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Patent Searching and Data


Title:
GROOVE CUTTER
Document Type and Number:
WIPO Patent Application WO/2005/011937
Kind Code:
A1
Abstract:
A groove cutter (10) for forming a groove (38) in a material (30), the groove cutter comprising: a blade (52) having a cutting edge for forming the groove, the blade including two lateral portions (76a, 76b) and an intermediate portion (80) located between the lateral portions, whereby the groove cutter can be used to form the groove and thereby define a fold line in the material with a gap provided at least in part by the intermediate portion.

Inventors:
MAKINS DAVID (AU)
KASALO STIPO (AU)
Application Number:
PCT/AU2004/000945
Publication Date:
February 10, 2005
Filing Date:
July 13, 2004
Export Citation:
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Assignee:
EXI FORMA PTY LTD (AU)
MAKINS DAVID (AU)
KASALO STIPO (AU)
International Classes:
B26D3/06; B27C5/00; B27G5/04; B28B11/00; B28B11/12; (IPC1-7): B27F1/02; B27F1/04; B27G13/14; B26D3/06; E04C2/04
Domestic Patent References:
WO1992003263A11992-03-05
WO1996021779A11996-07-18
Foreign References:
US5603253A1997-02-18
GB1445339A1976-08-11
US3964944A1976-06-22
Attorney, Agent or Firm:
Griffith, Hack (509 St Kilda Road Melbourne, VIC 3004, AU)
Download PDF:
Claims:
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A groove cutter for forming a groove in a material, the groove cutter comprising: a blade having a cutting edge for forming said groove, said blade including two lateral portions and an intermediate portion located between said lateral portions, wherein each of said lateral portions of said blade is at an obtuse angle to said intermediate portion whereby said groove cutter can be used to form said groove and thereby define a fold line in said material with a gap provided at least in part owing to said intermediate portion of said blade.
2. A groove cutter as claimed in claim 1, wherein said lateral portions are straight so that said groove, once formed, has planar sides.
3. A groove cutter as claimed in either claim 1 or 2, wherein said intermediate portion is straight so that said groove, once formed, has a planar base.
4. A groove cutter as claimed in any one of the preceding claims, wherein said blade comprises a single integral member.
5. A groove cutter as claimed in any one of claims 1 to 3, wherein said blade comprises two separable blade members locatable immediately adjacent to each other to form said blade.
6. A groove cutter as claimed in any one of the preceding claims, wherein said groove cutter includes a depth guide for determining a maximum depth to which said groove cutter can cut said groove, so that said groove has a predetermined and uniform depth.
7. A groove cutter as claimed in any one of the preceding claims, wherein said material is plasterboard.
8. A groove cutter as claimed in any one of the preceding claims, including a groove guide corresponding to a desired path of said groove.
9. A groove cutter as claimed in claim 8, wherein said groove guide is straight and includes a drive chain driven about a pair of cogs, said chain engaging said blade so that said blade can be drawn parallel to said chain to form a linear groove in said material.
10. A groove cutter as claimed in any one of the preceding claims, wherein said lateral portions are located in respective planes at substantially 90° to one another.
11. A groove cutter as claimed in any one of the preceding claims, wherein said blade has a size and profile to form a groove in plasterboard substantially equal to but less than the thickness of the plasterboard such that a rear facing paper of said plasterboard remains intact once said groove is formed, whereby said plasterboard when provided with said groove can be bent along said groove and remain integral.
12. A groove cutter as claimed in any one of the preceding claims, wherein said groove comprises a 90° V shaped groove with a flat base, so that a 90° angle can be formed in said material, and said gap is provided between surfaces of said material cut by said groove cutter.
13. A groove cutter as claimed in any one of the preceding claims, wherein said cutting edge is square to a longitudinal axis of said blade.
14. A groove cutter as claimed in any one of claims 1 to 12, wherein said cutting edge is oblique so that, in use, the portion of said blade deepest in said material trails the portion of said blade closest to the surface of said material.
15. A groove cutter as claimed in any one of the preceding claims, wherein said groove cutter is provided with depth adjustment means so that the depth to which said blade cuts can be adjusted, whereby the depth of said groove can be selected.
16. A blade member, locatable immediately adjacent to another such blade member so as to form a groovecutter as claimed in any one of the preceding claims.
17. A method of forming an angle in a material, involving : forming a groove in said material by means of a groove cutter according to any one of the preceding claims ; wherein said groove is formed with sufficient depth to allow said material to be readily bent to form said angle but leaving sufficient thickness of said material so that said material remains integral, and said groove is formed with a base that, when said material is bent along said groove, provides a gap.
18. A method as claimed in claim 17, including forming said groove so as to have substantially planar sides and said base so as to be substantially flat.
19. A method as claimed in either claim 17 or 18, wherein said sides are located in respective planes that are at substantially 90° to one another.
20. A method as claimed in any one of claims 17 to 19, wherein said material is plasterboard and said groove leaves the paper on one side of said plasterboard intact.
21. A plasterboard cutter for providing plasterboard with an edge, comprising: a first blade portion for cutting a groove in said plasterboard without cutting a facing sheet of said plasterboard ; and a second blade portion for cutting said facing sheet so as to leave a flap of facing material that can be folded over to an opposite facing sheet ; whereby said flap can be affixed to said opposite facing sheet thereby providing said plasterboard with said edge.
22. A plasterboard cutter as claimed in claim 21, wherein said first blade portion has a"U"shaped profile, and said second blade portion comprises an extension of one sideof said"U"shaped profile,whereby said cutter can be used to provide said plasterboard with a square edge.
23. A plasterboard cutter as claimed in claim 21, wherein said first blade portion has a"U"shaped profile with one side of said first blade portion concave as seen from its exterior, whereby said concave side of said first blade portion is, in use, located against a portion of the plasterboard to be retained so that a rounded edge is provided.
Description:
GROOVE CUTTER FIELD OF THE INVENTION The present invention relates to a groove cutter, of particular but by no means exclusive application for cutting plasterboard and, in particular, in providing a suitable groove in plasterboard so that the plasterboard can be provided with an angle. The invention also relates to a method of forming external angles in, for example, plasterboard by means of the aforementioned groove cutter.

