CHISEL

Abstract: A chisel for removing material (5) from a crack defined between two adjacent bricks, comprising a body (1) supporting an elongate tip (2) and defining shoulders (4) extending transversely of the tip. The width of the tip is less than the width of cracks from which it is desired to remove material, and the width of the shoulders is greater than the width of the cracks such that the shoulders limit the depth of insertion of the tip into the cracks. The shoulders may be fixed surfaces, which may be covered with or fabricated from materials which will not mark bricks across which they slide, or alternatively the shoulders may be defined by rollers (22).

Description: CHISEL The present invention relates to a chisel, and in particular to a chisel for removing material from a crack defined between two adjacent bricks. Masonary walls are generally built from bricks of regular or irregular shape with the bricks being separated by thin layers of mortar or the like. The primary purpose of the mortar is not to adhere adjacent bricks together but to provide a secure bed for one brick when it is placed upon an immediately adjacent lower brick. Over time the mortar becomes weakened and can become seriously eroded. If this occurs it is necessary to repair the wall by removing loose mortar from the cracks defined between adjacent bricks and repointing the wall, that is inserting fresh mortar or the like into the cracks. Traditionally, when a wall has been repointed, loose material is hacked out of the cracks between adjacent bricks using a simple pick the point of which is hammered into the mortar manually. This is a laborious process and accordingly alternative methods have been suggested. The most widely used alternative method is to insert a rapidly rotating abrasive disc into the- cracks between adjacent bricks. This is a highly effective method for removing unwanted mortar but presents various problems in that it generates large quantities of dust and can be highly dangerous in that there is a ' tendency for the disc to act as a driving wheel and pull the disc and its associated power tool across the face of the wall. This can cause physical injury and also can damage the wall surface if the disc runs across the face of bricks making up the wall. Furthermore it is difficult with a disc to clean mortar from a crack of only limited length, such as that defined between the adjacent ends of house bricks of conventional size. It has also been known to use simple narrow headed chisels to remove loose material from the cracks defined between bricks. Unfortunately there is a tendency either for the chisel to skate across the surface of the mortar or for it to be driven too deeply into the mortar. It is an object of the present invention to provide a chisel which obviates or mitigates the above problems. According to the present invention there is provided a chisel for removing material from a crack defined between two adjacent bricks, comprising a body supporting an elongate tip and defining shoulders extending transversely of the tip, wherein the width of the tip is less than the width of cracks from which it is desired to remove material, and the width of the shoulders is greater than the width of the said cracks such that the shoulders limit the depth of insertion of the tip into said cracks. Preferably the edges of the shoulders and the end of the tip are wedge shaped. The tip and shoulders may be of substantially the same thickness or alternatively the thickness of the shoulders may be greater than the thickness of the tip so as to increase the area of the shoulders facing the adjacent bricks. The area of the shoulders facing the adjacent bricks may be substantially planar or rounded. The end of the tip may be hollowed out on the side of the tip which in use faces away from the wall defined by the bricks. The end of the tip may also be provided with wear-resistent characteristics, for example by securing a sharpened tungston tip thereon, or by appropriate surface treatments. The shoulders of the body may be formed from the same material as the rest of the chisel, for example steel. If the shoulder is formed from a hard material however the surface of the bricks across which the shoulders slide may be marked by scratching or deeper surface damage. To prevent this happening, the shoulders may be covered with a material which slides easily over the brick surface, e.g. a plastics material such as nylon. The nylon may be in the form of one or more jackets screwed, rivetted or otherwise secured by for example a snap fit to the shoulders. Alternatively the shoulders may be formed of a plastics material. For example, a solid block of nylon may be fashioned with a central hole through which the tip of the chisel extends to project from the block, the block being prevented from slipping too far along the tip by a flange on the chisel. Alternatively, the shoulders may be in the form of one or more wheels or rollers which support the chisel and run against the surface of the bricks across which the chisel is advanced. This arrangement reduces wear to the shoulders, reduces resistance to the movement of the