GB2283191A

GB2283191A - Reducing clamp pressure and unintentional detachment of motor-driven hand machine disc-shaped tool on braking

Info

Publication number: GB2283191A
Application number: GB9419776A
Authority: GB
Inventors: Winfried Helm
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-10-29
Filing date: 1994-09-30
Publication date: 1995-05-03
Anticipated expiration: 2014-09-30
Also published as: GB9419776D0; DE4337023B4; DE4337023A1; ITMI942184A0; GB2283191B; FR2711570A1; ITMI942184A1; IT1271698B; FR2711570B1

Description

2283191 1 Motor-driven hand machine tool

Background art

The invention proceeds from a motor-driven hand machine tool according to the preamble of claim 1.

A hand machine tool of the type described is known from US-A 4,735,020. Its workspindle may be arrested or braked by means of a spindle-stopping device, whereupon the screw moment for releasing the fixing nut for the grinding tool may be produced by the drive motor. The fixing nut may then be completely detached from the workspindle by hand.

The known hand machine tool has the drawback that, when the workspindle is suddenly brought to a halt after cut-out of the motor by operation of the spindle-stopping device, the grinding wheel owing to its inertia has a tendency to continue rotating and, while so doing, detach the clamping device and itself from the workspindle.

Said unintentional detachment of the clamping device may lead to the grinding wheel detaching at high speed from the workspindle and, as a result of its inherent high energy, placing the operator or bystanders at risk.

Advantages of the invention In contrast, the hand machine tool according to the invention having the characterizing-features of claim 1 has the advantage that unintentional detachment of the disc-shaped tool, in particular of the grinding wheel, is avoided even 2 upon operation of the spindle-stopping device at a high rotational speed of the workspindle. Thus, a considerable increase in safety is achieved.

Further advantageous refinements of the invention are indicated in the dependent claims.

Drawings Embodiments of the invention are explained in greater detail in the following description with reference to the accompanying drawings.

Figure 1 shows a sectional side view of a region of a right angle grinder having an external flange according to the invention, Figure 2 an exploded view of the external flange according to Figure 1 and Figure 3 a second embodiment of an external flange.

Description of embodiments

From the sectional side view of a right angle grinder 10 shown in Figure 1, its gear case 11 flange-mounted onto a motor housing (not shown) is evident. In the gear case 11, a workspindle 12 is held by turned collars 13 and 14 in bearings 15 and 16 respectively. Axially adjoining the collar 14 is a further collar 17 which carries in a non-rotatable manner a housing-side clamping flange 18.

The workspindle 12 carries a bevel gear 19 in a non-rotatable manner between the collars 13, 14. Associated with the bevel gear 19 is a spindle-arresting device 20, which is disposed in the gear case 11 and substantially comprises a pressure pin 22, which is supported so as to be axially displaceable against a spring 21 and, when manually operated, may engage into a recess 23 in the outer periphery of the bevel gear 19.

3.

i- v 3 By its engagement, said pin may abruptly stop the bevel gear 19 and hence the workspindle 12.

At the free end 24 of the workspindle 12, a grinding wheel 26 is clamped between the internal flange 18 and an external flange 25. The external flange 25 is seated on an external thread 27 on the free end 24 of the workspindle 12. The grinding wheel 26 has a central recess 28, with which it engages with play over the workspindle 12 and a centring collar 29.

The direction of rotation of the workspindle 12 is to the left as shown by an arrow 30.

The workspindle 12 carries on its free end 24 in the region of the external thread 27 at least one paraxial flattened portion 32. The cylindrical free end 24 is therefore designed as a single-faced body, preferably as a double-faced body. The free end 24 may alternatively be a square, on the four sides of which the external thread 27 is disposed.

The external flange 25 corresponds to a flat nut and comprises a base element 33, whose central hub 34 has a central bore 35 provided with an internal thread 36. The hub 34 centrically carries a retaining ring 37. The retaining ring 37 embraces the hub 34 and is supported rotatably on its end face 47. The retaining ring 37 has a circular central recess 38 with at least one flattened portion 39.