BACKGROUND OF THE INVENTION In the construction industries, grooves are typically formed by means of routing devices. However, particularly when a groove is to be provided in a piece of plasterboard (comprising plaster to which a stiff external facing-paper is adhered on both faces), large quantities of dust are produced. Excessive dust and associated respiratory health risks are avoided only by means of time consuming and expensive safety measures. In addition, such work environments are closely monitored by unions, occupational health and safety officials, and insurers ; consequently, such work must generally be formed off-site. All these factors lead to greater expense and introduce delays.

Further, existing methods for forming external angles in plasterboard generally comprise placing a metal external angle over a rough plasterboard corner and attaching it thereto by means of staples. The corner (and particularly the metal angle, which is generally of galvanised steel) is then stopped and sanded to provided a smooth finish.

Although this approach can be avoided by forming a groove in the plasterboard and bending the plasterboard to form the required angle, this is done by the techniques (as described above) that introduce cost and raise safety issues.

SUMMARY OF THE INVENTION The present invention provides, therefore, a groove cutter for forming a groove in a material, the groove cutter comprising: a blade having a cutting edge for forming said groove, said blade including two lateral portions and an intermediate portion located between said lateral portions, wherein each of said lateral portions of said blade is at an obtuse angle to said intermediate portion whereby said groove cutter can be used to form said groove and thereby define a fold line in said material with a gap provided at least in part owing to said intermediate portion of said blade.

Thus, the groove allows the material to be bent but leave a gap into which may be inserted, for example, a protective strip.

Preferably the lateral portions are straight so that said groove, once formed, has planar sides.

Preferably the intermediate portion is straight so that said groove, once formed, has a planar base.

The blade may comprise a single integral member, but preferably the blade comprises two separable blade members locatable immediately adjacent to each other to form said blade.

Preferably the groove cutter includes a depth guide for determining a maximum depth to which said groove cutter can cut said groove, so that said groove has a predetermined and uniform depth.

