GB2252061A

GB2252061A - Powered hand tool with quick-acting tool clamping device

Info

Publication number: GB2252061A
Application number: GB9200316A
Authority: GB
Inventors: Walter Barth
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-01-28
Filing date: 1992-01-08
Publication date: 1992-07-29
Anticipated expiration: 2012-01-08
Also published as: DE4102420A1; CH686238A5; GB9200316D0; GB2252061B

Abstract

A powered hand tool, in particular an angle grinder, has a motor-driven drive spindle (11) for a tool, in particular a grinding wheel (12), and a quick-acting clamping device (14) for clamping the tool in place on the drive spindle (11). The quick-acting clamping device (14) consists of a pressure plate (15) for the tool (12), a threaded part (16) for applying force to the pressure plate (15), and of a hand-screw part (17) which, via a rolling-contact epicyclic mechanism (26), moves the threaded part (16), carrying an internal thread (19), in a screwing manner on an external thread (18) on the drive spindle (11). To avoid screwing the clamping device (14) onto the drive spindle (11) the wrong way round, the thread profile of external and internal thread (18, 19) is designed asymmetrically in such a way that one thread flank, over at least a section of its flank length, has a smaller flank angle than the other thread flank. <IMAGE>

Description

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Powered hana tool, in particular an angle crrinder Prior art

The invention starts from a powered hand tool, in particular an angle grinder, of the generic category defined in the preamble of Claim 1.

DE 3,841,181 A1 discloses, for example, such powered hand tools. In this prior art, the quick-acting clamping device, also called quick-acting clamping nut, serves to quickly change the tool on the drive spindle without any auxiliary tool, the tool at the same time being secured with defined tightening torque to the drive spindle. In the process, the quickacting clamping device only acts in one direction of rotation and must not be screwed onto the drive spindle the wrong way round, since it can be destroyed during release after incorrect assembly.

In order to eliminate such incorrect assembly, in the case of quickacting clamping devices which can be retrofitted the internal thread of the threaded part has been closed on the outer end face with a plastic stopper which, when the clamping device is, screwed, inevitably correctly, onto the drive spindle for the first time, is pushed by the latter out of the internal-thread section. On subsequent changing of the tool, however, there is no longer any protection and the correct assembly of the quick-acting clamping device depends solely on the attentiveness and care of the user. Destruction of the quick-acting clamping device through incorrect assembly cannot therefore be reliably eliminated at least in the long term.

Advantages of the invention Against this background, the powered hand tool according to the invention, having the characterising features of Claim 1, has the advantage that permanent protection against incorrect assembly is provided. Due to the asymmetric design of the -gearing profile, the profile cross-section of the internal thread is enlarged on the one hand and the profile section of the external thread is reduced on the other hand, in each case in comparison with the conventional standard thread profile, with the desired result that the threaded part of the quick-acting clamping device can be screwed onto the drive spindle solely from one side. The user can thus be certain that he will always only put the quick-acting clamping device on correctly and that he will not destroy the latter through incorrect assembly. An additional manufacturing and assembly operation for the plastic stopper is dispensed with.

Coding of the quick-acting clamping device can be obtained by varying the thread profile, possibly also at both f lanks,, in such a way, for example, that the quick-acting clamping device, depending on the design. can be screwed only on a one-hand angle grinder or on a two-hand angle grinder.

In a preferred embodiment of the invention, the flank region having the greater flank steepness or the smaller flank angle starts from the profile root in the external thread of the drive spindle and from the profile crest in the internal thread of the threaded part of the quick- acting clamping device. In this design of the thread profile. nuts having a standard thread or tools having an integrated standard thread remain suitable for the powered hand tool having the external thread according to the invention on the drive spindle, so that, as an alternative, tools having standard nuts can also be clamped in place on the drive spindle with the use of auxiliary tools.

Drawing The invention is explained in more detail in the description below with reference to an exemplary embodiment shown in the drawing, in which:

Fig. 1 shows a side view of an angle grinder having a quick-acting clamping device, partly sectioned, Fig..2 shows a detail of a development of the thread profile between quick-acting clamping device and drive spindle in the angle grinder according to Fig. 1.

Description of the exemplary embodiment

The angle grinder shown in side view in Fig. 1 as an example of a powered hand tool has a drive spindle 11 which-projects at right angles from a housing 10 and is driven via gearing by an electric motor accommodated in the housing 10. The drive spindle 11 has an annular flange 13 as a stop shoulder for a grinding or cutting-off wheel 12, on which flange 13 the grinding wheel 12 is clamped in place by means of a quick-acting clamping device 14 which is screwed onto the drive spindle 11.

