Titman, Malcolm John (7 Boley Drive Clacton-on-Sea Essex CO15 6LA, GB)
| 1. | A boring bit comprising a shank part and a cylindrical boring part, the boring part having a boring tip, a first longitudinally extending rectilinear grooved cutting channel in the surface of the boring part to form a pair of cutting edges for the boring bit, and a second longitudinally extending rectilinear grooved cutting channel in the surface of the boring part to form an additional pair of cutting edges for the boring bit. |
| 2. | A boring bit as claimed in claim 1 wherein said second grooved cutting channel is of shorter longitudinal extent than said first grooved channel, with respect to the boring tip. |
| 3. | A boring bit as claimed in claim 1 or 2 wherein the axes of the first and second cutting channels are at 180° to one another around said cylindrical boring part. |
| 4. | A boring bit as claimed in claim 3 wherein said cutting edges have cutting edge portions which lie in a common circumferential plane with the boring tip leading the cutting edge portions during a boring operation. |
| 5. | A boring bit as claimed in claim 3 wherein the bit is a lip and spur bit with said cutting edges having cutting edge portions which lie in a common circumferential plane together with the boring tip. |
| 6. | A boring bit as claimed in any preceding claim wherein the axes of the cutting channels lie parallel to one another and are concave in cross section. |
| 7. | A boring bit substantially as herein before described with reference to the drawings. |
BACKGROUND OF THE INVENTION In the furniture and related trades, rapid boring operations for blind and through holes in work pieces are performed using relatively complicated tungsten carbide tipped spiral cutters of right and left hand rotation.
The machines used to perform these boring operations are of the Morbidelli type with multi heads and gear boxes connected to slim, quick-release chucks which screw or clamp on to the sides of the shank of the boring bit being used. In some cases the machines are provided with right and left hand driven chucks.
Close hole centre work and economics of design makes linked gear boxes and counter rotating chucks a necessity and therefore the need arises to produce boring bits with right hand rotation and left hand rotation. As a result existing boring bits of the spiral cutter type which are used with all types of fumiture material, such as wood, M. D. F., plastics and chipboard, have to be colour coded to ensure that the correct bit is placed in the correct matching rotational chuck spindle.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a boring bit which eliminates the need for rotational coding and also avoids the possibility of severe production problems which occur when the wrong rotation bit is placed in the chuck spindle.
According to the present invention there is provided a boring bit comprising a shank part and a cylindrical boring part, the boring part having a boring tip, a first longitudinally extending rectilinear grooved cutting channel in the surface of the boring part to form a pair of cutting edges for the boring bit, and a second longitudinally extending rectilinear grooved cutting channel in the surface of the boring part to form an additional pair of cutting edges for the boring bit.
In a preferred embodiment one of the cutting channels is of shorter longitudinal extent with respect to the boring tip than the other cutting channel.
Advantageously the axes of the first and second cutting channels are at 180° to one another around the cylindrical boring part of the bit.
BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features of the present invention will become apparent from the following description of a preferred embodiment of the invention taken with reference to the accompanying drawings wherein: Fig. 1 (a) and (b) show perspective opposing side views of a boring bit to which the present invention has been applied; and Fig. 2 (a) and (b) shows perspective opposing side views of a different type of boring bit to which the present invention has been applied.
BEST MODES OF CARRYING THE INVENTION INTO EFFECT In Fig. 1 (a) and (b) the invention is shown applied to a boring bit 1 having a shank 2 and a cylindrical cutting or boring part 3.
The cutting part 3 has a conical boring tip 4 and a longitudinal cutting groove 5 formed in its cutting surface, see Fig. 1 (a).
In the embodiment shown, the cutting groove 5 is in the form of a rectilinear concave channel extending along the surface of the cutting part 3 to the conical tip 4 to form a pair of trailing rectilinear side cutting edges 5'and a pair of leading side cutting edges 5"which taper to meet at the conical lip 4. The trailing edges 5'and the leading edges
5"meet to form a pair of angularly spaced cutting edges 6 lying in a common circumferential plane.
On the opposing side of the cylindrical cutting part 3 see Fig. 1 (b) a further concave channel 7 is formed in the surface of the cutting part 3 of shorter longitudinal extent with respect to the boring tip 4 than the longitudinal channel 5.
The shorter length channel 7 as with the channel 5 forms two further angularly spaced cutting edges 8 on the same circumference as the two angularly spaced cutting edges 6.
In the embodiment shown in Figure 2, (a) and (b) the invention is applied to a lip and spur boring bit having a shank 2 and cutting part 3 as before, to form, as with the Figure 1 embodiment, four angularly spaced cutting edges 9 lying in a common circumferential plane together with the boring tip 4.
Although in the above preferred embodiment the channels 5, 7 formed in the surface of the cutting part 3 of the boring bits shown are opposed at 180° to one another around the surface of the cutting part 3 of the bit, this is not a limiting feature rather the invention envisages that the longitudinal channels 5, 7 in the boring bit may be at other angular dispositions and may be more than two in number.
Boring bits produced in accordance with the present invention have the following advantages: 1 Cutting occurs strongly in both rotation directions.
2 A balanced cutting load is produced which reduces the likelihood of producing an oversized hole when used in machinery with worn spindle and chuck systems.
In this connection the size of the hole to be produced is, in most cases, critical.
3 A more rigid boring bit is possible both in compression and bending, which assists with hole diameter consistency.
4 Considerably longer operational life and, if required, a regrind allowance.
5 Cleaner holes both on entry and exit are produced, due to the combined end and side cutting action. The lip and spur version is particularly good for exit holes, leaving a clean fibre-free edge eliminating the need for clean-up operations.
6 Production processes are considerably easier than with existing spiral designs and enable an extremely strong one-piece boring flute to be produced in solid tungsten carbide.
7 The need to colour code boring bits as with the prior art is eliminated.
8 For deep hole drilling, the use of two cutting channels aids swarf clearance.
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