GB2140884A - Locating and holding means e.g. for the latch plate for the steel of a percussive roadbreaker - Google Patents

Abstract

The tool (45) of a percussive roadbreaker is held by a latch (52) is located and held alternatively in its retaining position behind the tool collar (48) or in a release position by a flange (59) of a resilient bush (54). The flange (59) is formed in one radial face with two angularly-spaced pairs of aligned radial grooves (67, 68) (Figs. 3A, 36) into either of which a pair of axially-protruding aligned radial nibs (70), formed on the latch (52), can enter to locate and hold the latch (52) in a corresponding position. When the latch (52) is rotated between its retaining and release positions, the nibs (70) ride out of the respective pair of grooves (67 or 68) onto the portion of the flange between them, deforming the flange, until they reach and enter the other pair of grooves. <IMAGE>

Description

SPECIFICATION Locating and holding means e.g. for the latch plate for the steel of a percussive roadbreaker This invention relates to means for locating and holding a first member in a predetermined position or orientation, or in any one of two or more predetermined positions or orientations, in relation to a second member on which the first member is movably mounted. The invention further relates to a percussive tool, for example a pneumatic road breaker, incorporating such locating and holding means in association with the retainer for retaining a tool steel in its chuck.

According to the present invention from one aspect, such locating and holding means includes a pair of cooperating locating members comprising a deformable locating member made of resilient material and fixed to one of the relatively movable first and second members, and a rigid locating member fixed to or forming part of the other of the first and second members, one of the said pair of locating members having a surface formed with at least one recess, and the other of said pair of locating members being held against the recessed surface of the said one locating member and having a protruding portion arranged, when the said first member is moved into a said predetermined position or orientation, to enter and engage in the recess and thereby to locate and hold the said first member in that position or orientation, movement of the said first member out of that position or orientation being resisted by the deformation of the deformable locating member as the protruding portion rides out of the recess and onto the adjacent unrecessed portion of the surface of the respective locating member.

From another aspect, means for locating and holding a first member in a predetermined position or orientation, or in any one of two or more predetermined positions or orientations, in relation to a second member on which the first member is mounted, comprises a deformable locating member made of resilient material and fixed to one of the relatively-movable first and second members, the deformable locating member having a surface formed with at least one recess, and a cooperating rigid locating member fixed to or forming part of the other of the first and second members and held against the recessed surface of the deformable locating member, the rigid locating member having a protruding portion arranged, when the first member is moved into a said predetermined position or orientation, to enter and engage in the said recess and thereby to locate and hold the first member in that position or orientation, movement of the first member out of that position or orientation being resisted by the deformation of the deformable locating member by the protruding portion of the rigid locating member as it rides out of the recess and onto the adjacent unrecessed surface of the deformable member.

Where the first member is pivotally-mounted on the second member, the deformable locating member may comprise an annular washer, or a bush having a radial flange, and be mounted coaxially with the pivotal axis of the first member. The or each recess may comprise a radial groove formed in a side face of the washer or flange which is a surface of revolution with respect to the pivotal axis, and the cooperating rigid locating member may comprise a plate or disc formed with a radially-extending axially-protruding rib or nib, or may be a radiallyextending cylindrical bar.

The surface of the washer or flange opposite to its grooved surface may be formed with a relieved area which reduces the wall thickness of the washer or flange locally in the region of the recess, or between two recesses, to enable the washer or flange to be deformed by the flexing of its wall under the pressure of the protruding portion of the rigid locating member.

Whilst in a preferred embodiment of the invention, the grooves are formed in the deformable locating member and the protruding portion is on the rigid locating member, this is not essential, and an "inverse" arrangement of the invention may be devised in which the locating recess or recesses are formed in the rigid locating member and the protruding portion is on the deformable locating member. In that case a returning recess may be provided under the protruding portion, between the opposite side of the deformable locating member and a supporting surface for it.

Whilst the locating and holding means of the present invention may be employed in conjunction with a wide variety of different first and second members, one particularly advantageous application of the invention is to a percussive tool, for example to a pneumatic road breaker, in conjunction with the pivoted latch retainer used to prevent inadvertent withdrawal of a steel from the chuck of such a tool.