DE 3,841,181 Al has already disclosed the known quick-acting clamping device 14 and describes its construction and mode of operation in detail, so that it is suf f icient here to give only a brief outline of the quickacting clamping device 14. The quick-acting clamping device 14 has a pressure plate 15 for pressing the grinding wheel 12 pushed onto the drive spindle 11 against the flange 13. a threaded part 16 for applying force to the pressure plate 15, and a hand-screw.part 17 for screwing the threaded part 16. The free end section 111 of the drive spindle 11 is provided with an external thread 18 on which the threaded part 16 of the quickacting clamping device 14 having a corresponding internal thread 19 is screwed. The annular pressure plate 15 surrounds the threaded part 16 concentrically and is secured against axial displacement relative to the latter by a retaining ring 20. The hand-screw part 17 surrounds the pressure plate 15 and also the threaded part 16 like a sleeve and is axially secured in position relative to the latter by appropriately designed stop-like projections 161 and sealing rings 21, 22. The threaded part 16 is driven by the hand-screw part 17 via a rolling-contact epicyclic mechanism 26 consisting of rolling-contact bearings 23, 24 and disc spring 25.

To clamp the grinding wheel 12 in place, the quick-acting clamping device 14 having the threaded part 16 is put onto the drive spindle 11 and, by turning at the hand-screw part 17, is moved in the direction of the grinding wheel 12 until the pressure plate 15 bears against the grinding wheel 12, that is, frictional connection is obtained. During this first screwing phase, the threaded part 16 is turned in synchronism with the hand-screw part 17. As soon as the friction between the pressure plate 15 and the grinding wheel 12 exceeds the friction in the rolling-contact epicyclic mechanism 26, the threaded part 16 is driven at half the rotational speed of the hand-screw part 17. Combined with this speed reduction is an increase in the transmittable torque to twice the input torque acting on the hand-screw part 17.

The quick-acting clamping device 14 acts only in one direction of rotation and must not be put onto the drive spindle 11 the wrong way round, since it can be destroyed duringrelease after incorrect assembly. In order to reliably eliminate incorrect screwing of the quick-acting clamping device 14 onto the drive spindle 11, the matching thread profile of external thread 18 and internal thread 19,, as apparent from the development shown in Fig. 2. is designed asymmetrically in such a way that one thread flank 181 or 191. over a section of its flank length,, has a greater flank steepness. i.e. a smaller flank angle %, than the other thread flank 182 or 192, the flank angle a, of which is equal to the flank angle in the remaining section of the thread flank 181 or 191. Due to this asymmetric design. the cross-sectional area of the thread profile of the external thread 18 is smaller and that of the internal thread 19 larger than the profile cross-section of a conventional thread profile having the thread flanks a,. The flank region having the greater flank steepness or the smaller flank angle % starts from the profile root in the external thread 18 and from the profile crest in the internal thread 19. This has the advantage that a nut having a standard thread whose flank angle is a, can be screwed without problem onto the external thread 18 (sketched in Fig. 2) on the drive spindle 11, so that if need be the grinding wheel 12 can also be clamped in place by a conventional nut with the use of an auxiliary tool, such as a spanner. In the same way, grinding wheels 12 having an integrated standard thread can also be put onto the drive spindle 11.

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Claims

1. Powered hand tool, in particular an angle grinder, having a motordriven drive spindle for a tool, in particular a grinding or cutting-off wheel, and having a quick-acting clamping device for clamping the tool in place on the drive spindle. which quick-acting clamping device has a pressure plate for pressing the tool against a stop.shoulder on the drive spindle, a threaded part which can be screwed to an external thread of the drive spindle having a corresponding internal thread and is intended for applying force to the pressure plate, and a hand-screw part which, when turned, moves the threaded part in a screwing manner on the external thread of the drive spindle, characterised in that the thread profile of external and internal thread (18, 19) is designed asymmetrically in such a way that one thread flank (181, 191), over at least a section of its flank length, has a greater flank steepness or a smaller flank angle than the other thread flank (182, 192).

2. Powered tool according to Claim 1, characterised in that the flank region having the greater flank steepness or the smaller flank angle (C2) starts from the profile root in the external thread (18) and from the profile crest in the internal thread (19).

3. A power hand tool substantially as herein described with reference to the accompanying drawings.