This invention relates to a cutting tool.

It is known to provide a cutting tool, for example a hand chisel, in which a usually rectilinear cutting edge is driven into a workpiece in a direction perpendicular to the cutting edge. The smaller tools of this kind have not been motorized because of the difficulty of providing drive means capable of delivering an effective percussive force to the cutting edge.

It is an object of the present invention to provide a cutting tool of the kind described with power operation using currently available drive means.

According to the present invention there is provided a cutting tool having a cutting edge defined by a plurality of blades arranged in contacting side-by-side relationship, and drive means for advancing the blades in predetermined sequence.

The invention will now be further described by way of example only, with reference to the accompanying drawings, in which: -

Fig. 1 is a perspective view of one embodiment of cutting tool in accordance with the invention;

Fig. 2 is a part-sectional and cut-away view of the front end of the tool of Fig. 1, to an enlarged scale;

Fig. 3 is a central vertical section of the tool;

Fig. 4 is a section on line IV-IV in Fig. 3;

Fig. 5 is a vertical section of the front end of the tool to an enlarged scale illustrating diagrammatically successive stages in the action of the tool, and

Figs. 6 A - 6F illustrate various blade configurations in plan view and end elevation.

Referring now to the drawings, the exemplified hand tool comprises a casing 1 of rigid, moulded synthetic plastics material including an elongate body 2 connected by an integral neck 3 of reduced width to a detachable cutter head 4 with a front opening 5 from which projects a set of six cutting blades 6 together defining a cutting edge 7. The body 2 has a rear opening (not shown) giving access to a battery compartment 8 containing a rechargeable battery 9 which is in electrical connection through a body partition 10 with

an electric motor 11 arranged in a motor compartment- 12 closed at its front end by a partition 13 separating the body 2 from the neck 3. The motor 11 is operatively connected to a switch 14 mounted in the wall of the body 2. A drive shaft 15 of the motor 11 extends through the partition 13 to provide the input drive for a transmission 16 housed within the neck 3.

The cutter head 4 has a rearward socket portion 17 which is a sliding fit on the neck 3. Manually releasable catches 18 on opposite sides of the socket portion 17 of the cutter head 4 engage in respective recesses 19 in the neck 3. The catches 18 are slidable in the recesses 19 to permit axial movement of the cutter head 4 relative to the body 2. The front end of the socket portion 17 of the cutter head 4 is defined by an internal shoulder 20 which provides a seat for an elastomeric ring 21 engaged at its other side by the front end of the neck 3. The elastomeric ring 21 acts as a spring urging the cutter head 4 in the forward direction away from the body 2. The catches 18 serve to retain the cutter head 4 on the neck 3 against this spring pressure. Axial retraction movement of the cutter head 4 with respect to the neck 3 is permissible to an extent that may be determined by a suitable stop which can be provided by the engagement of the catches 18 with the rear edges of the recesses 19.

In the front end of the cutter head 4 are mounted two spaced transverse bearing pins 22 extending through oversized slots 23 in the blades 6. In the back of the rear slot 23 of each blade 6 and behind the rear pin 22 is located a block 24 of elastomeric material which is compressed on forward movement of the blade 6 so as to provide a return force for the blade. The part of the cutting edge 7 provided by the blade 6 is at the front end of a rectilinear bottom edge 25 of the blade 6. The action of the tool in certain applications is facilitated by virtue of the fact that the cutting edge 7, the bottom blade edges 25 and the bottom walls of the cutter head 4, neck 3 and body 2 lie substantially in a common plane.

The transmission 16 transmits power from the drive shaft 15 of the motor 11 to the individual blades 6 so as to cause the blades to advance in a predetermined sequence. The shaft 15 is fixed to a bevel gear 26 which meshes with a bevel gear 27 fixed to one end of a rotary cam shaft 28 carrying six cams 29 for driving the respective

blades 6. Each cam 29 is of similar irregular shape and the cams are offset on the cam shaft so as to achieve the required sequence of operation of the blades 6. Each cam 29 rotates within an appropriately dimensioned oval opening within a cam follower 30 in the form of a rectangular striker plate mounted for axial sliding movement within the neck 3. The cam configuration is such that the rotary motion of each cam is translated into an abrupt and forceful striking action of each cam follower striker plate against the rear edge of the respective cutter blades 6, as best seen with reference to Fig. 5 illustrating the drive of one blade 6. In Fig. 5a the cutter head 4 is in its foremost position with respect to the neck 3 and the body 2 by virtue of the action of the elastomeric ring 21. As a result, the blade 6 is likewise in its foremost position with its cutting edge 7 on the final line of cut X. Assuming that the axis of the camshaft 28 remains on line A and the cutting edge 7 is positioned on the initial line of cut Y the cutter head 4 is retracted into the position of Fig. 5b so positioning the rear edge of the blade 6 on the line C in the optimum position for being struck by the striker plate 30. The striker plate 30 remains stationary in positions A and B although the cam 29 has turned through a quarter of a revolution in the clockwise direction as indicated by the arrow. The front striking edge 31 is spaced a short distance (for example 2mm) behind the line C and the rear edge 32 of the plate 30 is positioned on line B. During the following quarter turn of the cam 29 the striker plate 30 is abruptly advanced into percussive or striking contact with the rear edge of the blade 6 on the base line C (Fig. 5c) and further movement of the cam 29 (into the position shown in Fig. 5d) causes the blade 6 to advance from the initial cutting line Y to the final cutting line X with a force sufficient to penetrate the workpiece material. During such advance energy is stored in the elastomeric block 24 so that as the striker plate 30 returns to the starting position shown in Figs. 5a and 5b a return force is available for returning the blade 6 to the position shown in Fig. 5b in which the rear edge of the blade is again positioned on the line C ready for the next striking action of the follower plate 30.

