GB2092033A - Twist drill with secondary cutting tooth - Google Patents

Abstract

A twist drill (1) is provided remote from its cutting tip (2) with at least one fixed tooth (3) for counterboring and/or countersinking, having a cutting edge (4) projecting radially beyond at least one land (5) of the twist drill. The tooth is adjacent to where the lands (5) merge into a plain cylindrical shank portion (6). The (or each) tooth (3) is formed separately and bonded in a groove parallel to the drill axis and the leading edge (4) of the tooth may protrude into the flute preceding the land (5). <IMAGE>

Description

SPECIFICATION Drill bits This invention relates to drill bits, more particularly to drill bits provided with means for effecting a secondary function, e.g., counterboring and/or countersinking.

It is known from tìB-PS 594 312 to form a boring and countersinking tool having a tapered boring portion of semicircular crosssection integral with a countersinking portion of larger diameter and which is gapped by an oblique face adjacent the flat of the boring portion to form a cutting edge. The disadvantage of this tool is that it is limited to boring and countersinking wood for receiving woodscrews.

It is also known from GB-PS 594312 to provide a normal twist drill (or helically fluted drill) with a separate countersinking portion of tubular form bevelled off at an oblique face to form a cutting edge. The disadvantage of this tool is the difficulty of securing the coutersinking portion for rotation with the twist drill. It is therefore known from GB-PS 1 378 868 or GB-PS 1 378 869 (among others) to provide a twist drill with a separate assembly including cutter parts provided with cutting edges, and with means for urging the cutter parts towards each other to grip the twist drill.

The disadvantage of this assembly is that it is costly and if not secured properly on a drill it can slip and cause damage to the drill if not also to itself.

The object of the present invention is to provide a drill bit with means for effecting a secondary function in a reliable and inexpensive manner, yet capable of counterboring and/or countersinking a wide variety of materials.

According to the present invention, a twist drill is provided remote from its cutting tip with at least one fixed tooth having a cutting edge projecting radially beyond at least one land of the twist drill.

Although the invention embraces the possibility of having two (or more) fixed teeth each having a cutting edge, it is preferable to employ only one tooth as this substantially eliminates vibration or "chatter" when counterboring or countersinking hardwood, laminates, and aluminium, in particular, thus ensuring a smooth accurate finish.

The (or each) tooth is preferably disposed adjacent to where the lands of the twist drill merge into a plain cylindrical shank portion, and the (or each) tooth is preferably formed separately from the twist drill (e.g., of hardmetal such as tungsten carbide) and is bonded (e.g. brazed) into a groove in one land of the twist drill, which groove preferably extends parallel to the axis of the twist drill.

The (or each) tooth is preferably formed with a bevelled leading cutting edge, enabling it to be used for counterboring and/or countersinking, and the leading edge may protrude into the flute preceding the land. The leading cutting edge preferably has an included angle of less than 90 and an outer cutting edge substantially parallel to the axis of the twist drill preferably also has an included angle of less than 90 .

The drilling tip of the twist drill is preferably provided on a hardmetal insert (e.g. of tungsten carbide) in a slot (which is conveniently in line with the groove for the or each tooth), whereby the twist drill can serve as a multipurpose drill bit capable of being used for masonry (or brickwork) and other materials spearately or together, an example of which will be given presently after a number of embodiments of the invention have been described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an elevation of a twist drill in accordance with the invention provided with one tooth for effecting counterboring and/or countersinking; Figure 2 corresponds to Fig. 1 but shows a twist drill in accordance with the invention provided with two teeth; Figure 3 is a plan view of Fig. 1 or Fig. 2; Figures 4 and 5 correspond to parts of Figs.

1 and 3 respectively but show a twist drill in accordance with the invention with a slightly different position of the tooth; Figures 6 and 7 are enlarged fragmentary axial sections corresponding to parts of Figs.

1 and 4 respectively around the tooth; Figure 8 is an elevation of a fastener for securing a member to masonry assisted by a twist drill as in the preceding Figures; and Figures 9 to 11 are fragmentary sections of masonry and another member illustrating the use of the twist drill as aforesaid and the fastener of Fig. 8.

In Fig. 1, a twist drill 1 is provided remote from its cutting tip 2 with a fixed tooth 3 having a cutting edge 4 projecting radially beyond one land 5 of the twist drill. The tooth 3 is disposed adjacent to where the lands of the twist drill 1 merge into a plain cylindrical shank protion 6. In Fig. 2, a twist drill 1 is provided with two teeth 3 similarly to the twist drill of Fig. 1, but it is emphasised that it is preferable to employ only one tooth as this substantially eliminates vibration or "chatter" when counterboring or countersinking hardwood, laminates, and aluminium, in particular, thus ensuring a smooth accurate finish.

