Regulation 3.2 Revised 2/98 AUSTRALIA Patents Act, 1990 ORIGINAL COMPLETE SPECIFICATION TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: Macsim Fastenings Pty Ltd (ACN 000 056 119) ACTUAL INVENTOR: MACKAY-SIM, Fraser ADDRESS FOR SERVICE: Peter Maxwell and Associates Level 6 60 Pitt Street SYDNEY NSW 2000 INVENTION TITLE: DRILL HOLE DEPTH LIMITING DEVICE DETAILS OF ASSOCIATED APPLICATION NO(S) Nil The following statement is a full description of this invention including the best method of performing it known to me: m:\docs\20111009\228462.doc 2 DRILL HOLE DEPTH LIMITING DEVICE FIELD OF THE INVENTION The present invention relates to an improved drill hole depth limiting device which is removably attachable to a rotary drilling tool. 5 BACKGROUND ART Depth limiting devices facilitate precision drilling of holes through workpieces by regulating the depth to which a drill bit rotatably connected to a rotary drilling tool penetrates a workpiece, such as may be made from wood, plastic, metal, cement and composites of these materials, during a drilling 10 operation. A typical depth limiting device includes a stop collar or skirt and a connecting spindle of a rotary drilling tool. The skirt fits axially over the connecting spindle which has a connector end adapted to be inserted into a chuck or other gripping device of the tool, and an opposite bit retaining end 15 adapted to be structurally coupled to a required drill bit, thereby enabling the transmission of rotational power from the drilling tool to the drill bit. The skirt can rotate with the connecting spindle, and hence with the drill bit, and is attached to the connecting spindle of the drilling tool at a selected position which defines the depth to which the drill bit can penetrate the workpiece. That 20 depth corresponds to the point at which the rotating skirt comes into frictional contact with the workpiece during the drilling operation. Early depth limiting devices had skirts which would continue to rotate after contact with the workpiece because they were so attached to the connecting spindle that they could not stop rotating independently of the drilling 25 tool, thus marring the surface of the workpiece. More recently, depth limiting devices for drilling tools have been developed that reduce marring by having the skirt, or a portion of the skirt that 07/09/11 3 first comes into contact with the workpiece, independently rotatable with respect to the connecting spindle so that when the skirt or said portion comes into contact with the workpiece during the drilling operation, it stops rotating, albeit not immediately, whilst the drill bit continues to rotate but not advance. 5 These depth limiting devices, which have a workpiece contact structure that can stop rotating independently of the connecting spindle and coupled drill bit, have typically a closed skirt or cup-like contact structure that traps therewithin flying debris generated by the interaction of the drill bit and the workpiece during the drilling operation. Some of the trapped debris may be 10 compacted against the inside of the closed skirt to form an agglomerated mass which must be subsequently removed by the user. For a hole being drilled into a horizontal workpiece, any trapped debris that is not compacted against the inside of the closed skirt settles around the sides of the hole being drilled. The trapping of debris within the closed skirt accelerates after the skirt stops 15 rotating and remains stationery upon the workpiece, and whilst the drill bit continues rotating within the workpiece. Indeed, a significant amount of debris may become trapped within the closed skirt even before the skirt becomes stationery, such as when a countersink connecting spindle is used. For example, when it is required to drill a hole to receive a countersink insert so 20 that the head of the insert is countersunk within the hole at a selected depth, a connecting spindle is used that has a bit retaining end formed as an integral fluted drill portion (or countersink portion) for cutting a frustoconical cavity into the surface of the workpiece that precisely matches the head of the countersink insert. Due to the greater diameter range of the countersink portion than of the 25 drill bit, and its fluted structure, the countersink portion will generate a significant amount of debris from the workpiece towards the end of the drilling operation when the closed skirt is about to come into contact with the 4 workpiece. This debris will agglomerate within the closed skirt or settle around the sides of the hole being drilled. To reduce or prevent such agglomeration and settlement of debris, depth limiting devices have been developed that include open skirts that have 5 gaps or vents in the side of the skirt through which the flying debris may