GB2201362A - Collet holder for an elongate member - Google Patents

Abstract

The holder comprises a collet 275 having a plurality of fingers alongside one another with adjacent fingers extending in opposite directions, and collet operating means 245, 276, 280 to move the ends of the fingers radially to engage the elongate member at longitudinally-spaced regions. The collet is molded of plastics material to provide the fingers with inherent resiliency, each of the fingers being molded to comprise an end portion interconnecting first and second longitudinally extending limbs, the first limb being common to the next adjacent finger to one side and the second limb being common to the next adjacent finger to the other side. The collet operating means comprises two surfaces 271, 277 relatively movable longitudinally of the collet and in frusto-conical engagement with the said lingers, the two surfaces being relatively non-movable angularly of the collet The holder may, for example, be for a drill bit to be sharpened in drill sharpening apparatus, the holder being supported in a pivoted carrier 235 on a twin grinding wheel sharpener. <IMAGE>

Description

HOLDING MEANS This invention relates to holding means for an elongate member and in particular to such holding means wherein a the fingers of a collet are urged laterally into tight frictional engagement of the elongate member.

According to one aspect of the present invention there is provided a holder for an-elongate member characterised in that the holder comprises a collet having a plurality of fingers extending in opposite directions, and collet operating means to move the ends of the fingers radially to engage the elongate member at longitudinally spaced regions.

Preferably said fingers extend alongside one another with adjacent fingers extending in opposite directions.

Advantageously each of said fingers comprises an end portion interconnecting first and second longitudinally extending limbs, the first limb being common to the next adjacent finger to one side and the second limb being common to the next adjacent finger to the other side.

Preferably said collet operating means comprises two surfaces relatively movable longitudinally of the collet and in engagement with said fingers for effecting said radial movement, the two surfaces being relatively non-movable angularly of the collet axis.

Advantageously two relatively rotatable, screw-thread cooperating parts are provided for effecting said longitudinal relative movement of the two surfaces.

Preferably the collet fingers are in use urged resiliently against the direction of their radial movement.

Advantageously the collet is molded of plastics material to provide the collet fingers with an inherent resiliency.

The collet operating means may be arranged to move the ends of the collet's fingers radially inwardly or, alternatively, radially outwardly.

Preferably the said two surfaces are frusto-conical and/or they engage frusto-conical surfaces of the ends of said fingers.

Advantageously the holder forms part of drill sharpening apparatus.

By way of non-limiting example, one embodiment of this invention will now be described with reference to the accompanying drawings of which Figure 1 is an "exploded" perspective view of drill sharpening apparatus including a holder according to the present invention, and Figure 2 is an "exploded" perspective view of the holder of Fig 1 and a carrier therefore.

The sharpening and grinding apparatus shown in Fig 1 comprises a stepped base structure 236, a bridge member 241 slidably mounted on the stepped base structure 236, a carrier 235 molded of glass-filled nylon with a pair of trunnion arms 259 by which the carrier is to be mounted on the bridge member 241, and a drill holder 233 for holding the drill (either a masonry drill or a twist drill) to be sharpened and for. insertion into the carrier 235. The stepped base structure 236 and the bridge member 241 are also molded of glass-filled nylon. The stepped base structure 236 has two co-axial grinding wheels 31,34 mounted therein. The grinding wheel 31 is a right-cylinder with its cylindrical abrading surface comprising silicon carbide. It is thus suitable for sharpening masonry drills having# a tungsten carbide tip of conventional Vshaped outline.The grinding wheel 34 is a right-cylinder with its cylindrical abrading surface comprising aluminium oxide. It is thus suitable for sharpening twist drills, e.g.

manufactured of high speed steel.

