Router Cutter

The present invention relates to a router cutter and particularly to a fluted router cutter.

A router cutter is often used for cutting thin material, for example, in the machining of extruded plastics or aluminium for use in the manufacture of windows and doors. A router or cutting head is typically mounted on a multi-axis computer controlled machine, which is programmed with a cutting pattern and speed. The feed rate of the cutter across a work-piece is determined by the program controlling the machine and is set according to the type of material being cut, the depth of cut, which may correspond to the thickness of material being cut, the type and size of cutter and the rotational speed of the cutter. The rotational speed of the cutter is usually limited by the speed of the motor driving the cutter, but a typical rotational speed is around 18,000 revolutions per minute (rpm).

The work-piece being cut is usually held to a bed of the machine using pneumatic clamps, which are quick to operate, and which typically grip the outer edge of the material. It is essential for the work-piece to be securely clamped. Any unintentional movement of the work-piece, be it lateral movement within the clamps or excessive vibration caused by the cutting process, can lead to a router cutter being damaged, for example, chipping of a cutting edge and damage to the work-piece.

Thin material, for example between 2mm and 4mm in thickness, can be cut using a router cutter having a pair of straight parallel flutes with respective straight and parallel cutting edges. The cutting edges are usually diametrically opposed.

However, this type of cutter has been found to be somewhat inefficient in use, and causes a considerable vibration in the work-piece. As shown in prior art Figure 4, a standard straight fluted router cutter throws up burrs on both sides of a work-piece, which usually need to be removed after machining. When machining, for example, complex multi-layered components, the removal of burrs is an extremely onerous and expensive task, which generally has to be carried out by hand.

The friction between the cutter and work-piece, caused by the combination of the cutter's rotation and lateral movement relative to the work-piece, can also cause "snagging" of the cutter and hence the feed rate is relatively slow.

The feed rate can be increased to some extent by using a spiral cutter, for example, having a pair of diametrically opposed spiral flutes, with respective spiral cutting edges. However, a problem of spiral cutters is that the friction between the cutter and work-piece, resulting from the combination of the cutter's rotation and lateral movement relative to the work-piece, causes the cutter to force the work-piece in the direction of the spiral. For example the work-piece may be lifted from the machining table if the spiral twist is upwards. Also, a burr is thrown up along the cut edge of the work-piece, which has to be removed after machining. Whenever possible, the cutter and work-piece are selected such that the burr not need be removed, for example, if the burr can be arranged to face an internal cavity of the work-piece.

When machining extrusions for plastics doors comprising two thin sections spaced by a cavity, it is known to machine both sides of the door in a single cut. The spiral cutter can be formed with two spiral twists. An upper portion twists in one direction and a lower portion twists in the other direction. This means that the burrs on both cuts are thrown up in the internal cavity of the extrusion and need not be removed. An example of this is shown in prior art Figure 5, in which a cutter having two opposed spiral twists disposed at respective ends of the cutting portion is shown cutting through a complex component. Although the burrs are thrown up inside the component, in some applications, for example, in the aerospace industry, the burrs must be removed. Furthermore, a disadvantage of this cutter in use is that the walls of the component are forced in the direction of the spiral, inwardly, in the example shown. This causes the work-piece to bend and can cause inaccurate machining and irreparable damage to thin members.

Another problem of spiral and straight fluted cutters is that the work-piece tends to vibrate at a very high resonant frequency causing a very loud noise. This makes the machining process extremely unpleasant for human beings. Ear defenders must be worn at all times to prevent deafness, and aural communication in a machining environment is not possible.

With advances in CAD design and CNC machining, there is a much greater need for cutters to be able to machine delicate and complex parts.

It is an object of the invention to provide a router cutter which is particularly suitable for cutting thin material and which reduces or substantially obviates the abovementioned problems.