In known pneumatic road breakers, for example as described in our British patent specification No.

A-2045348 (Case 49A), a rotary latch pivotally mounted on the lower end of the tool body can be moved into a latching position in which a nose on the latch lies behind a circumferential shoulder on the steel to prevent its withdrawal, and a helical spring is provided to bias the latch into that position against a stop.

Thus from another aspect the present invention comprises a pneumatic road-breaker having a chuck which receives a breaker steel and a rotary latch pivotally mounted on the lower end of the tool body or on a member mounted thereon, and rotatable into a retaining position in which a nose on the latch lies behind a circumferential shoulder on the steel to prevent its withdrawal, and having locating and holding means in any of the forms aforesaid associated with the latch, the first member whereof comprises the latch and the second member whereof comprises the tool body or a member mounted thereon, and which is arranged to locate and hold the latch in its retaining position.

The locating and holding means may also be arranged to locate and hold the latch in a release position, angularly-spaced from the latching position, in which the nose is clear of the shoulder on the steel to allow its withdrawal.

No separate biassing spring, such as the usual helical compression spring provided as aforementioned in known road-breakers, need be provided to urge the latch towards its retaining position.

The present invention from another aspect provides a locating and holding means for the retainer for the tool steel of a percussive tool, wherein the protrusion of a portion of one locating member into a locating recess formed in a surface of a cooperating locating member, one of the two locating members being movable relatively to the other, and one of them being a deformable member made of resilient material and the other being rigid, is used to resiliently locate and hold the retainer in its retaining position, movement of the retainer out of its retaining position being resisted by the local deformation of the deformable locating member as the protruding portion is forced by such movement to ride out of the surface recess and onto the adjacent unrecessed portion of the surface of the respective locating member.

Thus from another aspect the invention comprises a percussive tool having a chuck in which a tool steel is withdrawably insertable, and a retainer movably mounted on the tool and movable into and out of a retaining position in which it prevents withdrawal of the inserted steel, and locating and holding means for the retainer, comprising a pair of cooperating locating members, namely a deformable locating member made of resilient material and a rigid locating member, which are relatively movable into a relative position wherein the protrusion of a portion of one of the locating members into a locating recess formed in a surface of the other locating member, against which surface the said one locating member is held, resiliently locates and holds the retainer in its retaining position, move ment ofthe retainer out of its retaining position being resisted by the local deformation of the deformable retaining member as the protruding portion rides out of the recess and onto the adjacent unrecessed portion of the surface of the respective locating member.

From yet another aspect the invention comprises a percussive tool having a chuck in which a tool steel is withdrawably insertable, and a retainer movably mounted on the tool and movable into and out of a retaining position in which it prevents withdrawal of the inserted steel, and locating and holding means for the retainer, comprising a rigid locating member movable into a position wherein the protrusion of a portion of the rigid locating member into a locating recess formed in a surface of a cooperating deform able locating member of resilient material, against which surface the relatively-movable rigid locating member is held, resiliently locates and holds the retainer in its retaining position, movement of the retainer out of its retaining position being resisted by the local deformation of the deformable locating member by the protruding portion of the rigid locating member as that protruding portion is forced by such movement to ride out of the surface recess and onto the adjacent unrecessed portion of the surface of the deformable locating member.

The invention is particularly although notexclu- sively applicable to a tool having a pivotallymounted rotatable retainer for its steel.

Thus according to the invention in one form, in which the percussive tool has a pivotally-mounted latch which is angularly-movable into and out of a retaining position in which it prevents withdrawal of a steel from the tool chuck by lying behind a shoulder on the steel, and is provided with the means for locating and releasably holding the latch in its engaged position as aforesaid, one or other of the said pair of cooperating locating members is secured toor forms part of the latch so that pivotal movement of the latch causes relative rotation between them, the locating recess or recesses being formed in a surface of the respective locating member which is a surface of revolution with respect to the pivotal axis.