The holder 233 (Fig 2) comprises a main, generally tubular, body 270 molded of glass-filled nylon and having a centrally apertured end wall 271 providing a frusto-conical internal surface. The external surface of end wall 271 is similarly of generally frusto-conical form but provided integrally with a diametrically extending rib 272 which, as will be explained below, provides an index mark. Towards its opposite end, the main body 270 is externally provided with an integral encompassing flange-like projection forming a cam member 245 composed of two identical, diametrically opposite, cam lobes 251,252. Each of the two lobes 251,252 of cam member 245 is of somewhat spiral form - with its generatrix parallel to the axis of holder 233 (and hence, in use, to the axis of the twist drill) - each lobe 0 extending over approximately 1800.From the cam 245 t & said opposite end the main body is provided externally with a male screw thread 273 and is provided internally with a pair of diametrically opposite, longitudinally extending channels or slots 274.

A collet 275 is disposed within the main body 270 to lie between the frusto-conical end wall 271 and an intermediate cap member 276. The latter is molded of glass-filled nylon, is centrally apertured and has a frusto-conical internal surface 277 to engage the adjacent end of the collet 275.

The intermediate cap member 276 has an integral pair of diametrically opposite, external ribs 278 to engage slidingly in the channels or slots 274. The bight wall of the intermediate cap member 276 has an integral centering rim 279 of circular form fitting within the circular central hole of an internally threaded, main cap member 280. The main cap member 280 is also molded of glass-filled nylon and is in screw-threaded cooperation with the screw-threaded end 273 of the main body 270. Tightening rotation of the main cap member 280 causes the intermediate cap member 276 to slide longitudinally along the slots 274 towards the end wall 271 and compress the collet 275 between the frustoconical surfaces 271 and 277.

The collet 275 is molded of plastics material, e.g. nylon, to provide eight fingers 281-288 with an inherent resiliency resisting their radial deflection or displacement. The fingers 281-288 extend alongside one another with adjacent fingers extending in opposite directions, i.e. fingers 281, 283, 285 and 287 extend in one direction and alternate with fingers 282, 284, 286 and 288 which extend in the opposite direction. Each of said fingers 281-288 comprises an end portion of frusto-conical form interconnecting first and second longitudinally extending limbs, the first limb being common to the next-adjacent finger to one side and the second limb being common to the next-adjacent finger to the other side. The arrangement is such that slot-like spaces 289 separate the fingers from one another, and these slots interdigitate with one another.By engaging the drill at longitudinally spaced regions, the latter can be held by the holder 233 with great stability and with the drill and holder axes in accurate alignment with one another.

Furthermore, due to the inherent resiliency of the fingers 281-288 molded in the shape shown, the collet 275 is capable of holding drills of wide variation in diametral size. For example, a single collet 275 can be used to hold any drill with a diameter in the range 3mm to 9.5mm (1/8" to 3/8"). It will also be apparent that the collet 275 holds the drill at longitudinally spaced regions corresponding to the two ends of the collet, such holding being effected by relatively rotating the two relatively rotatable, screw-thread cooperating parts 273,280 to effect longitudinal relative movement of the two frusto-conical surfaces 271,277 and thus compress radially inwards the frusto-conical ends of the collet's fingers 281-288.It will be appreciated that, notwithstanding such relative rotation, the fingers of the collet are restrained against twisting by virtue of the relative angular immovability of the two surfaces 271,277 due to the cooperation of the ribs 278 in slots 274.

The main body 270 of the drill holder 233 is also provided externally with an integral pair of diametrically opposite ribs 290, these ribs being located adjacent cam 245 to the other side thereof to that of the male screw thread 273. The holder's body 270 is for fitting coaxial insertion into a tubular body 295 of the carrier 235. The mouth of the tubular body 295 is provided with first and second slots 291,292 adjacent one another and with a further slot 293 diametrically opposite them. Slot 291 is of very narrow angular extent - just sufficient to accomodate fittingly a rib 290 of the holder 233. Slot 291- is also of a depth somewhat less than the axial length of the ribs 290, the difference corresponding to the maximum depth to which material -may be ground away from the tip of a twist drill being sharpened. The slot 292 is of greater angular extent and throughout of a greater, constant, depth than the slot 291. The difference in depth between slots 291 and 292 corresponds to the said maximum depth to which drill material may be ground away. The diametrically opposite slot 293 is of the same depth as slot 292 and of an angular extent equal to the aggregate angular extent of the slots 291 and 292 plus the the small finger-like portion 294 of body 295 that separates slots 291 and 292.