According to the present invention there is provided a router cutter for producing a straight sided cut parallel with a central axis of the cutter comprising a shank portion and a cutting portion, the cutting portion having first and second flutes and respective first and second cutting edges, the first cutting edge being inclined at an angle relative to the central axis of the cutter, and the second cutting edge being inclined at a substantially equal negative angle relative to the central axis of the cutter.

The router cutter has the advantage that the inclination of the first cutting edge tends to force the work-piece in one direction, eg upwards away from the table, but the inclination of the second cutting edge tends to force the work-piece in the other direction, ie downwards onto the table. Because the angles of the cutting edges are equal and opposite, their individual effects on the work-piece are neutralised.

Furthermore, it has been found in testing that the work-piece does not tend to vibrate, with the advantage of noise levels during cutting being reduced significantly. The reduction in vibration also increases tool life, and tests to date have shown that a tool used for cutting thin plastic, for example, around 4mm thick, will continue cutting for at least four times the duration of a conventional spiral or straight fluted router cutter.

The reduction in vibration also reduces the chance of the tool "snagging" on the work- piece and hence feed rates can be increased to around double the feed rate of a conventional spiral or straight fluted router cutter.

These advantages bring associated cost reductions in machining, and in particular, reduce the amount of "down-time" for each machine, usually necessary for tool changes due to wear and damage. Also, because the tool changes are now required so

infrequently, the number of personnel engaged in changing the tools where multiple machines are employed, can be reduced.

Preferably the first and second cutting edges are substantially straight and extend substantially along the entire length of the cutting portion and are preferably continuous.

This gives the advantage that the cutter cuts evenly or with equal effect at all positions along the length of the cutting portion.

In one embodiment a portion of the distal end of the cutting portion is rounded. The cutter may be a bull-nose cutter or have any substantially curved end for producing a curved cut. This is advantageous in plunge cutting, for example, where it is undesirable to machine slots with substantially square bottoms, the corners of which act as stress raisers.

The first and second cutting edges may be inclined at an angle of between 0.5 and 6 degrees relative to the longitudinal axis of the cutter.

The first and second cutting edges may be inclined at an angle of between 1.5 and 4 degrees relative to the longitudinal axis of the cutter.

Preferably the first and second cutting edges are inclined at an angle of substantially 2 degrees to the longitudinal axis of the cutter. In initial trials of the cutter, it has been found that an inclination of 2 degrees is highly effective.

Preferably the first and second cutting edges are substantially diametrically opposed. The cutting action and weight distribution of the cutter must be balanced, and this is most easily achieved if the cutting edges are diametrically opposed.

Preferably the cutter is made from tungsten carbide, most commonly known as carbide.

Alternatively the cutter may be made from high speed steel.

The first and second cutting edges may be provided on carbide blades which are brazed to a tool steel cutting portion.

Alternatively the first and second cutting edges are provided on ceramic blades which are bonded to a tool steel cutting portion.

The first and second cutting edges may be provided on removable blades. The removable blades may be made from carbide, ceramic or may be coated with Polycrystaline Diamond.

Preferably the diameter across the first and second cutting edges describes a parallel sided tubular cut, in use.

Preferably the diameter of the cut described by the first and second cutting edges is between 4mm and 13mm. It is perceived that the router cutter could be made to cut larger than a 13mm diameter, and if necessary could include four flutes and four respective cutting edges, ie two opposed pairs of substantially oppositely inclined cutting edges. However, it has been found that the optimal and preferred arrangement is to include only two flutes and two cutting edges.

However, it is also perceived that because tool life is so greatly enhanced and feed rates can be increased so dramatically, a smaller tool can be selected for a particular task. This has the benefit that tool changes become even less frequent, because a small tool can be used for machining tight radii as well as removing large amounts of material.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1 shows a schematic side view of a first embodiment of cutter in accordance with the invention from one side;

Figure 2 shows a schematic side view of the cutter of Figure 1 from the other side;

Figure 3 shows a schematic end view of the cutter of Figure 1;

Figure 4 shows a prior art straight fluted router cutter, in use, cutting through a laminated member;

Figure 5 shows a prior art twin spiral cutter, in use, cutting through a complex component comprising three thin spaced members; and

Figure 6 shows a schematic side view of a second embodiment of cutter in accordance with the invention from one side, in use, cutting through a complex component.