The respective locating member may be formed with a second locating recess in its surface, separated from the first recess by an unrecessed portion of its surface, into which second recess the protruding portion of the other locating member enters after being forced to traverse the unrecessed surface portion by the continued movement of the retainer away from its retaining position, the engagement of the said protruding portion in the second recess resiliently locating and holding the retainer in a predetermined release position.

In a case where the percussive tool has a pivotallymounted rotatable retainer for its steel, the deformable locating member may conveniently comprise an annular washer or a bush having a radially projecting flange as aforementioned, and mounted coaxially with the pivotal axis of the latch, with one side face of the washer or flange supported against a rigid supporting surface. In a preferred arrangement, the locating recess or recesses is or are formed on one side face of the washer or flange, and the protruding portion is on the rigid locating member.

In one such construction, particularly although not exclusively applicable to a pneumatic percussive road breaker, the rigid member itself may comprise the pivoted latch for retaining the tool steel, and the said protruding portion may comprise a radiallyextending axially-protruding integral rib or nib, or set of aligned ribs or nibs, on one radial face of the latch plate, and the deformable locating member may comprise a resilient bush on which the latch is pivotally mounted, the bush being fixed against rotation and having an integral radially-projecting circumferential flange in one side face of which flange the or each locating recess is formed as a radially-extending groove or set of aligned grooves.

Two such grooves, ortwo pairs of aligned grooves, may be provided at different angular positions to define respectively the retaining and release positions of the latch by cooperating with a single rib or nib, our a single pair or set of aligned ribs or nibs. In an arrangement in which the pivoted latch bears against a rigid stop on the tool body or on a member carried thereby when in its retaining position, according to a preferred feature of the invention the or each protruding rib or nib is arranged to bear asymmetrically against one side of the respective groove when the latch is in its retaining position against the stop, such asymmetrical engagement in the groove causing a slight deformation of the deformable locating member by the rib or nib by which the latch is pressed resiliently against its stop.

This feature, and the use of a resilient bush for mounting the latch, helps to reduce rattle and wear of the latch in use.

The height of each protruding rib or nib preferably equals the depth of each groove.

The or each of the protruding ribs or nibs is preferably of symmetrical trapezoidal cross-section, although other cross-sections are possible.

Preferably the or each groove is of a cross-section corresponding to, and dimensioned the same as, that of the rib or ribs.

A preferred resilient material for the deformable locating member is polyurethane rubber, although natural rubber or some other elastomeric plastics material may be used.

The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a side elevation in longitudinal section of a percussive road breaker tool provided with a latching arrangement embodying the invention for retaining its steel; Figure 2 is a cross-section on the line ll-ll in Figure 1,showing details of the latching arrangement; Figures 3A and 3B, 4A and 4B, and 5A and 5B show respectively in top and side view the latch and its locking bush of the tool of Figure 1, in three different positions of the latch;; Figures 6A, 6B and 6C show three different views, two of them partly sectioned, of the retaining sleeve of the tool of Figure 1, which carries the latching mechanism for retaining a steel in the sleeve; Figures 7A to 7D inclusive show the latch member of the tool of Figure 1 from four different viewpoints; Figure 7E is a fragmentary view on a larger scale showing the cross-section of the radial nibs on the latch member of Figures 7A to 7D; Figures 8A to 8D show the locking bush for the latch of the tool of Figure 1, from four different viewpoints; and Figure 8E is a fragmentary view on a larger scale showing the cross-section of the radial locking grooves in the locking bush of Figures 8A to 8D.

Figures 1 and 2 show a percussive road breaker tool of a type which is generally known, operated by compressed air, which is supplied via an air line to the air inlet spigot 10 of the tool shown in Figure 1, and thence via a spring-loaded bail valve 11, 12 controlled by a trigger 13 and plunger rod 14to a chamber 15 in the upper end of the head portion 16 of the tool. The trigger 13 is pivoted to the head 16 and extends along one of the two handle arms 17 of the tool which are integral with the head 16. The head 16 and the two handle arms are made of steel or other suitable metal and are encased in a covering 18 of hard rubber or polyurethane rubber or other plastics material, and the grip portions of the two handles 17 are provided with vibration-absorbing handle grips 19.

