GB2414947A

GB2414947A - Rotary tool holding means

Info

Publication number: GB2414947A
Application number: GB0511752A
Authority: GB
Inventors: Albrecht Hofmann; Harald Krondorfer; Markus Heckmann; Thomas Schomisch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-06-11
Filing date: 2005-06-09
Publication date: 2005-12-14
Anticipated expiration: 2025-06-09
Also published as: FR2871401B1; CN100522482C; GB0511752D0; GB2414947B; CN1706596A; DE102004028529A1; FR2871401A1

Abstract

Means for attaching a rotary tool (not shown) to a hand-held electric machine-tool comprises a drive shaft 17 and a planar disc-shaped flange 18 which has a central aperture and a bearing surface 191. The drive shaft 17 is connected in a torsion-resistant manner to the flange 18 by fitting it into the central aperture. The end of the drive shaft 17 forms a collar 20 which lies against the flange's bearing surface 191. In use a tool such as an angle grinder blade or a circular saw is centred by the collar 20 on the bearing surface 191 against which it is clamped. Connection of the drive shaft 17 to the flange 18 may be by force fitting, form fitting, adhesion or circumferential welding or caulking. For example, the central aperture of the flange 18 may have inwardly projecting cams 29 which respectively engage axial grooves 23 in the drive shaft 17 that extend into a cylindrical recess 22 formed in the end face of the collar 20.

Description

ROBERT BOSCH GMBH, 70442 Stuttgart Tool holding device for an insert tool

Prior art

The invention takes as its starting point a tool holding device for a disc-shaped, rotating insert tool of an electric hand-held machine tool, particularly a hand-held angle grinder or hand-held circular saw, according to the precharacterising clause of Claim 1.

In a known tool holding device for an insert tool of a hand-held angle grinder (DE 101 36 459 Al), the driving flange, which is constructed as a sintered part with a stepped diameter, has an annular flange and two axially continuing collars formed on each end face of the annular flange. A bearing surface for clamping the disc-shaped insert tool, e.g. of a cutting-off or grinding wheel, is constructed on the annular flange. The one collar continuing axially from the bearing surface is constructed as a centring collar for centring the insert tool and, to this end, engages with form fit in the hub of the disc- shaped insert tool abutting against the annular flange.

During operation of the machine, the centring collar absorbs the radial forces arising at the insert tool. The pushing-on collar which continues axially from that side of the annular flange which is remote from the centring collar serves for sliding the driving flange onto the drive shaft and fixing it in torsion-resistant manner on the drive shaft, e.g. by pressing on or inserting a securing ring.

Alternatively, the pushing-on collar can also be connected to the drive shaft by way of a tongue-and-groove connection and can be secured against axial displacement by a cap screw screwed into the end face of the drive shaft. Axial openings are incorporated in the annular flange, through which clamping means reach and clamp the insert tool axially and radially on the bearing surface of the annular flange. The clamping means have a sheet metal plate with axially projecting clamping legs, a zigzag spring, a driving disc with axially projecting latching bolts and a spring element which can be axially pre-stressed. An unlatching button, which is pressed into the hollow- cylindrical centring collar and acts on the clamping means by way of unlatching pins, serves to release the clamping means.

Advantages of the invention The inventive tool holding device having the features of Claim 1 is advantageous in that, by dividing the clamping and centring function of the driving device between the drive shaft and driving flange as a result of displacing the centring collar onto the drive shaft, the centring collar, which absorbs the radial forces arising when working with the insert tool, can be constructed such that it has a much greater load bearing capacity and better wear resistance than the driving flange of the known driving device, which can only be manufactured as a sintered part due to its multi-stepped geometry. The drive shaft is manufactured from wear-resistant, so-called compact steel, e.g. as an extruded part, whilst the driving flange in the known driving device can only be manufactured from porous sintered steel, which is usually granular and has a considerably lower load bearing capacity of the centring collar. The flange disc has a simple geometry which is planar on both sides and it can be manufactured as a simple precision cut or blanked part made of compact steel or as a sintered shaped part. No finishing machining work is required after the shaping process. All in all, as a result of the inventive displacement of the centring collar from the driving flange to the drive shaft and the construction of the driving flange as a planar flange disc, the manufacturing costs for the driving device are considerably reduced. Should the torsion-resistant connection between the drive shaft and the flange disc possibly fail, the latter cannot come free from the machine, but instead remains captured against the machine as a result of its contact with the annular end face of the centring collar, thus reliably preventing any risk to the operator. The torque-transmitting, torsion-resistant connection between the drive shaft and the flange disc can be realised in a variety of forms.

The measures described in the further sub-claims enable advantageous further developments of, and improvements to, the tool holding device described in Claim 1.