Below slot 293, the carrier 235 is molded integrally with an outwardly extending radial projection 296 having a recess or depression 297 formed in its upper surface. This radial projection 296 is diametrically opposite the finger-like portion 294 and extends radially outwards at right angles to the axis A-A of the pair of diametrically opposite trunnions 259.

The stepped base structure 236 (Fig 1) has an upper level 229 (located rearwardly when the apparatus is in use) and a lower level 231 (located forwardly when the apparatus is in use). The upstanding region connecting the levels 229,231 and adjoining portions of these levels are apertured to reveal a substantial angular extent (e.g. 1350) of each of the two grinding wheels 31,34. The common shaft or spindle 239 upon which these wheels 31,34 are mounted, is journalled in nylon bearings 240 and projects laterally outwards below a raised shield plate 228 formed integrally with the upper and lower levels 229,231 of the base structure 236.The shield plate 228 protects the user of the sharpening/grinding apparatus 230 against injury from the rotating chuck of the "electric drill" or other power tool (not shown) in which the spindle or shaft 239 of grinding wheels 31,34 is in use engaged, the power tool resting on its side on the work bench or table upon which the base structure 236 is located. Alternatively, the spindle 239 may be belt driven from a remote motor or engine.

The shield plate 228 also provides a pivotal mounting for an alignment or drill setting device 310 which, in a rest or inoperative condition, lies in a recess 307 provided in the shield plate. The alignment or drill setting device comprises a pair of plate-like limbs 308 interconnected at their upper ends by an i#ntegral plate 309, the lower ends of the limbs 308 being pivotally mounted on the base structure 236 by outwardly extending trunnions. Adjacent the upper plate 309 the limbs 308 are provided with outwardly extending engagement lugs 311. The upper plate 309 is formed with a depression of generally conical form defined by two diametrically opposed, triangle-like, guide portions 312 which can cooperate with the fluted end of a conventional twist drill.It will be appreciated that the full line view of the alignment or drill setting device 310 in Fig 1 shows the underside of the conical depression.

The bridge member 241 overlies the wheels 31,34 and is removably mounted on the base structure 236 for sliding motion in opposite directions parallel to spindle 239. The two limbs 221 of bridge member 241 are of differing height and engage in a groove 234 provided in the rearward upper level 229 and in a stepped slot 302 provided in the forward lower level 231 of the base structure 236. An integral resilient tag 301 depending from the longer (forward) limb 221 projects into, and co-operates with, the stepped slot 302 in the lower level 231 of the base structure. The arrangement is such that the bridge member 241 cannot be lifted off the base structure when the tag 301 is engaged in the slot 302 but can be removed, e.g. by pivoting about groove 234, when the resilient tag is depressed rearwardly of the apparatus and disengaged from the slot 302.This stepped slot serves to restrict the bridge member 241 to slide along base structure 236 within first and second ranges. The first range corresponds to a position shown diagramatically in chain-dot outline in Fig 1 and is--adopted where a twist drill (e#.g. of high speed steel) is to be sharpened. The second range corresponds to the position shown in full lines in Fig 1 and is adopted where a masonry drill is to be sharpened.

The bridging element across the top of the two limbs 221 comprises an upstanding inclined wall 232 molded integrally with the limbs 221. The upper portion of the inclined wall 232 provides a planar abutment surface 255 of generally rectangular outline, this abutment surface 255 being intersected by the-vertical plane containing the axis of wheels 31.34. To each side of abutment surface 255 the wall 232 is provided with a rectangular aperture 303 surmounted by a depending resilient hook 304 that is molded integrally with the wall 232. A recess 305 of generally rectangular form is molded into the wall 232 below the abutment surface 255.