The road breaker tool comprises a steel cylinder 20 which is embedded in a surrounding sleeve 21 of hard rubber, polyurethane rubber or other suitable plastics material and is attached at its upper end to the head 16 by tie bolts shown at 22. A hammer piston 23 is slidable within the cylinder 20 and can be caused to reciprocate up and down the cylinder by compressed air admitted alternately to opposite ends of the cylinder from the chamber 15 under the control of a pressure-responsive control valve 24 having a movable valve disc 25 which cooperates alternately with upper and lower valve seats 26, 27.

The construction and operation of the valve 24 are known from our British patent specification No.

A-2045348 and will not be further described. Air passageways formed in the thickness of the wall of the cylinder sleeve 21 conduct the compressed air from the valve 24, when in its position shown in Figure 1, to an inlet air port 28 at the lower end of the cylinder 20 to drive the piston 23 upwardly. When the piston approaches the upper end of the cylinder 20 the valve disc 25 lifts to admit compressed air from the chamber 15 through an upper inlet port 29 into the upper end of the cylinder to drive the piston down through its next working stroke.Air exhausted from the working chambers of the cylinder 20 at the end of each working and upward return stroke of the piston 23 escapes through an exhaust port (not shown), controlled by the travel of the piston, into a muffler chamber 30 within a muffler 31 of hard rubber, polyurethane rubber or other suitable plastics material which is fitted around the cylinder 20 and its surrounding sleeve 21 and affords a discharge port 32 to atmosphere.

A steel retainer sleeve 40 is attached to the lower end of the cylinder 20 by cooperating screw threads 41, details of the shape of the retainer sleeve 40 being shown in Figures 6A to 6C. The hexagonalsection shank 44 of a breaker steel or bit 45, referred to as the steel, can be inserted into a chuck 46 within the lower extension 47 af the cylinder 20, the shank 44 fitting loosely in the hexagonal bore of the chuck, and being retained by a latch mechanism embodying the present invention and generally indicated at 50, the latch mechanism being carried by the retainer sleeve 40.The forward or down stroke of the hammer piston 23 is the power stroke, which accelerates the piston towards the steel 45 until the hammer portion 23A of the hammer piston impacts against the end of the shank 44 of the steel, which on impact absorbs the kinetic energy contained in the hammer piston sending a shock wave through the steel 45 towards the work surface to be fractured.

Figure 1 shows the piston at the moment of impact, after it has uncovered the exhaust port in the cylinder 20. After the energy of the piston has been transferred to the steel 45 the control valve 24 admits compressed air to the under side of the piston 23 to lift it through its return stroke.

The forward travel of the steel 45 on impact in normal operation is a few millimetres, i.e. the approximate penetration per impact of the steel into the material to be fractured. The steel however is free to travel forwards until its collar 48 comes into contact with the retaining nose 51 of a rotary latch member 52 forming part of the latch mechanism 50 and shown in its latching position in Figure 1. The latch member 52 is used to retain the breaker steel 45 in place in the tool, so that it does not become detached from its chuck 46 when the tool is moved from point to point. Aiso, when the operator attempts to extract the steel from a stuck hole, he pulls on the tool handles 17, 19 until the collar 48 comes in contact with the latch nose 51, enabling the steel to be extracted.

In order that the steel can readily be removed when desired for the purpose of changing it, the latch 52 must be capable of being rotated to swing its retaining nose 51 out of the path of the collar 48 on the steel 45, to allow the collar to pass out of the tool.

The latch member 52 is shown in detail in Figures 7A to 7D. It is a heat-treated steel memberjournalled on a resilient bush 54 surrounding a pair of coaxial, axially-split tubular spindles 55, 56 which extend between spaced integral lugs 57,58 of the extension sleeve 40. As shown in Figure 2, the latch member 52 abuts on one side against the inner face of the lug 57, and an integral radial flange 59 of the locking bush 54 is interposed between the other side of the latch member 52 and the lug 58 of the extension sleeve 40.

In the latching position of the latch member 52, shown in Figure 1, a finger 60 on the latch member 52 abuts against a stop surface 61 on the extension sleeve 40.

