10). This means that the distance between any two summits (10b) of protrusions (10) on the first surface area (1 1 -1 ) is equal to or larger than the largest dimension of the base (10a) of the protrusions. The largest dimension of the base (10a) of a protrusion (10) is the longest line that can be drawn from one point on the base (10a) to another point of the base (10a), along the circumference of the elongate member (2). As an example, when two square pyramidal protrusions are present adjacent to each other {i.e. no surface of the elongate member (2) is present between two neighboring protrusions), then the separation of the summits (10b) is equal to the size of the base (10a) measured along the circumference of the elongate member (2). In case two neighboring protrusions (10) have a different largest dimension of their base (10a), then these protrusions (10) are separated by a distance that is equal to or larger than the average largest dimension of the base (10a) of the two protrusions (10), measured along the circumference of the elongate member (2).

As stated above, Distance 1 is at least 5% of the circumference (9) of the elongate member (2). It may also be at least 4%, at least 3%, at least 2.5%, or at least 2% of the circumference of the elongate member (2).

In the event that the two summits (10b) of two neighboring protrusions (10) are separated by a distance that is smaller than the smaller of Distance 1 and Distance 2, then these two neighboring protrusions (10) are regarded as one single protrusion (10) - also with regard to the counting of the number of protrusions as required under point 4) hereinbelow.

A circumferential surface on the first surface part that does not contain a protrusion (10) constitutes less than 50% of the surface area of the first surface part (1 1 -1 ). By a circumferential surface is meant the surface that is present between two circumferential lines (12). This means that the first surface part (1 1 -1 ) may contain areas wherein there are no protrusions, but only to the limit that such area is a circumferential area that constitutes maximally half of the surface area of the first surface part (1 1 -1 ). The circumferential surface that does not contain a protrusion (10) may also constitute less than 45%, less than 40%, less than 35%, less than 30% or less than 25% of the surface area of the first surface part (1 1 -1 ).

The largest dimension of the base (10a) of the protrusions (10) on the first surface part (1 1 -1 ), measured along the circumference of the elongate member (2), is not more than 20% of the circumference (9) of the elongate member (2). In other words, the protrusions (10) extend over a distance in circumferential direction on the surface of the elongate member (2) that is not more than 20% of the circumference of the elongate member. This puts a limit to the maximal size of the protrusions (10) on the first surface part (1 1 -1 ). The largest dimension of the base (10a) may also be 18% or less, 16% or less, 14% or less, 12% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less or 2% or less, of the circumference (9) of the elongate member (2), measured along the circumference (9) of the elongate member (2). It is in principle possible that a protrusion is present on the first surface part of the elongated member wherein the protrusion has a largest dimension of the base (measured along the circumference of the elongate member) that exceeds the value of 20% of the circumference (9) of the elongate member (2). If protrusions of such type are present, their number is usually not higher than 50% of the number of protrusions that fulfill the requirements of a dowel of the invention, and which number is defined under point 4) below. Preferably, their number is 30% or less, more preferably it is 20% or less and even more preferably it is 10% or less. It is preferred that the number is as low as possible.

The number of protrusions (10) on the first surface part is at least thirty. The number may also be at least at least 35, at least 40, at least 45, at least 50, at least 60, at least 70, at least 80, at least 90, at least 100, at least 1 10, at least 125 or at least 150. The protrusions that are counted here, are those protrusions that fulfill the requirements of those of a dowel of the invention (as elaborated in the above points 1 ) - 3). For example, protrusions wherein the largest dimension of the base

(measured along the circumference of the elongate member) exceeds the value of 20% of the circumference (9) of the elongate member (2) are not included in the required number of protrusions of at least thirty that are present on the first surface part (1 1 -1 ).

Although dowels (1 ) with protrusions (10) or other surface reliefs are known, it was found that connections of these dowels with a panel, made by inserting the dowel into a hole of the panel, were not capable to withstand certain realistic forces that pull the dowel out of the hole. In other words, known dowels can too easily be pulled out of the hole of a wooden panel. A dowel of the invention, however, requires much more force to be pulled out of a hole of a panel. This is due to the particular spacing, distribution, size and number of the protrusions on the surface of the dowel. It was found, for example, that when the conventional circumferential grooves were interrupted for a number of times, the dowel is surprisingly much more difficult to release from a hole. This appeared especially the case when the force that is applied is not completely in line with the dowel itself, but also has a significant component in a direction perpendicular to the dowel. It also appeared that the presence of a higher number of smaller prutrusions gave an unexpected improvement of the attachment strength.