chisel, and avoids damage to the brick surface. The chisel may be provided with two pairs of rollers to provide a four point support for the chisel. The roller sizes may be adjustable, or the position of the rollers on the chisel may be adjustable, to determine the chisel depth of penetration for a given orientation of the chisel. The chisel tip may be removable to enable tips of various widths to be mounted on the chisel body, and to enable the replacement of worn tips. Generally however the chisel tip will be permanently secured to the chisel body. As is common with various tool assemblies, it is desirable in the case of the fixed-tip chisel described above to provide a quick release mechanism so that a chisel of one tip width can be rapidly replaced in a reciprocating tool by a chisel of a different width. This can be necessary where the width of a crack from which mortar is being removed varies along its length. Various quick release tool assemblies are known. For example, so-called "snap-on" tools are known which comprise a tool drive shaft having a square end which is a snap fit in a square-section socket of the tool head. There are also many quick release chuck assemblies where for example a tool can be released by pulling a retaining collar along the body of the chuck. There are circumstances however in which the known quick release tool assemblies are inadequate either because they are too bulky or because they require two-handed operation. For example, in the case of the chisel described above, the spacing between adjacent bricks from between which mortar is to be removed, and hence the maximum chisel width, can vary considerably from one part of a wall to another, and yet it is important for the chisel head to be as wide as possible if effective mortar removal is to be achieved. This means that it is often necessary to repeatedly switch between say three or more standard chisel tipsizes as one progresses along a single course of bricks. In such circumstances it is necessary to be able to hold the reciprocating tool in one hand while switching the chisel tip or the entire chisel with the other. This can be achieved satisfactorily if the chisel is a simple sliding fit in a bore of the reciprocating tool, the chisel being retained against accidental release from the tool by a simple spring-loaded latch. Unfortunately if, as is often the case, the chisel becomes jammed between adjacent bricks, it cannot be removed by simply pulling on the reciprocating tool body as such an action would simply disengage the reciprocating tool from the chisel and leave the chisel embedded in the wall. It is a further object of the present invention to provide an improved quick release tool assembly which can obviate or mitigate the above problems. According to a second aspect of the present invention, there is provided a quick release tool assembly comprising a tool holder which in use is driven by a power source, and a tool shaft which is in use received in the tool holder, wherein a groove is defined in the outer surface of the shaft, the groove comprising a first portion extending substantially axially from one end of the shaft, a second portion spaced from the said one end of the shaft and extending substantially circumferentially from the first portion, and a third portion extending substantially axially from the second portion and away from the said one end of the shaft, wherein the tool holder defines a tool shaft receiving bore into which a retaining pin projects radially to engage in said groove, the pin preventing movement of the shaft within the bore except in a direction which enables the pin to slide along the groove. Preferably retaining means are provided to prevent movement of the shaft relative to the bore unless a predetermined minimum force is applied to the shaft. When the shaft is inserted into the bore, it is positioned so that the pin can slide along the first portion of the groove, rotated about its axis so that the pin slides along the second portion of the groove, and then pushed home axially so that the pin slides along the third portion of the groove. If an attempt is then made to pull the shaft straight out the pin slides along the third portion of the groove but jams against the side wall of the second portion of the groove where it meets the third portion of the groove. Removal of the shaft requires rotation of the shaft about its axis. The retaining means ensures that the shaft cannot fall from the tool under its own weight as the result of for example random vibrations causing the shaft to rotate within the bore. The bore may be of circular cross-section, the retaining pin extending radially towards the bore axis. The retaining means may be a spring-loaded member which presses against a flat formed on the tool shaft to hold the shaft in friction engagement with the wall of the bore. The pin and spring-loaded member may be located on diametrically opposed sides of the bore, with the third portion of the groove in the flat being on diametrically opposed sides of the shaft. Alternatively the retaining means may be associated with the retaining pin, for example by arranging for the pin to be spring-loaded. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a first embodiment of the present invention; Fig. 2 is a view on the lines 2-2 of Fig. 1; Fig. 3 is a view on the lines 3-3 of Fig. 2; Figs. 4 and 5 are respectively schematic side and plan views of the chisel of Figs. 1 to 3 in use; Figs. 6 and 7 are respectively perspective views of a second embodiment present invention; Figs. 8 and 9 are respectively perspective views of a third embodiment present invention; Fig. 10 is a schematic side view of the embodiment of Figs. 8 and 9 in use; Fig. 11 is a side view of a modified tip of an embodiment of the present invention. ; Fig. 12 illustrates plastics jackets mounted on shoulders of the chisel; Fig. 13 is a view in the direction of arrows 13-13 of Fig. 12; Fig. 14 is a view of one of the shoulders of Fig. 12 in the direction of arrows 14-14 of Fig. 12; Fig. 15 is a perspective view of a one-piece shoulder assembly; Fig. 16 is a perspective view of a shoulder assembly for fitting on the tip of a chisel. Fig. 17 is a side view of a further chisel in accordance with the invention; Figs. 18 and 19 are views on the lines 18-18 and 19-19 of Fig. 17; Fig. 20 is a view of a still further embodiment of the invention; Fig. 21 is a view of the chisel of Fig. 20 after removal of support rollers. Fig. 22 is a side view of the body and tip of a further embodiment of the invention; Figs. 23 and 24 are respectively views in the lines 23-23 and 24-24 of Fig. 22; Fig. 25 is a side view of a tool shaft for use in a quick release mechanism to enable rapid replacement of one chisel by another; Figs. 26 and 27 are views in the lines 26-26 and 27-27 respectively of Fig. 25; Fig. 28 is a view on the lines 28-28 of Fig. 26; Fig. 29 is a view on the lines 29-29 of Fig. 28; Fig. 30 is an end view of a tool holder adapted to receive the shaft illustrated in Figs. 25 to 29; and Fig. 31 is a sectional view through the tool holder of Fig. 30 after insertion of the shaft illustrated in Figs. 25 to 29. Referring to Figs. 1 to 5, the illustrated chisel comprises a body 1 supporting an integral tip 2, the body 1 being mounted on a shaft 3 of conventional form which is intended for insertion into an appropriate tool of conventional design which reciprocates the shaft 3 parallel to the shaft axis. The body 1 defines shoulders 4 which extend transversely on either side of the elongate tip 2. As best seen from Fig. 2, the end of the tip 2 is wedge shaped as are the edges of the shoulders 4, the leading edges of the shoulders 4 being rounded to reduce the tendency of the shoulders to be embedded in a surface against which they are applied. In contrast the edge of the wedge shaped tip 2 is sharp. As shown in Figs. 4 and 5, the chisel of Figs. 1 to 3 is used by inserting the tip 2 into a crack defined between adjacent bricks 5 into contact with the surface 6 of mortar present in that crack. The shaft of the chisel is then reciprocated causing the tip 2 to dislodge any loose material and penetrate the crack until the shoulders 4 abut the surface of the bricks 5. Thus the depth of insertion of the chisel into the crack is limited by the shoulders. By adjusting the angle a (Fig. 4) the depth of insertion perpendicular to the face of the bricks can be adjusted. The tool can be advanced with the tool effectively being supported by the face of the bricks 5 on the shoulders 4. In the arrangement of Figs 1 to 3, the tip 2 and body 1 are of the same thickness and could be formed from a plate of material of uniform thickness. The thickness of the chisel of Figs. 1 to 3 is relatively limited however and is insufficient to prevent one of the shoulders 4 dropping into a crack running transverse to the crack along which the chisel is being advanced. To prevent this possibility the thickness of the chisel could be increased as in the case of the embodiment shown in Figs. 6 and 7. The same reference numerals are used in the case of the embodiment of Figs. 6 and 7 as in the case of the embodiment of Figs. 1 to 3 and further detailed explanation is therefore not required. As an alternative to the arrangement of Figs. 6 and 7, the body 1 of the chisel could be non-uniform so as to define a rounded surface 7. With such an arrangement as illustrated in Fig. 10 whatever the angle of inclination of the chisel to the plane defined by the wall surface the body 1 of the chisel always presents a relatively large area which bears against the bricks adjacent the crack along which the chisel is being advanced. Again the same reference numerals are used in the case of Figs. 8 to 10 as in the case of Fig. 1 to 3. Fig. 11 schematically illustrates an alternative formation for the tip of the chisel of Figs. 1 to 3. As indicated by dotted line 8 a central portion of the surface of the chisel which in use faces away from the material across which the tool is advanced can be hollowed out. This effectively makes it possible to use a sharper chisel tip whilst retaining a reasonable strength. Figs. 12 to 14 illustrate jackets which in use are placed on the shoulders of a chisel as shown. The jackets 9 cover the shoulders to prevent damage to the surface of bricks across