The flange 59 of the locking bush 54 has a portion 59A of circular profile, and a nose 59B which lies between the lugs 57 and 58 of the extension reeve 40 and over the stop surface 61, to give a smooth external appearance to the front portion of the road breaker. The locking bush 54 is prevented from rotating relatively to the extension sleeve 40 by an interrupted semi-cylindrical rib 62 formed integrally on the exterior face of its radial flange 59, the rib 62 being diametrical with respect to the bush 54, and being entered and engaged in a semicylindrical groove 63 formed in the inner face of the extension sleeve lug 58. That face of the flange 59 is also recessed in two sectors 64, 65 for a purpose to be described.The opposite radial face of the flange is formed with two pairs of aligned radial grooves 67, 68 which are inclined at 40 to one another and which cooperate with a single pair of aligned radial integral nibs 70 on the opposite face of the latch member 52 to define two alternative operative positions of the latch, namely the locking position and the released position. When the latch member 52 is in either of these two positions it will be held there by the nibs 70 protruding into the corresponding pair of grooves 67 or 68.The bush 54 is made as a moulding of a suitable elastomeric plastics material or rubber, its resilience allows the latch member 52 to be rotated between these operative positions, the nibs 70 deforming the material of the flange 59 whilst moving from one pair of grooves 67, 68 to the other. Twill be observed that the sector-shaped relieved portions 64 and 65 on the other side of the flange 59 are situated opposite the spaces between the grooves 67 and 68, and facilitate the distortion of the wall of the flange by the nibs 70. The crosssectioned shape of each of the nibs 70 on the latch member 52 is preferably that of a symmetrical trapezium, as shown in Figure 7E, and the grooves 67 and 68 are of a similar cross-section and dimensior, as shown in Figure 8E,when the grooves are not deformed.

Figures 3A and 3B show the latch held in its operative or latching position by the bush 54, with the nibs 70 engaged in the grooves 67 of the flange 59. When the latch is in this position, it is important that it is firmly held against its stop 61 so that if there should be wear or slight manufacturing variaticns of the latch or of the retainer sleeve 40, the latch wiii not vibrate or rattle against its stop.This is ensured by arranging that there shall be a slight deliberate angular discrepancy of about 2" between the manufactured orientations of the nibs 70 and of the grooves 67 corresponding to the position of the latch member 52 against its stop, so that the wall of the flange 59 is slightly distorted by the nibs 70 in the sense tending to press the latch member resiliently against the stop 61. This angular discrepancy and distortion can be seen in Figures 3A and 3B.

Figures 4A and 4B shown an intermediate position of the latch member 52, with its nibs deforming the wall of the flange 59 between the grooves 67 and 68 and behind the relieved portions 64, 65.

Figures 5A and SB show the latch member 52 held by the bush 54 in its release position, with the nibs 70 centrally engaged in the grooves 67. In this position there is no metallic stop to define the latch position, which is determined solely by the position of the grooves 67 in the flange 59 of the bush.

A suitable material for the resilient bush 54 is the polyurethane rubber sold under the trade name ADIPRENE L-167 and available from Uniroyal Chemical Ltd., Avon Bridge Road, Bridge Street, Evesham, Worcestershire, England. A suitable curing agent is MBOCA (methylene bis-chloroaniline) also available from Uniroyal Chemical Ltd, which when mixed with the ADIPRENE L-167 pre-polymer yields vulcanizates of a hardness approximately equal to 95 (Durometer A).

As an example, the resilient bush 54 made from the ADIPRENE L-167 material may have a radius of 20mm over its circular-profile portion 59A, and each of the grooves 67 and 68 may have a depth of 2mm, with an angle of 90" subtended between its opposite sloping side walls when the groove is undeformed.

The nibs 70 may be 2mm in height, corresponding to the depth of the grooves 67,68, and of corresponding cross-section. The wall thickness of the unrelieved portions of the flange 59 of the bush 54 may be 7.15 - 7.25mm, and the depth of each sectorshaped recess 64,65 may be 1.5mm, leaving a relieved flange wall thickness of 5.65 - 5.75mm behind each of the recesses 64 and 65. The shank portion 54A of the bush may have a bore diameter of 15.5mm and a maximum external diameter of 21.50 21.87 mm adjacent the root of the flange 59.The exterior surface of the shank 54A of the bush may be tapered at i/2 to the bore axis towards the end of the shank remote from the flange, and its bore may also be tapered at 1/4" to the bore axis, in each case to aid extraction of the bush from the mould in which it is cast.

