This invention relates to accessories for use with power tools and in particular to a jig adapted for use in conjunction with a fixed router equipped with a slot cutting bit so as to facilitate the cutting of slots for receiving biscuit plates as used in plate joinery. Background of Invention

Plate joinery, or biscuit joinery as it has become known, is a method of joining wood products in a manner similar to doweling. However, where dowel joints rely on a length of cylindrical dowel to join two or more pieces of wood, biscuit joinery uses oval shaped "biscuits" made of solid wood cut at 45° to the direction of the grain and slightly compressed with a surface embossed cross- hatched pattern. The pieces of wood to be joined are provided with slots in the faces edges or ends to be joined and once the biscuits are inserted into the slots and supplied with adhesive the biscuits swell upon absorbing the adhesive and effect a particularly strong joint.

While not so critical as in dowelling, the success of the joint depends on the accurate alignment of the slots that must receive the biscuit. To that end, a range of dedicated machines have been available which generally comprise a motor driven 4" diameter saw blade and a reciprocally movable shoe assembly such that the shoe of the machine can be accurately positioned on a workpiece and the rotating saw blade moved forward into the workpiece to cut the required slot at the selected distance from the datum face of the workpiece.

Although the dedicated machines operate very well they are complex in design and costly to produce and have only this one basic function. In response to these problems a range of alternative machines have emerged, but more particularly a range of lower cost accessories have emerged which aim to operate in conjunction with existing machines, for example: angle grinders, drill presses, routers etc. The accessories generally use the existing machines powerhead to operate the saw blade, or an alternative cutter, and provide a jig or means of guiding the cutter.

To date the most effective accessories have provided attachments for fitting

to existing hand held power tools so as to convert the hand power tools into facsimiles of the existing dedicated biscuit joiners, even so far as mimicking the mode of operation of dedicated biscuit joiners.

In particular the attachments available for right angle grinders produce a machine having a very similar configuration to the dedicated biscuit joiners.

The router is another popular power tool of choice for biscuit joinery because of the ready availability of slot cutters as standard router bits and because the high rotation speed of the cutter in the router is particularly well adapted for biscuit joinery. The router is primarily a hand held tool and as with right angle grinders, the majority of biscuit cutting accessories for use with routers have concentrated on providing an assembly for attachment to a router as a hand held tool with the combination of router and accessory mimicking the mode of operation of a dedicated biscuit joiner. US Patent 4,942,912 discloses such a router accessory comprising an attachment for fitting to the base of a router. The attachment mimics the shoe assembly of a dedicated biscuit cutter, including the reciprocally movable action of the shoe relative to the cutter. As such, this accessory is principally adapted for use with a hand held router and imposes the limitations common with dedicated biscuit joiners including the complex sliding mechanisms required to ensure parallel reciprocity of the shoe assembly relative to the blade. When used hand-held, the weight, awkwardness and start-up torque thrust of the router can all contribute to possible inadvertent movement of the tool in relation to the proposed slot, resulting in an inaccurate slot. As well it is awkward and difficult to locate and hold such a modified router against the ends of workpieces, especially narrow workpieces or mitre cut or bevel cut ends. More significantly, such router accessories have the limitation where only one half of a joint can be cut during a single operation of the machine. It is not practical or even possible with any of the existing machines or accessories to cut more than one slot (or one half of a joint) without having to relocate the machine to cut the other half of the joint.

The action of moving the machine to effect each cut in two separate

workpieces intended for jointing, introduces many possible sources of error into the action of jointing. Firstly, each workpiece to be jointed must be accurately marked to determine the position of the centre of the slot. Each workpiece must then in turn be securely clamped in a vice or work holder in an orientation which presents the face end or edge to be slotted in the most safe and comfortable manner and in the correct orientation for the desired joint. This is especially difficult in the case of mitred corners, and slots in the ends of narrow stock. The reciprocating fence of the tool must in these cases be precariously balanced on a very small support area. As well, the support face of the tool or attachment is only bearing on a narrow portion of the workpiece, making precise alignment of the slot parallel to the datum face difficult. Tool control is consequently very difficult, especially if the tool kicks sideways upon start-up or upon the cutter entering the workpiece. In addition, the requirement to move the machine and the workpieces about generally results in the moving of the workpieces away from their intended orientation in the joint which can cause confusion and result in incorrect cutting. The process is slow, and there is no easy method of setting up for the identical slotting of multiple workpieces, which is often required in plate joinery.