which the shoulders slide in use. The jackets are secured in position by screws 10 to enable their replacement when worn. A wear resistent tip 11 is provided on the end of the chisel. Fig. 15 shows a one-piece jacket assembly comprising two jackets 12 interconnected by a strip 13 to prevent their separation. Lips 14 are designed to snap over the top edges of the shoulder, thereby obviating the need for securing screws. Fig. 16 shows a one-piece block 15 of nylon which defines a square section through hole 16. The tip of the chisel (not shown) is also of square section and is pushed through the hole 16 to project beyond the block. A flange is provided on the chisel shaft (not shown) to prevent the shoulder block slipping too far along the shaft. The block may be simply a tight fit in the chisel tip or may be secured against accidental removal by appropriate clip formations. It will be appreciated that different thicknesses of material may be used for the jackets or shoulder block to provide a range of effective lengths for the chisel tip to thereby adjust depth to which mortar is removed. Figs. 17, 18 and 19 illustrate a further embodiment of the invention in which the shoulders that prevent penetration of the full chisel into the space between adjacent bricks are defined by two pairs of rollers. In detail the chisel comprises a shaft 17 for engagement in a conventional power tool. The shaft 17 is secured to a body 18 from beneath which projects a blade 19. The tip of the blade 19 supports a tungsten cutting edge 20. Four pins 21 project from the sides of the body 18 and support respective rollers 22. When the chisel is placed on a brick surface as indicated by broken line 23 in Fig. 17 the underside of the body 18 is supported clear of that surface on the four wheels and the blade 19 extends beneath the surface 23 to a predetermined depth indicated by broken line 24. It would of course be possible to tip the chisel up so that it ran on either only the front pair of rollers or the back pair of rollers so as to adjust the penetration depth but ideally the chisel will be used with all four rollers 22 in contact with the brick surface as this determines the penetration depth. The rollers 22 may be fabricated from any suitable material, for example nylon or silicon rubber. Although the rollers are shown as being relatively narrow they could of course be of whatever width is required. For example the body 18 could be of the same width as the blade 19 and the width of the rollers 22 could be extended appropriately. The rollers 22 may be a simple snap-fit on the pins 21 so as to make it possible to rapidly and easily replace rollers which become worn or otherwise damaged. The embodiment of Figs. 17 to 19 incorporates four rollers. It will however be appreciated that only two rollers could be provided if it was not desired to have a clear indication of the penetration depth as is provided where two pairs of rollers are supported on the body 18. It would also be possible if desired to have a single roller, preferably supported in line with the blade 19. A single roller could be accommodated in an aperture in the body 18, the aperture being in line with the blade 19. A further embodiment of the invention is illustrated in Figs. 20 and 21. This embodiment is similar to that of Figs. 17 to 19 and accordingly the same reference numerals are used where appropriate. In the embodiment of Figs. 20 and 21 however rollers 22 are supported on a spring clip 25 the ends of which can be inserted into alternative blind holes 26. As best shown in Fig. 21, two pairs of holes 26 are provided on each side of the body 18 when the ends of the spring clip 25 are supported in the uppermost holes 26 (as viewed in Fig. 21). The rollers 22 assume the position shown by broken lines 27. If the ends of the spring clip 25 are inserted in the lower holes 26 the rollers 22 assume the position shown by the broken lines 28. Thus by appropriate positioning of the spring clip 25 the chisel can be arranged so that with all four wheels in contact with the brick surface the under surface of the body 18 assumes one of two spacings from the brick surface or is either tipped up to reduce the depth of penetration whilst swinging the shaft 17 down towards the brick surface or is tipped down to increase the depth of penetration whilst swinging the shaft 17 away from the brick surface. It will be appreciated that a variety of chisels could be provided having a variety of tip and shoulder widths to enable material to be efficiently removed from gaps of a variety of widths. Referring now to Figs. 22 to 24, this illustrates details of the shape of a further chisel body intended to support four wheels 29 shown in outline only on axles (not shown) which are an interference fit in holes 30 defined by the body. The wheels are secured on the pins by resilient split pins (not shown) so that wheels can be exchanged simply by pulling out the pins, pulling the wheels off the axles, pushing on fresh wheels, and reinserting the pins. The holes 30 are defined in a central portion of the body from which projects a tip 31 supporting a tungston cutting tip 32. -The tip 32 is wider