WO2004002688A1

WO2004002688A1 - Chisel

Info

Publication number: WO2004002688A1
Application number: PCT/GB2003/002776
Authority: WO
Inventors: Stephen John Hall; Arthur Priest
Original assignee: Irwin Industrial Tool Company Limited
Priority date: 2002-07-01
Filing date: 2003-06-30
Publication date: 2004-01-08
Also published as: GB0215149D0; EP1551598A1; AU2003251136A1; GB2390320A

Abstract

A chisel (1) has a handle (3), a shank (2) and a blade (4) retained on the end of the shank. The shank is formed of reinforced nylon. One end of the shank is moulded onto the blade, through an interference connection therebetween. On the other end of the shank is formed a spigot (7) for connection to the handle which is moulded thereon from plastics material (eg polypropylene). The blade has a plurality of undercut keys (24, 25) through which plastics material is moulded during formation of the shank. A method of constructing the chisel using a 2-stage injection moulding process is also claimed.

Description

CHISEL

This invention relates to hand tools. In particular the invention relates to chisels formed essentially of plastics material .

Chisels formed essentially of plastics are known. Such a chisel is described in Practical Wood Work Volume 33, Issue 4. The chisel is described as having an essentially plastic body bonded to a thin strip of steel.

A similar chisel is also disclosed in GB-A-1582330. A problem with such a chisel is that, like any chisel, it needs to be strong enough to withstand being struck with a mallet. Plastics material is not inherently strong and can shatter, but some plastics materials having substantial glass fibre reinforcement are now very strong. On the other hand, although much cheaper than steel, such plastics material is relatively expensive. A plastics material sold under the brand name Verton (RTM) is an example.

It is, of course, desirable with such a chisel to make its manufacture as inexpensive as possible. The primary incentive for such a design of chisel is to render it essentially disposable. It is replaced when its blade gets blunt, rather than it being resharpened more than once or twice.

Furthermore, the bond between the steel blade and the plastics may become less effective over time, especially when constantly exposed to stresses caused by chiselling action.

It is therefore the object of the present invention to provide an essentially plastics chisel which does not suffer from the aforementioned disadvantages, or at least mitigates their effect.

According to a first aspect of the invention there is provided a hand tool having a handle, a shank and a blade retained on the end of the shank, characterised in that the shank is formed of reinforced moulded plastics material, one end of which is moulded onto the blade through an interference connection therebetween, and on the other end of which is formed a spigot for connection to the handle, which is moulded thereon from plastics material

Preferably, the tool blade comprises a plurality of undercut keys through which plastics material is moulded during formation of the shank. The keys may each comprise a dovetailed aperture through the tool blade.

Preferably, the shank is formed of a shatter resistant plastics material, for example, a glass filled reinforced nylon. Verton (RTM) is suitable.

The handle may be formed from an inexpensive material such as polypropylene.

In this respect, the present invention appreciates that strength, such as provided by glass reinforced nylon, is necessary in the shank of a chisel. The shank is necessarily relatively thin and flat to accommodate the job it has to perform. On the other hand, the material of the handle does not have to have the same strength, because it can be given bulk. Consequently, relatively inexpensive and common materials such as polypropylene are suitable for the handle. The tool blade may be formed of steel . Where the tool is a chisel having a bevelled front face, the plastics material of the shank preferably extends to said bevelled face. In this event, an inset step is preferably provided in the plastics material in said front face where the plastic material meets the tool blade. This prevents the plastics material of the shank at its connection with the steel forming a feathered edge, which chips of wood can prise apart when the chisel is in use. Instead, the line of connection is in the base of the inset step, and is therefore not in the line of splinters that may be travelling up the bevelled front face while the chisel is in use. In any event, that connection is supported by more bulk of plastics material above the step, and therefore tendency for the plastics to be prised away from the steel is resisted.

In a second aspect, the present invention provides a method of constructing a hand tool as defined above, wherein a strip of steel is stamped to form said tool blade which is then positioned in a mould in which is injected reinforced plastics to form said shank, the shank then itself being positioned in a further mould into which plastics material is injected to form said handle on the spigot of the shank.

Preferably, said keys are formed in the same stamping operation that separates the tool blade from said strip.

An embodiment of a chisel assembly and its components, in accordance with the invention, is now described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a chisel in accordance with the the present invention;

Figure 2 is a side view, partly in section, of the shank of the chisel of Figure 1;

Figure 3 is a side view, partly in section, of the handle of the chisel of Figure 1; and

Figures 4 a and b are a side view and a top view of the blade of the chisel of Figure 1.

In Figure 1, a chisel is indicated generally at 1. The chisel 1 comprises a shank 2, having connected thereto at one end, a handle 3, and at the other end, a blade 4.

Referring to Figure 2, the shank 2 comprises a body member 5 having a top surface 29 and a base 11. The body member 5 has an integral collar 6 which comprises a face 8 extending from one end thereof . A spigot 7 , extends from, and is integral with, face 8. The distal end of the shank 2 is provided with an inclined leading face 9 having an edge 10.

