IES940932A2 - A knife with replaceable blade unit - Google Patents

Abstract

A knife comprising a body (1) and a replaceable blade unit (14) which fits inside the body, wherein the blade unit comprises a housing (16) and a multi-point blade (17) rotatably mounted inside the housing, the blade (17) being rotatable between rest positions in which all of the points of the blade are within the housing and cutting positions in which one of the points (18) of the blade projects from the housing and extends outside the body. The blade is rotatable by means of a spindle (23) which carries a knob (33) outside the body and which has a portion engageable with the blade (17) inside the housing. <Fig.2>

Description

A KNIFE WITH REPLACEABLE BLADE UNIT This invention relates to a knife or cutter with a replaceable blade unit. The knife is intended for many uses in cutting materials such as paper, fabric, cardboard, plastic, floor coverings and the like and is generally of the type used in Do-It-Yourself work or by craftworkers.

Known knives of this type are usually provided with very sharp blades, which give rise to two different problems. Firstly when cutting a material on a table or other substrate, the blade tends to cut down into the substrate, causing damage to it. Secondly, a sharp blade when projecting from a knife can cause injury if it encounters a hand or other part of the body of the user or of another person.

Injury can also occur when changing the blade in such a knife. It is an object of the invention to provide a knife in which the blade can be changed without touching it by hand.

Irish Patent Application No. S940625 describes a knife or cutter comprising a body, a blade projecting from the body, a guard plate adjacent to the blade and facing the cutting element thereof, and a thin spring member attaching the guard plate to the body, the spring member being forward of the blade and aligned therewith, and a gap fbeing present between the blade and the guard plate in the rest □position of the spring member, the flexibility of the spring member allowing this gap to be substantially closed when pressure is applied on the blade. 940932* - 2 In a preferred embodiment of Application No. S940625, a groove is provided in the guard plate, aligned with the blade. Although the blade presses the material to be cut against the guard plate, the blade tip should not reach the base of the groove in order to minimise wear on the blade tip.

In Application No. S940625 the spring element is preferably a thin strip suitably having a thickness (perpendicular to the blade) not more than 5 times the thickness of the blade. The spring element should be thin enough to permit easy passage of it along the cut in the material made by the blade. If desired the spring member may comprise a substantially rigid upper portion, e.g. having a V-shaped cross section with the apex of the V facing the blade, and a lower spring portion adjacent to its attachment to the guard plate.

The present invention provides a knife comprising a body and a replaceable blade unit which fits inside the body, wherein the blade unit comprises a housing and a multi-point blade rotatably mounted inside the housing, the blade being rotatable between rest positions in which all the points of the blade are within the housing and cutting positions in which one of the points of the blade projects from the housing and extends outside the body.

Preferably the blade is rotatable by means of a spindle which carries a knob outside the body and which has a portion engageable with the blade inside the housing.

In the preferred embodiment the spindle carries a locking mechanism for retaining the blade in either a rest position or a cutting position, the locking mechanism being releasable by axial retraction of the spindle.

In one aspect, the present invention provides a blade unit for a knife, comprising a housing and a multi-point blade rotatably mounted inside the housing, the blade being rotatable between rest positions in which all of the points of the blade are within the housing and cutting positions in which one of the points of the blade projects from the housing. 940932’ - 3 Preferably the blade has four points. Most preferably the blade has a generally square configuration with indentations in the four sides. The blade may be star-shaped.

In the preferred embodiment, the housing has one dimension slightly greater than the diagonal distance between opposed points on the blade and a second dimension at right angles thereto which is less than the said distance but slightly greater than the length of a side of the blade.

The invention is illustrated in the accompanying drawings, in wh i ch: Figure 1 is a pictorial view of a knife according to the invention.

Figure 2 is an elevation of the knife from one side.

Figure 3 is an elevation from the other side of the knife, showing a flap open.

Figure 4 is an exploded projection of the knife.

Figure 5 is a side elevation of a multi-point blade for the knife.

Figure 6 is a projection of the multi-point blade.

Figure 7 is a projection of a box housing for holding the blade.

Figure 8a & 8b is a pair of projections showing the blade inside the box unit in two different orientations, the rest position (a) and the cutting position (b).

Figure 9 is a pictorial view of a shield assembly from above.