According to an advantageous embodiment of the invention, the centring collar has a cylindrical cutout starting from its free end face and the drive shaft has axial grooves which are offset along the circumference by preferably approximately the same circumferential angle and extend through below the flange disc to terminate freely in the cutout. The unlatching pins of an unlatching button, which has to be guided into the cutout in the centring collar to release the clamping means clamping the insert tool on the flange disc, can be guided through these axial grooves.

The axial grooves can, at the same time, also be advantageously used to produce a torsion-resistant connection between the drive shaft and the flange disc in that, according to an advantageous embodiment of the invention, radially projecting cams are constructed on the inner circumferential disc edge of the flange disc, which cams are offset by approximately the same circumferential angle as the axial grooves and engage with form fit in the axial grooves in the direction of rotation. The radial height of the cams here is substantially smaller than the groove depth of the axial grooves, so that the unlatching pins of the unlatching button can be guided into the axial grooves through the remaining clearance.

Drawing The invention is described in more detail below with reference to an exemplary embodiment illustrated in the drawing, which shows: Fig. 1 a plan view of a hand-held angle grinder in a schematic illustration; Fig. 2 an exploded illustration of a detail of a tool holding device for the insert tool of the angle grinder in Fig. 1 with a driving device, said insert tool being constructed as a cutting-off or grinding wheel; Fig. 3 a longitudinal section through the driving device in Fig. 2; Fig. 4 a detail of a longitudinal section of a modified driving device according to Fig. 2.

Description of the exemplary embodiment

Fig. 1 shows, as an exemplary embodiment of an electric hand-held machine tool, a plan view of a schematically illustrated angle grinder. The angle grinder has a housing 11 in which an electric motor (not illustrated) and an angular gear are integrated, and also a rotating disc- shaped insert tool 12, here in the form of a cutting-off or grinding wheel, which is driven by the electric motor and is partially covered by a protective hood 13. The angle grinder can be guided by way of a first handle 14, which is integrated in the housing 11 and extends in the longitudinal direction, and by way of a second handle 15, which is fixed to the housing 11 in the region of the insert tool 12 and extends transversely to the longitudinal direction.

The insert tool 12 is held in a tool holding device which has a driving device 16 (illustrated in Figs. 2 to 4) and clamping means (not illustrated here) for fixing the insert tool 12 in the driving device 16. The driving device 16 comprises a drive shaft 17 and a driving flange 18 fixed in torsion-resistant manner to said drive shaft. The drive shaft 17 is rigidly coupled to the drive shaft of the angular gear or is itself the drive shaft of the angular gear. The driving flange 18 is constructed as a planar, annular flange disc 19 which is manufactured as a simple precision cut or blanked part made of compact steel or as a wintered shaped part. That annular face of the flange disc 19 which faces the insert tool 12 forms a bearing surface 191 for the insert tool 12, on which the insert tool 12 lies with its hub and is clamped on the flange disc 19 by clamping means acting on the hub. DE 101 36 459 Al describes an example of a disc-shaped insert tool with a hub and the possible construction of the clamping means.

The hub of the insert tool 12, which lies against the flange disc 19, is centred on the bearing surface 191. To this end, a centring collar 20 is provided onto which the insert tool 12 is pushed with form fit by means of its hub.

When the insert tool 12 rotates, the centring collar 20 absorbs the radial forces of the insert tool 12.

The centring collar 20 is constructed as an end portion 171 of the drive shaft 17, the end portion having the greater diameter. The drive shaft 17 is manufactured from wear resistant, so-called "compact" steel, e.g. as an extruded part, so that the radial forces of the insert tool 12 rotating at high speed can also be absorbed over a long period without any notable wear. Starting from the free end face of the drive shaft 17, a cylindrical cutout 22 is incorporated in the centring collar 20. Incorporated along the circumference of the drive shaft 17, there are three axial grooves 23 which are arranged offset from one another by approximately the same circumferential angle and of which only two are shown in Fig. 2. On the one hand, the axial grooves 23 extend through below the flange disc 19 to lead into the cutout 22 and, on the other, continue over three shaft portions 172 to 174 which have increasingly stepped diameters and directly adjoin that end portion of the drive shaft 17 which forms the centring collar 20. The axial grooves 23 likewise terminate freely at the end of the last shaft portion 174.

The flange disc 19 is pushed onto the drive shaft 17 from the lower end of the drive shaft 17 (as seen in Fig. 2) until its inner annular face 192 is seated on the shaft portion 172 directly adjacent to the centring collar 20 and the flange disc 19 abuts against the annular transition shoulder between the end portion 171 and the shaft portion 172 of the drive shaft 17 by means of its end face forming the bearing surface 191. In this position, the flange disc 19 is connected with force fit and/or form fit to the drive shaft 17 so that the drive shaft 17 is capable of transmitting a torque to the flange disc 39 and therefore to the insert tool 12 clamped on the flange disc 19.

