GB2359774A

GB2359774A - Drill bit guide

Info

Publication number: GB2359774A
Application number: GB0000205A
Authority: GB
Inventors: James Patrick Titmuss
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-01-06
Filing date: 2000-01-06
Publication date: 2001-09-05
Also published as: GB0000205D0

Description

2359774 1 - DRILLING BIT APPARATUS The present invention relates to the

drilling bit apparatus and more particularly, but not exclusively to drilling of 5 recess holes.

At present, the usual method of drilling a recess in a workpiece, such as a piece of wood, is by using a spade bit (also called a flat drill bit). Figure 1 shows such a standard bit which comprises two flat blade portions 1 and 2 separated by a central prong portion 3. On commencing drilling, the spade bit is ideally applied to a workpiece (for example a piece of wood 4) such that the axis of the bit is at right angles thereto.

A downward force is applied along the central axis of the spade bit whereby the central prong portion 3 will first begin to cut into the wood 4. As the prong cuts further into the wood it acts to stabilise the bit as the blade portions 1 and 2 come into contact with the workpiece, the prong acting in this respect as a guide. In this manner the cutting direction of the bit through the wood is relatively controlled.

As shown in Figure 2, a problem associated with conventional spade bits particularly when the bit is being used in a hand held drill, is that they are unsuitable for cutting recesses extending through the workpiece at an angle other than 90 degrees (or approaching 90 degrees) to its surface. Where the recess required is other than 90 degrees to the surface, as shown in Figure 2, the corners of the blade portions 1 and 2 will tend to cut into the material before the prong 3 penetrates the material sufficiently to establish and maintain the bit's positioning. Without the stabilising effect of the prong 3, the blade portions 1 and 2 will jump around the workpiece, scuffing its surface, thereby making the production of an accurately and attractively drilled recess extremely difficult. Even where the bit is held within a fixed rig or clamping arrangement, the bit will tend to tear the material at the entrance to the recess thereby producing an unattractive finish.

Further problems encountered with current spade bits arise when, for example, cutting into a concave or uneven surface.

Again the blade portions of the spade bit can disadvantageously begin attempting to cut a recess into the material before the central prong can be established as a reliable guide to maintain the bit's position on the workpiece.

Also, when drilling a recess concentric with an existing hole, the central prong can have difficulty in maintaining the position of the spade bit. This difficulty is increased when the existing hole is large in relation to the desired recess hole and/or spade bit prong.

An object of the present invention is therefore to provide reliable positioning of a spade bit throughout drilling of a recess hole.

According to one aspect of the present invention, there is provided a guide assembly for use with a spade bit, the guide assembly comprising a guide element mountable along the longitudinal axis of the bit and projecting longitudinally beyond the cutting edges of the spade blade, the extent to which the guide element projects beyond the cutting edges of the spade blade being greater than the radial dimension of the spade blade.

In preferred embodiments, the extent to which the guide element projects beyond the cutting edges of the spade blade is greater than twice the radial dimension of the spade blade.

Conveniently, the extent to which the guide element projects beyond the cutting edges of the spade blade is at least 2.42 times greater than the radial dimension of the spade blade.

Preferably, the guide assembly is attachable to a conventional spade bit, the guide element extending beyond the point of the prong thereof. In this manner, the guide assembly acts as a convertor, converting a conventional spade bit for use in accordance with the present invention. Conveniently, the guide element is removably attachable to the conventional spade bit.

In preferred embodiments, the guide element extends in a tubular configuration in its longitudinal direction. The guide element may in this regard have a substantially constant circular cross-section.

Preferably, the guide assembly further comprises a guide insert for reception by the workpiece, the guide insert being apertured to receive the guide element and being configured externally to engage the workpiece.

Conveniently, the dimensions of the aperture of the guide insert closely match the external dimensions of the guide element.

Preferably, the external surface of the guide insert is threaded. This enables the guide insert to be accurately and securely screwed into position in the workpiece.

In preferred embodiments, an upper surface of the guide insert has a key slot, to allow a tool to be used to screw the guide insert into position. Conveniently, the key slot is configured to prevent engagement with the spade blade. In this manner the guide insert can be used to accurately establish the depth of recess to be cut, since once the spade blade cutting edges reach the upper surface of the guide insert they will be prevented from progressing further into the workpiece.

The guide element may be detachable from the spade bit to allow normal usage of the bit, but an integral spade bit/guide element may be used with pre-drilled guide holes.

Various coatings may be applied to the converter depending on specific uses, for example, Teflon (Trade Mark) may be applied to reduce frictional forces present between the predrilled material and converter.

A further embodiment of the invention may comprise an auger bit at the lower end of the guide element.

In certain preferred embodiments, the guide element has a slot for accepting the spade bit. The slot may have a flat stop which specifically limits the degree of insertion of the spade bit, or may extend along the guide element sufficiently to allow insertion of the spade bit at variable lengths. The guide element may be secured to the spade bit by a simple bolt arrangement passing through both the guide element and the spade bit, or for example by projections on the guide element which latch over upper shoulders of the spade bit to clip or snap the guide element in place.

The slot in the guide element can be formed by various means 35 and may for example comprise solid side bars, hinged bars, or detachable bars. The guide element may be attached at either the spade, prong or shaft of the spade bit using various attachment methods.

According to a second aspect of the present invention there is provided a wood working aid for use in association with a spade bit, the aid comprising a tubular member adapted to be carried by the spade bit for rotation coaxially therewith, and extending beyond a prong of the bit, the tubular member being radially dimensioned to rotate within a similarly radially dimensioned aperture provided in a workpiece.