For sharpening either a masonry drill or a twist drill, the drill is inserted into the holder 233 to extend therethrough with the drill's cutting edges in radial alignment with the index ribs 272. The holder 233 is then fittingly inserted into the main body 295 of carrier 235 with one of the holder's ribs 290 engaged fittingly in the carrier's first slot 291 whereby the holder and carrier are held against relative rotation.

The carrier's trunnion arms 259 are removably engageable, selectively, in either a-first set 19 or a second set 219 of recesses provided in the limbs 221 of bridge member 241, and in each case such as to permit pivotal motion of carrier 235 about the common axis A-A of the trunnions. The pivot axis A-A extends horizontally so as to intersect orthogonally the axis of the drill holder 233 (when supported by carrier 235), preferably at or adjacent to the point of intersection of the drill axis and the rectilinear generatrix of grinding wheel 31 or 34, depending on whether the trunnion arms 259 are engaged in the first or second set of recesses 19 or 219.Preferably the pivot axis A-A is substantially tangential to the cylindrical abrading surface of the grinding wheel 31 or 34 (again depending on whether the trunnion- arms 259 are engaged in the first or second set of recesses 19 or 219)-.

The recesses 219 (shown schematically in Fig 1) are arranged to. receive the trunnions 259 in any one of three fixed foreand-aft positions, the most forward and rearward positions being for use when sharpening the four facets of a "four facet" percussion masonry drill, and the intermediate position being for use when sharpening the two facets of a conventional "two facet" masonry drill (with the drill axis in a vertical plane offset forwardly of the vertical .plane through the spindle 239).

For sharpening a conventional "two-facet" masonry drill, the carrier's trunnion arms 259 are engaged in the recesses 219 in the intermediate fixed position they provide, and the bridge member 241- is moved rightwards (when viewed as in Fig 7) to the second range of slot 302. The masonry drill, loosely held by the holder 233 that is mounted in carrier 235, is then pushed down, without rotation, to engage the surface of grinding wheel 31. The holder 233 is then removed and the drill advanced manually a further small distance (e.g. up to approximately 1mm). The cap 280 is then fully tightened to operate the collet 275 and cause it to clamp the drill tightly within the holder 233 whilst ensuring that the cutting or leading edges of the drill remain aligned with the index ribs 272, and the holder 233 is then reinserted into into the carrier 235 with the slot 291 again accomodating a rib 290.

The mode of cooperative engagement between the trunnions 259 and the recesses 219 is such that, with the engagement in the said intermediate fixed position, the colinear axes of the masonry drill and the tubular body 295 of holder 233 are offset forwardly from, and parallel to, the vertical plane containing the axis of spindle 239, and such that this non zero offset provides for the sharpening of a conventional "two-facet" masonry drill at the usual facet incline of 150 to the horizontal. The engagement is effected with the carrier's radial projection 296 directed leftwards (as viewed in Fig 1) so that, by rocking the carrier clockwise about the trunnion axis, the tubular body 295 can abut against the camming surface 255.In this position the "two facet" masonry drill in holder 233 is held irrotatably in the tubular body 295 of carrier 235 by the interengagement of rib 290 in slot 291; the colinear axes of the drill, holder 233 and tubular body 295 of carrier 235 are inclined to a rectilinear- generatrix of the grinding wheel 31 coincident with the drill's cutting edge and at an "approach" angle of half the point angle of the masonry drill to be sharpened; and a tangent to the wheel 31 at that rectilinear generatrix is inclined to the horizontal at an angle of 150.

