This invention relates to a drilling jig and is more particularly concerned with a jig or attachment which can be used with a portable rotary power tool, such as a portable electric drill, to facilitate drilling in inaccessible places. The invention is particularly concerned with a jig to facilitate boring of joists, eg to accommodate electrical leads or pipe work.

It is difficult to bore axially aligned holes through a row of joists in situ because the distance between joists is generally insufficient to receive a standard size of portable electric drill wherein the chuck and therefore the drill bit extends axially of the motor shaft. It is possible to fit a right angle drive adapter to a drill to enable drilling at right angles to the axis of the motor shaft. However, these adapters are time consuming to fit because they require the standard drill chuck to be removed before, the adapter can be fitted. Also, it is difficult to apply the necessary axial pressure and control to the drill bit in use when a right angle drive adapter is fitted.

An object of the present invention is to obviate or mitigate at least some of the above disadvantages.

According to the present invention, there is provided a drilling jig which is adapted to be driven by a portable rotary power tool, said drilling jig comprising a first rotary connector adapted to be operably connected with the power tool, a second rotary connector adapted to have a drill bit or other cutter connected therewith in use, a transmission operably interconnecting the first and second rotary connectors, a body mounting the first and second rotary connectors and said transmission, and a support structure connected with the body and including

(a) abutment means adapted to abut a joist or the like, and (b) a manually operable linkage for effecting relative movement between the abutment means and the body in a direction substantially axially of the second rotary connector to enable a joist or the like to be drilled.

Whilst the abutment means may be adapted to abut a joist or the like, or other fixed structure eg a wall, adjacent to that which is to be drilled, it is preferred for the abutment means to be adapted to abut the joist or the like which is to be drilled. For this purpose, it is necessary for the abutment means to face the second rotary connector so that the abutment means and the drill bit or other cutter can engage against opposite sides of the joist or the like.

The body is preferably an elongate body which extends substantially perpendicularly with respect to the axis of rotation of the second rotary connector. In one embodiment, the first and second rotary connectors are mutually parallel and spaced apart sufficiently for the first rotary connector to be disposed above the joist or the like in use when the second rotary connector is disposed in the required drilling position. In another embodiment, the first rotary connector is inclined, preferably at right angles, relative to the second rotary connector.

In a preferred arrangement, there is provision for setting the distance below the top of the joist or the like at which drilling can be effected.

The linkage is preferably a substantially parallel movement linkage so that, in use, the second rotary connector is moved substantially axially upon operation of the linkage.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic perspective view of one example of drilling jig according to the present invention,

Figure 2 is a schematic perspective view of a second example of drilling jig according to the present invention,

Figure 3 is a schematic side elevation of a third example of drilling jig according to the present invention, and

Figure 4 is a schematic side elevation of a fourth example.

Referring now to Figure 1 of the drawings, the drilling jig is intended for the in situ drilling of holes in joists 10 in a house using a standard portable electric rotary power tool 12. The jig comprises a box section elongate body 14 provided with a mounting sleeve 16 at one end and a chuck 18 at the opposite end. The mounting sleeve 16 is arranged to be clamped to the body of the power tool 12 so that the chuck of the latter is received within the sleeve 16 and engages a rotary drive shaft (not shown) constituting a first rotary connector. The chuck 18 is mounted on a second rotary shaft 20 constituting a second rotary connector. The first and second rotary shafts extend from opposite sides of the body 14 and have substantially parallel axes of rotation. A toothed belt and pulley transmission (not shown) is disposed within the body 14 and serves to interconnect the first and second rotary shaft so that operation of the tool 12 causes rotation of the chuck 18. As shown in Figure 1, the chuck 18 carries a wood boring bit 22.

The drilling jig further comprises a support structure indicated generally by arrow 24. The support structure comprises a sleeve 26 slidably mounted on the body 14, and a pair of cranked link arms 28 which are mutually parallel and which are pivotally attached at their top ends to the sleeve 26. The link arms 28 extend downwardly and outwardly of the body 14 to a location approximately midway along the latter, although this is not critical. It is possible indeed for the body 14 to be extended well above sleeve 26 in order to enable the operator to avoid having to bend over to use the jig. The link arms 28 are pivotally attached to a pair of straight link arms 30 also forming part of the support structure. The link arms 30 are pivotally attached at their lower ends to the body 14 and extend upwardly and outwardly. Beyond their pivotal connection with the link arms 28, the link arms 30 extend further upwardly and outwardly to be interconnected at their upper ends by a handle 32. Beyond their pivotal connection with the arms 30, the link arms 28 bend so as to extend more perpendicularly away from the body 14 in order to acommodate the joist 10 to be drilled, before bending downwardly to extend substantially parallel with the body 14. At their lower ends, the link arms 28 are turned inwardly towards the body 14 to define a pair of sharp abutments 34 which are directed towards the lower end of the body 14, ie towards the second rotary shaft 20, chuck 18 and boring bit 22.

The support structure 24 further includes an additional sleeve 36 slidably mounted on the body 14 but provided with a securing screw 38 to enable the sleeve 36 to be fixed in any desired sliding position on the body 14. The sleeve 36 carries a stop 40 in the form of a flange which is freely slidable between the pairs of link arms 28 and 30.