Generally, when a dowel is attached to a panel by inserting it into a hole of the panel, there is a very tight fit of the dowel into the hole. This is to generate the desired friction, which results in a good attachment to the panel. A tight fit may however hinder the initial insertion of a dowel into a hole. A known method to overcome this problem is to make the particular end(s) (3) of the elongate member (2) of a conical shape, i.e. the edges of the shape are rounded off. This allows a good alignment of the dowel with a hole, so that the initial insertion into the hole is more convenient. A dowel (1 ) of the invention preferably has ends that are of a conical shape. A dowel wherein one or both ends are provided with conical ends is shown in any of Figures 3-5 and 7-1 1 .

The first surface part (1 1 -1 ) may in principle be present on any location of the dowel's cylindrically shaped surface. It may also cover essentially its entire surface. Usually, however, the first surface part (1 1 -1 ) covers only a part of the dowel's cylindrical surface, for example 75% or less or 50% or less. In such cases, the first surface part (1 1 -1 ) containing the protrusions (10) in a manner as required by the invention, is preferably present in the proximity of an end (3) of the elongate member (2). This end will be referred to as end (3-1 ). Since the use of a dowel typically involves the attachment of each of both ends to a panel or another object, both ends of the dowel should be designed to be capable of realizing an attachment.

Therefore, the end (3-2) that is most remote from the first surface part (1 1 -1 ) is typically provided with an alternative means for fixation. Such means for fixation is for example selected from the group of 1 ) a screw thread, 2) a cap, and 3) a neck. It is understood that the situation with respect to the ends (3) may also be reversed, i.e. the first surface part (1 1 -1 ) containing the protrusions (10) may also be present in the proximity of the end (3-2), while the other end (3-1 ) is provided with the alternative means for fixation.

Thus, in a dowel of the invention, the end (3-2) may be provided with a means for fixation that is selected from the group of 1 ) screw thread (13), 2) a cap (14) having a diameter that is significantly larger than that of the elongate member (2) and 3) a local narrowing (15) so that a head (16) is formed at the second end (3-2). The head at the local narrowing can be cought by a fork, split pin or the like, to yield an attachment of the dowel to a panel.

Each of figures 3-5 shows a dowel according to the invention wherein the end (3-2) is equipped with an alternative fixation means. In figure 3, the alternative means for fixation is a screw thread, in figure 4 it is a cap and figure 5 it is a head (16) on a neck (15). In each of the figures 3-5, the first end (3-1 ) of the elongate member (2) is of a conical shape.

As already stated above, besides the protrusions that are present on the first surface part (1 1 -1 ), other protrusions may also be present on another surface part. Therefore, a second surface part (1 1 -2) may be defined on the elongate member (2) of a dowel (1 ), wherein protrusions (10) are present that meet the same requirements as those on the second surface part (1 1 -2), and wherein the requirements for arranging the protrusions (10) on the second surface part (1 1 -2) are the same as those for arranging them on the first surface part (1 1 -1 ). In addition, it is required that the first surface part (1 1 -1 ) does not overlap with the second surface part (1 1 -2).

In this way, a dowel is obtained that contains two surface parts with protrusions (10) that are arranged according to the invention. Typically, each of the two ends (3) of the elongate member (2) is in the proximity of one of the two surface parts (1 1 ), so that each end (3) of the dowel (1 ) comprises the fixation means {i.e. the arrangement of the protrusions) according to the invention and can be fixated in a hole of a panel accordingly. This is usually accomplished by locating the first surface part (1 1 -1 ) on the surface of the elongate member (2) that extends between the first end (3-1 ) and the centre point (6) and by locating the second surface part (1 1 -2) on the surface of the elongate member (2) that extends between the second end (3-2) and the centre point (6). In this way, a dowel may be provided that is essentially symmetrical, so that it does not matter which of the ends (3) is inserted into a particular part that is to be connected to another particular part.

