GB2105768A - Improvements in or relating to cutting tools - Google Patents

Abstract

A cutting tool comprises a shank insertable into a mounting bore from the front and releasably held in the bore by a retaining device (32). The retaining device has a collar (34) the rim (46) of which forms a rear end seal between a portion (24) of the shank and the adjoining mounting bore (18). The retaining device includes a series of resilient tabs (42) projecting forwards and outwards to a radius greater than the minimum bore radius, such that with the device in position on the tool shank, the tabs are deformed as the shank is inserted through the bore but they offer a greater resistance to return of movement once the shank has been inserted. <IMAGE>

Description

SPECIFICATION Improvements in or relating to cutting tools This invention relates to cutting tools for use in mining and ground engineering (including civil engineering and the construction industry), in the form of cutter picks or point attack tools, for example. It is also concerned with the combination of such cutting tools with their mounting blocks or boxes.

It is known to support a point attack tool in a mounting comprising a support block or box having a stepped bore into which the tool shank is inserted from the front, the tool shank having a stepped shank with a configuration complementary to that of the bore. This configuration comprises a larger diameter forward region and a smaller diameter rearward region which both engage the tool shank closely to support it against transverse forces. A rearwardly directed annular face on the shank engages a forwardly directed face on the front of the support block or in the bore between its forward and rearward regions to provide a support face against the axial forces of the cutting action of the tool.It is also necessary to provide some means of retaining the tool against sliding forwardly out of the bore, although this is counter to the direction of the cutting forces themselves, and that may be done by attaching a locking metal snap ring or washer in a groove at the rear of the shank where the shank protrudes from its support block so that the washer bears against a rear face of the block.

This is inconvenient, in that the user must attach the locking washer in a separate operation after inserting the tool in the bore, and must also remove the washer in a separate operation before he can change the tool. It has been proposed to mount a resilient locking ring on a tool shank before inserting the tool in its bore, the ring being located in a groove in a region of the shank that lies within the mounting bore. The ring is deformed as the shank is pushed into the bore but engages with a rearwardly facing peripheral shoulder of the bore when the tool is in place.This form of locking has also be proposed for an arrangement in which the bore is not stepped and the tool is supported against rearward axial forces by a flange or skirt that bears on a forward face of the support block. in either case, the resilient ring is placed on the shank beforehand, and on insertion a relatively large force is required to push the tool into place; there is therefore a risk of damage to the ring, resulting from which a relatively low force will be sufficient to draw the tool forwards again, as might occur randomly during the operation of the tool.

It has also been proposed to retain a pick shank in place using an element with resilient tabs on a reduced diameter rear end of the pick shank, a locking member behind said element engaging the shank rear end frictionally to retain the tabbed element in place and the element also being supported by said member in such manner that the tabs yield more easily for the insertion of the pick shank into the mounting bore than for the subsequent removal of the shank.

According to the present invention, there is provided a cutting tool comprising a shank having a main part for insertion into a bore of a mounting for engagement with the bore to support the tool transversely thereof, the shank also having a rearwardly directed face intermediate the length of the tool for engagement with the mounting to support the tool against the cutting forces acting rearwardly on the tool, there being mounted on the rear of the shank a retaining device comprising an annular form portion adapted to fit closely between opposed peripheral surfaces of the tool and the mounting bore and said device further comprising at least one resilient element disposed rearwards of said portion and having an operative position at the rear end of the bore in which position said element has a maximum transverse dimension greater than at least the region of the shank axially coincident with said annular form portion, said at least one element being resiliently deformable to permit its passage through the bore to and from said operative position and being adapted to offer a greater resistance to movement forwards away from said operative position than movement rearwards towards that position.

Conveniently, said at least one resilient element is disposed at least partly behind the rear end of the shank.

Analogously to the known forms of tool already referred to, said rearwardly directed face of the shank may be in the form of a shoulder between larger and smaller cross-section points of the shank and arranged for engagement with a complementary shoulder in the mounting bore, or in the form of a flange or skirt arranged for engagement with a face at the entry to the mounting bore.

In a preferred form of the invention, the retaining device is positively engaged with the tool against relative axial movement. It may also be non-rotatably engaged with the tool.

The positive location of the retaining device on the tool shank against rotation and/or axial movement may be obtained by integral profiled portions, e.g. such a portion on the device engaging a non-circular region of the tool shank to prevent rotation and the same or further portion engaging a recess the shank circumference to prevent axial movement.

Alternatively, one or more separate fixing elements may be employed, e.g. a clamping ring or a circlip may fix the tool and retaining device together axially, or a radial pin or screw through the retaining device and into the tool shank may be used to fix them together both circumferentially and axially, or there may be a combination of integral and separate fixing elements if the parts are to be secured both circumferentially and axially.

Preferably, said at least one resilient element is in the form of one or more tabs, or a skirt, inclined forwardly and radially outwardly when in the undeformed state, whereby a greater resistance is offered to movement forwards once the tool has been fully inserted than when said at least one element is being passed through the bore from the front as the tool is inserted.

The invention will be described in more detail by way of example with reference to the accompanying diagrammatic drawings, in which: Fig. 1 is a side view of a point attack tool according to the invention, its retaining device being shown in section, Fig. 2 is a detail illustration of the rear portion of the shank of the tool in Fig. 1, and Figs. 3 and 4 are axial section and rear views respectively of the retaining device of the tool in Fig. 1.