In Figs. 4 and 5 the tooth 3 has its leading edge 4 protruding into the flute 7 preceding the land 5.

The (or each) tooth 3 is formed separately from the twist drill (e.g., of hardmetal such as tungsten carbide) and is bonded (e.g., brazed) into a groove 8 (Fig. 6 or Fig. 7) in the land 5 and extending parallel to the axis of the twist drill 1. The (or each) tooth 3 is formed with a bevelled leading cutting edge 4, enabling it to be used for counterboring and/or countersinking, and the leading edge has an included angle of less than 90". An outer cutting edge 9 substantially parallel to the axis of the twist drill also has an included angle of less than 90".

The drilling tip 2 of the twist drill 1 is provided on a hardmetal insert 10 in a slot 11 in line with the (or each) groove 8 for the (or each) tooth 3, whereby the twist drill can serve as a multi-purpose drill bit capable of being used for masonry (or brickwork) and other materials separately or together.

In Fig. 8, a fastener 12 consists of a tubular plug 13 with a flared flange 14 at one end and ribbed fingers 15 at the other, together with a screw-nail 16 closely fitting the bore 17 of the tubular plug and urging the fingers 15 apart. To facilitate use of this fastener 12 to secure to masonry 18 (Figs. 9 to 11) a member 19 of another material (such as wood, metal or plastics, e.g., laminate), the member 19 is held in appropriate location against the masonry 18 and a hole 20 drilled through both together by the twist drill 1 (preferably that of Fig. 1 with only one tooth 3) and the member 19 is provided with a countersink 21 (preferably also slightly counterbored) by the tooth 3 before the drill 1 is withdrawn from the hole 20 (see Fig. 9). The tubular plug 13 (without the screw-nail 16) is inserted into the hole 20 until the flared flange 14 abuts the countersink 21 (see Fig.

10) and then the screw-nail 16 is driven (as with the hammer) into the tubular plug until the head 22 of the screw-nail abuts the flared flange 14 of the plug (see Fig. 1 1), and the screw-nail urges the ribbed fingers 15 apart and into firm gripping contact with the hole in the masonry 18. The head 22 of the screwnail is preferably recessed to enable it to be unscrewed, if necessary, by a suitable tool.

A pack of fasteners of the type shown in Fig. 8 may be sold complete with its own twist drill as described in any one or more of the preceding Figures, the distance between the tip 2 and the tooth (or teeth) 3 being somewhat greater than the length of the fasteners 12, but a twist drill 1 with a much greater length between the tip 2 and the tooth (or teeth) 3 may be used with a wide range of lengths of fasteners 12 and/or other types of fasteners all having the same nominal plug diameter. Indeed, a drill in accordance with the invention can be used other than for drilling and counterboring and/or countersinking holes if the distance between the tip 2 and the tooth (or teeth) 3 is adequate for the depth of hole to be drilled without bringing the tooth (or teeth) 3 into contact with the material being drilled; thus, a drill in accordance with the invention can be a useful item in any workman's or "do-it-yourself" toolbox.

The tooth 3 (or one or both teeth) can serve for engagement in a jig (not shown) affording precise location of the twist drill 1 for regrinding of the tip 2.

Claims (12)

1. A twist drill provided remote from its cutting tip with at least one fixed tooth having a cutting edge projecting radially beyond at least one land of the twist drill.

2. A twist drill as in Claim 1 wherein the tooth is disposed adjacent to where the lands of the twist drill merge into a plain cylindrical shank portion.

3. A twist drill as in Claim 1 or Claim 2, wherein the tooth is formed separately from the twist drill and is bonded into a groove in one land of the twist drill.

4. A twist drill as in Claim 3, wherein the groove extends parallel to the axis of the twist drill.

5. A twist drill as in any one of the preceding Claims, wherein the tooth is formed with a bevelled leading cutting edge.

6. A twist drill as in Claim 5, wherein the leading edge protrudes into the flute preceding the land.

7. A twist drill as in Claim 5 or Claim 6, wherein the leading edge has an included angle of less than 90".

8. A twist drill as in Claim 7, wherein an outer cutting edge substantially parallel to the axis of the twist drill also has an included angle of less than 90".

9. A twist drill as in any one of the preceding Claims, wherein the drilling tip of the twist drill is provided on a hardmetal insert in a slot.

10. A twist drill as in Claim 9 in combination with Claim 4, wherein the slot for the insert is in line with the groove for the tooth.

11. A twist drill as in any one of the preceding Claims having two such teeth as aforesaid.

12. A twist drill substantially as hereinbefore described with reference to any one or more of Figs. 1 to 7 of the accompanying drawings.