Accordingly, a dowel (1 ) of the invention further comprises a plurality of protrusions (10) extending from a second surface part (1 1 -2) of the

elongate member's surface, which second surface part (1 1 -2) is defined as the surface that is present between a third circumferential line (12-3) and a fourth circumferential line (12-4) on the elongate member's surface, wherein 1 ) the distance between the third circumferential line (12-3) and the fourth circumferential line (12-4), measured in the direction of the longitudinal axis (5) of the elongate member (2), is not shorter than the diameter (8) of the elongate member (2);

2) the second surface part (1 1 -2) does not overlap with the first surface part

(1 1 -1 );

the protrusions (10) having

1 ) a base (10a), which is the side of the protrusions (1 0) that is adjacent to the surface of the elongate member (2);

2) a summit (10b), which is a point on the surface of the protrusions (10) that is most remote from the base (10a);

3) a height (10c), which is the shortest distance between the summit (10b) and the base (10a); wherein

1 ) the summits (1 Ob) of the protrusions (10) on the second surface part (1 1 - 2) are separated by at least a distance that is the smaller of 1 ) 5% of the circumference (9) of the elongate member (2); and 2) the largest dimension of the base (10a), measured along the circumference of the elongate member (2), of the protrusions (10);

2) a circumferential surface within the second surface part (1 1 -2) that does not contain a protrusion (10) constitutes less than 50% of the surface area of the second surface part (1 1 -2), wherein a circumferential surface is defined as the surface that is present between two circumferential lines;

3) the largest dimension of the base (10a), measured along the

circumference of the elongate member (2), of the protrusions (10) on the second surface part (1 1 -2) is not more than 20% of the circumference (9) of the elongate member (2); and

4) the number of protrusions (10) on the second surface part (1 1 -2) is at least thirty.

Figure 6 displays how the first surface part (1 1 -1 ) and a second surface part (1 1 -2) may be located on the elongate shape (2), and how these parts are defined by a third circumferential line (12-3) and a fourth

circumferential line (12-4) on the elongate member's surface.

When a dowel with a first surface part (1 1 -1 ) and a second surface part (1 1 -2) comprises directed barbs on each surface part, such barbs are preferably directed in opposite directions. This means that the barbs on either side of the centre point contain a surface of an oblique angle {i.e. oblique with respect to the elongate member's surface) that faces the most proximate end of the dowel (1 ) {i.e. those on the first surface part (1 1 -1 ) face the first end (3- 1 ) and those on the second surface part (1 1 -2) face the second end (3-2). In addition, the barbs on either side of the centre point contain a surface of a steep angle with respect to the elongate member's surface {i.e. an angle steeper than the said oblique angle) that faces the centre point (6) of the dowel (1 ).

Such dowel (1 ) is demonstrated in Figures 6-10. In addition to the protrusions on the first surface part (1 1 -1 ) and the second surface part (1 1 -2), a group of symmetrical protrusions (10) (square pyramids) is located around the centre point (6) and between the first surface part and the second surface part, wherein the first surface part comprises directed barbs in a direction that is opposite to that of the directed barbs on the second surface part. The square pyramids have an equal friction in either longitudinal direction, so it does not matter when they are inserted in one panel or the other. Figures 7- 10 display dowels having the additional square pyramidal protrusions outside the first surface part (1 1 -1 ) and the second surface part (1 1 -2).

A dowel (1 ) of the invention may comprise different types of protrusions (10). Usually, protrusions (10) of a particular type are grouped on an area of the elongate member's surface, For example, a dowel (1 ) may comprise directed barbs as well as symmetrical protrusions, wherein the directed barbs are grouped in two surface areas each of which is close to an end of the dowel, and wherein the symmetrical barbs are located in a surface area that lies in between the two surface areas with the directed barbs. This is advantageous, because in practice the centre point of the dowel (1 ) is often not present at the interface of the two parts connected by the dowel, but may be present in the hole of one of the parts at a substantial depth. This may occur when one or both holes have a depth that is substantially deeper than half the length of the dowel. If the directed barbs would also be present close to the centre point, they point into the wrong direction when the dowel is inserted more than half way into the hole.

A dowel with two different types of protrusions (10) is displayed in Figure 7. Herein, a group of symmetrical protrusions (10) (square pyramids) is located around the centre point (6) and between the first surface part (1 1 -1 ) and the second surface part (1 1 -2), wherein the first surface part (1 1 -1 ) comprises directed barbs in a direction that is opposite to that of the directed barbs on the second surface part (1 1 -2). The square pyramids have an equal friction in either longitudinal direction, so it does not matter when they are inserted in the hole of one panel or in the hole of the other panel.