Referring firstly to Figures 1 and 2, a first embodiment of cutter is indicated generally at 10. The cutter 10 includes a shank portion 12 for gripping in a rotary cutting head and a cutting portion 14. First and second flutes 16,18 are disposed on either side of the cutting portion 14 and are diametrically opposed, ie substantially 180 degrees apart. Respective first and second cutting edges or blades 20,22 are disposed at the outer edges of the flutes 16,18 at the periphery of the cutter, which are also diametrically opposed. The flutes 16,18 and cutting edges 20,22 extend the full length of the cutting portion 14.

The first and second cutting edges 20,22 are substantially straight, but unlike a typical fluted cutter in which the flutes and cutting edges are aligned with a longitudinal or central axis of the cutter, the first cutting edge 20 and first flute 16 are disposed at an angle α to a central axis 24 of the cutter and the second cutting edge 22 and second flute 18 are disposed at an equal and opposite angle, ie a negative angle -α to the central axis 24 of the cutter. The cutting edges 20,22 lie a constant distance from the central axis 24 of the cutter, ie equal to the maximum radius of the cutting portion 14 and slope into and away from the cutting direction respectively.

If the cutter is rotated in the direction indicated by the arrow A, then the first cutting edge 20 is angled towards the cutting direction as the cutting edge extends along the cutter from the shank 12 to the distal end or tip 26 of the cutting portion 14 and the cutting edge 22 is angled away from the cutting direction as the cutting edge extends

from the shank 12 to the tip 26. In the example shown, the cutting edge 20 is inclined at an angle of 2 degrees relative to the central axis of the cutter and the cutting edge 22 is inclined at an angle of -2 degrees relative to the central axis of the cutter.

In other embodiments, the cutting edges can be inclined at equal and opposite angles of between around 0.5 and 6 degrees, but 2 degrees has been found to be an optimum angle of inclination. If the angle of inclination is, for example, 6 degrees, then the cutting edges 20,22 take on a slight curve, which is necessary for the cutter 10 to produce a straight sided cut parallel with the central axis of the cutter. The cutting edges 20,22 describe a circular cylinder when the cutter 10 is rotated. The opposite inclination of the cutting edges 20,22, means that the cutting edges are closer together at one end of the cutting portion 14, than at the other end of the cutting portion 14.

An end view of the cutter 10 is shown in Figure 3. The construction of the tip 26 of the cutter is typical of that of a conventional plunge cutter. A third cutting edge 28 extends from the centre of the tip 26 and adjoins the upper end of the first cutting edge 20 and a fourth cutting edge 30 extends from the centre of the tip 26 and adjoins the upper end of the first cutting edge 22. Angled flats 34,36,38,40 provide relief around the cutting edges 28,30 which expose the cutting edges to a work-piece and provide for waste material to be thrown away from the cutting edges. Flats 38,40 back away from or slope away from the rear of the cutting edges 28,30 respectively and flats 34,36 slope downwardly in front of the cutting edges 28,30, in the direction of the arrows, thus exposing the cutting edges 28,30.

The cutting portion 14 also includes facets 42,44 behind the cutting edges, providing clearance around the cutting portion 14 in conventional manner. The facets 42,44 are inclined at the same angles α and - α as the respective preceding cutting edges.