To date an accessory for plate or biscuit joinery has not been available to overcome many of the aforementioned problems. In particular an accessory or dedicated machine has not been available which provides a fast, accurate and safe means of biscuit joining two or more workpieces where the workpieces are placed on the jig in the same orientation as they are intended to be joined, providing maximum support on three relevant datum faces (Table Top, Cross-Slide or Stop Means, Parallel Guide faces), and the two cuts being made consecutively in one swift operation without the need to realign or reposition the workpieces relative to the jig. Object and Statement of Invention

One object of this invention is to provide an improved plate/biscuit joinery jig- Accordingly the invention provides a jig for guiding workpiece(s) into engagement with a rotary cutter driven by a power tool such as a router for cutting

slots in the workpiece(s), said jig including an elongate fence having parallel guide faces formed with opposed windows, said fence having an internal cavity between said faces in the region of said windows for receiving the rotary cutter, means for mounting the fence for reciprocation or oscillation with respect to the cutter to allow the cutter to be alternately exposed through the opposed windows when the fence is reciprocated or oscillated to thereby form slots in workpieces held against said guide faces.

Preferably, a stop means is adjustably mounted on top of said fence to enable accurate location of workpiece(s) to be slotted with respect to said windows. Since the jig has parallel guide faces with opposed windows, two workpieces are able to be slotted in one (oscillatory) operation by locating the workpieces against the guide faces, using a stop means if desired, and then reciprocating the fence to form a slot in each workpiece. Thus, the jig enables two workpieces to be pre-positioned in their intended connected orientation, and then without changing their relative orientations, allows the workpieces to be grooved in one rapid oscillatory action to accurately form the biscuit receiving slots in the workpieces.

The fence is preferably formed as an elongate element, such as an aluminium extrusion or a rectangular hollow section substantially channel shaped. In one form of the invention, the mounting means comprises pivot means near one end of the fence. A limit means for limiting the pivotal movement of the fence to control the depth of the slots cut in the workpieces is also fitted to the fence. The limit means may be provided within the confines of the fence by providing adjustable abutments on a mounting plate secured to a supporting table or other workstation. If desired the same mounting plate can provide the pivot for the fence.

Alternatively, and preferably, the limit means may be arranged externally at the free end of the fence, such as by a slotted plate having adjustable stops and engaged by means attached to the free end of the fence. The fence is preferably spring biased to return to its central or inoperative position so that the cutter is always within the fence when the jig is not in use.

The stop means comprises a cross slide stop means adjustably and removably mounted for sliding movement along the fence. The stop means preferably has guide faces at 90° and at least additionally at 45° to both fence guide faces. Alternatively, the stop guide face(s) may be angularly adjustable. The opposed windows are preferably capable of being closed by one or more safety shutters to prevent finger contact with the cutter or its exposure through either window by inadvertent movement of the fence.

In another aspect the invention provides a jig as defined above in combination with a workstation adapted to support a rotary cutter in an inverted condition. The rotary cutter is preferably driven by a router. Brief Description of the Drawings

In order that the invention may be more readily understood, preferred embodiments thereof will now be described with reference to the accompanying drawings in which: Figure 1, is a perspective view from above of a jig according to one embodiment of the invention mounted on a router table top;

Figure 2, is a fragmentary exploded elevation showing the preferred method of mounting the cross slide to the guiding fence;

Figure 3, is a plan view of the jig of Figure 1; Figure 4, is a perspective end view of a limit stop and spring return mechanism for the jig fence;

Figure 5, is a plan view from beneath of the limit stop and spring return mechanism of Figure 4;

Figure 6, is a fragmentary sectional elevation of the limit stop and spring return mechanism;

Figure 7, is an enlarged fragmentary side elevation of the fence showing one window and its associated safety shutter;

Figure 8, is a sectional end elevation of the fence showing the safety shutters; and Figure 9, shows a selection of the joints able to be fabricated using the jig embodying the invention.