As shown in the sectional illustration of Fig. 3, the torsion-resistant connection there between the drive shaft 17 and the flange disc 19 is produced by a circumferential welded seam 24 which extends along the contact edge between the flange disc 19 and the shaft portion 173 on the underside remote from the bearing surface 191 of the flange disc 19.

In the exemplary embodiment shown in Fig. 4, the torsion- resistant connection between the flange disc 19 and the drive shaft 17 is produced by at least one transverse pin which is located with form fit in a radial bore 26 in the flange disc 19 on the one hand and engages with form fit in a blind hole 27 in the shaft portion 172 on the other, said blind hole being coaxial with the radial bore 26. Alternatively or additionally, the torsion-resistant connection between the flange disc 19 and the drive shaft 17 can also be effected by caulking the material, as additionally shown in Fig. 4. In this case, a bead 28 of material is produced by caulking the shaft portion 173 of the drive shaft 17 and this bead presses against the underside of the flange disc 19, which is remote from the bearing surface 191.

A further possibility for the force-fitting connection between the flange disc 19 and the drive shaft 17 consists in pressing the flange disc 19 onto the shaft portion 172 of the drive shaft 17. To ensure that the torque is not only transmitted by the force fit of the pressing contact, a further connection with form fit in the direction of rotation is produced between the flange disc 19 and the drive shaft 17. As shown in Fig. 2, radially projecting cams 29 are provided for this purpose on the circumferential, inner annular face 192 of the flange disc 19 and are spaced from one another by the same rotational angle as the axial grooves 23 on the drive shaft 17. When the flange disc 19 is pushed onto the drive shaft 17, the cams 29 engage in the axial grooves 23 with form fit in the direction of rotation. The radial height of the cams 29 is substantially smaller than the groove depth of the axial grooves 23 so that, in spite of the form-fitting connection between the flange disc 19 and the drive shaft 17, there is still a clearance in the axial grooves 23 through which unlatching pins of an unlatching button can still be pushed from the cutout 23 in the centring collar 20, said unlatching button being inserted into the cutout 22 in the centring collar 20 for the purpose of unlatching the insert tool 12.

Claims

ROBERT BOSCH GMBH, 70442 Stuttgart Claims 1. A tool holding device for a

rotating insert tool (12) of an electric hand-held machine tool, particularly a hand- held angle grinder or hand-held circular saw, having a driving device (16) which has a drive shaft (17), a driving flange (18) which is connected in torsion-resistant manner to said drive shaft and has a bearing surface (191) for clamping the insert tool (12) and a centring collar (20) which continues axially from the bearing surface (191) for the purpose of centring the insert tool (12) on the bearing surface (191), characterized in that the driving flange (18) is constructed as a planar flange disc (19) and the centring collar (20) is constructed as an end portion (171) of the drive shaft (17), the end portion having the greater diameter, and in that the flange disc (19) is fixed with force fit and/or form fit on the drive shaft (17) such that its end face lies against the centring collar (20).
2. A tool holding device according to Claim 1, characterized in that the drive shaft (17) and flange disc (19) are mutually connected on the side remote from the bearing surface (191) for the insert tool (12) by a circumferential welded seam (24).
3. A tool holding device according to Claim 1, characterized in that the drive shaft (17) and flange disc (19) are mutually connected on the side remote from the bearing surface (191) for the insert tool (12) by a bead (28) of material produced by caulking.
4. A tool holding device according to Claim 1, characterized in that the flange disc (19) is pressed onto the drive shaft (17) or adhered to the drive shaft (17).
5. A tool holding device according to Claim 1, characterized in that a radial bore (26) is provided in the flange disc (19) and a radial blind hole (27) is provided in the drive shaft (17) and in that a transverse pin (25) incorporated with form fit in the radial bore (26) dips with its end face into the blind hole (27).
6. A tool holding device according to one of Claims 1 to 5, characterized in that the centring collar (20) has a cylindrical cutout (22) starting from its free end face and in that the drive shaft (17) has axial grooves (23) which are offset along the circumference by preferably approximately the same circumferential angle and extend through below the flange disc (19) into the cutout (22).
7. A tool holding device according to one of Claims 1 to 6, characterized in that the flange disc (19) has, on its inner disc edge, radially projecting cams (29) which are offset by preferably approximately the same circumferential angle and whereof the circumferential offset angle corresponds to the axial grooves (23) in the drive shaft (17), and in that the cams (29) are constructed to engage in the axial grooves (23) with form fit in the direction of rotation.
8. A tool holding device according to Claim 7, characterized in that the radial height of the cams (29) is substantially smaller than the groove depth of the axial grooves (23).
9. A tool holding device according to one of Claims 1 to 8, characterized in that the flange disc (19) is manufactured as a precision cut or blanked part made of compact steel or as a sintered shaped part.
10. A tool holding device according to one of Claims 1 to 9, characterized in that the drive shaft (17) is manufactured from wear- resistant steel.
11. A tool holding device substantially as herein described with reference to the accompanying drawings.