The spindle 239 of grinding wheels 31,34 is then rotated and the bridge member 241 moved to and fro (right and left as viewed in Fig 1) to sharpen one facet of the "two facet" masonry drill against the rotating wheel 31. The holder 233 is then withdrawn, rotated through 1800, re-inserted into the carrier 235 with the slot 291 accomodating the opposite rib 290, and (with the carrier located in the same position) the bridge member 241 is again moved to and fro over the base structure 236 to sharpen the other facet of the "two facet" masonry drill.

If the masonry drill is of the "four-facet" percussion type having each "edge" 57,59 provided by two mutually inclined surfaces (i.e. each "edge" 57,59 is in the form of a tick or a V), then the trunnion arms 259 are initially inserted into the most forward fixed position they can adopt in the recesses 219. In this trunnion-engaged condition the colinear axes of the percussion masonry drill and the tubular body 295 of holder 233 are offset forwardly from, and parallel to, the vertical plane containing the axis of spindle 239, and such that this non-zero offset provides for the sharpening of a conventional "four-facet" percussion masonry drill at the usual main facet incline in the range of 25 to 450 to the horizontal.

With the trunnions 259 thus engaged, the carrier 235 is pivoted about the trunnion axis A-A until the carrier's outwardly extending radial projection 296 extends into the respective rectangular aperture 303 in wall 232. Thereupon, the recess or depression 297 in the upper surface of projection 296 becomes engaged by the depending resilient hook 304 molded integrally with the wall 232 above the rectangular aperture- 303. In this position the percussion masonry drill in holder 233 is held irrotatably in the tubular body 295 of carrier 235 by the interengagement of rib 290 in slot 291, the carrier 235 is held fast with the bridging member 241 (by the interengagement of hook 304 in recess or depression 297), the colinear-axes of the drill, holder 233 and tubular body 295 of carrier 235 are inclined to a rectilinear generatrix of the grinding wheel 31 coincident with the drill's cutting edge and at an "approach" angle of half the point angle of the masonry drill to be sharpened, and a tangent to the wheel 31 at that rectilinear generatrix is inclined to the horizontal at said angle in the range of 25 to 450.

The spindle 239 of grinding wheels 31,34 is then rotated and the bridge member 241 moved to and fro (right and left as viewed in Fig 1) to sharpen one face of the "four facet" percussion masonry drill against the rotating wheel 31. The holder 233 is then withdrawn, rotated through 1800, reinserted into the carrier 235 with the slot 291 accomodating the opposite rib 290, and (with the carrier located in the same position) the bridge member 241 is again moved to and fro over the base structure 236 to sharpen the "diametrically opposite" facet of the "four facet" percussion masonry drill.

To sharpen the other two inclined surfaces of the "four facet" percussion masonry drill, the whole procedure is repeated but with the carrier 235 re-located with its trunnions 259 engaged in the most rearward possible engage#ment position of the recesses 219, and with the recess or depression 297 in the upper surface of projection 296 engaged by the other depending resilient hook 304 molded integrally with the wall 232 above the rearward one of the rectangular apertures 303.In this rearward trunnion-engaged position, the colinear axes of the masonry drill and of the tubular body 295 of holder 233 are offset rearwardly (as viewed in Fig 1) from, and parallel to, the vertical plane containing the axis of spindle 239, and such that this nonzero offset provides for the sharpening of these remaining two facets of the percussion masonry drill at a facet incline in the range of 25 to 450 to the horizontal.

Conveniently, sharpening of the first two facets and of the second two facets is such as to provide all four facets with the same angular incline, e.g. of approximately 300, to the horizontal.

For sharpening a twist drill, the same holder 233 and the same carrier 235 are used, but in this case the trunnion arms 259 are engaged in recesses 19 to render the cam 245 engageable with the flat abutment surface 255 of the bridge member's upstanding wall 232. The bridge member 241 is moved leftwards (as viewed in Fig 1) to the first range of slot 302 to adopt the position shown in chain-dot outline in Fig 1. The drill alignment or setting device 310 is then lowered, i.e. pivoted downwards, until its two guide portions 312 rest upon the grinding wheel 34 and with the lugs 311 engaged in slots 313 provided therefor in the inner faces of the bridging member's limbs 221. The drill alignment or setting device 310 is thus engaged with the bridging member 241.