Preferably the material is plasterboard.

Preferably the groove cutter includes a groove guide corresponding to a desired path of said groove.

Preferably the groove guide is straight and includes a drive chain driven about a pair of cogs, said chain engaging said blade so that said blade can be drawn parallel to said chain to form a linear groove in said material.

Preferably the lateral portions are located in respective planes at substantially 90° to one another.

Preferably the blade has a size and profile to form a groove in plasterboard substantially equal to but less than the thickness of the plasterboard such that a rear facing paper of said plasterboard remains intact once said groove is formed, whereby said plasterboard when provided with said groove can be bent along said groove and remain integral.

Preferably the groove comprises a 90° V-shaped groove with a flat base, so that a 90° angle can be formed in said plasterboard, and said gap is provided between surfaces of said plasterboard cut by said groove cutter.

Preferably the cutting edge is square to a longitudinal axis of said blade, but the cutting edge may be oblique so that, in use, the portion of said blade deepest in said material trails the portion of said blade closest to the surface of said material.

Preferably the groove cutter is provided with depth adjustment means so that the depth to which said blade cuts can be adjusted, whereby the depth of said groove can be selected.

In another broad aspect, the invention provides a blade member, locatable immediately adjacent to another such blade member so as to form a groove-cutter as described above.

The invention also provides a method of forming an angle in a material, involving: forming a groove in said material by means of the groove cutter described above ; wherein said groove is formed with sufficient depth to allow said material to be readily bent to form said angle but leaving sufficient thickness of said material so that said material remains integral, and said groove is formed with a base that, when said material is bent along said groove, provides a gap.

Preferably the method includes forming the groove so as to have substantially planar sides and the base so as to be substantially flat.

Preferably the sides are located in respective planes at substantially 90° to one another.

Preferably the material is plasterboard and said groove leaves the paper on one side of said plasterboard intact.

The present invention also provides a plasterboard cutter for providing plasterboard with an edge, comprising: a first blade portion for cutting a groove in said plasterboard without cutting a facing sheet of said plasterboard ; and a second blade portion for cutting said facing sheet so as to leave a flap of facing material that can be folded over to an opposite facing sheet ; whereby said flap can be affixed to said opposite facing sheet thereby providing said plasterboard with said edge.

Preferably said first blade portion has a"U"-shaped profile, and said second blade portion comprises an extension of one side of said"U"-shaped profile, whereby

said cutter can be used to provide said plasterboard with a square edge.

It will be appreciated, however, that other blade profiles could be employed. For example, it may be desired to provide a rounded edge, in which case the first blade portion would have a"U"-shaped profile but with one side concave (as seen from its exterior), whereby that side would be located against the portion of the plasterboard to be retained.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the present invention may be more clearly ascertained, embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view of a groove cutter according to an embodiment of the present invention ; Figure 2 is a further view of the groove cutter of figure 1 ; Figure 3 is a further view of the groove cutter of figure 1 ; Figure 4 is a schematic view of a detail of the blade of the groove cutter of figure 1 ; Figure 5 is a perspective view of the blade of the groove cutter of figure 1 ; Figure 6 is a schematic view of the groove cutter of figure 1 in use with a piece of plasterboard ; Figure 7 is a further view of the groove cutter of figure 1 in use with a piece of plasterboard, showing the formation of a groove ; Figure 8A is a cross sectional view of a piece of plasterboard provided with a groove by means of the groove cutter of figure 1 ; Figure 8B is a view of a piece of plasterboard formed into a 90° edge once provided with a groove by means of the groove cutter of figure 1 ;