Remote from the base element 33, the retaining ring 37 carries a threaded hub 40, onto whose external thread 41 a supporting ring 42 having an internal thread 43 is screwed. The supporting ring 42 is supported by its sliding surface 44 facing the retaining ring 37 against a supporting surface 45 of a supporting collar 46 of the retaining ring 37 and by its flange surface 48 facing the grinding wheel 26 on the end face 49.

4 The flange surface 48 has a high surface roughness. As a result, the friction between the grinding wheel 26 and the supporting ring 42 is increased. This ensures the latter's co-rotation even when the clamping force between the external flange 25 and the grinding wheel 26 is low. The base element 33 is non-rotatably embraced at its outer periphery by an external ring 50 by means of at least one spot weld 56. The external ring 50 surrounds the retaining ring 37 and the supporting ring 42 in the manner of a housing with radial and axial play. It secures said rings against loss or axial displacement by means of a collar 51. The flange surface 48 projects axially beyond the collar 51 of the supporting ring 42 so as to produce a contact pressure in the desired manner.

Situated between the supporting ring 42 and the retaining ring 37 is an annular hollow chamber 55 formed by the supporting collar 46.

At its side remote from the grinding wheel 26, the base element 33 carries recesses 53, 53 which are used for the engagement of an auxiliary tool should the internal thread 36, as a result of rust, dust or the like, be seated too tightly on the external thread 27 of the workspindle 12.

The external flange 25 is aligned and balanced in relation to its centrical axis 54.

The internal thread 36 may be screwed onto the external thread 27 of the workspindle 12. In the process, the retaining ring 37 may slide axially over the free end 24 of the workspindle 12 and may, without itself corotating, follow the axial displacement of the external flange 25 during the screw motion.

The external flange 25 according to Figure 1 is shown in an exploded view in Figure 2, which shows in particular the base element 33, its central hub 34 having the central bore 35 with r the internal thread 36, the retaining ring 37 having the recess 38 with at least one radial flattened portion 39 and the threaded hub 40, onto whose external thread 41 the supporting ring 42 with the internal thread 43 is screwed.

From Figure 2 it is clear that the supporting ring 42 and the retaining ring 37 are accommodated between the base element 33 and the external ring 50 as in a housing, the retaining ring 37 and the screwed-on supporting ring 42 being centred on the base element 33 on the hub 34.

The further embodiment of an external flange 75 shown in Figure 3 differs from that in Figure 2 only in that rolling elements 76 are disposed in the hollow chamber 55 between the supporting ring 42 and the retaining ring 37 so as to produce rolling friction between the supporting ring 42 and the retaining ring 37.

When the external flange 25 or 75 is screwed onto the external thread 27 of the workspindle 12, only the base element 33 is axially rotated by means of the external ring 50. The retaining ring 37 with the supporting ring 42 remains locked against rotation on the free end 31 of the workspindle 12 and, upon a rotation of the base element 33 relative to the retaining ring 37, is displaced axially until it strikes against the grinding wheel 26.

Once the grinding wheel 26 has been firmly clamped or preclamped on the workspindle 12 of the right angle grinder 10 between the internal flange 24 and the external flange 25 or 75 by screwing of the internal thread 36 onto the external thread 27, grinding work may commence.

When the grinding wheel 26 is held against a surface to be ground, the friction forces which then arise strive to hold the grinding wheel 26 fast. As a result, the grinding wheel is braked relative to the workspindle 12. Consequently, slip 6 arises between the internal flange 24 of the grinding wheel 26 and the external flange 25. Since the internal flange 18 is fastened non- rotatably to the workspindle 12, it continues to rotate with the workspindle relative to the grinding wheel 26. The external flange 25 or 75 may with its supporting ring 42 follow the movement of the grinding wheel 26, the supporting ring 42 being driven by friction between the end face 49 and the flange surface 48. In the process, the external flange 25 with the base element 33 and the external ring 50 remains, relative to the workspindle 12, locked against rotation or non-rotated in its original position. Owing to the fact that the threaded connection 41, 43 between the supporting ring 42 and the retaining ring 37 is a left-hand thread, preferably a coarse thread with a steep lead, the supporting ring 42 upon its clockwise rotation is axially clamped against the grinding wheel 26.

The high surface roughness of the flange surface 48 facilitates the corotation of the supporting ring 42, the retaining ring 37 owing to the single-faced, double-faced or square design of the central recess 38 being prevented from rotating relative to the workspindle 12.