At the distal end of the base 11 of the body member 5, there is a recess 12 that receives the balde 4.

Referring now to Figure 3, the handle 3 has an end face 14. An aperture 15 extends from the centre of the face 14 into the handle 3 and receives the spigot 7.

The handle has an upper surface 16 and a lower surface 17, each of which is provided with a friction panel 18 and 18' respectively, to aid gripping of the device by a user (not shown) . The handle is of size and shape suitable for gripping by a user.

Referring to Figures 4 a and b, the blade 4 comprises a body section 19 and an inclined blade face 20 having a knife-edge 21. The body section comprises an upper face 22 and a lower face 23. The upper surface has a plurality of hollow projections 24 extending therefrom. A bore 25 extends downwardly through each projection, ending at an opening 26 on the lower face 23. Each of the bores 25 is hour-glass in shape.

The shank 2 is moulded with the blade 4 positioned within the mould. The plastics material of the shank 2 flows into each of the bores 25 forming keys 13. The shape of the bores 25 ensures that the plastics material within the bore secures the blade to the shank.

As illustrated in Figure 5, the blade 4 is of greater length than the recess 12. The blade projects past the front face of the shank. The top surface of the recess 12 abuts the upper face 22 of the blade. This forms a step 10 between the inclined blade face 20 and the shank 2. The step prevents feathering of the shank plastic, and potential damage to the plastics as a result of wood chips being driven between the shank 2 and blade 4 when the chisel is used.

The handle 2 is constructed from moulded plastics material and is over-moulded on the blade and shank assembly shown in Figure 2. Indeed, the shank spigot 7 has ribs 7a, b that provide an undercut to help key the shank in the handle and prevent the handle from detaching from the shank.

The shank 2 is constructed from moulded shatter resistant plastics material, preferably of glass or carbon fibre filled reinforced nylon, containing long fibre-lengths

(of the order of 5 mm strands) . A suitable material is marketed under the brand Verton (RTM) . The blade 4 is necessarily made of quality steel, so that the knife-edge 21 remains sharp for a reasonable working life. Stamping the blades from steel strip allows the blade to be produced quickly and cheaply, and for the projections 24 to be formed in the same operation as the separation of the blade from the strip. It is feasible to form the sharp face 20 before the blade is assembled into the shank mould, but it is preferred that the blade is formed symetrically so that it does not matter what orientation it has with respect to the mould on insertion. However, sufficient blade length needs to be left so that the face 20 can be ground afterwards while connected to the shank 2 and so that the face 20 is parallel the face 9 of the shank.

The present invention therefore achieves the best possible compromise between strength and reliability, on the one hand, and inexpensiveness and disposability, on the other. This compromise is achieved by virtue of the combined effect of a composite structure of the chisel (a common plastics handle, shatter-resistant plastics blade shank and moulded on blade tip) , and the reliable connection of the blade tip to the shank. The arrangement is strong and reliable enough to last through one or two blade sharpenings following normal use, while inexpensive enough to dispose of thereafter and be replaced by a new chisel .

Claims

1. A chisel having a handle, a shank and a blade retained on the end of the shank, characterised in that the shank is formed of reinforced moulded plastics material, one end of which is moulded onto the blade through an interference connection therebetween, and on the other end of which is formed a spigot for connection to the handle which is moulded thereon from plastics material.

2. A chisel according to claim 1, wherein the tool blade comprises a plurality of undercut keys through which plastics material is moulded during formation of the shank.

3. A chisel according to claim 2, wherein the keys each comprise a dovetailed aperture through the tool blade.

4. A chisel according to any preceding claim, wherein shank is formed of a shatter resistant plastics material .

5. A chisel according to claim 4, wherein the shatter resistant material is a glass filled reinforced nylon.

6. A chisel according to any preceding claim, wherein the handle is formed from a polypropylene material .

7. A chisel according to any preceding claim having a bevelled front face, and wherein the plastics material of the shank extends to said bevelled face, an inset step being provided in the plastics material in said front face where the plastic material meets the blade.

8. A chisel having a handle, a shank and a blade retained on the end of the shank, characterised in that the shank is formed of reinforced moulded plastics material, one end of which is moulded onto the blade through an interference connection therebetween, and on the other end of which is formed a spigot for connection to the handle which is moulded thereon from plastics material, the chisel having a bevelled front face, and wherein the plastics material of the shank extends to said bevelled face, an inset step being provided in the plastics material in said front face where the plastic material meets the blade.

9. A chisel according to any preceding claim, wherein the blade is formed of steel .

10. A method of constructing a chisel as claimed in claim 9, wherein a strip of steel is stamped to form said blade which is then positioned in a mould in which is injected reinforced plastics to form said shank which is then itself positioned in a further mould into which plastics material is injected to form said handle on the spigot of the shank.

11. A method as claimed in claim 10 when dependent on claim 2, wherein said keys are formed in the same stamping operation that separates the tool blade from said strip.

12. A chisel, substantially as hereinbefore described with reference to the accompanying drawings.