It is found that the latch mechanism described and illustrated in Figures 1 to 8E will allow repeated operation of the latch without wear of the bush.

Consequently, the life of the latch components may be as long as the life of the tool itself, in contrast to previous constructions of steel latch in percussive road breakers which have relied on latch pins and helical springs, which suffer from premature fatigue failure. Because in the present embodiment of the invention the latch is mounted on what amounts to a flexible bearing, any shock transmitted to it by the impact of the collar 48 of the steel is cushioned and hence the stress loading is reduced. Furthermore, noise caused by vibration or rattle of the latch is similarly reduced or eliminated.

The nibs 70 could have profiles other than the trapezoidal profiles illustrated, for example their tips could be of smoothly-rounded, e.g. semicircular cross-section. In addition or alternatively, the crosssections of the cooperating grooves could be appropriately modified.

Whilst in the illustrated embodiment the protruding nibs 70 are formed on the face of the latch member 52 and cooperate with grooves 67 and 68 formed in the cooperating face of the flange 59 of the bush 54, this arrangement could be modified to provide an inverse arrangement in which the grooves are formed in the face of the latch member 52 and the nibs are integral moulded parts of the flange of the bush. In that case, instead of the sector-shaped recesses 64, 65 formed in the opposite face of the bush in positions lying between the positions of the grooves, sector-shaped recesses would be provided in register with the positions of the grooves, these recesses being formed either in the face of the flange of the bush opposite to that in which the grooves are formed, or in the opposed face of the lug 58 against which the flange lies, or in each of these opposed faces. The extent and depth of the relief provided by these recesses should be such asto allowthewall of the flange to deflect sufficiently for the nibs to be fully depressed when riding out of the respective grooves, without undue deformation or excessive stressing of the nibs themselves.

Claims (29)

1. Means for locating and holding a first member in a predetermined position or orientation, or in any one of two or more predetermined positions or orientations, in relation to a second member on which the first member is mounted, which means comprises a pair of cooperating locating members comprising a deformable locating member made of resilient material and fixed to one of the relatively movable first and second members, and a rigid locating member fixed to orforming part of the other of the first and second members, one of the said pair of locating members having a surface formed with at least one recess, and the other of said pair of locating members being held against the recessed surface of the said one locating member and having a protruding portion arranged, when the said first member is moved into a said predetermined position or orientation, to enter and engage in the recess and thereby to locate and hold the said first member in that position or orientation, movement of the said first member out of that position or orientation being resisted by the deformation of the deformable locating member as the protruding portion rides out of the recess and onto the adjacent unrecessed portion of the surface of the respective locating member.

2. Means for locating and holding first member in a predetermined position or orientation, or in any one of two or more predetermined positions or orientations, in relation to a second member on which the first member is mounted, which means comprises a deformable locating member made of resilient material and fixed to one of the relativelymovable first and second members, the deformable locating member having a surface formed with at least one recess, and a cooperating rigid locating member fixed to or forming part of the other of the first and second members and held against the recessed surface of the deformable locating member, the rigid locating member having a protruding portion arranged, when the first member is moved into a said predetermined position or orientation, to enter and engage in the said recess and thereby to locate and hold the first member in that position or orientation, movement of the first member out of that position or orientation being resisted by the deformation of the deformable locating member by the protruding portion of the rigid locating member as it rides out of the recess and onto the adjacent unrecessed portion of the surface of the deformable locating member.

3. Locating and holding means as claimed in Claim 1 or Claim 2, in which the first member is pivotally-mounted on the second member for rotation relative thereto, and in which the deformable locating member comprises an annular washer, or a bush having a radial flange, and is mounted coaxially with the pivotal axis of the first member.

