GB2393676A

GB2393676A - Bit attachment adapted to create a countersink chamfer

Info

Publication number: GB2393676A
Application number: GB0222773A
Authority: GB
Inventors: James Philip Turner
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-10-02
Filing date: 2002-10-02
Publication date: 2004-04-07
Also published as: GB0222773D0

Abstract

A bit attachment adapted to create a countersink chamfer in conjunction with a drill bit, comprises an at least partially split shank portion 1 having an internal longitudinal channel 5 along its length to receive a drill bit, and a countersink head 2 at a distal end shaped to cut a countersink chamfer. Preferably the bit attachment is received and retained within a conventional chuck 12 of a drill, without the need for a separate locking mechanism. The drill bit may be slid within the channel provided in the shank portion of the attachment so that a desired length of the bit projects beyond the countersink cutting head. The shank portion of the attachment may be provided in two or more distinct parts, which may be bound together into a single unit by a suitably flexible resilient material.

Description

1 2393676

COUNTERSINK BIT ASSEMBLY

The invention relates to a machine tool taking the form of a countersink bit 5 assembly for use with a drill bit to provide for the formation of a countersink chamfer simultaneously with the milling of a hole.

It has long been desirable, particularly but not exclusively in relation to wood working, to drill a hole into a work piece to receive a fixing such as a screw, 10 and to drill a countersink (that is a frustoconical chamfer) at or about the surface of the hole to receive a countersink head of a fixing such as a screw.

At its simplest, this operation can be carried out in two stages. The primary hole is first drilled within the work piece by a primary drilling bit, and a 15 second operation follows in which the countersink chamfer is formed by a suitable cutting member having a suitably shaped, for example frustoconical, cutting edge.

It is also known in the art to combine the two operations into a single 20 operation by providing a single drill and countersink assembly, comprising a primary drill bit adding an edge to the cylindrical hole and a countersink bit to cut the frustoconical chamfer. Such bits are necessarily more complex, requiring as they do three cutting surfaces performing different purposes: a drill tip at a distal end of the primary bit to start the hole; an elongate 25 cylindrical shank having fluted cutting blades to effect cutting of a deep cylindrical hole; and a frustoconical countersink cutting portion at a proximal end of the bit.

( Such tools are specific to the given application. They are useful only with wood and like substrates where a countersink is required. The respective sizes of drilled hole and countersink chamfer are fixed. Such tools are suitable for specialist machine tool users, but in practice in a domestic situation, for 5 example for a do it yourself enthusiast, more flexibility is required. In practice, the enthusiastic amateur is likely to have a set of bits which are used both for wood and for other substrates, and will consequently desire a solution where in the first case a countersink facility can be provided, but in the second case it can be omitted.

Accordingly, it has been suggested in the prior art, for example in US

5482410, that a separable countersink cutting member can be provided in adjustable association with a drill bit. The countersink cutting member has a frustoconical cutting surface to cut a countersink chamfer, and an annular 15 body with an actual aperture into which a drill bit can be received. The length of the drill bit can be adjusted, and the assembly is fixed together by locking the countersink cutter to the drill bit using a hexagonal key lock or like locking means prior to fitment of the drill bit into a drill chuck in conventional manner. In this way, a countersink cutter can be used in association with a number of drill bits, to a number of drilling lengths and orientations, and several countersink cutters can be provided to cut countersink chamfers of different sizes. There is nevertheless still some effort involved in assembling the 25 combination.

There is a general desire to provide a simple removable countersink cutter for use with a drill bit, in particular a drill bit of conventional design, which is simple to use in applications where a countersink chamfer is desired, for

l example in wood, but which is readily removed when the drill bit is used in other substrates where a countersink is not required.

In accordance with the invention, a bit attachment adapted to create a 5 countersink chamfer in conjunction with a drill bit for milling a deep generally cylindrical hole, for example a conventional drill bit, comprises an at least partially longitudinally slit elongate shank portion having an internal longitudinal channel along the length thereof to receive a drill bit, and a countersink cutting head at a distal end thereof suitably shaped to cut a 10 countersink chamfer.

In use, the shank portion fits over the drill bit in snug engagement to surround entirely the shank of the bit. The combined assembly is received within a chuck of a conventional drill, the chuck engaging around both a proximal end 15 of the shank portion of the bit attachment in accordance with the invention, and a proximal end of a shank portion of the drill bit contained therein. The drill bit can be slid within the channel provided in the shank portion of the attachment according to the invention so that a suitable length of the bit projects beyond the countersink cutting head to drill a desired length of hole 20 before the countersink cutting head engages upon a substrate surface.

Since the shank portion of the attachment of the present invention engages wholly around a shank of the drill bit, with the combined assembly being retained directly into a drill chuck, attachment is via a simple operation, taking 25 place automatically as the combined assembly is loaded into the chuck. No separate locking mechanism is required. No separate tooling is required, for example in the form of a screw or hexagonal key, to effect such locking. The mere act of locking the assembly in place on the chuck is sufficient.

Operation is thus simpler and more convenient than with prior art systems.

( It is envisaged that one or more attachments in accordance with the invention will be provided in association with each diameter of drill bit. The attachment can be kept in conjunction with each drill bit in a tool kit, so that it is readily 5 available for optional use when the drill bit is used to cut wood or the like, and readily removable when the drill bit is used on other substrates.

The key to the present invention is the slit in the shaft portion. It is the presence of this slit that enables a drill bit to be slidingly received within the 10 receiving channel in the shank portion of the attachment, but which then enables a snug and mechanically stable engagement between the attachment and the bit lo be effected when the combined assembly is tightly retained within a drill chuck in conventional manner.

