GB2164283A - Slotting cutter and removable tip - Google Patents

Abstract

The cutter has a single cutting tip (10) secured in a seating formed at the forward end of an axially extending recess (4) in the cutter shank (2). The seating comprises a portion (13) projecting from the main forward face of the shank so that the tip is given support forwards of the shank proper. The cutting tip is reversible, with respective sets of cutting edges comprising an axially forward edge (16) and radially outer and inner edges (14,20) on each side of the forward edge, the inner edge lying at an obtuse angle to the forward edge and having a negative cutting rake. <IMAGE>

Description

SPECIFICATION Cutters and cutting tips This invention relates to routing cutters for machining slots in a workpiece.

The machining of workpieces from the solid, and in particular the provision of slots or recesses in such workpieces is common in aircraft structural components. Problems are encountered in obtaining a high rate of metal removal especially if the slotting leaves the component with thin-walled portions, possibly as little as imm thick, which also is a common requirement for aircraft components. Thus, cutting pressures can cause flexing of the thin web of material in the region of the cutting tool and there may also be undesirable burn marks produced. The high value of such components make it particularly difficult to accept the scrapping of components from these causes.

It is an object of the present invention to improve slotting operations, particularly although not necessarily exclusively in the machining of tFin- walled components.

According to one aspect of the present invention, there is provided a routing cutter for machining a slot in a workpiece, comprising a shank having an axially extending recess with a seating for a single replaceable cutting tip, said tip projecting forwardly from the shank with the portion extending past a main forward face of the shank being spaced from the central rotary axis thereof, a radially inner face of the tip providing, in a substantially radial plane of the shank, a cutting edge inclined to the shank axis, the cutting tip seating in the recess having a clamping face against which the tip is secured and said clamping face continuing into a projecting portion forming an extension from said main forward face of the shank.

According to another aspect of the invention, there is provided a replaceable cutting tip for a rotary routing cutter, said tip being arranged to be secured at a spacing from the centre of rotation of the cutter and being reversibly positionable thereon, in each of its reversible positions the cutting tip comprising a forward cutting edge disposed between inner and outer cutting edges, said inner edge lying at an obtuse angle to the forward edge and having a negative cutting rake.

The invention will be described in more detail by way of example with reference to the accompanying drawings, in which: Figures 1 and 2 are side and end views of a routing cutter according to the invention, Figures 3 to 5 are mutually transverse views of the replaceable cutting tip of the cutter of Figures 1 and 2, Figure 6 illustrates the operation of the cutter in machining a slot in a workpiece, showing both plan and sectional views, and Figures 7 to 10 illustrate further forms of routing cutter according to the invention.

The body of the cutter illustrated in Figures 1 to 6 has a shank 2 of mainly cylindrical cross-section with a right-angled recess or pocket 4 running axially along most of its length from its forward end.

A balancing recess may be provided substantially diametrically opposite the recess 4. The two faces of the pocket are perpendicular to each other but are angularly offset from the axis of the shank, as can be most clearly seen in Figure 2. At the forward end of the pocket a seating 6 is formed in the face 8 leading in the direction of rotation of the tool and the main or bottom face of the seating recess lies in a parallel plane to that face of the pocket. A replaceable insert 10 in the form of a reversible cutting tip is secured by a central screw 12 sunk into its top face to engage a tapped hole in the shank, the insert thus being held in place with its top face exposed and unobstructed.

The insert 10 projects forwards of the shank on the forward face of which an integral arcuate extension 13 is formed to give additional support for the insert. The extension 13 provides a continuation of the bottom face of the seating 6 beyond the shank proper over substantially the remaining portion of the bottom face of the insert.

The insert is reversible to provide two alternative sets of cutting edges and its profile can be regarded as a modified rhomboid, with a pair of main cutting edges 14, 16, each pair of cutting edges subtending an acute angle with each other close to 30 . In this example, the junction 18 between the two edges 14, 16 is radiussed. A feature of the insert profile is the oblique inner cutting edge 20 that extends at 45 to the axial direction almost as far as the main body of the shank.

The insert is held in the seating so that the outer cutting edge 14 lies parallel to the shank axis. The forward cutting edge 16 is thus slightly inclined rearwards to provide clearance with respect to the face it machines. The main edges 14, 16 of the insert are formed with a positive clearance angle.

