GB2185200A - Drilling tool bit - Google Patents

Abstract

A drilling tool, in particular for use as a multi-spur machine bit, for wood, plastics and similar materials is provided with a tool bit blade located in a slot in the front section of a base structure (1). Two fixing screws (19) in cross-holes (8) in the base structure are inserted through bores in the tool bit blade. <IMAGE>

Description

SPECIFICATION Drilling tool The invention relates to a drilling tool, in particular for use as a multi-spur machine bit, for wood, plastics and similar materials.

Drilling tools of this type have carbide tips soldered to a base structure, a centre point and several rough-cutters depending on application.

The life of the drilling tool therefore depends on the wear of the carbide tip. If its cutting edges are worn or chipped, the tool is unusable. It can no longer be used. Since the carbide tip was soldered to the base structure, the latter, too, is unusable. The result of this was that in large workshops and production plants, where drilling tools of this type are used a great deal, correspondingly large replacement stocks were required. This, of course, means high investment and tooling costs.

Drilling tools often have to be ordered from a central distributor, leading to long-distance transport and loss of time when the tools have to be replaced.

The present invention therefore aims at creating a drilling tool of the type mentioned above, the life of which can be extended by simple means.

According to the present invention there is provided a drilling tool for use as a multi-spur machine bit for wood, plastics and similar materials, the tool comprising a tool bit removably located in a slot in a base structure, and means for fixing the tool bit to the base structure, the fixing means comprising a locking member arranged to locate in each of two through-holes in the base structure and operatively connect with the tool bit.

By using a replaceable tool bit, tool life can be extended significantly. If the tool bit is worn it can be replaced very easily and quickly and the base structure can be re-used.

Since several bits can be stored on site without any problems, on-site replacement can be achieved without any major loss of time.

The tool bit may be fixed to the base structure by way of the fixing screw in any way desired.

The tool bit may, of course, be fixed to the base structure in a different manner. It may, for instance, be clamped by means of the screw as an alternative to positive locking by way of the bore in the tool bit.

The slot is advantageously arranged to extend through the longitudinal centre plane of the drilling tool.

To facilitate swarf removal and to achieve a positive rake angle, the tool bit may be provided with a deflection shoulder. By the provision of deflection shoulders, rake angles of 100 to 200 may be achieved.

The life of the drilling tool can be further extended and thus tooling costs lowered by designing the tool bit as a reversible bit with cutting edges both on the upper and on the lower side.

If either cutting edge is worn, the tool bit is simply turned by 1800, thereby virtually doubling tool life.

An extremely advantageous embodiment of the reversible tool bit may have laterally projecting rough-cutters for bores or chamfers for through-holes arranged on the upper and lower side, a free space being provided on either side between the two rough-cutters or chamfers respectively.

Known drilling tools with lateral rough-cutters either have the lateral tool edge straight throughout, extending parallel to the longitudinal or rotational axis of the drilling tool, or else a slight taper towards the rear. If the lateral edges of the drilling tool are parallel to the axis, a correspondingly high friction occurs during drilling, since the lateral edge reams against the wall of the bore with its entire surface. This may lead to tightness and-in extreme cases even to burning in. If the lateral edges are conical, this problem is avoided, but there is the disadvantage that the drill diameter is reduced by regrinding, making accurate drilling impossible.

By providing the free space according to the invention, i.e. a recess created by a shoulder, friction is reduced, because the lateral edges no longer contact the bore wall with their entire surface, but only with the rough-cutter section. Neither is the diameter reduced when the cutting edges are reground.

In a further embodiment of the invention, the cutting edges of the reversible bit may be different on the upper and lower side.

This provides for universal application of the tool. The upper part may, for instance, be provided with roughcutters for blind bores. If the lower part is now chamfered, the same tool may be used for through-holes as well since, owing to the omission of rough-cutters, the edges are not stripped when the tool emerges.

The tool may further be provided with bits of varying diameters. Since they are replaced simply by removing the two fixing screws, the tool is capable of universal application on site.

Embodiments of the invention resulting in further features and advantages are described below by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a side elevation of the drilling tool according to the invention; Fig. 2 is an enlarged front elevation of the drilling tool; Fig. 3 is an enlarged side elevation of a tool bit according to the invention; Fig. 4 is a section along IV-IV of Fig. 3; Fig. 5 is a plan view of the tool bit; Fig. 6 is a sectional enlargement according to X of Fig. 4; and Fig. 7 is a side elevation of another embodiment of the tool bit.

Referring to the drawings, a drilling tool is basically of a known design, and only those parts which are relevant to the invention will be described in detail below. The tool comprises a base structure 1 with a shank 2 and a drilling head 3 consisting of two quarter circles 3A and 3B arranged on diametrically opposite sides and in mirror image relative to the rotational axis 4. Between the quarter circles 3A and 3B, there is a slot 6 in the longitudinal centre plane 5 of the drilling tool.