Tensile-strength tests were performed to test the strength of the connection of a dowel with a panel. This is performed by measuring the maximum force that is required for pulling the dowel out of the panel. This force represents the strength of the connection of the dowel with the panel. It was surprisingly found that a dowel of the invention realizes a significantly stronger connection to a panel than a conventional wooden does.

With regard to the performance of the dowels in combination with a glue, it was found that an exceptionally strong connection is formed when a dowel of the invention is inserted into a hole that:

1 ) is in the alongside of the wood {i.e. substantially perpendicular to the direction of the fibers); and

2) contains unhardened/undried glue.

This is highly advantageous for the manufacturing of objects from separate panels (such as window-frames or door-frames), wherein:

1 ) glue is present in the connection of a dowel with a panel {i.e. the glue as well as the dowel are present in a hole in the panel); and

2) the connections between two panels are loaded directly after their

assembly and well before the glue has been hardened.

Thus, the invention makes it possible to let a newly manufactured object hang freely on a minimal number of attachments (typically in a vertical fashion), allowing immediate transport to a paint shop or a storage place, without having to wait until glue has hardened or without having to be cautious not to disturb the newly formed connection.

Another advantage manifests when glues are used that require the exertion of a continuous pressure on the connection during drying, for example because the glue tends to expand or shrink during drying and so loosens the connection. For example, for polyurethane glue (which expands due to the formation of CO ₂ ) and polyvinyl acetate) glue (which shrinks due to the loss of water), clamping during drying is normally preferred. The continuous clamping to achieve the pressure on the connection is

inconvenient, even in the case of fast-drying glues where for example a ten minutes of clamping has to be performed. A dowel of the invention, however, is capable of taking over the function of external clamps, and so provide the required continuous pressure on the connection. It is then only required to push the two parts of the connection together until the parts arrive at their desired position (typically in close contact with each other). Thus, with a dowel of the invention, it is not necessary anymore to exert a continuous pressure on the connection until the glue has dried or hardened enough. Exerting an essentially instantaneous pressure to realize the connection is then normally enough, which saves a lot of time and efforts.

In case a connection has to be made between the surfaces of two panels wherein the wooden surface of only one panel is at the alongside of the wood {i.e. substantially perpendicular to the direction of the fibers) and the wooden surface of the other panel is end grain {i.e. substantially parallel to the direction of the fibers), then the dowel is preferably first inserted into a glued hole in the end grain and given the time to harden. In the next step (in which the actual connection of two panels is realized), the dowel is inserted into the glued hole in the alongside. The resulting connection between the two panels is strong enough to be loaded directly after the assembly. This even accounts for heavy panels, for example panels having a length of up to three meters.

A dowel of the invention preferably comprises a longitudinal groove (17) parallel to the longitudinal axis. Usually, the groove (17) extends over the entire length of the dowel (1 ), i.e. from the first end to the second end. Such groove (17) has the advantage that it allows the dowel (1 ) to be compressed in a direction perpendicular to the longitudinal axis (5), because the two parts on each side of the groove (17) may be squeezed together. In this way, when the dowel (1 ) is inserted into the hole of a panel, the protrusions are pressed into the surface of the hole with an increased force as compared to the situation wherein a massive dowel of a slightly smaller diameter is present in the hole.

Figure 8 displays a dowel of the invention comprising a longitudinal groove (17). The groove (17) has a depth, which is the distance it penetrates into the dowel. Usually, the depth is in the range of 90-50% of the diameter (8) of he elongate member (2). The thickness of the groove (17) is the distance between the two parts that are separated by the groove. The thickness is dependent on the size of the plug, in particular it is 10% or less of the diameter (8) of the elongate member (2). In another embodiment, the groove may also be V-shaped, wherein the tips of the two legs of the V are at the surface of the elongate member (2).

A dowel (1 ) of the invention may comprise a ring (18), wherein the ring (18) is present around the elongate member (2) between the first end (3- 1 ) and the second end (3-2). The ring (18) has an inner diameter that is defined as the diameter of the circular hole of the ring (18). The ring has an outer diameter that is defined as the diameter of the entire object {i.e. it is the largest dimension of the ring). Figure 9 shows a dowel according to the invention wherein a ring (18) is present around the dowel.