Figure 9 is a plan view of a groove cutter according to a second embodiment of the present invention; Figure 10 is a cross-sectional view through the groove cutter of figure 9 along line B-B ; Figures 11A and 11B are further views of the groove cutter of figure 9 with optional packing plates ; Figure 12 is a view of a guide for cutting straight grooves according to another embodiment of the present invention, for use with the groove cutter of figure 9 ; Figure 13 is an end view of the guide of figure 12 ; Figure 14 is a plan, partially cut-away view of the guide of figure 12, illustrating its chain drive mechanism; Figure-15 is a-view of-the groove-cutter--of figure 9 mounted to a linear chain drive for forming linear grooves of the type shown in figure 12; Figure 16 is a view similar to that of figure 15 of the groove cutter of figure 9 in use with a piece of plasterboard; Figure 17A is a side elevation comparable to that of figure 9 or 10 of a groove cutter according to further embodiment, provided with adjustable legs for adjusting groove depth; Figure 17B is a side elevation of a variation of the groove cutter of figure 17A; Figure 17C is an end view (comparable to figure 10) of the groove cutter of either figure 17A or 17B; Figure 17D is an end view of a variation of the groove cutter of figure 17C; Figure 18A is a side view of a plasterboard cutter according to a further embodiment of the present invention, for providing the plasterboard with a square edge; Figure 18B is an end view of the plasterboard cutter of figure 18A;

Figure 19 is a schematic view of the plasterboard cutter of figure 18A in use with a sheet of plasterboard; and Figure 20 is a schematic view of the sheet of plasterboard of figure 19, illustrating the formation of a square edge.

DETAILED DESCRIPTION A groove cutter according to a first embodiment of the present invention is shown generally at 10 in figure 1.

For clarity, in this figure (and also in figures 2 to 5), the handle of the groove cutter 10 has been omitted for clarity.

Groove cutter 10 comprises a blade 12 of hardened stainless-steel and of 3 mm thickness, provided at its leading end 14 with a cutting edge 16. This cutting edge has an angle of 20°, though it will be understood that other angles may be preferred according to the material to be cut, the desired cutting speed, etc.

Blade 12 comprises two blade members 13a and 13b, aligned within groove cutter 10 at 90° to each other (into the page as seen in figure 1). The meeting of the two blade members 13a, 13b defines an apex 18 ; each member 13a, 13b is provided with screw holes 24 for attaching to a blade holder.

Figure 2 is a side elevational view of groove cutter 10, in which it can be seen that the cutting edge 16 is square to the longitudinal axis or apex 18 of the blade 14.

Figure 3 is a cross-sectional view of groove cutter 10 along A-A. In this figure, the profile of groove cutter 10 is clearly visible, and in particular the 90° meeting of blade members 13a, 13b along apex 18.

Figure 4 is a more detailed cross-sectional view of groove cutter 10 along A-A. In this figure, the manner in which members 13a and 13b meet is more clearly shown. The two members 13a, 13b are individually mounted to a holder, and that mounting holds the two portions in the illustrated relationship. It is therefore unnecessary to weld or otherwise join the two portions. Further, the two portions are provided separately rather than by bending a single piece of steel, because steel of the preferred thickness 20 (i. e. 3 mm) can be difficult or expensive to bend.

However, blade members 13a, 13b are machined flat at their lower extremities (as shown in figure 3B), so that apex 18 is essentially flat, with a width of approximately 2 mm.

The advantages-of this flat portion-are discussed further below.

Figure 5 is a perspective view of blade 12, in which is visible cutting edge 16. It may be seen in this view that the cutting edge 16 is arranged to pull wasted material upwards.

Figure 6 is a schematic view of the groove cutter 10 in use with a piece of plasterboard 30. Firstly, it should be noted that plasterboard 30 comprises compressed plaster core 32 and paper facing sheets 34 and 36. In use, groove cutter 10 (shown here in a view comparable to that of figure 2) is drawn from left to right as seen in this figure. As the groove cutter 10 is advanced, the upper facing paper 34 and the plaster 32 is cut by the groove cutter 10. However, the lower facing paper 36 is left intact.

This procedure is also depicted in figure 7, a perspective view of the groove cutter 10 once it has been advanced somewhat through plasterboard 30. A groove 38 has been

formed with sides 40a, 40b generally at 90° to each other.

However, as can be seen at figure 8A, the resultant cut is not a triangular v-shape but instead has a 2 mm wide base 42 owing to the 2 mm width of apex 18 (cf. figure 4).

