The present invention relates to cutting tools and in particular to cutting tools suitable for cutting planar sheet material.

BACKGROUND OF THE INVENTION

To date the only reliable alternative to an industrial guillotine for the trimming or cutting of sheet materials such as sheet metal has been the use of metal snips. However, the repeated use of such snips for trimming or cutting is time and effort cosuming, does not yield a cleanly trimmed edge and is potentially unsafe because the operator's hand is positioned behind the cutting edge where it can be injured by contact with the sharp trimmed edges or metal slivers.

Motorized guillotine machines are presently very expensive and also have inherent dangers.

It is an object of the present invention to overcome or at least substantially ameliorate the abovementioned disadvantages.

SUMMARY OF THE INVENTION

According to the invention there is provided a cutting tool for cutting sheet material/ said tool comprising first and second cutting rollers, said first cutting roller having a first axis of rotation substantially parallel to a corresponding second axis of rotation of said second cutting roller, each said cutting roller having a cutting face substantially perpendicular to its axis of rotation, said cutting face of said first cutting roller being in sliding contact with said cutting face of said second cutting roller over a contact region, said tool including a handle by which said tool can be drawn across said sheet material.

The contact region preferably extends from a perimeter of the first cutting roller to a perimeter of the second cutting roller along a diameter of each for a diameter contact distance of 0.5 mm plus or minus 0.1 mm, with the preferred contact distance being 0.5 mm.

Preferably, "sliding contact" is defined as an approximately 1 micron separation between the sliding surfaces.

The diameter and length of each cutting roller is preferably in the order of 40 mm and 15 mm respectively.

The cutting tool may include a power unit such as an electric or pneumatic motor connected to at least one of the cutting rollers to accommodate heavier gauge material.

The invention may be applied to the cutting of a wide

range of sheet materials such as tin plate, steel plate, cardboard, plastic, paper or similar. The maximum thickness which can be comfortably handled will vary depending upon the material, the size of the rollers and whether or not power assistance is employed. By way of example, the illustrated apparatus is capable of cutting sheet steel in the order of 0.7 mm in thickness. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a front perspective view.

Figure 2 is a left side elevation.

Figure 3 is a right side elevation.

Figure 4 is a front elevation.

Figure 5 is a rear elevation.

Figure 6 is a plan view.

Figure 7 is a underside plan view.

Figure 8 is a section taken on line 8-8 of Figure 3.

Figure 9 is a fragmentary view taken in direction 9-9 of Figure 8.

Figure 10 is fragmentary view showing the engagement of the cutting rollers.

Figure 11 is a front perspective view showing a power unit applied to the cutter.

DETAILED DESCRIPTION OF THIS PREFERRED EMBODIMENT

Referring to the drawings, the cutting tool 1 includes first and second cutting rollers 2 and 3

respectively located on first and second support arms 4 and 5. The support arms are joined at their apex 6 and are mutually divergent, defining respective oppositely directed bearing faces 7 and 8 to guide the cut sheet away from the cutting rollers.

^•' A handle 9 is located at the outer end 10 of the first support arm 4 and extends in a direction generally normal to the sheet. In other examples, the handle may extend in a direction parallel to the sheet or be selectively rotatable between desired positions, for example through 90°.

As best shown in Figure 8, the cutting rollers are mounted for rotation about respective first and second axes of rotation 11 and 12, in this example by means of double roller angular contact bearings 13 and 14. These bearings substantially eliminate side play without the need for additional thrust bearings.

The first cutting roller 2 is mounted to an eccentric shaft 15 such that the lateral spacing between the first and second axes can be adjusted by releasing lock nut 16 and rotating the main shaft 17 about its axis 18 by means of an end slot 19. The eccentricity between the main and eccentric shafts is indicated at E in Figure 8.

The second cutting roller 3 is mounted to a finely threaded shaft 20 such that lock nut 21 and end slot 22 permit selective adjustment of the axial spacing of the two cutting rollers.

A guide roller 23 is conveniently mounted to the main shaft 17 on bearing 24 and serves both to resist twisting of the tool and to act as a gauge to limit the maximum thickness of material that can be presented to the tool. The positions of the various rollers can be reversed to provide a left-handed tool if required.

As best shown in Figures 8 and 10 the two cutting rollers include respective first and second opposed cutting faces 25 and 26 which are arranged to slidingly engage each other over a contact region generally designated 27. The diameter contact distance A is determined by the material to be cut and the available operating force. It is critical to the operation of the invention and is preferably 0.5 mm plus or minus 0.1 mm in this particular embodiment. This dimension is preferably adjustable by means of the eccentric shaft 15.

A further important dimension is the lateral clearance B between the sliding contact region 27 and the side surfaces 28 of the support arms around which the cut material must pass. For sufficient clearance and easy cutting this clearance B preferably lies in the range of 0.5 mm to 1.0 mm.

The third critical dimension is the axial clearance C between the respective cutting faces as shown in Figure 10. This clearance must be sufficient to allow sliding of the respective cutting faces and is preferably in the

order of 1 micron. It is preferably adjustable by the finely threaded shaft 20.

Preferably the first axis 11 of the first cutting roller 2 lies ahead of the second axis 12 in the cutting direction towards the handle, thereby producing an inclined angle of. pull in the range of 10 to 15 .

The cutting rollers in this example are approximately 40 mm in diameter and 15 mm wide. They may be dimensioned and formed according to the desired application. For example, the above described embodiment is intended for industrial use on sheet metal and so the rollers would be formed from material such as carbon, high chrome, high speed, carbide or case hardened steel. The support arms would preferably be steel or an aluminium alloy. The handle could also be integrally formed or removable, being formed of metal or plastics material.

In domestic applications plastics material could be used for all the components, although it would still be preferable for the cutting rollers to be formed from durable metal, even for small paper cutting units intended to be held by the fingers. The invention provides improved safety over scissors and snips because the size and geometry of the rollers make it difficult to get one's fingers into the cutting region.

In all cases the operation of the cutter is basically identical. Sheet material is presented to the rollers and the cutter is drawn forward in the direction shown in

Figure 2 for a smooth and continuous cut in one motion. The three rollers firmly grip the material immediately prior to and during the cut.

The rollers can be easily removed for cleaning or sharpening. The bearings can be disassembled by means of screws 29 and cover plates 30. Preferably, the cutting surface of the second roller is defined by a peripherally stepped portion 31.

In other embodiments one or both of the cutting rollers can be motor driven by any suitable means such as an electric or pneumatic motor 32, as shown in Figure 11. The cutter in this example is still guided by hand in a manner similar to a router or nibbler.

In other embodiments the cutter may be permanently or releasably fixed to a bench such that the material is moved passed the cutter rather than vice versa. A suitable bracket may be provided on the bench or the tool to permit this.

In another embodiment an adjustable linear guide may be provided such that the cutter can slide along the guide to produce a controlled straight line cut.

The cutter of the present invention will cut other than in exactly straight lines. For extremely sharp curves modifications to the lead out part of the cutter assembly may be required to avoid significant fouling. A split conical support for the three rollers is envisaged in this situation.

Although the invention has been described with reference to a specific example it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.