Description of Preferred Embodiment

Referring firstly to Figure 1 of the drawings, the jig according to the presently preferred embodiment of the invention comprises an elongate fence or arm 1 comprising a hollow rectangular section member having a top wall 2, a bottom wall 2a and side walls 3 and 4 defining parallel guide faces, each of said side walls 3 and 4 being formed with opposed rectangular windows 5 and 6 dimensioned to enable passage of the cutter C of a router mounted on the workstation table top 21 to be described below. The side walls 3 and 4 of the fence 1 are extended at the top by flanges 9 and 10 which extend outwardly from the top wall 2 and then inwardly to define a track 11 in the top of the fence or arm 1. The outward angling of the flanges 9 and 10 provide an excellent finger grip when manually holding a workpiece against the fence 1.

As shown most clearly in Figures 1 and 2, a cross-slide stop 12 is adjustably attached to the fence 1 and, slides on the side portions 9 and 10 and is clampable in any desired position on the fence 1 by means of a threaded T-nut 13 engaging a coach bolt 14 which engages a square aperture in a shaped clamping plate 15 positioned in the slot 11 to engage the inner faces of the inwardly directed portions of flanges 9 and 10, as illustrated most clearly in Figure 2 of the drawings. The cross slide stop 12 has a central saddle portion 16 which is shaped to rest on the side walls 3 and 4 and supported by the upper edges of flanges 9 and 10, and is formed with perpendicular guide faces 17 and 18 and angular guide faces 19 and 20 each formed as an integral part of a sheet metal pressing to provide both rigidity and accuracy, although the cross slide stop 12 may be formed in other ways.

As shown in Figures 1 and 3, the jig embodying the invention is fitted to a workstation, such as a router table top 21, usually of pressed sheet metal construction, and the fence 1 is mounted on the table top 21 by pivot means, indicated by the general reference numeral 22, at one end of the fence 1, while limit stop means, indicated by the general reference numeral 23, is fitted to the other end of the arm and to the table top 21. In the present embodiment, the pivot means 22 comprises a molded plastic "bung" having a head 24 and a shank 25 having an upper portion 26 which is a frictional fit in an opening in the base of an end closure

27 for the fence 1 having a triangular wedge shape as shown.

The shank 25 has a waist portion 28 and a deformable end portion 29 which engages a burst-formed hole 30 in the table top 21. The end closure 27 has triangular sides 31, 32 extending from the base, and the sides have outwardly extending securing dimples 33, 34 which engage locating holes 35, 36 in the sides 3 and 4 of the fence 1 and this allows the fence 1 to be lifted at its free end to an elevated temporary rest position almost perpendicular to the table top 21, dimensioned to give access to the cutter C of the router mounted on the table top 21. The end closure 27 can be made from molded plastic or formed from metal sheeting. When the fence 1 is lying horizontally along the table top 21, the engagement between the shank 25 and the hole 30 allows the fence 1 to be pivoted with respect to the table top 21 within the limits provided by the limit stop means 23 to be described further below.

The limit stop means 23 includes two cooperating parts, the first part comprising a molded plastic vacuum attachment 37 which closes the other end of the fence and has side portions 38, 39 having dimples 40, 41 which engage locating holes 42, 43 in the sides 3, 4 of the fence 1. The attachment 37 is able to pivot in the holes 42, 43, and the side portions 38, 39 have shaped cam portions 44, 45 at their lower edges which are dimensioned to engage the table top 21 as the fence 1 is lowered onto the table to pivot the attachment 37 in a clockwise direction. The attachment 37 has a downward extension 46 having an inwardly directed tongue 47 which is adapted to engage a slot in the other part of the limit stop means 23 when the fence is lowered onto the table top 21.

The other part of the stop means 23 is shown most clearly in Figures 4 and 5, and comprises an arcuate guide plate 50 having a central slot 51 dimensioned to receive the tongue 47 and adjustable limit stops 52, 53 having clamping knobs 54, 55 which anchor the limit stops 52, 53 in any desired position along the length of the slot 51. Guide marks 56 for the limit stops 52, 53 can be marked on the guide plate 50 as shown for the slot sizes to suit the three most common sizes of biscuits commercially available. The guide plate 50 is bolted to the end flange of the table top 21 by means of bolts 57 engaging the holes 58 shown in Figure 4.