In an assembly wherein the dowel (1 ) connects two panels, such ring

(18) is present at the interface of the two panels. It acts as a spacer between both parts, and prevents that glue that is eventually present between both parts is squeezed out of the interface, making it unavailable to strengthen the connection of the two parts.

Such ring (18) is usually connected to the elongate member (2), typically at a position on the surface that is located closest to the center point (6). Since the center point (6) not always ends up exactly at the interface of the two parts that are connected by the dowel, it is preferred that the ring (18) is capable of becoming disconnected from the elongate member when the elongate member is used to connect two parts. This means that the force that is required to disconnect the ring is smaller than the forces that are exerted to the ring (18) when the dowel comprising the ring (18) is applied in connecting two panels. A person skilled in the art will know how to connect the ring (18) to the elongate member (2) in such a way that it gets loose from it when the dowel is inserted into a hole by using e.g. a hammer or an instrument that provides a similar force.

Preferably, the ring has an inner diameter that is larger than the diameter of the elongate member plus twice the height of the protrusions. This allows the ring to slide easliy along the elongate member. Such sliding may be necessary when the ring is not initially present at the position of the elongate member (2) that ends up at the interface between the two parts that are connected by the dowel (1 ). The dowel may be provided with means that are capable of roughening the surface of the hole into which the dowel is inserted. This has the advantage that the grip of the protrusions (10) on the surface of the hole is increased. The increased friction results in a stronger fixation of the dowel in the hole.

Means for roughening (18) are for example sharp protrusions that pull some wooden pieces {e.g. fibers) from the surface of the hole when the dowel is inserted into the hole. In doing so, these pieces partially release from the surface of the hole, so that the surface becomes less smooth. Such roughening means (18) are preferably present between the first surface area (1 1 -1 ) and the first end (3-1 ); and between the second surface area (1 1 -2) and the second end (3-2); i.e. they are preferably present close to the ends of the dowel so that they travel a longer path on the surface of the hole when the dowel is inserted in the hole as compared to when the roughening means occupy a position closer to the center point (6).

Figure 10 displays a dowel (1 ) of the invention comprising means for roughening the surface of a hole into which the dowel is inserted. The means are sharp knive-like protrusions that are in an angle with the longitudinal axis (5), so that they make scratches into the surface and so roughen the surface of the hole, preferably at an angle of less than 45°.

A dowel according to the invention may be hooked. This means that the elongate member is hooked at one point of the longitudinal axis, such that the elongate member comprises two legs at a particular relative angle. This angle is less than 180°, in particular in the range of 1-179°. More in particular, the angle is 45°, 90°, or 135°. The point of the longitudinal axis where the dowel (1 ) is hooked may be the center point (6). In a symmetrical dowel, the hook is also present at this point.

In case the dowel (1 ) is hooked, the longitudinal axis (5) is also hooked. Further, the length (7) of the dowel (1 ) is defined as the distance between the first end (3-1 ) and the second end (3-2) measured along the longitudinal axis (5). Such dowel may be useful when a certain part that is to be connected by the dowel is relatively thin, i.e. too thin to accommodate for the length of the dowel (1 ) intended for insertion. By inserting the dowel (1 ) into a hole that is not normal to the surface of the respective part to be connected, the hole may be made deeper so that more protrusions (10) can be contacted with the surface of the hole.

A dowel of the invention may in principle be made from any solid material that has the required strength, not only with regard to the elongate member, but also with regard to the protrusions. The advantages of a dowel of the invention result from the particular surface properties of the surface of the elongate shape. It is therefore essential that the protrusions are accurately shaped, and that they are tough. It is possible to make a dowel of the invention from wood, but iron and pastic are preferred in view of the strength of these materials.

In case the dowel is provided with a groove (17) parallel to the longitudinal axis (5), it is required that the material of the dowel has some resilience. In such cases, plastic is a particularly preferred material.

In case the dowel (1 ) is made of plastic, the plastic may be a plastic selected from the group of acrylonitrile butadiene styrene (ABS), polyamide {e.g. nylon), polyolefin (polyethylene or polypropylene), polycarbonate, polyester and a fibre-reinforced version of any of said plastics.