A knife according to the invention comprises a handle 2 adapted to be gripped manually and a body 1 which houses a blade unit 14. The body has a shield assembly 3 similar to that described in Application S940625. The shield assembly comprises a guard plate 6 and a spring 940932 - 4 member 7 by which the guard plate is attached to the body 1. The spring member comprises a thin strip of metal which is anchored at the top end 8 to the body. A free portion 9 of the strip extends downwardly at the front of the body, inside a nose portion 11 which closes the front of the body and protects the spring member. The free portion 9 of the strip is on the vertical mid-line of the body and thus is aligned with the blade (described below). It is preferably formed of a strip of metal bent into a V-shaped cross section, with the ridge pointing rearwardly. At its bottom end the spring member is fixed to the guard plate 6 which extends underneath the blade. As shown in the drawings, the guard plate has the shape of an isosceles triangle with the apex pointing rearwardly. However the guard plate may if desired have at least one edge parallel to the longitudinal direction of the body so that the guard plate can be moved along a straight edge such as a ruler when the knife is being used.

The guard plate suitably comprises a rigid abrasion-resistant plastics material. It should be readily slidable on a smooth substrate surface and it may be described as a skid. It has converging top and bottom surfaces reducing from a thickness of 3 - 3.5mm at the front edge (where it is attached to the spring member) down to a minimal thickness e.g. 0.25mm at the trailing edge or apex.

The guard plate has a groove 10 in its top surface (or a slot extending through the guard plate) aligned with the blade. During cutting the blade enters the groove but the blade point should not reach the base of the groove so that it is kept sharp.

A roller 12 is mounted at the rear of the body, above the apex of the guard plate, to facilitate movement of the knife over material to be cut, the material being pressed against the guard plate by the roller, and to restrict the depth of entry of the blade point into the groove 10. Alternatively the roller may be replaced by roller bearing(s). The roller or roller bearing(s) may be spring mounted in the body.

The body has a flap 13 in one side wall. As illustrated, this flap 13 is hinged at the top of the body 1. However it may 940932 - 5 alternatively be slidable relative to the body. A blade unit 14 may be installed inside the body via the opening 15 in the side wall 26 which is revealed by moving the flap 13. The blade unit comprises a hollow box 16 which houses the multi-point blade 17. As shown the blade has four points 18 each with cutting edges 19, 20 leading to the point. The blade resembles a square with slightly indented edges. The blade 17 is rotatably mounted in the box 16, e.g. by means of annular ribs (not shown) which project axially from the blade around the central hole 22 and fit slidably inside corresponding annular ribs (not shown) on the inside of the side walls of the box.

Figure 4 shows a divider wall inside the body 1, against which the blade unit 14 buts. Slots to accomodate the spring member 7 and a recess to accomodate the top end 8 of the spring member are also shown in Figure 4.

The box 16 has a generally rectangular cross section, with a width slightly greater than the diagonal span of the blade from point to point, but with a height less than this diagonal span but greater than the length of a side of the blade. The blade is mounted in the box with its centre spaced from the top of the box by a distance slightly greater than one half of the diagonal span of the blade, and spaced from the bottom of the box by a distance less than one half of the diagonal span of the blade. Thus the blade can be turned from the position of figure 8a, in which the blade is entirely housed inside the box (with its sides parallel to the edges of the box), to the position of figure 8b in which one point 18 of the blade projects downwardly from the box through a slot 21 in the base thereof. The blade point 18 extends below the bottom edge of the body 1 into a position in which it can cut material between the body 1 and the guard plate 6 (see figure 2).

The blade 17 has a central hole 22 which as illustrated is hexagonal but which could be another non-circular shape or could have grooves to receive splines. The hexagonal hole 22 co-operates with a hexagonal portion of a spindle 23 which extends through the body and carries a knurled knob 33 outside the body, beside one side wall 24.

If the hole 22 is other than hexagonal, the cooperating portion of the spindle 23 has a complementary shape. The spindle is rotatable in 940932 - 6 round apertures 25 in the side walls 24,26. Mounted on the spindle, inside the side wall 24, is a spring 27 and a locking member 28 comprising a disc with two diametrically opposed pins 29 projecting therefrom parallel to the spindle. These pins enter into a pair of holes 30 in one side wall of the box 16. The other side wall of the box has similar holes so that the blade unit 14 can be reversed. The locking member 28 is rotatably mounted on the spindle 23, retained by a ring 32, which may suitably be a rubber 0-ring.