escape. The debris can now circulate around the outside of the depth limiting device, but may settle on or around an outer exposed screw, which is normally a hex key receiving set screw used to clamp or adjust the skirt to a selected position along the spindle. With prolonged use, the debris may build up to such 10 an extent that it impedes access to the set screw, such as by filling the hex socket head adapted to receive the hex key. When it is time to disconnect or adjust the position of the skirt relative to the spindle, time is lost cleaning out this debris filled set screw to enable the engagement thereof by the hex key. SUMMARY OF INVENTION 15 It is an object of the present invention to provide an improved drill hole depth limiting device that, during a drilling operation, prevents the build-up of debris on or around the set screw. According to the present invention, there is provided a depth limiting device for use with a rotary drilling tool in drilling a hole in a workpiece to a 20 depth limited by the device, the device comprising: (a) a skirt having an upper end portion and an open lower end portion adapted to frictionally engage the workpiece at the completion of the drilling of the hole, the skirt having gaps communicating between an inside space of the skirt and an outside space around the skirt, 25 (b) a spindle located axially through the skirt and having a connector end extending from the upper end portion of the skirt for connection to a gripping device of the rotary drilling tool, and an opposite bit retaining 5 end located internally of the skirt for retaining a hole forming drill bit at a precise position at which the drill bit projects through the open lower end portion to a predetermined extent corresponding to the required depth of hole to be drilled in the workpiece, the spindle providing a rotatable 5 mounting for the skirt, but the spindle and skirt being jointly rotatable during the drilling of the hole, (c) means for isolating the rotation of the spindle from the skirt when the open lower end portion of the skirt is frictionally engaged with the workpiece whereupon the skirt ceases to rotate, the isolating means 10 comprising an outer annular collar formed around the upper end portion of the skirt and an inner cylindrical neck formed intermediate the ends of the spindle, the collar rotatably mounted to the neck, (d) means for preventing the relative axial movement between the spindle and the skirt during the drilling of the hole, 15 (e) a set screw retained radially in the cylindrical neck for removably attaching the skirt to the spindle, and (f) a cut-out portion of the annular collar, wherein, in use, the skirt is manually rotatably positioned relative to the spindle so that the set screw is covered by the annular collar during the drilling of the 20 hole to prevent the build-up of debris on or around the set screw, but is manually repositioned after the drilling of the hole by rotating the skirt relative to the spindle so as to expose the set screw through the cut-out portion of the annular collar, thereby enabling access to the set screw. Preferably, the cut-out portion of the annular collar defines a mouth 25 which opens into one of the gaps of the skirt.
6 It is preferred that the said gap is between an adjacent pair of support arms which connect the outer annular collar with the open end portion of the skirt. In another preferred form, the open lower end portion of the skirt 5 includes a rubber O-ring which is compressibly engaged within, and protrudes partly from, a downwardly facing circular groove formed around the bottom surface of the open lower end portion. In yet another preferred form, the upper end of the inner cylindrical neck of the spindle has a first circumferential groove, and the lower end of the inner 10 cylindrical neck of the spindle has a second circumferential groove, the first and second circumferential grooves engaging therewithin respective means for preventing upward and downward movement of the skirt relative to the spindle. SUMMARY OF THE DRAWINGS In order that the invention may be more readily understood and put into 15 practical effect, reference will now be made to the accompanying drawings, in which; Figure 1 is a side, exploded view of a depth limiting device according to a preferred embodiment of the present invention, and also showing a hex key for use with the device, 20 Figure 2 is a side, partly sectional, assembled view of the depth limiting device of Figure 1, and Figure 3 is a perspective view from the underside of the depth limiting device of Figure 1. DETAILED DESCRIPTION OF THE INVENTION 25 The depth limiting device 10 shown in Figures 1 to 3 is for use with a rotary drilling tool, and serves to limit the depth of a hole drilled in a workpiece by the device 10.