Upon attainment of the maximum clamping moment between the supporting ring 42 and the grinding wheel 26, a clamping rotation of the supporting ring 42 relative to the retaining ring 37 is no longer possible.

After the motor (not shown) has been switched off, the workspindle 12 is brought abruptly to a halt with high brake acceleration, e.g. by an electromagnetic brake (not shown) or by engagement of the spindlearresting device 20. The grinding wheel 26 which is still striving to rotate, because of its inertia and the friction at the flange surface 48, causes the supporting ring 42 to co-rotate. Upon said lefthand rotation relative to the workspindle 12, the supporting ring 42 is rotated on the threaded connection 41, 43 and moves 17 7 axially away from the grinding wheel 26. Thus, without manual effort, the clamping moment of the external flange 25 is automatically released by the centrifugal force of the grinding wheel 26. The external flange may then, without an auxiliary tool, be completely unscrewed by hand using a minimal amount of force.

The unintentional, slackening co-rotation with the grinding wheel which occurs with conventional tensioning nuts and the feared sudden detachment of the grinding wheel 26 is prevented because, at the external flange 25, the flattened portion 39 prevents rotation of the retaining ring 37 relative to the workspindle 12 and hence automatic detachment of the external flange 25 or 75 as a result of the mass inertia and the friction force of the grinding wheel 26 from the free end 24 of the workspindle 12. This is an important step towards increasing safety at work.

In a further embodiment of an external flange, low-friction sealing means are disposed between the supporting ring and the external ring to prevent dust passing into the interior of the external flange 25 and impeding rotation of the base element relative to the retaining ring and/or rotation of the supporting ring relative to the retaining ring.

8

Claims

Claims

Motor-driven hand machine tool, in particular a right angle grinder (10) with a spindle-arresting device (20) or brake, having a workspindle (12) on which a discshaped tool (26) having a central bore (28) engaging with play over the workspindle (12) is firmly clamped between an internal flange (24) and an external flange (25, 75), wherein the external flange (25, 75) may be firmly screwed onto an external thread (27) on the free end (31) of the workspindle (12) counter to the operating direction of rotation of said workspindle, wherein upon braking of the workspindle (12) the clamping pressure upon the tool (26) between the internal and the external flange (24, 25, 75) may be automatically reduced by the driving action of the tool (26) striving to continue to rotate relative to the workspindle (12), characterized in that the external flange (25, 75) has means of reducing the clamping pressure (37, 42) as well as retaining means (39) which prevent its unscrewing from the external thread (27) as a result of co-rotation of the tool (26) upon braking of the workspindle (12).
2. Hand machine tool according to claim 1, characterized in that the workspindle (12) is provided with means (32) which hold the retaining means (39) of the external flange (25, 75) non-rotatably on the workspindle (12).
3.

0 Hand machine tool according to claim 1 or 2, characterized in that part of the external flange (25, 75) carries an internal flattened portion (39), preferably an internal double face, which engages over 9 the workspindle (12) and that the workspindle (12) carries an external flattened portion (32), preferably an external double face, which is associated with said flattened portion (39).
Hand machine tool according to claim 3, characterized in that the external flange (25, 75) comprises annular parts supported axially, in particular in a centred manner, one upon the other, namely a base element (33) with a hub (34), on which a retaining ring (37) is rotatably supported in a centred manner, onto which a supporting ring (42) carrying the flattened portion (39) is screwed in the direction of rotation of the workspindle (12), an external ring (50) accommodating the base element (33) in a non-rotatable manner and embracing the retaining ring (37) and the supporting ring (42) with radial clearance and securing the latter axially by means of a collar (51).
Hand machine tool according to claim 4, characterized in that the supporting ring (42) has a flange surface (48) projecting axially beyond the collar (51) of the supporting ring (42) and having a high surface roughness for high frictional engagement with the tool (26).
6. Hand machine tool according to claims 4 or 5, characterized in that rolling elements (76) are disposed between the supporting ring (42) and/or the retaining ring (37) and/or the base element (33).

A hand machine tool substantially as herein described with reference to Figures 1 and 2, or Figure 1 as modified by Figure 3, of the accompanying drawings.