CA2165416A1 - Biscuit joinery jig - Google Patents

Abstract

A biscuit joinery jig for guiding workpiece(s) (W) into engagement with a rotary cutter driven by a power tool such a router for cutting biscuit receiving slots in the workpiece(s), including an elongate fence (1) having parallel guide faces (3, 4) formed with opposed windows (5, 6) said fence having an internal cavity between said faces (3, 4) in the region of the windows (5, 6) for receiving the rotary cutter (C) pivot means (22) at one end of the fence for pivotally mounting said fence with respect to a table top (21) to which the rotary cutter (C) is mounted to allow reciprocation or oscillation of said fence with respect to said cutter whereby the cutter is alternatively exposed through the opposed windows (5, 6) when the fence (1) is reciprocated or oscillated to thereby cut biscuit receiving slots in workpieces held against said guide faces, a cross-slide stop means (12) adjustably mounted on said fence (1) and having guide faces (17, 18) and angular guide faces (19, 20) for locating workpieces to be slotted with respect to the windows (5, 6) and limit means (23) mounted at the free end of said fence (1) and comprising an end fitting (37) for the fence (1) having a downwardly and inwardly directed tongue (47) which engages a slot in a limit plate including stop means for limiting the angular movement of the fence with respect to the cutter (C) to control the depth of the biscuit receiving slot formed in the workpiece. The jog arrangement allows virtually simultaneous slotting of workpieces by holding the workpieces against the fence, in a orientation similar to the intended biscuit joined orientation of the workpieces, and oscillating the fence about the pivot to engage the cutter with the workpieces.

Description

wo 95/00302 216 S 41~ PCT/AU94/00336 BISCUIT JOINERY JIG
Field oi~ the Inver tion l~' This invention relates to accessories for use with power tools and inparticular to a jig adapted for use in conjunction with a fixed router equipped with 5 a slot cutting bit so as to f~cilit~te the cutting of slots for receiving biscuit plates as used in plate joinery.
R~-k~ound of Inven~ion 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 10 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 thedirection of the grain and slightly co~ e~sed with a surface embossed cross-h~trhPd p3ttçrn 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 15 supplied with adhesive the biscuits swell upon absorl,hlg the adhesive and effect a particularly strong joint.
While not so critical as in dowelling, the success of the joint depends on the accurate ~lignmpllt of the slots that must receive the biscuit. To that end, a range of dedicated m~chine~ have been available which generally comprise a motor driven 20 4" diameter saw blade and a reciprocally movable shoe assembly such that the shoe of the m?~hine can be accurately positioned on a workpiece and the rotating saw blade rnoved forward into the workpiece to cut the required slot at the selected~i.ct~nrJE from the datum face of the wo~hpicce.
,Although the dedicated m~rhines operate very well they are complex in 25 design and costly to produce and have only this one basic function. In response to these problems a range of alternative m~rhines have emerged, but more particularly a range of lower cost ~rc-pssories have emerged which aim to operate in conjunction with e~icting m~rhinPs, for Px~mple: angle grinders, drill presses, routers etc. The Xolies generally use the çxicting m~rhines powerhead to operate the saw blade, 30 or an alttorn~tive cutter, and provide a jig or means of guiding the cutter.
To date the most effective accessories have provided ~tt~chments for fitting 216~

2 PCT/AU94/00336 ~

to existing hand held powcr tools so as to convcrt the hand power tools into f~ccimiles of the existing dedicated biscuit joiners, even so far as mimicking the mode of operation of dedicated biscuit joiners.
In particular the ~tt~chments available for right angle grinders produce a 5 m~rhine 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.
10The router is primarily a hand held tool and as with right angle grinders, themajority of biscuit cutting accessories for use with routers have concentrated on providing an ~sembly for att~rhment 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.
1~US Patent 4,942,91'' discloses such a router acce~ol y Co~ lg an ~tt~Ç~ t for ~tting to the base of a router. The ~tt~rhment mimics the shoe ~c~e.mbly of a ~etiic~ted biscuit cutter, including the reciprocally movable action of the shoe relative to the cutter. As such, this ~ccec~ory is principally adapted for use with a hand held router and imposes the limit~tions common with dedicated biscuit 20 joiners including the complex sliding mech~ni.~m~ required to ensure parallelreciprocity of the shoe assembly relative to the blade. When used hand-held, theweight, 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, resl-lting in an in~Ccllrate slot. As well it is ~wkw~ld and difficult to locate and hold such 25 a morli~led router against the ends of workpieces, especially narrow workpieces or mitre cut or bevel cut ends. More significantly, such router accessories have the limisation where only one half of a joint can bc cut during a single operation of the m~rhine. It is not practical or even possible with any of the existing m~chines or ories to cut more than one slot (or one half of a joint) without having to 30 relocate the m~rlline to cut the other half of the joint.
The action of moving the m~chine to effect each cut in two separate 21fi5~1B