A mounting plate 59 is secured under the table top 21 by the bolts 57, 58 and a pair of fence biasing arms 60, 61 are mounted on the plate 59 on pivot pins

62, 63 secured to the plate 59. The fence biasing arms 60, 61 are spring biased by means of a tension spring 64 engaging holes 65, 66 in the arms 60, 61. A central stop 67 is provided by a downwardly directed burst-formed tab in the plate 59 and the stop 67 in co-operation with spring 64 keeps the arms 60, 61 in a central rest position when the fence 1 is at rest. The limit stop 67 also ensures the fence does not substantially over-run the central rest position when returned from its pivoted condition by spring 64. It will be appreciated that the tongue 47 on the downward extension 46 engages the slot 51 and is located between the down-turned ends of the arms 60,

61. As the fence 1 is manually pivoted in either direction, the tongue 47 engages one or other of the arms which is then pivoted about its pivot pin until the inwardly directed tongue 47 strikes one of the stops 52, 53. Thus, by locating the stops 52, 53 at one of the marks 56 corresponding to the depth of the desired biscuit slot, the fence 1 is easily pivoted to cause the required depth of slots to be cut by the router cutter C in the workpieces held against the fence 1 and the cross-slide stop 12.

When the cuts have been completed the fence 1 is returned to its central rest position by the action of the spring 64 and the stop 67, in which position the cutter C is located safely within the fence 1 and the cutter C is therefore never exposed while at rest.

The table top 21 has an opening 70, the edge of which is covered by a protective insert 71 through which the cutter C of a router R attached to the table top 21 in a standard manner (not shown) protrudes. As described above, the windows 5 and 6 in the sides 3 and 4 allow the fence 1 to be pivoted to expose part of the cutter C on either side of the fence 1 to form a groove in a workpiece to a depth determined by the adjustment of the stops 52, 53. The height of the cutting blade of cutter C can be adjusted by the user in its vertical height above table top 21, for slotting different thicknesses of material. To prevent finger entry, and to assist in sawdust containment, the windows

5 and 6 are preferably provided with "roller shutter"-type guards 75, 76 each

formed with a narrow rectangular opening 77 dimensioned to allow passage of the cutter blade C when the fence 1 is pivoted as described above. The shutters 75, 76 are formed from ribbed or grooved flexible plastic material formed with narrowed top end portions 78, 79 having their facing edges formed with rack teeth 80 adapted to mesh with pinion teeth 81 formed on a pinion member extending from a control knob 82 rotatably fitted to the top wall 2 of the fence 1 in the manner shown in the drawings. The shutters 75 and 76 are guided for sliding vertical movement within the fence 1 by means of tabs 83 and 84 which have been struck from the sides 3 and 4 of the fence 1 as shown in Figures 7 and 8. Thus by rotating the control knob 82 in the required direction, the shutters 75 and 76 are simultaneously raised or lowered within the fence 1 to bring the openings 77 into alignment with the cutting blade of cutter C. Since the shutters 75, 76 are made from plastic, the cutter C wjll not be damaged in the event that it accidently contacts the shutters and the shutters are easily replaced in the event that they are severely damaged. The end fitting 37 is formed with a generally cylindrical nozzle to which a suction pipe from a vacuum cleaner or other suction source can be fitted to extract sawdust from the fence 1 as the cutter operates to form slots in the workpieces. A deflector D is mounted within the fence 1 on the pivot side of the windows 5, 6 to deflect the sawdust formed by the cutter C towards the suction end of the fence 1. Since the lower edges of the fence engage the table top 21, the application of suction to the fitting 37 causes an air stream to flow through the restricted openings 77 in the safety guard, past the cutter C to collect substantially all of the sawdust created during the slotting operation. The sawdust collecting efficiency is further enhanced if the fence 1 is made of a rectangular hollow section extrusion with a bottom wall 2a, as described above, or if the fence 1 is a channel-section extrusion, it should preferably be fitted with "snap-in" bottom sections (not shown) on either side of the cutter hole 70.