The cutter 10 has only two flutes 16, 18 and two respective cutting edges 20, 22. This has been found in testing to be the optimum arrangement. It is envisaged that a large diameter cutter, for example, in excess of 19mm diameter may have four flutes and four respective cutting edges, but this is not desirable, because of the increased machining in manufacturing the cutter. A four flute cutter would have two substantially diametrically opposed cutting edges inclined at the angle α to the central

axis of the cutter and two further substantially diametrically opposed cutting edges inclined at the negative angle -α to the central axis of the cutter. The positive and negative angled cutting edges relative to the axis of the cutter would be alternate.

The cutter 10 is intended for use in a router, typically a computer controlled router mounted on a multi-axis machine as previously described. The shank 12 is typically held in a collet. The cutter 10 can be used as a plunge cutter, ie it can be moved vertically downwards into a work-piece, before or at the same time as being moved laterally. The first and second cutting edges 20,22 which engage and cut in the thickness of the work-piece, cut along their entire length. This is necessary for even cutting and to generate a smooth finish. The cutting action must also be balanced, that is, one side of the cutter 10 must remove the same amount of material as the other side of the cutter, assuming that the speed of rotation and feed rate is constant.

Referring now to Figure 6, a second embodiment of cutter is indicated at 50. The cutter 50 is substantially similar to the first embodiment of cutter 10, save that the distal tip of the cutter 50 terminates in a bullnose tip 52. The cutter 50 is shown cutting a complex part 54 including an base portion 56 integral with a side portion 58 and spaced first and second thin webs 60,62 cantilevered from the side portion 58. The bullnose tip 52 of the cutter 50 is cutting a slot having a rounded bottom in the base portion 56, whilst the straight cutting portion of the cutter is cutting through both the first and second webs 60,62. It can be seen that no burrs are created on either side of the webs 60,62 or on the base portion 56. This is in contrast to burrs created using conventional cutters as shown in Figures 4 and 5 of the prior art.

The bullnose tip is necessary, particularly for cutting slots in high stress applications, because sharp corners produce stress concentrations, which can lead to failure of a machined component, in use. The bullnose tip can be substantially curved or rounded in any way, although a semi-circular curve for producing a semi-circular cut is most desirable.

As previously described, it has been found in testing that the work-piece does not tend to vibrate, with the advantage that noise levels during cutting are reduced significantly. The reduction in vibration also increases tool life, and tests to date have

shown that a tool used for cutting thin plastic, for example, around 4mm thick, will continue cutting for at least four times the duration of a conventional spiral or straight fluted router cutter, with flutes parallel to the central axis of the cutter.

The reduction in vibration also reduces "snagging" on the work-piece and hence feed rates can be increased to around double the feed rate of a conventional spiral or straight fluted router cutter.

Furthermore, as the tool is moved through a work-piece, the positive and negative angles of inclination of the cutting edges neutralise the "grab" of the cutter, ie the tendency of the cutter to be drawn uncontrollably into the work-piece. This reduces the forces on the cutter and the router head and reduces wear in the bearings and tracks of a multi-axis machine.

In the manufacture of cooling fins for a computer, it can be necessary to machine a plurality of spaced thin metal layers, for example, less than lmm in thickness, disposed one-above the other, the layers being supported on only one edge. Machining of these components is extremely difficult, if not impossible, using a standard straight flute cutter, because of vibration in the work-piece caused by the cutting action. Using the cutter of the invention, this work-piece vibration is substantially eliminated, and accurate cutting of the spaced thin webs has now been found to be possible.

In further embodiments of the invention, the cutting edges or blades 20,22 are removable and replaceable. The blades 20,22 may be made from carbide, ceramic or a base material, for example, tool steel coated with polycrystaline diamond. The blades may be fitted to the cutting portion 14 in conventional manner, using screws.

It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, the elements and teachings described may be combined in whole or in part. In addition, one or more of the elements and teachings described may be omitted, at least in part, and/or combined, at least in part, with one or more of the other elements and teachings described.

Although an illustrative embodiment of the invention has been shown and described, a wide range of modification, changes and substitution is contemplated in the foregoing disclosure. In some instances, some features of the invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.