workpieces intended for jointing. introduces many possible sources of error into thc action of jointing. Firstly, each workpiece to be jointed must bc accurately marked to ~etermine 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 ~tt~chment is only bearing on a narrow portion of the workpiece, m~king precise alignment of the slot parallel to the datum face diifficult. Tool control is consequently very difficult, especially if the tool kicks sideways upon start-up or upon the cutter entering the workpiecc. ln addition, the reguirement to move the nl~rhine and the workpieces about generally results in the moving of the workpieces away from their inten~le~l orientation in the joint which can cause confusion and result in incorrect cutting. The process is slow, and thlere is no easy method of setting up for the identical slotting of multiple wor~ieces, which is often required in plate joinery.
To date an ~t cçssory for plate or biscuit joinery has not been available to overcome many of the aforementioned problems. In particular an accessory or dedicated m~chine 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 in~Pn-~ed to be joined, providingm~Ximlum 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.
O12ject alld ~t~t~nent of Inven~ion One object of this invention is to provide an improved plate/biscuit joinery jig-Acco~il~gly 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 2165 ~

WO 95100302 ` PCT/AU94/00336 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 cuttcr, means for mounting the fence for reciprocation or oscillation with respect to the cutter to S allow the cutter to be alternately exposed through the opposed windows when the fence is le~ ocated 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~g~in~t 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 intt~.n~le(l connected orientation, and then without ch~nging their relative orientations, allows the workpieces to be grooved in onerapid oscillatory action to ac~;ul~tely form the biscuit receiving slots in the w~,h~ieces.
The fence is preferably formed as an elongate element, such as an aluminium extrusion or a rectangular hollow section subst~nti~lly 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 tableor other work~t~tion. If desired the same mounting plate can provide the pivot for the fence.
~lt~ tively, 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.

216~

The stop means co,..~1ises 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 col-t~rt 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 ~u~o- I a rotary cutter in an inverted condition. The rotary e utter is ~efc1dbly driven by a router.
Rrief ~3~ .liQn ~f the Drawi-~gc In order that the invention may be more readily understood, p1efe11t;;d embo~l;ment.c thereof will now be described with reference to the acco"1panying drawings in which:
Figure 1, is a ~e1~e. Ii~/e view from above of a jig according to one embodrm~nt of the invention mounted on a router table top;
Figure 2, is a fragmentary exploded elevation showing the ~.~fe..ed method of mounting the cross slide to the guiding fence;
Figure 3, is a plan view of the jig of Figure I;
Figure 4, is a ~Gl~e~ e end view of a limit stop and spring return mech~ni~m for the jig fence;
Figure 5, is a plan view from beneath of the limit stop and spring return meçl~ m of Figure 4;
Figure 6, is a fragmentary sectional elevation of the limit stop and spring return meçh~ni~m;
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 shull~ ; and Figure 9, shows a selection of the joints able to be fabricated using the jig embodying the invention.

2165 41~
Wo 95/00302 PCT/AU94/00336 r~escription of P.~re,.~d Fmbodiment Referring firstly to Figure 1~of thé drawings, the jig according to the presently prefelled embodiment of the invention comprises an elongate fence or arm 1 COlll~liSillg a hollow rectangular section member having a top wall 2, a bottom wall 2a and side walls 3 and 4 ~l~.fîning 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 exten~ed at thetop by flanges 9 and 10 which extend outwardly from the top wall ~ and then inwardly to define a track 11 in the top of the fence or arm 1. The out~,vard ~n~ling of the flanges 9 and 10 provide an excellent finger grip when manually holding aworkpiece ~in.ct the fence 1.
As shown most clearly in Figures 1 and , a cross-slide stop 12 is adjustably ~tt~fh~A to the fence 1 and, slides on the side portions 9 and 10 and is cl~mp~ble in any desired position on the fence 1 by means of a threaded T-nut 13 e~gin~
a coach bolt 14 which engages a square apellule in a shaped clamping plate 1~
positioned in the slot 11 to engage the inner faces of the inwardly directed portions of fl~n~Ps 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 ' 1, usually of pressed sheet metal construction, and the fence 1 is mounted on the table top 21 by pivot means, in~lir~terl by the general reference numeral '2, at one end of the fence 1, while limit stop means, indicated by the general reference numeral "3, is fitted to the other end of the arm and to the table top ~1. ln the present embodiment, the pivot means c~ e a molded plastic "bung" having a head 24 and a shank 5 having an upper portion 26 which is a frictional fit in an opening in the base of an end closure -216~

