DESCRIPTION

The present invention relates to a milling tool with improved profile for angularly rounding the edges of panels according to the preamble of the main claim.

More particularly, the milling tool in question is intended to perform an angular joining and rounding operation on the corners of the edges of the panels so as to join together continuously the mutually perpendicular sides of the said panels.

In the wood processing industry, in particular in the furniture industry, the panels are usually finished by applying strips which form the edges of the panels and which are then machined so as to round their corners with the desired profiles.

For this purpose, machines for angularly rounding the edges of panels, referred to below as "edging machines", have been introduced onto the market, said machines being able to perform automatically complete rounding of the edges once mounted. The tool according to the present invention is therefore intended to be advantageously used on these edging machines, namely on panel edging machines, which may also be very complex, being equipped with various workstations arranged in series and comprising for example an end-butting unit, milling unit, levelling unit, gluing unit, trimming unit, edging unit or other units. Automatic machines are known in the market where a milling tool is able to follow the panels during their displacement between an entry gate and an exit gate and perform the angular rounding also of the corners which are associated with the two end sides of the advancing panels.

For this purpose, the edging tools have a curved circular profile with a radius of curvature equal to the thickness of the edge so as to join together correctly the two 90- degree sides of the panel, one of which is the top or bottom side and the other one a lateral or end side.

Thus, for example in order to performing joining on a panel with a mounted edge which is 2 mm thick a milling cutter with a radius of curvature of 2 mm is used. The ends of the curved profile of the milling cutter are provided with clearances inclined usually at an angle of 5-15 degrees and preferably 10 degrees so as to allow the tool to mill the edge of the panel without the risk of scoring its surfaces and ruining them.

As is known, depending on the specific application (for example the type of furniture), the thickness of the edges to be applied to the panels to be rounded may vary usually from 0.4 mm to 3 mm.

For example, the patent US 2003/106613 discloses a milling tool 1 for angularly rounding the edges of panels, which is provided with a substantially disc-shaped body centrally fixed to a rotating spindle and having a peripheral profile provided with inclined portions for the milling tool clearance. Several milling blades arranged at regular intervals are mounted on the peripheral profile of the support body, along the circumference of said peripheral profile.

The simpler edging machines are equipped with the possibility of displacing the milling tool along an adjusting axis so as to allow the tangency with at least one side of the panel to be maintained upon variation in the thickness of the edge which is applied. The other sides of the panel is, however, no longer correctly joined to the edge, with the drawback that a discontinuous line is visible, this not being appreciated by the market from an aesthetic point of view.

More sophisticated edging machines are also known on the market where it is possible to displace the milling tool along two mutually perpendicular axes. By means of these adjustments it is possible to centre a milling cutter with a larger radius of curvature on a smaller thickness edge so as to reduce the discontinuity at the connection points between the two surfaces to be joined together. This solution is however not optimal since the rounded joint of the edge nevertheless has, albeit in a less obvious manner compared to the case described above, discontinuous lines which are not appreciated by the market.

In order to overcome these drawbacks, milling tools provided with multiple profiles having different radii of curvature have been developed. The latter are mounted on edging machines provided with two mutually perpendicular adjusting axes. In order to round the edges of panels of different thickness it is sufficient to centre the profile with the corresponding radius of curvature by displacing the tool along the two adjusting axes.

The aforementioned design of milling tool solves in fact the drawbacks of the solutions previously mentioned but in turn has the drawback that it is particularly costly and therefore can only be used for machining panels which are intended to form high- quality articles.

In this situation the problem forming the basis of the present invention is therefore to overcome the drawbacks of the known solutions by providing a milling tool with improved profile for angularly rounding the edges of panels, able to round in an optimum manner the corners of the edges of the panels of different thickness without discontinuous lines being visible at the points where the sides of each panel are connected together.

Another object of the present invention is to provide a milling tool which can be produced at a low cost.