This allows a metal or other strip to located within the plasterboard for protection of a finished corner and also to allow for minor adjustments to leveling, etc. This will be more readily seen by reference to figure 8B: once the groove has been completely formed from one edge of the plasterboard 30 to the other (though leaving lower facing paper 36 intact), the plasterboard 30 is bent 44 through 90°. Owing to the 2 mm base 42 of the groove 38, the surfaces 40a, 40b exposed by the formation of the groove 38 do not meet but are rather separated by a gap 46 for receiving the aforementioned protective strip. However, because the sides 40a, 40b of the groove 38 are at 90° to each other, the plasterboard 30, once fully bent and including such a strip, forms a 90° angle at its vertex 48. The vertex 48 remains covered by facing paper 36 and strengthened by the protective strip.

The protective strip can be inserted after the plasterboard has been bent, or laid on the groove after its formation but before the bending process.

A groove cutter according to another embodiment of the present invention is shown in plan view at 50 in figure 9.

Groove cutter 50 includes a block 54 to whose underside is attached a blade holder with a two-part blade (neither visible in this figure: see figure 10). The blade holder is attached to the underside of the block 54 by means of six screws 56 located about the periphery of the block 54.

Block 54, as shown in this figure, has a forward end 58 and rear end 60. Approximately mid-way between its two ends, the block 54 is provided with a pair of access holes 62 through which the bolts (not shown) holding the blade

to the blade holder can be tightened.

Block 54 is provided with two chain attachments 64,66 for attaching the block and hence the groove cutter 50 to a chain driven guide (not shown: see figures 12 and 14).

Rear chain attachment 64 is a simple plate for clamping one end of the chain to the block 54. Forward chain attachment 66 also includes such a plate 68, but is provided additionally with a threaded tensioning adjustment for adjusting the tension of the chain.

Tension is adjusted by means of a pair of bolts 70 attached to a threaded rod 72 extending either side of chain attachment 74.

The location of blade 52 within blade holder 53, and in relation to block 54, is--shown in cross--section B-B in figure 10. As is particularly apparent in figure 10, blade 52 comprises two blade members 76a, 76b of stainless steel located to define the 90° V-shaped blade 52. Each blade members 76a, 76b is attached to the blade holder 53 by means of bolts 78. The two portions of blade holder 53 are formed with 45° inner faces so that blade 52 can be located therebetween and attached by means of bolts 78 with the central axis or apex 80 of blade 52 protruding downwardly beyond the lower face of holder 53 by a distance equal to the depth of the desired groove.

The holder 53 is also provided with a pair of laterally disposed grooves 82a, 82b for receiving the guide rails (not shown) of the aforementioned chain driven guide.

In this embodiment, holder 53 functions both as a depth plate and as a holder for the blade 52. The depth of the ultimate groove can be varied by adjusting the distance to which the blade 52 extends below the blade holder 53.

This can be done in a number of ways. For example, the blade holder 53 can be detached from the blade 52 and the

block 54, and replaced with a substitute alternative holder that has a smaller or greater distance from grooves 82a, 82b to its base. Alternatively, and referring to figures 11A and lIB, to decrease the groove depth a pair of packing plates 84a, 84b (each extends the full length of the holder 53) can be bolted to the base of the holder 53. The packing plates 84a, 84b include holes 86 by means of which the plates 84a, 84b can be bolted to the base of the holder 53 by bolts that are received in tapped bores 88 in the base of the holder 53. Figure 11A depicts the packing plates 84a, 84b being raised under the holder 53 into position, while figure 11B depicts the plates 84a, 84b in their final position attached to the holder 53 by mean of bolts 90. Thus, by using a set of such packing plates of different thicknesses, a convenient range of groove depths can be achieved.

In another alternative, the two portions of the blade holder 53 can moved towards or away from each other, thereby raising or lowering, respectively, the blade 52.

In this arrangement, holes in the blade 52 through which bolts 78 secure the blade 52 to the blade holder 53, and the holes 92 in block 54 through which pass screws 56, are slotted ; the adjustment is effected by loosening these bolts 78 and screws 56, moving the holder 53 inwards or outwards (with bolts 78 and screws 56 sliding within these slots), and then re-tightening bolts 78 and screws 56.