By removing the suction hose from the fitting 37, if necessary, the fence 1 is able to be pivoted upwardly to expose the cutter C for necessary adjustment or servicing operations.

Referring now to Figure 9 of the drawings, examples of the types of joints

that can be formed using the jig embodying the invention are shown. As shown in broken outline in Figure 3 of the drawings, a first workpiece Wl requiring a biscuit jointing slot to be cut in the end of the workpiece is positioned on the table 21, against the guide face 17, and up against the side 3 of the fence 1 while a second workpiece W2 requiring a biscuit jointing slot to be cut in the edge is positioned on the table, against the guide face 18, and up against the side 4 of the fence 1 following which the router is activated to turn the cutter C and the fence 1 is pivoted first in one direction and then in the other to cut corresponding slots in the workpieces Wl and W2 while the workpieces are held in the orientation in which they are to be joined. If a mitred joint is required, the guide faces 19 and 20 are used, the cross slide stop 12 being re-positioned or reversed if required, so that the mitred ends to be joined are adjacent with the windows 5 and 6. Depth of cut is controlled by adjustment of the stops 53, 54 to the desired positions corresponding to the biscuit size being used. It will be appreciated that the jig embodying the invention allows workpieces to be slotted without the need for marking and careful location of the workpiece with respect to the cutter since this function is achieved by the cross slide stop 12.

The jig described also allows the fence 1 to be held in any desired angular position to expose the cutter through either of the openings 5 or 6 thereby allowing longitudinal slitting or shaping/molding of workpieces guided along the length of the fence 1.

One further safety feature will be noted from Figures 1 and 2 of the drawings wherein the cross slide stop is shaped at either side to provide clearance for the maximum allowable exposure of the cutter C through either of the openings 5 and 6. This is to prevent accidental contact between the cross slide stop and the cutter. It also allows the cross slide stop to be used as a moving guide during slitting across the end-grain of small workpieces.

If desired, the cross slide stop guide faces 19 and 20 could be made adjustable to allow workpiece supporting angles other than 90° and 45° as shown in each of the embodiments.

A still further safety device is illustrated in Figure 10 of the accompanying

drawings to provide a rest for bevel cut workpieces, and a support for workpieces standing on edge against the fence 1. It comprises an angular skate member 90 which is configured to engage the side portion 9 of the fence 1 as shown in Figure

10 and having a window 91 formed with side flanges 92, 93 which engage the window 5 in the side wall 3. The skate 90 has a generally flat portion 95 which rests on the table top 21 and is formed with raised slotted tracks 96, 97 which are engaged by grooves formed in an angular fence 98 which is capable of being clamped at any desired position in the slotted tracks 96, 97 by bolts and wing nuts as shown. The fence has a pair of flat leaf springs 99, 100 mounted in openings to enable the safety fence 98 to be reversed in the case of very thin workpieces standing on edge and the springs 99, 100 engage the workpiece to press it against the vertical wall of the skate 95 engaging the main fence 1. The skate member 95 can be fitted to either side of the main fence 1 and protects the user in the event that the cutter C breaks through the outer face of a thin workpiece (for example less than about 18mm thick). When cutting biscuit slots on bevel cut pieces, the fence

98 is adjusted on its tracks 96, 97 until it is in the correct position for its vertical face to support the underside of the workpiece at the required angle; i.e. the bevel cut face will be flush against the vertical wall of skate 90.

The jig according to the embodiment of the invention can be easily retrofitted to any suitable sized router table by drilling the required holes in the table top 21 to fit the plates 50 and 59, and to fit the fence 1. If it is not practical to create a flanged hole (as in 30, Figure 1) in the table, the "snap-in" bung can be reversed and bolted to the table top 21 via an 8mm bolt hole. The head 24 then becomes a large washer and pivot centre for end closure 27. While one presently preferred embodiment and several safety devices have been described above, it should be appreciated that different mechanisms may be utilised to achieve the same or similar operation of the jig embodying the invention.

In this regard, different mechanisms have been described in our Provisional Patent

Specification PL 9446 dated 17 June 1993 forming the priority document of the present application and the contents of that provisional specification are incorporated herein by cross-reference.