Examples of the present invention will now be described with reference to the accompanying drawings, in which:

Figures 1 and 2 show a known spade bit; Figure 3A shows a spade bit attached to a guide element of a first embodiment from a front view; Figure 3B shows a side view of the first embodiment of Figure 3A; Figure 4A shows a spade bit attached to a guide element of a 25 second embodiment; Figure 4B shows a side view of the second embodiment of Figure 4A; Figure 4C shows the plan view from above of the second embodiment of Figure 4A; Figure 5 shows further embodiments of the present invention; Figure 6 shows a guide element and a guide insert arrangement of a further embodiment of the present invention; and Figure 7 shows the guide insert shown in Figure 6 in greater detail.

Referring now to Figure 3A, there is shown a standard spade bit 20 having spade cutting edges 1 and 2 and a prong 3.

A guide element 10 of the present invention takes the form of 10 a tubular member which is slotted at slot 11 to accept the spade bit.

The slot is configured to accept the prong 3 of the spade bit 20 and a certain amount of the spade blade itself. A pin 12, or equivalent fixing mechanism e.g. grub screw, bolt securely fastens the spade bit to the guide element 10. Figure 3B shows the above embodiment from a side on view.

The insertion of the pin 12 in the above arrangement secures the guide element converter to the spade bit to provide stability when drilling a recess hole. It may be advantageous in providing an improved connection between the spade bit 20 and guide element 10 to use additional pins in vertical alignment.

In an alternative method of attaching the guide element 10 to the spade bit 20 (Figures 4A, 4B and 4C), the guide element is slid upwards towards the shaft of the spade bit, passing over the said spade bit to releasably attach by means of projections or flanges 14 which clip over the shoulders of the spade bit blade.

In the above embodiments of the invention, attaching the guide element securely to the spade bit allows the guide element to be retrieved easily from a cut hole and ensures - 7 that the spade bit is guided accurately into position onto and through the material to be drilled.

As shown in Figure 5, different sized guide elements can be used to cater for different sized guide holes and/or different sized spade bits (e.g. a guide element used in an existing hole of 10 mm may be able to cater for spade bits in the range of 15 mm to 32 mm).

Further, as shown in Figure 6 a guide insert or nut 30 may be used to guide the spade bit 1 into position to drill larger recess holes, where particularly an oversize guide hole already exists. In this manner different sized guide nuts may be used to allow use of a single guide element for different sized guide holes 31,32. The guide nut 30 is apertured and has an external configuration adapted for securing it within a recess. In the example shown in Figure 7 the guide nut is threaded 33 so that it can be screwed into a recess to the required drill depth thereby specifying the depth of the recess hole.

It may be advantageous if the guide nut 30 has a reversed thread 33 to ensure that the guide nut is not inappropriately screwed deeper into the guide hole by friction with the spade blade. The guide nut may also possess screw slots 35 extending partially across the upwardly facing end for extraction and insertion of the guide nut 30 into and out of the guide hole.

The guide nut 30 may thus be extracted via a screw driver. Alternatively, the slots 35 may extend across the entire diameter of the upwardly extending end of the guide nut 8 in order to facilitate removal of the guide nut via the spade bit. However, this may lead to damage of the spade bit.

8 - The guide elements may be formed of various diameters adapted for different sized spade bits and to drill different diametered holes.

The guide assembly components need to be formed of materials of suitable hardness and durability, and remain substantially unaffected by working temperatures. For this reason, metals and metal alloys are considered suitable as well as certain composite materials.

9

Claims

1. A guide assembly for use with a spade bit, the guide assembly comprising a guide element mountable along the longitudinal axis of the bit and projecting longitudinally beyond the cutting edges of the spade blade, the extent to which the guide element projects beyond the cutting edges of the spade blade being greater than the radial dimension of the spade blade.

2. A guide assembly according to claim 1, wherein the extent to which the guide element projects beyond the cutting edges of the spade blade is greater than twice the radial dimension of the spade blade.

3. A guide assembly according to claim 1 or 2, wherein the guide assembly is attachable to a conventional spade bit, the guide element extending beyond the point of the prong thereof.

4. A guide assembly according to claim 3, wherein the guide element is removably attachable to the conventional spade bit.

5. A guide assembly according to any preceding claim, wherein the guide element extends in a tubular configuration in its longitudinal direction of substantially constant circular cross-section.

6. A guide assembly according to any preceding claim, wherein the guide assembly further comprises a guide insert for reception by the workpiece, the guide insert being apertured to receive the guide element and being configured 35 externally to engage the workpiece.

7. A guide assembly according to claim 6, wherein the dimensions of the aperture of the guide insert closely match the external dimensions of the guide element.

8. A guide assembly according to claim 6 or 7, wherein the external surface of the guide insert is threaded.

9. A guide assembly according to any one of claims 6, 7 or 8, wherein an upper surface of the guide insert has a key slot configured to prevent engagement with the spade blade.

10. A guide assembly according to any preceding claim, wherein the guide element has a slot for accepting the spade bit.

11. A wood working aid for use in association with a spade bit, the aid comprising a tubular member adapted to be carried by the spade bit for rotation coaxially therewith, and extending beyond a prong of the bit, the tubular member being radially dimensioned to rotate within a similarly radially dimensioned aperture provided in a workpiece.

12. A guide assembly substantially as hereinbefore described with reference to the accompanying drawings.