4. Locating and holding means as claimed in Claims 2 or 3, in which the or each recess is a radial groove formed in a side face of the washer or flange which is a surface of revolution with respect to the pivotal axis, and the cooperating rigid locating member comprises a member having a face formed with a radially-extending axially-protruding rib or nib, or comprises a radially-extending cylindrical bar.

5. Locating and holding means as claimed in Claim 4, in which the face of the washer or flange opposite to its grooved face is formed with a relieved area which reduces the wall thickness of the washer or flange locally in the region of the recess, or between two recesses, to enable the washer or flange to be deformed by the flexing of its wall under the pressure of the protruding portion of the rigid locating member.

6. A locating and holding means as claimed in Claim 1, in which the locating groove or grooves is or are formed in the rigid locating member, and the protruding portion is on the deformable locating member.

7. A locating and holding means as claimed in Claim 6, in which the deformable locating member is a resilient washer or a resilient washer or a resilient bush having a radially-protruding circumferential flange, the protruding portion being formed on one side face of the washer or flange and the opposite side face thereof being supported against a rigid supporting surface, and there being a recess formed either in the opposite side face of the washer or flange, or in the supporting surface, or in each, in a position opposite to the protruding portion, to allow the deflection of the wall of the washer or flange by the depression of the protruding portion as it rides out of a locating recess.

8. A percussive tool having a chuck and a latch which retains a tool steel against inadvertent withdrawal from the chuck, the latch being provided with locating and holding means as claimed in any one of the preceding claims for holding the latch in its retaining position.

9. A percussive road-breaker having a chuck which receives a breaker steel and a rotary latch pivotally mounted on the lower end of the tool body or on a member mounted thereon, and rotatable into a retaining position in which a nose on the latch lies behind a circumferential shoulder on the steel to prevent its withdrawal, and having locating and holding means as claimed in any one of Claims 3 to 7 whereof the first member comprises the latch and the second member comprises the tool body or the said member mounted thereon, and which is arranged to locate and hold the latch in its retaining position.

10. A road-breaker as claimed in Claim 9, in which the locating and holding means is also arranged to locate and hold the latch in a release position, angularly-spaced from the latching position, in which the nose is clear of the shoulder on the steel to allow its withdrawal.

11. A percussive tool having a chuck in which a tool steel is withdrawably insertable, and a retainer movably mounted on the tool and movable into and out of a retaining position in which it prevents withdrawal of the inserted steel, and locating and holding means for the retainer, comprising a pair of cooperating locating members, namely a deformable locating member made of resilient material and a rigid locating member, which are relatively movable into a relative position wherein the protrusion of a portion of one of the locating members into a locating recess formed in a surface of the other locating member, against which surface the said one locating member is held, resiliently locates and holds the retainer in its retaining position, movement of the retainer out of its retaining position being resisted by the local deformation of the deformable retaining member as the protruding portion rides out of the recess and onto the adjacent unrecessed portion of the surface of the respective locating member.

12. A percussive tool having a chuck in which a tool steel is withdrawably insertable, and a retainer movably mounted on the tool and movable into and out of a retaining position in which it prevents withdrawal of the inserted steel, and locating and holding means for the retainer, comprising a rigid locating member movable into a position wherein the protrusion of a portion of the rigid locating member into a locating recess formed in a surface of a cooperating deformable locating member of resilient material, against which surface the relativelymovable rigid locating member is held, resiliently locates and holds the retainer in its retaining position, movement of the retainer out of its retaining position being resisted by the local deformation of the deformable locating member by the protruding portion of the rigid locating member as that protruding portion is forced by such movement to ride out of the surface recess and onto the adjacent unrecessed portion of the surface of the deformable locating member.

13. A percussive tool as claimed in Claim 11 or Claim 12, in which the retainer comprises a pivotallymounted latch which is angularly-movable into and out of its retaining position, and in which one or other of the said pair of cooperating locating members is secured to or forms part of the latch so that pivotal movement of the latch causes relative rotation between them, the locating recess or recesses being formed in a surface of the respective locating member which is a surface of revolution with respect to the pivotal axis.