Initially the twist drill is inserted into the holder 233 and the main cap 280 is partially tightened until the drill is held by the collet but can still be readily moved with respect to the holder. The holder is then inserted fittingly into the main body 295 of carrier 235 with one of the holder's ribs 290 entering into the carrier's first slot 291. In this position the colinear axes of the twist drill and the holder 233 are then in the same vertical plane through the axis of spindle 239 of the wheels 31,34 (i.e.

they are not offset therefrom) and are inclined to a rectilinear generatrix of the grinding wheel 34 generally coincident with the drill's cutting edge (or with the line of contact between the drill and the cylindrical abrasive surface of the grinding wheel) at an "approach" angle of generally half the point angle of the twist drill to be sharpened.

The drill is then advanced to contact the wheel 34, and turned gently clockwise about the drill axis to engage the guide portions 312 of device 310. The latter ensure that the drill's cutting or leading edges are correctly aligned parallel to the grinding wheel axis and in the vertical plane containing the drill axis and the axis of the grinding wheels. The main cap 280 is fully screwed up to cause collet 275 to hold the twist drill tightly in the holder 233, and the holder 233 is then removed to check that the index ribs 272 are correctly aligned with the drill's leading or cutting edges. The drill alignment or setting device 310 is then restored to its upper, inoperative or rest position, the grinding wheels 31,34 are rotated, and the holder 233 re-inserted into the tubular body 295 of carrier 235 with a rib 290 entering the slot 292 of the carrier adjacent the finger-like portion 294.

The twist drill can then have the necessary relief ground away by simply rotating the drill either unidirectionally or back and forth about its axis through the angle defined by slot 292. Such rotation simultaneously effects a corresponding pivotal motion of the twist drill about the axis A--A (orthogonal to the drill axis) by co-operation between a cam lobe 251 or 252 and the cam engagement surface 255 of inclined wall 232. Thus, a simple rotation of the twist drill about its axis causes grinding of a drill land (i.e. the part-conical surface between a trailing and a cutting (or leading) edge of the drill tip) at a half-cone angle that is reduced progressively across said land from the drill tip's leading edge to trailing edge.Moreover it will be apparent that the relief h provided to the said land of the drill tip is solely dependent on the cam-induced angular movement of the carrier about the axis A-A orthogonal to the drill axis due to the interaction of the cam 245 and surface 255. Grinding of the drill "land" proceeds until the free end of rib 290 in slot 292 abuts against the bottom of slot 292 so as to prevent further longitudinal movement of the twist drill held in the holder 233.

In this way it is possible to sharpen one half of the twist drill against the rotating wheel 34. The other half of the twist drill can then be sharpened by withdrawing the holder 233, rotating. it through 1800, re-inserting it into the carrier 235 (located in the same position) with the slot 292 accomodating the opposite rib 290 and with the holder's opposite cam lobe 252 or 251 engaging surface 255, and then again simply rotating the drill about its axis through the angle defined by slot 292.

Thus both half-conical "lands" of the drill tip are ground to the same leading edge angle and to the same trailing edge angle and are symmetrical about the twist drill axis. In effect, the arrangement is substantially that each land has the general form of a half cone, the two half cones being skew to one another with their axes mutually inclined at an angle corresponding to the relief angle.

Whilst the twist drill is being sharpened, the outwardly extending radial projection 296 is received by the generally rectangular recess 305 in wall 232 below the wall's planar abutment surface 255, and therefore does not impede the latter's engagement by the cam lobes 251,252. The lateral engagement of the external sides of the projection 296 and the sides of the rectangular recess 305 in wall 232 aids in holding the twist drill in the vertical- plane containing both the drill axis and the axis of spindle 239 and- wheels 31,34 throughout resharpening of the twist drill.