An advantage of a plastic dowel as compared to a wooden dowel is that mismatches between the diameter of the hole and the diameter of the dowel are much less likely to occur with plastic dowels than with wooden dowels. This is because plastic has a much lower thermal as well as moisture expansion coefficient than wood has. For example, when a dowel after its manufacture is exposed to an atmosphere with a different humidity and/or temperature, then the diameter of the dowel may undergo a substantial change. When such dowel is applied in a connection, it may not fit well into the hole. It may be too small so that grip with the panel is lacking, or it may be too large so that it does not fit into the hole.

A dowel of the invention may in principle have any size. Usually, however, the dowel (or the elongate member (2)) has a length (7) of 250 mm or less. The length may also be 200 mm or less, 150 mm or less or 100 mm or less. The length is in particular in the range of 90-140 mm or in the range of 25-100 mm. More in particular it is in the range of 100-120 mm or 60-90 mm.

Even more in particular, the dowel has the following dimensions:

- the elongate member (2) has a length (7) in the range of 75-85 mm;

- the elongate member (2) has a diameter (8) in the range of 13-15 mm;

- the protrusions (10) on the first and the second surface part have a

height (10c) of 0.2-1 .5 mm;

- the distance between the first circumferential line (12-1 ) and the second circumferential line (12-2), measured in the direction of the longitudinal axis (5) of the elongate member (2), is at least 15 mm or at least 20 mm and at most as long as the distance between the first end (3-1 ) and the center point (6) of the elongate member (2); and

- the distance between the third circumferential line (12-3) and the fourth circumferential line (12-4), measured in the direction of the longitudinal axis (5) of the elongate member (2), is at least 15 mm or at least 20 mm and at most as long as the distance between the second (3-2) end and the center point (6) of the elongate member (2).

- the number of protrusions (10) on the first surface part (1 1 -1 ) is at least fourty.

- the number of protrusions (10) on the second surface part (1 1 -2) is at least fourty.

In another embodiment, the dowel has the following dimensions:

- the elongate member (2) has a length (7) in the range of 100-120 mm;

- the elongate member (2) has a diameter (8) in the range of 15-17 mm; - the protrusions (10) on the first and the second surface part have a

height (10c) of 0.2-1 .5 mm;

- the distance between the first circumferential line (12-1 ) and the second circumferential line (12-2), measured in the direction of the longitudinal axis (5) of the elongate member (2), is at least 20 mm and at most as long as the distance between the first end (3-1 ) and the center point (6) of the elongate member (2); and

- the distance between the third circumferential line (12-3) and the fourth circumferential line (12-4), measured in the direction of the longitudinal axis (5) of the elongate member (2), is at least 20 mm and at most as long as the distance between the second (3-2) end and the center point (6) of the elongate member (2).

- the number of protrusions (10) on the first surface part (1 1 -1 ) is at least fourty.

- the number of protrusions (10) on the second surface part (1 1 -2) is at least fourty.

A dowel of the invention may in principle be used to connect parts of any material. The dowel is particularly useful for connecting two wooden parts. By a woorden part is not only meant a section of a tree, as is usually obtained by sawing a piece of wood from a tree, but also a re-formed piece of wood that is not obtained as such from a tree. Such wood is usually obtained by processing wood pieces or word fibers and pressing them together in a particular shape, such as woodfibre board.

Accordingly, the present invention further relates to an assembly comprising a dowel as described hereinabove, and two wooden parts each comprising at least one hole suitable for receiving the dowel, wherein the first end (3-1 ) of the dowel (1 ) is in a hole of the first wooden part and the second end (3-2) of the dowel (1 ) is in a hole of the second wooden part so that both woorden parts are connected to each other. Optionally, a glue is present in the hole of one or both wooden parts, for example a glue selected from the group of polyurethane glue, polyvinyl acetate) glue and glue based on silyl modified polymers.

The invention further relates to a method for connecting two parts, preferably two wooden parts, the method comprising the use of a dowel as described hereinabove. In such method, glue may be used to connect a dowel to a wooden part. The glue may be selected from the group of

polyurethane glue, polyvinyl acetate) glue and glue based on silyl modified polymers.