A further object of the present invention is to provide a milling tool which is constructionally simple and operationally entirely reliable. The technical features of the invention, in accordance with the abovementioned objects, may be clearly determined from the contents of the accompanying claims and the advantages thereof will emerge more clearly from the detailed description which follows, with reference to the accompanying drawings which illustrate a purely exemplary and non-limiting embodiment thereof, where:

- Figure 1 shows in schematic form a side view of a machine for angularly rounding panels, provided with a milling tool according to the present invention;

- Figure 2 is a geometric drawing of the profile of the milling tool shown in a cross- sectional side view performed along a central diametral plane;

- Figures 3 A and 3B show in schematic form two diametrally sectioned views of an example of a milling tool according to the invention, Figure 3A showing only the contour of the milling cutter and Figure 3B showing the milling tool in cross-section adjacent to a panel portion.

- Figures 4A and 4B show an enlarged profile of an example of a milling tool according to the invention, associated with two different-thickness edges of respective panels.

With reference to the accompanying drawings 1 denotes overall a milling tool with improved profile for angularly rounding the edges of panels, according to the invention.

The edges B are applied, in a manner which is per se entirely conventional, to the periphery of the panels P by means of an intervening layer of glue which a dispensing device removes from a containing tank.

The glue is generally of the heat-meltable (EVA) type with a heat-reversible reaction, or of the polyurethane type, with a non heat-reversible reaction.

The milling tool 1 in question may be used on a dedicated edging machine or may be provided on more complex edging machines for edging panels, where the edging machine forms an operating unit in series with other operating units such as an end- butting unit, a milling unit, a levelling unit, a gluing unit, a trimming unit or other units.

In the accompanying example, 2 denotes an example of a dedicated edging machine, it being understood that the milling tool may be used on any machine for rounding the edges of panels without thereby departing from the scope of protection of the present patent.

Thus, for example, the milling tool 1 may be mounted on an edging machine intended to round the corners of the front and rear edges of panels as described in patent application IT PD2005A000120, in particular from page 5, line 17, to page 10, line 20, which are regarded as being included in the present patent and are specifically referred to.

The machine 2, shown in the accompanying figures, has in an entirely conventional manner, means for feeding the panels P, in particular made of chipboard, MDF or the like (not shown). These means usually for example consist of a track-type conveyor belt which is able to feed the panels P individually in a horizontal position, in succession with each other, between an entry gate and an exit gate of the edging machine 2.

The support structure of the machine 2 is also provided with a milling unit 3 which has a motor 4 having, keyed onto its rotating spindle 5, the milling tool 1 according to the present invention.

In greater detail, the milling tool 1 is provided with a steel support body 6, with a substantially disc-shaped form, fixed centrally to the rotating spindle 5.

The outer perimeter of the support body 6 has, formed therein, a peripheral profile 7 with a curved form having its concavity directed towards the front so as to receive, in a position parallel to the axis of rotation X of the milling tool 1, a panel P to be milled on a corner A of its edge B.

In operational terms, the milling tool 1 rotates about its axis of rotation X, perpendicular to the direction of feeding Y of the panels P, and intercepts the latter at a corner A of the edge B so as to perform rounding thereof.

In accordance with the present invention, the milling tool 1 is intended to mill panels P having an edge B with a thickness varying between a first thickness SI and a second thickness S2 greater than the first thickness.

The peripheral profile 7 is provided at its end, in a manner entirely usual per se, with inclined portions 8 for the clearance of the milling tool 1. Advantageously, the inclination is in the region of 10° and allows the tool to have a certain machining tolerance so that it does not score and damage the sides F of the panel P.

According to the idea forming the basis of the present invention the peripheral profile 7 is shaped so as to define, in a symmetrical diametral cross-sectional plane, a curve formed by:

- at least one curved central portion 70 having substantially a first radius of curvature Rl lying between the first and second thicknesses SI and S2;

- at least two lateral portions 700, which are also curved and connected continuously to said central portion 70 and each provided substantially with at least one second radius of curvature R2 greater than the first and second thicknesses, SI and S2.

In accordance with a preferred embodiment of the present invention, the lateral portions 700 are formed by arcs of a circumference which are substantially tangentially connected to the central portion 70.

Advantageously, the three portions are formed by arcs of circumferences with their centres at CI (central portion) and C2 (lateral portions), it being understood, however, that they may be similarly formed by curves which also differ slightly from perfect arcs of a circumference, while it is still possible to interpret them as having a mean radius of curvature which may be referred to.