Fig. 1 shows a circular cross-section point attach tool with a conventional hard metal insert 2 at its tip, and behind a protective flange or skirt 4 a main supporting part 6 of the tool shank comrpises a larger diameter forward portion 8 and a smaller diameter rearward portion 10, these being separated by a rearwardly facing shoulder 12. The tool is mounted in a support block or box 14, shown only fragmentarily, that has a stepped bore with larger and smaller diameters 16, 18 and a forwardly facing shoulder 20 each complementary to the associated parts of the shank. The front face of the box lies immediately behind the tool skirt 4 and the rear face 22 lies a little forwards of the rear end of the shank.

Continuing from the rear of its smaller diameter portion 10 the tool shank has a series of concentric cylindrical extensions 24, 26, 28 of progressively smaller diameters, the final extension 28 being provided with an annular groove 30.

A retaining device 32 is mounted on the extensions 24, 26, 28. The device comprises a collar 34 mounted on an end cap 36, both of resilient material which may comprise plastics mouldings, retained in place by a circlip 38 engaging the groove 30.

The end cap 36 comprises a main sleeve 40 that is a close fit on the extension 26 and has a spider-like formation of tabs 42 at its rear region, these tabs being inclined forwards and radially outwards to project radially beyond the diameter of the bore 1 8 of the tool support block. The end cap is held against the rear face of the cylindrical extension 24 by the circlip 38. The collar 34, which is a close fit on the sleeve 40 of the end cap, is held between the end face of the shank rear portion 10 and shoulder 44 of the end cap and has a front rim 46 that fits closely into the annular space between the extension 24 and the bore 1 8. It should be noted that the two parts 34, 36 of the retaining device can be formed as a unitary member, although for convenience they are produced as two separate plastics, e.g.

polypropylene, mouldings.

In use, the collar 34 and end cap 36 are placed upon the end of the tool and secured by the circlip 38 before the tool is inserted into the mounting bore 1 6, 18. As the tool is inserted into the front of the bore, the tabs 42 are resiliently deflected as soon as they reach the region 1 8 of the bore until they emerge from the rear end of the bore to spring back into their unstressed state. The tool is then in the position illustrated in Fig. 1, securely mounted in place, and with the cylindrical rim 46 fitting closely between the tool shank and the mounting bore.

In this state, with the retaining device positively held on the tool shank by the circlip 38, removal of the tool from the mounting bore is hindered by the spider tabs 42 which have sprung out of the bore. The tabs are nevertheless deformable rearwards, when it is required to remove the tool, to such an extent that the spider can be drawn forwards through the bore 18, but it will be noted that because of the forwards inclination of the tabs they offer a much greater resistance to this forwards movement of the tool than when the tool is being inserted into the bore.

Although the retaining device is not positively secured against rotation on the tool shank, the close fit between the end cap and the shank will tend to hold them together rotationally. Because of its circular cross-section the tool shank is free to turn in the mounting bore in use and this action is beneficial in helping to spread the wear on the tip; if such turning movements are also imparted to the end cap 36, the tabs 42 are caused to sweep the area immediately behind the mounting bore so as to reduce the accumulation of foreign matter there that might otherwise prevent replacement of the tool if allowed to build up freely and become compacted.

A further feature of the retaining device is that in its operative position, because of the close fit with the bore 18 and the tool shank it acts as a bearing surface for any rotation of tool in the mounting bore, and also as a barrier against the entry of particles of foreign matter into the bore.

With the bore shielded both at the front, by the collar 4, and at the rear, by the retaining device 32, abrasive wear due to the penetration of particles between the tool and the bore can be substantially reduced.

It will be understood that many modifications are possible within the scope of the invention. For example, other configurations are possible for the retaining device collar and for the resilient tabs, and these latter may be replaced by a skirt-like resilient portion having a similar radial crosssection.

Claims (9)

Claims

1. A cutting tool comprising a shank having a main part for insertion into a bore of a mounting for engagement with the bore to support the tool transversely thereof, the shank also having a rearwardly directed face intermediate the length of the tool for engagement with the mounting to support the tool against the cutting forces acting rearwardly on the tool, there being mounted on the rear of the shank a retaining device comprising an annular form portion adapted to fit closely between opposed peripheral surfaces of the tool and the mounting bore and said device further comprising at least one resilient element disposed rearwards of said portion and having an operative position at the rear end of the bore in which position said element has a maximum transverse dimension greater than at least the region of the shank axially coincident with said annular form portion, said at least one element being resiliently deformable to permit its passage through the bore to and from said operative position and being adapted to offer a greater resistance to movement forwards away from said operative position than movement rearwards towards that position.

2. A cutting tool according to claim 1 wherein the retaining device comprises a first member providing said at least one resilient element and a second member providing said at least one resilient element and a second member providing said annular form portion.

3. A cutting tool according to claim 2 wherein the second member is supported on the first member.

4. A cutting tool according to claim 2 or claim 3 wherein said second member has an axial location with an abutment on the first member,

5. A cutting tool according to claim 4 wherein said second member is axially held between respective abutments on the first member and the shank.

6. A cutting tool according to any one of the preceding claims wherein said at least one resilient element is in the form of one or more tabs, or a skirt, inclined forwardly and radially outwardly when in the undeformed state, whereby the element offers a greater resistance to movement forwards into the bore once the tool has been fully inserted in its bore than when said at least one element is being passed through the bore from the front as the tool is inserted.

7. A cutting tool according to any one of the preceding claims wherein the retaining device is secured axially by a clamping ring or circlip.

8. A cutting tool according to any one of the preceding claims wherein said at least one resilient element is disposed at least partly behind the rear end of the shank.

9. A cutting tool constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.