The quarter circles 3A and 3B are further provided with threaded holes 7 and 8 respectively.

A reversible tool bit 9 is inserted into the slot 6. This reversible tool bit 9 is a narrow carbide tip with an upper side 10, a lower side 11 and two lateral edges 12 and 13. It can be seen that a cutting edge 14 is provided, on one side relative to the axis of rotation of the reversible tool bit 9, along one half of each of the upper side 10 and the lower side 11, the two cutting edges lying on diametrically opposite halves. On the other half relative to the axis of rotation 4, i.e. the half without a cutting edge 14, the upper side 10 and the lower side 11 of the bit are provided with respective horizontal deflection shoulders 15.

The upper side 10 and the lower side 11 are each further provided with a centre point 16 in the axis of rotation 4, this point having a cone angle of 60 .

The reversible tool bit 9 is provided with two bores 17 arranged in mirror formation relative to the axis of rotation 4. The bores 17 are provided with countersinking 18 on both sides, enabling countersunk screws 19 to be inserted from both sides and tightened in the threaded holes 7 or 8 respectively in the drilling head 3. In this way, the tool bit is securely but removably fixed to the tool. As cutting edges are provided both on the upper side 10 and on the lower side 11, the life of the tool bit 9 is virtually doubled.

In the enlargement of Fig. 6, the upper section of the tool bit 9 with the deflection shoulder 15 is clearly visible. The curved design results in a positive rake angle of 20 , this angle being determined the radius of curvature. In the example illustrated, this is 4 mm-5 mm.

Different radii are, of course, within the scope of the invention. The clearance angle may be 150. A cutting edge of this type achieves excellent results and perfect swarf removal.

The deflection shoulder may, of course, be of a conical or angled design, the only critical aspect being the production of a positive rake angle by a suitable necking of the tool bit in the upper region.

The tool bit 9 illustrated in Figs. 3 to 5 is designed for blind bores. For this purpose it is provided with lateral rough-cutters 20 both on the upper side 10 and on the lower side 11 of the reversible tool bit. As is best illustrated in Fig. 3, the lateral rough-cutters 20 project beyond the lateral edges 12 and 13, thus creating a free space or recess 21. As a result of this, only the rough-cutter section 20 of the lateral edges 12 or 13 is in contact with the wall of the bore during drilling.

The same applies to the embodiment of a reversible tool bit 9 for through-holes illustrated in Fig. 7. Instead of the rough-cutters 20, chamfers 22 are provided both on the upper side 10 and on the lower side 11. Here too, a free space 21 is provided between the two chamfers at the lateral edge 12 or 13 respectively.

Instead of the separate designs of the reversible tool bit 9 as illustrated in Figs. 3 and 7, the two designs may be combined in one and the same bit. In this case the upper side 10 may betequipped with the two rough-cutters 20, while the lower side 11 is provided with the chamfers 22. By this arrangement, the same bit may be used for both blind and through-holes.

Claims (14)

1. A drilling tool for use as a multi-spur machine bit for wood, plastics and similar materials, the tool comprising a tool bit removably located in a slot in a base structure, and means for fixing the tool bit to the base structure, the fixing means comprising a locking member arranged to locate in each of two through-holes in the base structure and operatively connect with the tool bit.

2. A drilling tool according to claim 1, wherein the slot extends through a longitudinal centre plane of the drilling tool.

3. A drilling tool according to claim 1 or 2, wherein the tool bit is provided with deflection shoulders extending substantially normal to the longitudinal axis of the base structure.

4. A drilling tool according to claim 3, wherein an angle of 100 to 200 is provided at the cutting edge by each deflection shoulder.

5. A drilling tool according to claim 3 or 4, wherein each deflection shoulder is of a curved design.

6. A drilling tool according to claim 5, wherein the radius of curvature is between 2 mm and 10 mm.

7. A drilling tool according to claim 6, wherein the radius of curvature is between 4 mm and 5 mm.

8. A drilling tool according to any of the preceding claims, wherein the tool bit is designed as a reversible tool bit with a cutting edge on each of an upper side and a lower side.

9. A drilling tool according to claim 8, wherein both the upper side and the lower side of the reversible tool bit are provided with laterally projecting rough-cutters for blind bores or with laterally projecting chamfers for through-holes, these rough-cutters or chamfers providing for a free space on either side of the tool bit.

10. A drilling tool according to claim 8 or 9, wherein the cutting edges of the reversible tool bit are of a different design on the upper side and the lower side.

11. A drilling tool according to any of the preceding claims, wherein each locking member comprises a screw which is inserted through a respective bore in the tool bit.

12. A drilling tool according to claim 11, wherein each of the bores in the tool bit is countersunk on each side thereof.

13. A drilling tool substantially as hereinbefore described with reference to the accompanying drawings.

14. Any novel subject matter or combination including novel subject matter herein disclosed in the foregoing Specification or Claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding claims.