15 The shank portion can be provided with one or more longitudinal slits along a part of the length thereof, and especially a substantial part of the length thereof, in particular at the end of the shaft portion lying distal to the chuck in use. The slit shank portion is then fabricated of a suitable resilient material, especially a metallic spring material such as spring steel. As the drill chuck is 20 tightened around the slit shank portion and the shank portion of a drill bit contained there within, a snug engagement is thereby effected.

In the alternative, the shank portion of the attachment can be provided in two or more distinct parts, in effect being slit for its entire length. In this 25 alternative, for convenience, the two or more distinct parts are preferably bound together into a single unit by suitable flexibly resilient material, which might be a suitable elastomeric material, for example taking the form of one or more circumferential bindings. Again, this allows the shank of a drill bit to be slidingly engaged within the recess in the shank of the attachment, but ensures

( that a tight mechanical engagement is formed as a drill chuck tightens around the whole assembly.

The shank portion of the attachment in accordance with the invention has an 5 external shape adapted to be received within a drill chuck with which it is intended to be used. For many applications, the shank portion will have a generally cylindrical external surface. The longitudinal channel is shaped to receive a bit therein in snug engagement. Again, for many applications a cylindrical channel will be appropriate. The channel conveniently extends 10 axially along the length of the shaft portion. A corresponding channel is provided within the countersink cutting head to allow a drill bit received within the attachment according to the invention to project a suitable length therebeyond. 15 The cutting head comprises any suitable material for cutting a countersink chamfer. For example, the cutting portion maybe a suitable tool steel. The cutting portion may comprise any suitable cutting blade design such as will be known from the prior art, in particular being adapted to cut a generally

frustoconical recess within the surface of a work piece. The cutting head may 20 be fabricated of single material, optionally with a treated for example hardened surface, or may have a surface layer or layers adapted for enhanced cutting properties.

The shank portion of the attachment maybe of any suitable relatively rigid 25 material, in particular metallic material. In the embodiment where the shank is slit for only a part of its length, the material needs to exhibit a degree of resilience, and might conveniently be a spring steel.

The shank portion and the cutting head maybe fabricated from different materials having the desired properties, with the two components then being joined together in suitable manner. However, it should be appreciated that for the applications primarily envisaged for the invention material specifications

5 are unlikely to be critical. In particular, the cutting head will in many applications be adapted merely to cut a countersink chamfer in wood or other relatively easily machineable material. Accordingly, it is unlikely to be necessary to use particularly high grade cutting materials for the cutting head.

It therefore becomes practical for the shank portion and cutting head to be 10 fabricated as a one piece assembly from a single material, for example, being machined as a one piece assembly, for example from a suitable steel having adequate hardness to effect cutting, and adequate resilience to give the shank the necessary properties. The cutting surface of the head of such a one-piece unity may be treated and (or coated to increase hardness or otherwise enhance 15 cutting properties).

The invention will now be described by way of example only with reference to Figures 1 and 2 of the accompanying drawings wherein: Figure 1 is a perspective view of an attachment in accordance of the invention; 20 Figure 2 is a cross section of a drill chuck, drill bit and attachment of Figure 1 assembled and engaged together.

Referring first to Figure 1, an attachment in accordance with the invention is shown machined as a single piece steel tool. The attachment comprises a 25 shank portion (1) and a cutting head (2). The cutting head (2) has a generally frustoconical profile, and is provided with bladed portions (3) to cut a generally frustoconical chamfer within the surface of a wood or other work piece whilst drilling. The cylindrical shank portion is provided with a cylindrical bore (5) extending axially along the length of the attachment. The

( aperture extends into a similar aperture (6) provided in the cutting head (2), with the aperture providing a recess into which a drill bit can be slidingly received in use. A through thickness longitudinal slit (8) is provided.

5 In use, a drill bit of suitable size is received within the recess (5) and slid to project a suitable length beyond the cutting head (3). When the whole assembly is retained in a suitable drill chuck, the action of the drill chuck compressing the shank portion operates in conjunction with the slit (8) to ensure that the drill bit is securely gripped there within.

This is shown in cross section in Figure 2. A drill bit (10) is shown receivingly engaged within a shank portion (1) of the attachment of Figure 1, with the combination being gripped in the above described manner within a drill chuck ( 12). The arrangement is set up so that a pre-determined length (L) 15 projects beyond the cutting head (2) of the attachment. It will be seen that this length (L) can be adjusted readily for use with different work pieces. In this arrangement, a hole of depth (L) can be machined in a work piece in conventional manner, at which point the cutting head (2) will engage the surface of the work piece and cut a counter sink chamfer. Thus it can be seen 20 that an attachment in accordance with the invention is simple to use and easy to attach, exploiting the attachment mechanism already used to engage the bit and thus requiring no further tools. The attachment adapts a drill bit, which may be an entirely conventional drill bit, to allow the drilling of both a hole and countersink chamfer is a single operation. The attachment is readily 25 removed, and can thus lend itself in particular to the enthusiastic amateur who uses all purpose drilling bits both for wood and like work pieces where a countersink application is likely to be desirable and for other work pieces where a countersink application is not likely to be appropriate.

Claims

Em CLAIM.

1. A countersink hit assembly being a spilt slccvc which slates over a ttrill hit allowing; the drill hit lo Irill and counicrsmk a hole al the same tunic.

?. A countersink hit assembly as clamctt in Claim I were the ttrill hill Is not hctLt in the countcrsmk

hit Trill assembly by a scparalc locking mcchamsm olher than the chuck ol a drill