27 for the fence 1 having a triangular wedge shape as shown.
The shan~ '75 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 7 has triangular sides 31, 32 extending from the base, and the sides have outwardly e~ten~l;ing 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, ~limP.n!~;ioned 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 Iying horizontally along the table top 1, the en~gement between the shank '5 and the hole 30 allows the fence 1 to be pivoted with respect to the table top 1 within the limits provided by the limit stop means 23 to be described further below.
The limit stop means '~3 int~ des two cooperating parts, the first part co~ ,fl~Lg a molded plastic vacuum ~tt~chment 37 which closes the other end of the fen,ce and has side portions 38, 39 having dimples 40, 41 which engage locatin~
holes 42, 43 in the sides 3, 4 of the fence 1. The ~t~chment 37 is able to pivot in the ho:les 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 ~t~çhment 37 in a clockwise direction. The ~tt~hment 37 has a downward exte-~ion 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 ~ll",lises 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 5'', 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 ';0 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 enp~ging the holes 58 shown in Figure 4.

2;~65~1~
WO 95tO0302 PCT/AU94/00336 A mounting plate 59 is secured under the table top '1 by the bolts ~7, 58 and a pair of fence biasing arms 60, 61 are mounted on the plate S9 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 eng~gin~ holes 65, 66 in the arms 60, 61. A centralS stop 67 is provided by a do~,lw~ldly 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 subst~nti~lly over-run the central rest position when returned from its pivoted condition by spring 64.
lt 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 ~, 53. Thus, by locating the stops 52, 53 at one of the marks 56 collc:,~onding 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 wulh~ieces held ~g~in~t 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 1 has an opening 70, the edge of which is covered by a protc~live 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 2~ windows S 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 d~ ed by the adjustment of the stops 52, ~3. 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 di~el.t thiclrn,os~es of m~teri~l.
To prevent finger entry, and to assist in sawdust containment, the windows ~ and 6 are ~re~l~bly provided with "roller shutter"-type guards 7~, 76 each 2165 11~
WO 9~i/00302 PCT/AU94100336 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 m~teri~l formed with narrowedtop end portions 78,79 having their facing edges formed with rack teeth 80 adapted o 5 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 m~nner shown in the drawings. The shutters 75 and 76 are guided for sliding vertical movement withinthe 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 ~2 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 will not be ~m~ged in the event that it ~ ently contacts the shutters and the ~h~ult~l~ are easily replaced in the event that they are severely damaged.
The end fitting 37 is formed with a generally cylindrical nozle to which a sl~ction pipe from a vacuum cleaner or other suction source can be fitted to extract SdWdl~ from the fence 1 as the cutter operates to form slots in the workpieces. A
deflec:tor 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 1, 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 subst~nti~lly all of the sawdust created during the slotting operation. The sawdust collecting efficiency is further enh~nce~ if the fence 1 is made of a rectangular hollow section extrusion with abottom wall 2a, as described above, or if the fence 1 is a channel-section extrusion, it should ~fe,ably 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 nece~ry, the fence 1 is able to be pivoted u~ ~dly to expose the cutter C for necessary adjustment orselvi~g operations.
Referring now to Figure 9 of the drawings, examples of the types of joints 21~5 ~16 ~ ~O 95/00302 PCTIAU94/00336 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 W1 re~uiring a biscuit jointing slot to be cut in the end of the workpiece is positioned on the table 21, ~g~in~t the guide face 17, and up ~g~in.~t the side 3 of the fence 1 while a second 5 workpiece W2 requiring a biscuit jointing slot to be cut in the edge is positioned on the table, ~in~t the guide face 18, and up ~g~in~t 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 co"c~,onding slots in the wulk~ieces W1 and W2 while the work~ieces are held in the orientation in which 10 they are to be joined. If a mitred joint is required, the guide faces 19 and '~0 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 S and 6. Depth of cut is controlled by adjustment of the stops 53, 54 to the desired positions col,~onding to the biscuit size being used. It will be appreci~ted that the jig embodying the 15 invention allows wo~h~ieces to be slotted without the need for m~rking and careful location of the w~rhyiece 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 20 longit~in~l 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 ma~ um 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 ~u~ollillg angles other than 90 and 45 as shown 30 in each of the embodiments.
A still further safety device is illustrated in Figure 10 of the accompanying 2165~1~