In this embodiment, and referring to figure 12, the groove cutter 50 is mechanical guided by means of chain driven guide 120 for cutting straight grooves according to another embodiment of the present invention. Figure 12 is a plan view of guide 120, which includes a U-shaped housing 121 with a chain 122 and a pair of cogs 124, 126 each located at one end of guide 120 about which chain 122 is driven. Cogs 124 and 126 have vertical axes. One of the cogs 124 has a vertical extension 125 extending

upwardly through the casing of guide 120 so that cog 124 and therefore guide 120 can be driven, such as by an electric drill, in either direction. A groove cutter 128 (similar to groove cutter 50) is located within guide 120 and attached to chain 122. The ends 130 of chain 122 are attached to the ends of groove cutter 128. Driving cog 124 drives chain 122 and therefore causes groove cutter 128 to be advanced along the length of the guide 120. It will be noted that cogs 124 and 126 are offset to the central axis of the guide 120: this is so that the chain draws the groove cutter 128 with a force that is in the direction of-and typically directly above-the groove being cut.

The chain driven guide 120 has the advantage of being lightweight and sturdy compared with alternatives such as a threaded rod driven guide or a motorized, hand-held device operated as one would a plane and guided against a straight edge.

Further, the chain drive permits the adjustment of the chain's tension (as described above by reference to figure 9). This allows the user-by suitable adjustment of the chain's tension-to minimize wear on both chain linkages and cogs, to set the tension according to the density of the material in which the groove is being formed, and to reduce slap'of the chain against the encasement. The alternative of the threaded rod, for example, would need to be too thick to prevent slapping, making it expensive and heavy.

The chain drive allows the direct transfer of torque from the power source (such as a drill) to the pushing and pulling of the groove cutter. A chain drive also permits the constructions of a collapsible unit, to minimize the overall length of the device during transport.

Further, the chain drive guide minimizes replacement costs when compared with a threaded rod or other drive mechanism. Chain is inexpensive, typically costing half or less the cost of a suitably machined threaded rod.

Similarly, chain can readily be repaired, by the replacement of one or more links. A chain driven system allows for more give'during operation, thereby reducing the tendency of the chain to jerk the user should it jam or become blocked.

Figure 13 is an end view of guide 120 provided with a groove cutter 128 and located on a piece of plaster board 132. Cog 124 provided with upwardly projecting pin 134 is also shown.

Casing-1-36 (of alumini-um-or s-teel)-of guide 120 is provided with internal lips or rails 138 running the length of casing 136, for guiding groove cutter 128.

Groove cutter 128 is provided with complementary recesses or grooves 140 for receiving lips 138.

Figure 14 is a partial cut-away plan view of guide 120, in which can be seen cogs 124,126 with chain 122 joined at ends 130 to groove cutter 128. It will be noted, again, that cogs 124 and 126 are located off-axis so that chain 122 is parallel to this axis and draws groove cutter 128 along the guide 120 with a tension having no lateral component.

Referring to figures 15 and 16, ends 130 of chain 122 are attached to groove cutter 128 as shown, with blade 144 extending downwardly. Blade 124 is provided with forward and rearward cutting edges 146a and 146b, so that the groove cutter 128 can be operated in either direction.

In use, the guide 120 is located on the plasterboard in which a groove is to be formed, and cog 124 is rotated

such that groove cutter 128 is drawn across the plasterboard.

Modifications within the scope of the invention may be readily effected by those skilled in the art. For example, in each of the embodiments described in detail above, the blade is fixed to the blade holder with a constant, predetermined exposed portion so that a groove of constant depth is formed. However, by conventional means it is possible to provide a blade that extends below the blade holder/depth guide to a variable degree so that grooves of different depths can be formed. Thus, referring to figure 17A, according to a further embodiment a groove cutter 152 (seen in this figure in side elevation) is provided with a series of legs 154 of adjustable height, so that the depth of blade-that is exposed can be adjusted, so that the depth of the groove can be selected. Corresponding legs are provided on the other side of the groove cutter 152. The blade is not shown in this figure for the sake of clarity.