In the advanced position shown in Fig. 5d, the leading edge 31 of the follower plate 30 projects beyond the line C by a short distance

(which may also be 2mm). When the cutter head 4 is extended relative to the neck 3 as shown in Fig. 5a the rear edge of the blade 6 is spaced forwardly of the line C by a distance slightly greater than the aforesaid short distance thereby removing the blade 6 from operative connection with the transmission 16. It will be appreciated that working pressure on the blade 6 causes the cutter head 4 to retract into the rearward working position of Fig. 5b. A light working pressure may cause partial retraction of the cutter head 4 such that the rear edge of the blade 6 is within striking distance of the front edge 31 of the striker plate 30 without being fully retracted to the base line C. In such an intermediate position the striker plate 30 will strike the blade 6 progressively more lightly as the spacing of the rear edge of the blade 6 from the line C increases. By changing the working pressure on the blades the force acting on the blades will therefore be automatically adjusted with a lighter working pressure producing a lighter cutting action. If desired, a manually adjustable stop (not shown) may be provided for arresting the cutter head 4 in such an intermediate position thereby limiting temporarily the cutting force to be applied.

Each of the six blades 6 of the cutter head 4 operates in the way described by reference to Fig. 5 but sequentially in a manner determined by the arrangement of the cams 29 on the cam shaft 28.

Preferably, the sequence of blade operations is such that in one angular position of the camshaft all the blades are fully retracted so that the cutting edge 7 is rectilinear and coincident with the initial cutting line Y and in another angular position of the camshaft all the blades 6 are fully extended so that the cutting edge 7 is again rectilinear and coincident with the final cutting line X. The arrangement of the cams . 29 is such that the blades 6 move successively from the retracted to the advanced position with preferably only one blade being subjected to a percussive force at any one time so that the full power of the electric motor 11 is concentrated on an individual blade 6. In such a sequence of operations one blade 6 is first advanced, then the next adjacent blade

6 is advanced, then the next blade 6 and so on until all the blades 6 are in the advanced position whereupon they are all retracted before the sequence of operations is repeated. In an alternative sequence of

operations, the blades are never simultaneously in the advanced position although each blade advances from a common initial cutting line Y to a final cutting line X as described with reference to Fig. 5. It will be noted particularly from Figs. 2 and 4 that the blades

6 are of the same size and shape and are held in closely contacting sliding relationships so as to give the appearance of segments of a larger solid blade, of a tool, for example a hand chisel, of the kind for which the power tool of the present invention is intended to substitute. As best seen in Fig. 2, the blades 6 are provided on inside faces thereof with vertical grooves 33 acting as deflectors of dust penetrating between the blades in use. In addition, the sliding interconnection of the blades 6 is improved by lengthwise interengaging formations of ribs 34 and grooves 35 on adjacent blade contact faces. The blade configuration illustrated in Figs. 1 to 5 and 6a is that of a typical straight cutter and alternative configurations are illustrated in Fig. 6b (convex cutter), Fig. 6c (concave cutter), Fig. 6d (pointed cutter), Fig. 6e (angled cutter), and Fig. 6f (complex cutter).

It is desirable that the blade 6 be grouped partly adjacent to one another to give a virtually unbroken cut along the cutting edge

7 in spite of the fact that the cutting edge is moved in separate segments. In the illustrated embodiment, the blades 6 are held in adjacent relationship by lateral compression springs (not shown) at opposite sides of the cutter head 4. Although all the blades 6 are preferably of the same width, the number of blades 6 and the overall length of the cutting edge 7 may be varied as desired. The width of the blades is dictated by the power of the drive means and the workpiece material. For example, a powerful motor and a narrow blade will penetrate hard material with ease whereas a wide blade and a weak motor will be suitable only for relatively soft material. The blades may be made of various metals or metal alloys suitably tempered to suit different workpiece materials. The blade displacement may also vary in different applications of the inventive concept.

The illustrated transmission may be modified without departing from the scope of the invention. For example, the impact cams may make direct contact with the blades without the intermediary of cam follower plates. Alternatively, the rear ends of the blades may be

extended so as to provide cam follower sections driven by the cams in the same way as the illustrated cam follower plates. In this case, the cutter head is not adjustable or removable but this may be unimportant particularly in heavy duty cutting tools. If necessary, the transmission may include more complex gearing between the motor drive and the camshaft. An external power source may be provided in which case the tool of the invention need only comprise a cutter head with cutter blades and a suitable transmission adapted to be connected to the external power source which may for example be a portable electric drill. Although the illustrated embodiment is provided with a battery it will be appreciated that the motor may be adapted to be driven by mains power. Alternative energy sources, e.g. pneumatic power, are also feasible in certain applications.

Preferably, the blades are individually narrow enough to facilitate penetration into the workpiece material in reaction to the weight of the device with a minimum of recoil so that a smooth continuous penetration from successive strokes of adjacent blades is achieved without undue manual pressure.