A dowel (1 ) of the invention may be manufactured by conventional methods such as die casting or injection molding. It may also be prepared by 3D-printing techniques. EXAMPLES

1 . Preparation of the dowels

Dowels of the invention were made by 3D-printing of ABS or by injection molding. Figure 8 displays a dowel of the invention that was used in the tensile tests of 2.1 (3D-printed); and Figure 12 displays a dowel of the invention that was used in the tensile tests of 3.1 (injection molded). As a reference dowel, a wooden dowel with longitudinal grooves was used. All the wooden dowels tested had a diameter of 14.0 mm +/- 0.1 mm and a length of 80 mm +/- 0.5 mm. The dowels of the invention had an elongate member of a diameter of 13.5 mm +/- 0.01 mm. The diameter of the dowel including the height of the protrusions was 15 mm +/- 0.01 mm.

2.1 . Procedure for determining the strength of the connection of dowels in a wooden block in the absence of a glue.

In this procedure, the connection strength of a dowel of the invention was compared to that of a conventional wooden dowel. No glue was used.

A hole with a diameter of 14.0 mm +/- 0.01 mm and a depth of 50 mm was drilled into a wooden block (meranti). The hole was made at the longitudinal end of a block, i.e. the hole was made substantially parallel to the direction of the fibers in the wood. The hole was made in a flat surface of the wood that has a surface area of 67 mm x 1 14 mm.

The dowel was inserted over a length of 50 mm into the 50 mm hole in the wooden block, which block was then clamped in a tensile-strength tester (drawbench). During the test, the tensile tester pulled the dowel back out of the wood (in the opposite direction of inserting the dowel). The tensile- strength tester measured the maximum force that had been exterted during the pulling {i.e. the top of a graph wherein the force is measured as a function of elongation). This force represented the strength of the connection of the dowel with the wooden block. 2.2. Results

The dowel of the invention released from the wood at a force of 1200 N, while the reference dowel released at a force of 600 N. Thus, a dowel of the invention realizes a significantly stronger connection to a block than a conventional wooden dowel does.

3.1 . Procedure for determining the strength of the connection of dowels in a wooden block in the presence of a glue.

In this test, the connection strength of a dowel of the invention was compared to that of a conventional wooden dowel in three different circumstances:

1 ) in the absence of glue;

2) in the presence of a glue based on polyvinyl acetate), hereinafter

identified as "PVAC-glue";

3) in the presence of a glue based on silyl modified polymers, hereinafter identified as "SMP-glue".

Since the tensile tests with glue (circumstances 2) and 3)) aim to determine the strength of the connection when the dowel is in a hole with an unhardened or undried glue, these tests were performed before the glue had a chance to harden.

A hole with a diameter of 14.0 mm +/- 0.01 mm and a depth of 40 mm was drilled into a wooden block (either pinewood or meranti). The hole was made either at the end grain of a block (so that the hole was substantially parallel to the direction of the fibers in the wood), or at the alongside of a block (so that the hole was substantially perpendicular to the direction of the fibers in the wood). The holes were made in a flat surface of the wood that has a surface area of 65 mm x 1 15 mm.

In case a glue was used, 1 imL of glue was applied into the hole of the wood and spread over the woodsurface inside the hole. Half of the dowel (40 mm) was then inserted into the 40 mm hole of the wooden block, which block was then clamped in a tensile-strength tester (drawbench). During the test, the tensile tester pulled the dowel back out of the wood (in the opposite direction of inserting the dowel). This was performed immediately after the insertion of the dowel into the hole, so that the glue was not allowed to dry or harden. The tensile tester measured the maximum force that had been exterted during the pulling {i.e. the top of a graph wherein the force is measured as a function of elongation). This force represented the strength of the connection of the dowel with the wooden block.

3.2. Results

The forces that are required to pull out the dowels in the different test set-ups are displayed in Table 1 . This table demonstrates that the dowel of the invention creates a stronger connection with the wood than a wooden dowel does - in any of the 24 tests that were performed. It is also evident from Table 1 that an exceptionally strong connection is formed when the dowel of the invention has been inserted into a hole that is:

1 ) in the alongside of the wood {i.e. substantially perpendicular to the

direction of the fibers); and

2) contains unhardened/undried glue.

Table 1 : Overview of the release forces of the dowels.

Release force of the dowels (N)

No glue PVAc-glue SMP-glue

Comparative ; Dowel of the Comparative Dowel of the Comparative Dowel of the dowel invention dowel invention dowel invention

Meranti 310 700 590 1400 250 600 end grain

Pinewood 280 500 550 700 210 700

Meranti 300 900 600 2000 290 1100 alongside

Pinewood 290 700 550 2250 200 2000