Advantageously, the peripheral profile 7 is symmetrical with respect a radius bisecting its subtended angle, with therefore the two lateral portions 700 identical to each other. The centre CI of the radius of curvature Rl of the central portion 70 therefore lies on this bisecting radius, while the two centres C2 of the radius of curvature R2 of the two lateral portions 700 lie with mirror symmetry relative to the bisecting radius, namely equally spaced from the bisecting radius.

Preferably, the range of thicknesses of the edge B of the panel P in which the milling tool 1 is able to operate will lie within 2 mm, since in the case of panels with edges of widely varying thickness the tool 1 must be replaced with another tool 1 having a different peripheral profile 7.

In greater detail, it is possible to envisage for example a milling tool 1 which is able to operate with thicknesses of the edges B to be rounded at the corners in order to join the sides F of the panels P, within the range of SI = 1 mm and S2 = 2 mm, namely it is possible to envisage a milling tool 1 able to operate with thicknesses of edges B in the range of SI = 2 mm and S2 = 3 mm.

With panels P having edges B with a thickness substantially equal to the greater thickness S2 envisaged, the central portion 70 of the peripheral profile 7 defines a projecting convexity 9 with respect to the ideal arc of curvature 9' which would be defined by a perfectly circular rounded line.

This projecting convexity 9 is widened so as to be oriented in the direction of the tangent to the perpendicular sides F of the panel P to be joined together, by means of the lateral portions 700 of the peripheral profile 7.

Differently, in the case of panels P having edges B with a thickness substantially equal to the smaller thickness SI envisaged, the central portion 70 of the peripheral profile 7 defines a flattened convexity 10 with respect to the ideal arc of curvature 10' which would be defined by a perfectly circular rounded line.

This flattened convexity 10 is widened so as to be oriented in the direction of the tangent to the perpendicular sides F of the panel P to be joined together, by means of the lateral portions 700 of the peripheral profile 7.

It is however possible that, for the minimum thicknesses envisaged, the central portion 70 may extend substantially so as to join together the two perpendicular sides of the panel P without having to use for this purpose the lateral portions 700 of the peripheral profile 7, which act as inclined portions for the clearance of the milling tool.

Preferably, however, the circle arcs connected to form the peripheral profile 7 are three in number.

Advantageously, it has been possible to establish during tests that there is a surprising optical joining effect between the surfaces of the sides F of the panels with edges having a thickness of between SI— 1 mm and S2 = 2 mm with Rl = 1.3 mm and R2 = 3.5 mm; and between the surfaces of panels with edges having a thickness of between S 1 = 2 mm and S2 = 3 mm with Rl = 2.3 mm and R2 = 6 mm.

In order to keep the tool 1 during milling of the edges B of the panel P constantly at a precise distance from the latter, advantageously a front coupling device 20 and vertical coupling device 21 are provided, the latter being formed preferably by an idle disc which is free to rotate with its axis parallel to the axis of the tool 1.

Pneumatic actuators are provided in order to keep the two coupling devices 20 and 21 constantly pressed against the panel and thus ensure the correct working position of the milling tool 1.

In greater detail, the milling unit 3 is provided with a support 30 consisting of a plate on which a milling head 33 is mounted and which supports the tool 1 and the two coupling devices 20 and 21. The position of the milling head 33 may be adjusted in mutually perpendicular directions by displacing said head along the first and second guides 31, 32.

Operationally speaking, in the case where it is required to mill the edges B with a different thickness S, the milling head 33 must be displaced along the two guides so as to centre it with respect to the edge B with the new thickness.

Advantageously, the milling tool 1 according to the invention is simple and inexpensive to manufacture and operationally entirely reliable.

Moreover, without changing the tool and without having to use expensive multi-profile milling cutters, the milling tool allows the joining together, within certain limits, of panel edges of varying thickness, without the connection lines of the sides F of the panels P being visible.

Obviously, the present invention may also assume, during its practical realization, forms and configurations different from that illustrated above, without thereby departing from the present scope of protection.

Moreover, all the details may be replaced by technically equivalent elements and the dimensions, the forms and the materials used may be of any nature according to requirements.