It will be noted that the illustrated embodiment provides a simple method of initially aligning the twist drill's leading edge, i.e. by the alignment or setting device 310, and also provides in a simple way for longitudinal grinding take-up by having the slots 291 and 292 in carrier 235 of differing depths, the depth of slot 292 being constant throughout its angular extent. Furthermore, by providing for the same holder and carrier to be used for a twist drill, a conventional "two-facet"- masonry drill and for a "fourfacet" percussion masonry drill, sharpening of each can be readily obtained with appropriate accuracy.

It will be appreciated that the illustrated embodiment can be readily employed for general grinding and sharpening (edge chisels, screw-drivers and the like) by simply disengaging tab 301 from slot 302 and removing the bridge member 141 to reveal substantial angular extents of both grinding wheels 31,34.

It will also be appreciated that, in the illustrated embodiment, for sharpening a twist drill, the pivotal motion of carrier 235 about axis A-A need only be of a few degrees of arc, e.g. of between 0.50 to 50, to provide an appreciably greater lip relief angle, e.g. of between 30 to 0 180. In preferred form of the embodiment, a twist drill of 1180 point angle (i.e. the angle between the cutting edges when viewing the drill in side elevation) can be provided with a lip relief angle of 90 by having cam 245 move the carrier 235 through an angle of approximately 30 about the axis A-A. As has been explained above, this angular motion about axis A-A is effected automatically by the cam means 245,255 upon rotation of the holder-held twist drill about the drill's longitudinal axis with the holder engaged within the carrier. If desired the lip relief angle can in use be altered from that normally provided by the apparatus. This is achieved by setting the line of the twist drill's cutting edges a few degrees (e.g. 0.50 to 50) to either side of the index marks or ribs (272 in Fig 2) with which those cutting edges are normally aligned, final tightening of the collet being performed with the drill in this alternative positional setting.

Claims (13)

1. A holder for an elongate member characterised in that the holder comprises a collet having a plurality of fingers extending in opposite directions, and collet operating means to move ~ the ends of the fingers radially to engage the elongate member at longitudinally spaced regions.

2. A holder according to Claim 1, characterised in that said fingers extend alongside one another with adjacent fingers extending in opposite directions.

3. A holder according to Claim 1 or Claim 2, characterised in that each of said fingers comprises an end portion interconnecting first and second longitudinally extending limbs#, the first limb being common to the next adjacent finger to one side and the second limb being common to the next adjacent finger to the other side.

4. A holder according to any one of Claims 1 to 3 characterised in that said collet operating means comprises two surfaces relatively movable longitudinally of the collet and in engagement with said fingers for effecting said radial movement, the two surfaces being relatively nonmovable angularly of the collet axis.

5. A holder according to Claim 4, characterised in that two relatively rotatable, screw-thread co-operating parts are provided for effecting said longitudinal relative movement of the two surfaces.

6. A holder according to any one of Claims 1 to 5 characterised in that the collet fingers are in use urged resiliently against the direction of their radial movement.

7. A holder according to any one of Claims 1 to 6 characterised in that the collet is molded of plastics material to provide the collet fingers with an inherent resiliency.

8. A holder according to any one of Claims 1 to 7 characterised in. that the collet operating means are arranged to move the ends of the collet's fingers radially inwardly.

9. A holder according to any one of Claims 1 to 8 characterised in that the collet operating means are arranged to move the ends of the collet's fingers radially outwardly.

10. A holder according to any one of Claims 1 to 9 characterised in that the two surfaces are frusto-conical.

11. A holder according to any one of Claims 1 to 10 characterised in that the said two surfaces engage frustoconical surfaces of the ends of said fingers.

12. A holder for an elongate element substantially as herein described with reference to and/or as illustrated in Fig 2 of the accompanying drawings.

13. A holder for a drill according to any preceding Claim and forming part of drill sharpening apparatus.