draw;ngs to provide a rest for bevel cut workpieces, and a support for workpieces st~n~1ing on edge against the fence 1. It comprises an angular skate member 90 which is confi_ured to engage the side portion 9 of the fence 1 as shown in Figure 10 and having a window 91 formed with side flanges 9'', 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 en~e~l 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 workpiecesst~nding on edge and the springs 99, 100 engage the workpiece to press it against the vertical wall of the skate 9~ eng~ging the main fence 1. The skate member 9~can be fitted to either side of the main fence 1 and protects the user in the event that tihe cutter C breaks through the outer face of a thin wolk~iece (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 ~g~in~t the vertical wall of skate 90.
The jig acco~Jillg 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 ~iese~ltly preferred embodiment and several safety devices have been described above, it should be appreciated that difft~ t mecll~ni~m~ may be tili~e-l to achieve the same or similar operation of the jig embodying the invention.
In this regard, difrelellt mech~ni~m~ 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.
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Claims (16)

CLAIMS:

1. A jig for guiding a 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 jigincluding 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 alternatively exposed through the opposed windows when the fence is reciprocatedor oscillated to thereby form slots in workpiece(s) held against said guide face(s), in their intended connecting orientation.

2. The jig of claim 1, wherein said mounting means comprises pivot means positioned near one end of the fence.

3. The jig of claim 1 or 2, further comprising limit means for limiting the pivotal movement of the fence to control the depth of slots cut in the workpieces by said rotary cutter.

4. The jig of claim 3, wherein said limit means is positioned at a free end of the fence and includes means adapted for attachment to a workstation such as a table supporting said rotary cutter.

5. The jig of claim 3 or 4, wherein said limit means includes an arcuate plate adapted for attachment to one end of said workstation/table and having a slot which is engaged by means fitted to a free end of the fence.

6. The jig of claim 5, wherein said slot engagement means includes a downwardly and inwardly directed tongue member projecting from an end fitting secured to the free end of the fence.

7. The jig of any one of claims 1 to 5, further comprising a stop means adjustably mounted on said fence to locate workpieces to be slotted with respect to said windows.

8. The jig of claim 7, wherein said stop means has guide faces which allow workpiece(s) to be aligned perpendicular or at angles to a longitudinal axis of said fence.

9. The jig of claim 4 or any one of claims 5 to 8 when appended to claim 4, wherein said limit means further comprises a pair of pivoted limit arms spaced at a rest position by a stop member to receive said slot engaging means between said limit arms, biasing means for biasing said arms towards said spaced rest position whereby when said fence is pivoted in one direction, said slot engaging means engages one of said limit arms and pivots it against the action of the biasing means which returns the limit arm and the slot engaging means to a central rest position when the fence is returned from its pivoted position.

10. The jig of claim 5 or any one of claims 6 to 9 when appended to claim 5, wherein said slot has adjustable stop means which limit the movement of said slot engaging means in the slot as the fence is oscillated with respect to the rotarycutter.

11. The jig of any one of claims 1 to 10, wherein said opposed windows are fitted with safety shutter means each having an opening which can be aligned with the rotary cutter at different heights above the table to allow passage of the rotary cutter through the respective opening and window whilst preventing finger entry and reducing sawdust escape.

12. The jig of claim 11, wherein said safety shutter means are movable by means of a control knob which directly drives the shutter means simultaneously with respect to each window through a gear mechanism.

13. The jig of claim 2 or any one of claims 3 to 12 when appended to claim 2, wherein said pivot means is in the form of a cylindrical bung member engaging the fence and adapted to engage a corresponding opening in said table to facilitate said pivotal oscillatory movement of said fence.

14. The jig of claim 13, wherein said bung is carried by means which pivotally engages the guide faces at said one end of the fence and which is configured to allow the free end of the fence to be raised in a plane generally perpendicular to the top of the table to allow access to the rotary cutter.

15. A biscuit joinery jig comprising a fence member having guide faces for two workpieces, window means in said guide faces, said fence member being formed to receive a rotary cutter between said guide faces in alignment with said window means, said fence member being mounted in use to enable said two workpieces to be previewed as to their joining by a biscuit joint, and then without changing their relative orientation, enables the workpieces to be accurately grooved in one oscillatory or reciprocating action to form corresponding biscuit receiving slots in the workpieces by means of which the workpieces are joined in the previewed condition.

16. A jig for holding two workpieces as they are grooved by controlled engagement with a rotary cutter driven by a power tool such as a router, said jig including a fence member having guide faces against which said workpieces are held during the grooving operation, said guide faces being orientated to allow said workpieces to be held in an orientation similar to the intended joined orientation of the workpieces.