The blade 17 has a circular array of eight holes 31, four on the radial lines leading to the points 18, and four spaced equiangular ly between them. The pins 29 can enter into any pair of the holes 31 to retain the blade 17 in a particular orientation. For example in the orientation of Figure 8a, the pins 29 would be engaged in holes 31a, while in the orientation of figure 8b, the pins would be in holes 31b.

In either position, the pins (which are held by the holes in the side wall of the box 16) lock the blade 17 against rotation, so that in the orientation of Figure 8b one blade point 18 can be used for cutting while in the orientation of figure 8a the blade is safely stowed inside the box. The box can only be inserted into or removed from the body with the blade in the position of figure 8a. This is also the position of the blade when the blade unit is packaged for supply to the consumer.

To rotate the blade from one position to the next, the user pulls the knob 33 in an axial direction to withdraw the pins 29 from the holes 31 in the blade. The spring 27 is compressed between the disc 28 and side wall 24. The user then rotates the knob by one eighth of a revolution and the blade 17 is turned accordingly from the position of figure 8a to that of figure 8b (or vice versa). The pins 29 then enter into the next pair of holes 31, urged by the spring 27.

The blade 17 can be turned progressively so that each of the cutting edges 19 on the four points of the blade are used. When these have become blunt, the blade unit 14 can be removed from the body 1 via the opening 15 and can be reinserted in the reversed position, so that the cutting edges 20 on the points of the blade are used for cutting.

A ratchet mechanism may be incorporated if desired, to restrict rotation of the spindle to one direction and to ensure that it stops in 940932 - 7 each of the eight chosen positions (figures 8a and 8b).

Instead of having a rectangular cross section, the blade unit 14 could be circular with a diameter slightly greater than the diagonal span of the blade but with one segment cut away so that a blade tip 18 protrudes (as in figure 8b). In either case, the blade unit should be shaped to fit neatly inside the hollow body 1, so that it does not move inside the body during use.

If desired, the flap 13 could be omitted and one side wall of the blade unit 14 could fill the opening 15 in the side wall 26 of the body.

In use, the knob 33 is rotated to bring a blade point 18 to the position of figure 8b. The handle 2 is then gripped by hand and the guard plate 6 is placed on a table, work bench or other smooth substrate surface. An edge of the material to be cut is introduced between the guard plate 6 and the body 1. Pressure is then applied on the body, the spring member 7 flexes and the point 18 of the blade is pressed towards the guard plate 6. The knife is pulled rearwardly, causing the blade to cut the material which is trapped against the guard plate, with the groove 10 defining a line on which the material is not supported so that the blade can more easily cut through it. As the knife is drawn rearwardly, the spring member 7 enters the cut formed in the material, and the material passes on either side of the V-shaped spring member.

The guard plate protects the table (or other substrate surface) from being cut by the knife. When the knife is not in use but the blade has not been rotated to the position of figure 8a, the guard plate shields the blade point and prevents accidental damage or injury being caused by the exposed blade.

The knife of the invention is particularly useful for cutting paper. As the knife is not adapted for sharpening pencils, a conventional pencil sharpener may be incorporated into the body e.g. at the end of the handle remote from the blade.

Claims (5)

1. A knife comprising a body and a replaceable blade unit which fits inside the body, wherein the blade unit comprises a housing and a multi-point blade rotatably mounted inside the housing, the blade being rotatable between rest positions in which all of the points of the blade are within the housing and cutting positions in which one of the points of the blade projects from the housing and extends outside the body.

2. A knife according to claim 1 wherein the blade is rotatable by means of a spindle which carries a knob outside the body and which has a portion engageable with the blade inside the housing.

3. A knife according to claim 2 wherein the spindle carries a locking mechanism for retaining the blade in either a rest position or a cutting position, the locking mechanism being releasable by axial retraction of the spindle.

4. A blade unit for a knife comprising a housing and a multi-point blade rotatably mounted inside the housing, the blade being rotatable between rest positions in which all of the points of the blade are within the housing and cutting positions in which one of the points of the blade projects from the housing.

5. A knife or a replaceable blade unit therefor, substantially as described herein with reference to and/or as illustrated in the accompanying drawings.