7 The device 10 includes a skirt 12, a spindle 14, and means for isolating the rotation of the spindle 14 from the skirt 12. The skirt 12 has an upper end portion 15 and an open lower end portion 16 for engaging the workpiece at the completion of the drilling of the hole. A 5 rubber O-ring 17 is compressibly engaged within, and protrudes partly from, a downwardly facing circular groove (shown occupied by the O-ring 17 in Figures 2 and 3) formed around the bottom surface of the open lower end portion 16 of the skirt 12 to provide an improved frictional surface against the workpiece. The skirt 12 also has gaps 18 communicating between an inside space of the 10 skirt 12 and an outside space around the skirt 12. The upper end portion 15 of the skirt 12 is formed as an outer annular collar 22. There is a cut-out portion 24 of the collar 22 which defines an open mouth between an adjacent pair of support arms 26 which, together with two other equally spaced apart support arms, connect the outer annular collar 22 with the open end portion of the skirt 15 12. The gaps 18 are defined between adjacent pairs of the support arms 26, and allow flying debris from the drilling operation to escape therethrough. The spindle 14 is located axially through the skirt 12, and has a connector end 28 extending from the upper end portion 15 of the skirt 12 for connecting to a gripping device, such as a chuck, of the rotary drilling tool. The 20 spindle 14 also has a bit retaining end 30 opposite to the connector end 28, and which is located internally of the skirt 12 for retaining a hole forming drill bit 32. The drill bit 32 is so retained at a precise position at which the drill bit 32 projects through the open lower end portion 16 of the skirt 12 to a predetermined extent (or length) corresponding to the required extent (or 25 depth) of hole to be drilled in the workpiece. Intermediate the ends of the spindle 14 is formed an inner cylindrical neck 34. The collar 22 of the skirt 12 is rotatably mounted to the neck 34 of the spindle 14 so that, during the drilling of 8 the hole, the skirt 12 can jointly rotate with the spindle 14 in the absence of any frictional opposition to the skirt's rotation. The means for isolating the rotation of the spindle 14 from the skirt 12, which allows the skirt 12 to cease rotating when the open lower end portion 16 5 of the skirt 12 frictionally engages with the workpiece at the end of the drilling operation, is thus provided by the above described rotatable mounting and interaction of the outer annular collar 22 of the skirt 12 with the inner cylindrical neck 34 of the spindle 14. Relative axial movement between the neck 34 of the spindle 14 and the 10 collar 22 of the skirt 12 is prevented during the drilling of the hole by means of a circlip 36 and washer 38 which are engaged within a circumferential groove 40 formed at the upper end of the inner cylindrical neck 34 of the spindle 14, and by means of a split ring 42 which is engaged within an outwardly facing circumferential groove (shown occupied by the split ring 42 in Figures 1 to 3) 15 formed at the lower end of the inner cylindrical neck 34 of the spindle 14. A set screw 44 (which is preferably a grub screw) is screwably retained in an internally threaded hole 46 formed radially in the cylindrical neck 34 of the spindle 14. The set screw 44 has a hex socket head for receiving a hex socket (or Allen key) 48. The set screw 44, when tightened so as to exert clamping 20 force through its leading tip that projects through the inner side of the hole, prevents separation of the skirt 12 from the spindle 14. The set screw 44 is located at a part of the cylindrical neck 34 of the spindle that can be exposed, and is accessible to a user, when it is aligned with the cut-out portion 24 of the collar of the skirt 12 (see Figure 3). The set screw 25 44 can also be hidden from exposure or covered, and no longer be accessible to a user, by rotating the skirt 12 around, or relative to, the spindle 14, so that 9 the set screw 44 is no longer aligned with the cut-out portion 24 of the collar 22 of the skirt 12. Prior to beginning a drilling operation with the depth limiting device 10, the skirt 12 is manually positioned relative to the spindle 14 so that the set 5 screw 44 is covered by the outer annular collar 22. That position is maintained during the drilling operation, as there is no or minimal rotation of the skirt 12 relative to the spindle 14 in that time, and so this prevents the build-up of debris on or around the set screw 44. The skirt can be manually repositioned after the drilling operation by rotating the skirt 12 relative to the spindle 14 so as to 10 expose the set screw 44 through the cut-out portion 24 of the annular collar 22. This will then enable access to the set screw 44. It will be apparent to persons skilled in the art that various modifications may be made in details of design and construction of the depth limiting device described above without departing from the scope or ambit of the present 15 invention.