A variation of the groove cutter 152 is shown, again in side elevation, in figure 17B. The plurality of legs 154 on each side of the groove cutter 152 are replaced on each side by a single continuous leg 156.

The legs 152 and 154 are adjustable in height by any suitable means. For example, the legs can be attached to the groove cutter 152 by bolts located in vertical slots in the sides of the groove cutter 152. Alternatively, for example, such bolts or pins can be receivable in multiple holes provided in vertical rows in the sides of the groove cutter 152.

The legs 152 or 154 can be seen more clearly in figures 17C and 17D, which are end views of the groove cutter 152 of figure 17A or 17B and of a variation thereof

respectively. Legs 152 or 154, as can be seen from these figures, have an L section with either outwardly directed feet 156 (cf. figure 17C) or inwardly directed feet 158 (cf. figure 17D). Blade 160 is also shown in these figures.

Alternatively, a removable blade can be employed so that blades for forming different depths can be substituted as desired, as can be blades of different profiles.

This technique can be combined with that described above by reference to figure 11, in which a packing plate can be added to the base of the blade holder to adjust the groove depth.

A plasterboard cutter according to a further embodiment of the present invention is shown generally at 170 in figure 18A and 18B. For clarity, in these figures (and also in figure 19), the holder of the plasterboard cutter 170 has been omitted for clarity. The view of figure 18A is comparable to that of figure 2, while the view of figure 18B is comparable to that of figure 3.

Thus, figure 18A is a side view of plasterboard cutter 170, for providing an existing plasterboard sheet of any size with a square edge.

The cutter 170 comprises two blade members: a"U"-shaped blade member 172 (comprising first and second straight sides 174a, 174b and a base 174c) and a second blade member 176 comprising a lower extension of first side 174a of the first blade member 172. In practice, second blade member 176 may be formed integrally with that first side 174a.

Second member 176 thus extends to a greater depth than does first member 172, extending below the base 174c of

the first member 172 (and providing first member 172 with a'tail').

Integrally formed with each of first and second sides 174a, 174b of the first member 172 is a respective lateral plate 178a, 178b provided with screw holes (not shown) for attaching the first member 172 to the holder of the plasterboard cutter 170, and to define the cutting depth of the cutter 170.

The depth of the base 174c from the lateral plates 178a, 178b is such that, like groove cutter 10, first member 172 can cut plasterboard while leaving the lower paper facing sheet intact. However, second member 176-as it extends below the base 174c of the first member 172-will cut the lower facing sheet, as is described below.

Referring to figure 19, in use the plasterboard cutter 170 is attached to and driven by chain driven guide 120 (not shown in this figure, but see figure 12) across a plasterboard sheet 180a, 180b. The first blade member 172 of the cutter 170 thereby cuts a square"U"shaped groove 182 but, owing to the elongation of second side blade member 176, severs the lower facing sheet 184 of the plasterboard sheet 180a, 180b. A portion of the upper facing sheet 186 and the interior plaster material 188 are removed as waste in forming groove 182.

Consequently, one portion 180b of the plasterboard sheet is discarded, while the other portion 180a is left with a flap 190 of lower facing sheet 184. As shown schematically in figure 20, this flap 190 can then be folded 192 up and over the plasterboard sheet 180 and affixed to the upper facing sheet 186 by means of appropriate adhesive, tape or other.

Thus, the plasterboard sheet 180 is left with a square

edge ; this process can also be repeated on the opposite edge of the plasterboard sheet 180 to provide a plasterboard sheet with both edges squared, as is often required.

It is to be understood, therefore, that this invention is not limited to the particular embodiments described by way of example herein above.

In the claims that follow and in the preceding description of the invention, except where the context requires otherwise owing to express language or necessary implication, the word"comprise"or variations such as "comprises"or"comprising"is used in an inclusive sense, i. e. to specify the presence of the stated features but not-to preclude-the presence or addition of further features in various embodiments of the invention.

Further, any reference herein to prior art is not intended to imply that such prior art forms or formed a part of the common general knowledge.