GB2225262A

GB2225262A - Drill bit

Info

Publication number: GB2225262A
Application number: GB8827879A
Authority: GB
Inventors: Barrie Nicholson
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-29
Filing date: 1988-11-29
Publication date: 1990-05-30
Also published as: GB8827879D0

Abstract

The bit, for cutting large diameter holes e.g. in wood, comprises a shank (10) with a centre cutter (11) and a plurality of outwardly extending arms (13) which are arranged with a series of slots (14) to receive a flexible toothed blade (15) in a spiral configuration which winds outwardly in a direction opposite to the intended direction of rotation (16) of the drill bit. <IMAGE>

Description

DRILL BIT This invention relates to a drill bit.

When holes of over 25rum in diameter are required the conventional method is to use a 'hole saw' which is able to make an annular cut to produce through-holes in material. If, however a blind hole is needed in the material the remaining plug must be removed by other means. To the applicants knowledge there is not available a drill bit which is capable of cutting large diameter (up to and over 250mm) ftatbottomed blind holes in hardwood and similar materials and it is the aim of the present invention to fill this gap.

The invention provides a drill bit having a shank for mounting the bit in a chuck at one end with the other end carrying the arms which support and hold a length of band saw blade, wound in a spiral, to provide an axial end cutting face.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is an elevational view showing a drill bit according to the invention, and Figure 2 is an underneath end view of the drill bit.

There is seen in the drawings a drill bit according to the present invention. the drill bit has a shank 10, which here is of bright steel. The drill bit is mountable in the chuck of a rotary device, eg machine tool, by one end of the shank 10. At its other end, the shank 10 is provided with a centre cutter 11. Here, the centre cutter 11 is a conventional spade drill which is mounted in a slot 12 in the shank 10. The centre cutter 11 helps to centre the drill bit during cutting, as well as cutting out the centre portion. The shank 10 is also provided with a number of outwardly extending arms 13. Here, there are four such arms13, which are arranged in a cru ciform extending radially outwardly. The arms here are of bright steel and are welded to the shank 10.The arms 13 are provided with a series of slots 14.The purpose of the slots 14 is to enable a toothed blade 15 to be spirally mounted on the shank, as is seen in Fiure 2, presenting a multiplicity of cutting teeth. The blade 15 here i3 a length of conventional band saw blade. The blade 15 is spirally wound outwardly in the opposite direction to the intended direction of rotation of the drill bit, indicated by arrow 16, ie, with the outer end of the blade trailing as indicated by arrow 17. The frictional forces between the blade 15, which is resiliently flexible and the slots 14 are sufficient for there to be no need for additional fixing for the blade. Thus, an old blade 15 can simply be knocked out and a replacement blade wound and tapped into position. The maximum outer diameter of the cut is determined by the penultimate arm 13 in the spiral. This arm 13 is designated OD in Figure 2, and the blade 15 simply abuts the outer end face of the arm OD.

The drill bit is particularly suitable for cutting blind holes in hard wood and also drilling wood on the endgrain, a process that quickly bluntens conventional drills. The drill bit is preferably used in a horizontal axis of rotation, rather than vertIcally, as this helps with clearance of sawdust from the cut. The spacing between the spiral windings of the blade can be adjusted to suit different materials to be cut, as also can the type of bandsaw blade be varied appropriate to the material to be cut.

Claims

1. A drill bit having a shank mounting the bit in a chuck, and an axial end cutting face which presents a multiplicity of teeth which are arranged in a spiral configuration around the axis of rotation of the bit.

2. A drill bit as claimed in Claim 1 wherein the spiral configuration of the teeth is arranged to spiral outwardly in a direction opposite to the intended direction of the bit.

3. A drill bit as claimed in Claim 1 or Claim 2 wherein the multiplicity of teeth is provided in the form of at least one elongate toothed blade and the shank is provided with means for mounting the blade in said spiral configuration.

4. A drill bit as claimed in Claim 3 wherein the means for mounting the blade comprises a plurality of outwardly extending arms on the shank, which arms are provided with a series of slots for receiving and retaining the blade.

5. A drill bit as claimed in Claim 3 or Claim 4 wherein the blade is resiliently flexible.

6. A drill bit as claimed in any preceding claim wherein the shank additionally has means to help to centre the bit during cutting.

7. A drill bit substantially as hereinbefore described with reference to the accompanying drawings.

8. A product having a hole cut therein using a drill bit as claimed in any preceding claim.