14. A percussive tool as claimed in Claim 9 or Claim 12 or Claim 13, in which a second locating recess is formed in the surface of the respective locating member, separated from the first recess by an unrecessed portion of that surface, into which second recess the protruding portion of the other locating member enters after being forced to traverse the unrecessed surface portion by the continued movement of the retainer away from its retaining position, the engagement of the said protruding portion in the second recess resiliently locating and holding the retainer in a predetermined release position.

15. A percussive tool as claimed in Claim 13, or Claim 14, or Claim 15, in which the deformable locating member comprises an annular washer or a bush having a radially-projecting flange, and is mounted coaxially with the pivotal axis of the latch, with one side face supported against a rigid supporting surface.

16. A percussive tool as claimed in Claim 15, in which the locating recess or recesses is or are formed in the opposite face of the washer or flange, which face is a surface of revolution with respect to the pivotal axis, and the protruding portion is on the rigid locating member.

17. A percusive tool as claimed in Claim 16, in which the side face of the washer or flange which is supported against the rigid support is formed with a relieved area which reduces the wail thickness of the washer or flange in the region of a locating recess, or between two locating recesses, formed in the other face of the flange or washer, the relieved area aiding the deformation of the wall of the washer or flange as the protruding portion of the rigid member rides over it.

18. A percussive tool as claimed in any one of Claims 13 to 17, in which the rigid locating member itself comprises the pivoted latch, and the said protruding portion comprising a radially-extending axially-protruding integral rib or nib, or a set of aligned ribs or nibs, formed on a face of the latch, and in which the deformable locating member comprises a resilient bush on which the latch is pivotally mounted, the bush being fixed against rotation and having an integral radially-projecting circumferential flange one side face of which is supported against a rigid supporting surface, and the or each locating recess being formed as a radially-extending groove or set of aligned grooves in the opposite side face of the flange.

19. A percussive tool as claimed in Claim 18, in which two such grooves, or two such sets of aligned grooves, are provided at different angular positions to define respectively the retaining and release positions of the latch.

20. A percussive tool as claimed in Claim 19, in which the supported side face of the flange is recessed behind the spaces between the angularlyseparated grooves, to form there a relieved portion of the flange of reduced wail thickness.

21. A percussive tool as claimed in any one of Claims 18 to 20, in which the or each rib or nib is of symmetrical trapezoidal cross-section.

22. A percussive tool as claimed in any one of Claims 18 to 21, in which the height of the or each nib equals the depth of the or each groove.

23. A percussive tool as claimed in Claim 22, in which the cross-section of the or each groove corresponds in shape and dimensions to that of the rib or nib.

24. A perccussive tool as claimed in any one of Claims 18 to 23 in which the pivoted latch when in its retaining position bears against a rigid stop on the tool body, or on a member carried thereby, and in which the protruding rib or nib or pair of aligned ribs or nibs is arranged to bear asymmetrically against one side of the respective groove or pair of grooves when the latch is in its retaining position against the stop, such asymmetrical engagement in the groove or grooves causing a slight deformation of the deformable member by the rib or nib by which the latch is pressed resiliently against its stop.

25. A percussive tool as claimed in Claim 11, in which the locating groove or grooves is or are formed in the rigid locating member, and the protruding portion is on the deformable locating member.

26. A percussive tool as claimed in Claim 25, in which the deformable locating member is a resilient washer or a resilient bush having a radiallyprotruding circumferential flange, the protruding portion being formed on one side face of the washer or flange, and the opposite side face thereof being supported against a rigid supporting surface, and there being a recess formed either in the opposite side face of the washer or flange, or in the supporting surface, or in each, in a position opposite to the protruding portion, to allow the deflection of the wall of the washer or flange by the depression of the protruding portion as it rides out of a locating recess.

27. A percussive tool as claimed in any one of Claims 11 to 26, which is a percussive road-breaker.

28. A locating and holding means as claimed in any one of Claims 1 to 7, or a percussive tool as claimed in any one of Claims 8 and 11 to 27, or a percussive road-breaker as claimed in Claim 9 or Claim 10, in which the deformable member of the locating and holding means is made of polyurethane rubber.

29. In a percussive road-breaker, the locating and holding means for the latch plate which retains the tool steel, substantially as specifically described herein by way of example and as illustrated in the accompanying drawings.