than the tip 31 and thus the tip 31 can move easily through a slot cut by the tip 32. The dotted line 33 represents the surface of a wall between the bricks of which tips 31 and 32 have been driven. The dotted lines 34 and 35 are respectively parallel to and perpendicular to line 33. A shaft 36 is provided for insertion in a reciprocatory tool intended to reciprocate the shaft parallel to the shaft axis. The shaft 36 defines an angle 37 with the dotted line 34, and the tip 32 defines an angle 38 with the dotted line 35. Tests have shown that the angle 37 should be in the range of 10° to 45°, preferably 20°, and that the angle 38 should be in the range of 35° to 75°, preferably 55°. The double rollers could be interconnected by a pair of endless belts in the manner of the track of a tracked vehicle. The depth of penetration of the chisel tip can be adjusted by changing the diameters of all of the wheels, or by changing the diameters of one pair only of the wheels. In the latter case however, the angles 37 and 38 could also be adjusted and care would therefore have to be taken to ensure that these angles were maintained within acceptable limits. For example, if the angle 38 became too small and the angle 37 became too large, there would be a tendency for the chisel tip to become embedded in the mortar to be removed. Various chisel tip shapes can be used, for example a simple square-ended "spade" as shown in the drawings, or tips of triangular, curved, serrated etc. shape. Referring now to Figs. 25 to 29, there is illustrated a tool shaft suitable for use as the shaft of one of the above-described chisels or any other tool requiring a quick-release engagement with a tool holder. The shaft has a tapered free end 39 and a tool head end 40 which is simply shown as a flat circular surface. In the case of a chisel as described above, the end 40 would be inserted in the chisel body. A groove is formed on the outer surface of the shaft, the groove comprising a first portion 41 leading axially from the tapered end 39 of the shaft, a circumferential second portion 42 connecting with the end of the groove portion 41 remote from the end of the shaft, and an axially extending third portion 43 which extends from the second portion 42. A flat 44 is also formed on the outside of the shaft, the flat 44 being positioned diametrically opposite the third portion 43 of the groove. Referring now to Figures 30 and 31, details of a tool holder bore adapted to receive the shaft illustrated in Figures 25 to 29 are shown. The tool holder comprises a cast body defining a circular bore 45 and a tubular side member 46 which communicates with the bore 45. The side member 46 has a spring-loaded latch member 47 and a retaining pin 48 is fixedly secured so as to project radially into the bore 45 opposite the latch member 47. It will be seen from Figure 31 that the retaining pin 48 is received in the third portion of the groove 43 when the tool is inserted into the holder and the latch member 47 bears against the flat 44. The latch member comprises a cylindrical body supporting a fixed flange 49 against which a compression spring 50 bears. The other end of the spring bears against an annular collar 51 which is slidable on the latch member 47. The end of the latch member 47 remote from the bore 45 is threaded and supports two lock nuts 52 the adjustment of which determines the distance to which the latch member 47 projects into the bore. The collar 51 is retained in the tubular member 46 by a grub screw 53. When the tool shaft is inserted the latch member 47 rides up the tapered end 39 of the tool shaft. The tool shaft is then rotated and pushed home and the latch member 47 drops down onto the flat 44. Removal of the tool shaft requires a reversal of these steps. It will be appreciated that axial movement of the latch member 47 as the tool is inserted and removed results in a gap appearing between the collar 51 and the lock nuts 52. The latch member 47 is effective to prevent the tool shaft sliding and vibrating free accidentally. Any attempt to simply pull the tool shaft straight out of the tool holder results in the retaining pin 48 jamming against the end of the third portion 43 of the groove adjacent the shaft end 39. It will be appreciated that the function of the latch member may be achieved with a less complicated structure than that shown in Figures 30 and 31. For example a simple spring-loaded bore could be used. Alternatively the retaining pin 48 could itself be spring-loaded. As a further alternative, the spring latch member 47 could be dispensed with entirely so that the tool shaft is free to slide axially within the holder. In such an arrangement it would be desirable to shape the end of the groove 43 adjacent the shaft tip 39 so as to prevent the retaining pin siding accidentally along the groove edge 54 (Fig. 25) . The edge 54 could define for example a semi circular recess aligned with the groove 43, or the groove 42 could be displaced along the shaft away from the tip 39 so that the groove 43 extends beyond the groove 42 towards the tip 39. In both cases a retaining pin receiving recess is defined at the end of groove 43.