In use, the stop 40 engages the upper surface of a joist 10 to be drilled and the sleeve 36 axially adjusted and fixed into position using the screw 38 so that the boring bit 22 lies at the required depth below the top surface of the joist 10. Usually, the joist 10 will be drilled at about half its depth. The power tool 12 is energised to rotate the bit 22 and the handle 32 is moved in the direction of arrow 42. This movement of the handle 32 causes the body 10 and the abutments 34 to be moved towards each other so that the abutments 34 are pressed against the opposite side of the joist 10 to that against which the bit 22 is engaged. Further movement of the handle 32 in the direction of arrow 42 causes a hole to be bored through the joist 10. During movement of the handle 32 in the direction of arrow 42, relative pivoting movement of the link arms 30 and 28 occurs together with sliding movement of the sleeve 26 on the body 14. The relative lengths of the arms 28 and 30 between their pivotal connection with the various parts is chosen so that substantially linear movement of the boring bit 22 takes place along its axis of rotation within the relatively limited range of movement required to bore a hole through the joist 10. Exact linear movement is achieved if the following distances are all equal:-

1. On link arms 28, the distance from the top pivot on sleeve 26 to the pivot at the intersection of arms 28 and 30.

2. On link arms 28, the distance from the pivot at the intersection of arms 28 and 30 to the abutments 34.

3. On link arms 30, the distance from the pivot at the intersection of arms 28 and 30 to the bottom pivot adjacent to shaft 20.

Referring now to Figure 2 of the drawings, the drilling jig illustrated therein is similar to that of Figure 1

and similar parts are accorded the same reference numerals. However, in this embodiment, the support structure 24 is disposed on the opposite side of the body 14 and is arranged so that the abutments 34 engage against a joist which is adjacent to that to be bored. Otherwise, the boring operation takes place in much the same way.

In both of the above described embodiments, it will be appreciated that the power tool 12 lies well above the joists 10 and so no restriction on the movement of the power tool 12 is imposed by the relatively limited spacing between the joists 10.

Referring now to Figure 3 of the drawings, the drilling jig illustrated therein operates in a similar way to that described above in relation to Figure 1 and similar parts are accorded the same reference numerals but in the 100 series. In this embodiment, sleeve 116, instead of being disposed at the upper end of body 114, is disposed approximately midway therealong. Sleeve 116 is axially split and provided with a tightening bolt 144 to enable sleeve 116 to be secured to the body of the power tool (not shown) . The sleeve 116 is provided with a slot 146 therein to enable a chuck key (not shown) to be engaged with the chuck of the tool when the latter is disposed within sleeve 116. This enables the chuck to be secured to the previously mentioned first rotary connector which, in Figure 3, is embodied by rotary shaft which is indicated in dotted line by reference numeral 148. Sleeve 126 is arranged for telescopic sliding movement within body 114 rather than over body 114 as was the case with sleeve 26 and body 14. A steadying handle 150 is secured to the top of sleeve 126, although it could be attached to an extension to arms 128 in a similar way to handle 132 at the top of arms 130.

Second rotary shaft 120 at the bottom end of body 114 detachably mounts a hole saw 152 in the place of a chuck. In this embodiment, the hole saw 152 is mounted in screw threaded fashion on the shaft 120. However, it is preferred to provide a quick release mounting such as a bayonet connection between the hole saw 152 and the shaft 120 so as to facilitate removal of wood cuttings from within the hole saw 152 after a boring operation. The hole saw 152 is provided with a central drill 154 which extends beyond the hole saw 152 to act as a guide to facilitate drilling at the correct location and to hold the hole saw 152 steady as it is presented to the joist 10.

The transmission (not shown) within body 114 takes the form of a toothed belt and pulley drive between first shaft 148 and second shaft 120.

In a further example, the arrangement of first and second connectors 148 and 120 and toothed belt and pulley transmission is replaced by a right angled drive which is mounted at the lower end of body 114. The right angled drive may be a standard right angled drive adapter or it may be made specially as an integral part of the device, and manufactured as such. An example of this latter type of arrangement is illustrated in Figure 4 in which elongate body 214 is of circular cross-section and has mounting sleeve 216 coaxially arranged at its upper end to receive the chuck of rotary power tool 212 which engages with a rotary drive shaft disposed internally of sleeve 216. Hole saw 252 with central drill 254 is mounted on a rotary connector similar to connector 120 of Figure 3 but extending at right angles relative to the body 214. A right angle drive transmission interconnects the rotary connector and the rotary drive shaft. The drilling jig of Figure 4 operates in a similar manner to that of Figure 3 and similar parts are accorded the

equivalent reference numerals in the 200 series. It will thus be appreciated that the rotary power tool extends with its axis of rotation substantially axially of the body 214 rather than perpendicular thereto as is the case in the embodiment of Figure 3. With this type of arrangement, depending on the length of the body 214, the power tool may or may not be accommodated partly between adjacent joists 10 (in the ilustrated example, it is not) but its orientation is such that there is sufficient room between the joists to enable drilling.