The oblique inner edges 20 on the other hand, may be formed with a positive clearance angle or be perpendicular to the top face of the insert. As the seating main face is inclined both relative to the diametrical plane containing the outer cutting edge and relative to the cutter axis, the operative main cutting edges of the insert have a 5 to 9 positive axial rake and a 5 to 9 positive radial rake with respect to the shank. This results in all the cutting edges 14, 16, 18, 20 having clearance angles when the insert is secured in position.

Figure 6 illustrates the use of the insert or cutting tip in routing a slot S in a workpiece W and shows the path of movement of the tip in a series of ramps R as it reciprocates from one end of the slot to the other while being fed into the slot, the motions conveniently being automatically controlled. As the cutting tip reaches the end of one ramp and begins to reverse into the next, because there is no cutting edge near the central axis, an upstanding core "cherry" C forms underneath the rotating tip, the active inner cutting edge 20 comes into operation at this stage to remove the projecting material so that the machining of the slot proceeds continuously. It may be noted that the action of the inner cutting edge is such that it is cutting with a negative front rake.

Figures 7 to 10 show further examples of cutting tips according to the invention that are similar in most aspects to the tip already described. In the cutters of Figures 7 and 8, the inserts have no separate forward cutting edge, and in the case of Figure 7 the insert is not reversible. Figure 8 shows a circular insert which can be indexed on the axis of the securing screw 12 to bring a fresh cutting edge into operation. The examples in Figures 9 and 10 differ from the cutting tip first described in that the junction between the two main cutting edges in the one case is bevelled and in the other case consists of a small radius followed by a flat only a degree or two less than 90 from the outer edge.

It is found that the use of a single bladed router as illustrated, in which the operative cutting edges do not cut to the centre of the cutter where effective cutting speeds are low, is able to form slots very rapidly with high rates of feed and material removal without encountering the problem described above. As an example, with the active outer cutting edge at a radius of 20mm the cutter may be rotated at some 9000 to 15000 r.p.m. and be traversed at very high feed rates. The fact that the cutter operates with only a single cutting tip limits the axial cutting pressures that cause flexing of a thin workpiece, while the projection of that insert well forwards of the body of the shank and the absence of any obstruction over its top face allow adequate chip clearance at the high rates of metal removal that are achieved.

Claims (12)

1. A routing cutter for machining a slot in a workpiece, comprising a shank having an axially extending recess with a seating for a single replaceable cutting tip, said tip projecting forwardly from the shank with the portion extending past a main forward face of the shank being spaced from the central rotary axis thereof, a radially inner face of the tip providing, in a substantially radial plane of the shank, a cutting edge inclined to the shank axis, the cutting tip seating in the recess having a clamping face against which the tip is secured and said clamping face continuing into a projecting portion forming an extension from said main forward face of the shank.

2. A rotary cutter according to claim 1 wherein the clamping face defines a cutting edge plane parallel to said face in which the forward and outer cutting edges are disposed with positive radial and axial rake respectively.

3. A rotary cutter according to claim 1 wherein said shank recess has an axial length that is .3 multiple of the axial length of the cutting tip.

4. A rotary cutter according to any one of claims 1 to 3 wherein clamping means for securing the cutting tip in its seating engage the shank at least substantially wholly rearwards of said main forward face of the shank.

5. A rotary cutter according to any one of the preceding claims provided with a reversible cutting tip, and the tip seating having locating side faces for the side faces of the inoperative inner and outer cutting edges of the tip, said side faces securing the tip against angular displacement in its seating.

6. A replaceable cutting tip for a rotary routing cutter, said tip being arranged to be secured at a spacing from the centre of rotation of the cutter and being reversibly positionable thereon, in each of its reversible positions the cutting tip comprising a forward cutting edge disposed between inner and outer cutting edges, said inner edge lying at an obtuse angle to the forward edge and having a negative cutting rake.

7. A cutting tip according to claim 1 wherein the inner and outer cutting edges subtend an angle of substantially 45".

8. A cutting tip according to claim 1 or claim 2 wherein said front and outer cutting edges are formed between a top face of the tip and side faces set at an acute angle to the top face, and the inner cutting edge is formed between the top face and a side face substantially perpendicular thereto.

9. A cutting tip according to any one of claims 1 to 3 wherein a radiused cutting edge extends between and blends with the forward and outer cutting edges.

10. A cutting tip according to any one of claims 1 to 3 wherein a chamfered cutting edge extends between the forward and outer cutting edges, obliquely to both.

11. A rotary cutter constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.

12. A cutting tip constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.