Claims: CLAIMS : 1. A chisel for removing material from a crack defined between two adjacent bricks, comprising a body supporting an elongate tip and defining shoulders extending transversely of the tip, wherein the width of the tip is less than the width of cracks from which it is desired to remove material, and the width of the shoulders is greater than the width of the said cracks such that the shoulders limit the depth of insertion of the tip into said cracks. 2. A chisel according to claim 1, wherein the edges of the shoulders and the end of the tip are wedge shaped. 3. A chisel according to claim 1 or 2, wherein the shoulders are of substantially the same thickness as the tip. 4. A chisel according to claim 1 or 2, wherein the thickness of the shoulders is greater than the thickness of the tip. 5. A chisel according to any preceding claim, wherein an area of the shoulders facing the adjacent bricks is substantially planar. 6. A chisel according to any one of claims 1 to 4, wherein an area of the shoulders facing the adjacent bricks is rounded. 7. A chisel according to any preceding claim, wherein the side of the tip which in use faces away from the wall defined by the bricks is hollowed out. 8. A chisel according to any preceding claim, wherein the shoulders of the body are formed from the same material as the rest of the chisel. 9. A chisel according to any one of claims 1 to 7 wherein the shoulders comprise at least one material which slides easily over the brick surface. 10. A chisel according to claim 9, wherein the said cover is in the form of a jacket secured to the shoulders. 11. A chisel according to any one of claims 1 to 7, wherein the shoulders are formed of a material different from the material of the rest of the chisel. 12. A chisel according to claim 11, wherein the shoulders are formed from a block of material fashioned with a central hole through which the tip of the chisel extends to project from the block, the block being prevented from slipping too far along the tip by a flange on the chisel. 13. A chisel according to claim 1, wherein the shoulders are in the form of at least one roller which supports the chisel and runs against the surface of the bricks across which the chisel is advanced. 14. A chisel according to claim 13, wherein two pairs of rollers are provided. 15. A chisel according to claims 13 or 14, wherein the size of the or each roller is adjustable. 16. A chisel according to claims 13 or 14, wherein the position of the or each roller on the chisel is adjustable. 17. A chisel according to any preceding claim, wherein the chisel tip is removable to enable tips of different widths to be secured to the chisel body. 18. A chisel according to any preceding claim, comprising a shaft which is in use received in a tool holder, wherein a groove is defined in the outer surface of the shaft, the groove comprising a first portion extending substantially axially from one end of the shaft, a second portion spaced from the said one end of the shaft and extending substantially circumferentially from the first portion, and a third portion extending substantially axially from the second portion and away from the said one end of the shaft, wherein the tool holder defines a shaft receiving bore into which a retaining pin projects radially to engage in said groove, the pin preventing movement of the shaft within the bore except in a direction which enables the pin to slide along the groove. 19. A chisel according to claim 18, wherein retaining means are provided to prevent movement of the shaft relative to the bore unless a predetermined minimum force is applied to the shaft. 20. A chisel according to claim 19, wherein the bore is of circular cross-section, the retaining pin extending radially towards the bore axis. 21. A chisel according to claim 19 or 20, wherein the retaining means is a spring-loaded member which presses against a flat formed on the shaft to hold the shaft in friction engagement with the wall of the bore. 22. A chisel according to claim 21, wherein the pin and spring-loaded member are located on diametrically opposed sides of the bore, with the third portion of the groove and the flat being on diametrically opposed sides of the shaft. 23. A quick release tool assembly comprising a tool holder which in use is driven by a power source, and a tool shaft which is in use received in a tool holder, wherein a groove is defined in the outer surface of the shaft, the groove comprising a first portion extending substantially axially from one end of the shaft, a second portion spaced from the said one end of the shaft and extending substantially circumferentially from the first portion, and a third portion extending substantially axially from the second portion and away from the said one end of the shaft, wherein the tool holder defines a shaft receiving bore into which a retaining pin projects radially to engage in said groove, the pin preventing movement of the shaft within the bore except in a direction which enables the pin to slide along the groove. 24. A quick release tool assembly ccording to claim 23, wherein retaining means are provided to prevent movement of the shaft relative to the bore unless a predetermined minimum force is applied to the shaft. 25. A chisel substantially as hereinbefore described with reference to Figs. 1 to 5, Figs. 6 and 7, Figs. 8, 9 and 10, Fig. 11, Figs. 12, 13 and 14, Fig. 15, Fig. 16, Figs. 17, 18 and 19, Figs. 20 and 21, Figs. 22, 23 and 24, and Figs. 25 to 31 of the accompanying drawings.

Inventors: STAUBLI JURG GOTTFRIED, STAUBLI, JURG, GOTTFRIED
Applicants: STAUBLI JURG GOTTFRIED, STAUBLI, JURG, GOTTFRIED
Application year: 1988
Main classification: B25D17
IPC codes: B25D17, E04F21