GB2209697A

GB2209697A - Clamping device for hand machine tools

Info

Publication number: GB2209697A
Application number: GB8821792A
Authority: GB
Inventors: Hermann Kieser; Norbert Schur
Original assignee: Metabowerke GmbH and Co
Current assignee: Metabowerke GmbH and Co
Priority date: 1987-09-16
Filing date: 1988-09-16
Publication date: 1989-05-24
Anticipated expiration: 2008-09-16
Also published as: GB2209697B; FR2620365B1; FR2620365A1; GB8821792D0; DE3826017C2; DE3826017A1

Description

I- 25F 53 222 2 2_ 0 S,' 6 9, 7 clamping device for hand machine tools The

invention relates to a device for clamping disc-type tools to the main spindle of a hand machine tool.

More particularly the invention relates to such a device having an inner washer and an outer counter washer, which between them accommodate the tool and the outer counter washer thereof being capable of being screwed onto or into the selflocking thread of an axially projecting spindle shaft to tighten the outer washer towards the inner washer in the working direction of rotation.

When a change of tool becomes necessary in o-oerated electric hand tools, like angle sanders, the release of the tool presents a special problem, since due to the moments of load and reaction arising in the tool, the counter washer gets increasingly braced via the tool against the inner washer. This is due to the fact-that the thread onto which the counter washer is screwed has a pitch, which, seen from the direction of the main spindle, runs in a clockwise direction; with a direction of rotation clockwise as seen from the direction of the spindle one is concerned with a right-hand thread. Furthermore, the thread has a normal pitch thus being self-locking. Due to this self-locking of the counter washer significantly high contact pressures occur on the clamping surfaces of the tool with correspondingly high friction, so that considerable counter moments have to be applied by tools between the inner washer and the outer counter washer, in order to be able to release the counter washer. This is entirely independent on whether in the first place the counter washer was tightened manually or by means of an tool against the toolAnserted.

Clamping devices similar to this known kind enabling an assembly of rotating tools without the use of tools are known from the US Patent 2.480,886 and 3,623,281. For this purpose external clamping elements with threads having a high pitch, are screwed directly into the main spindle. Since the high pitch of the thread reduces the clamping force of the clamping elements, though making the release easier, additional devices have to be provided in order to secure a sufficient force fit between the tool and the main spindle. This leads to the fact that commercial tools, like sanding discs, which can be clamped between the flat clamping surfaces of an inner and a counter washer, cannot be used.

In order to easily release by hand the counter washer in clamping devices of the type mentioned at the beginning, it is also known from DE-Cl- 34 05 885 to form the spindle shaft as part of a draw spindle which is guided through a hollow drive shaft and on whose outer end the counter washer may be screwed. At the rear end of the drive shaft and the inner spindle a displacement mechanism is provided, by which the inner spindle may be displaced axially relative to the drive shaft. The inner washer is thereby rotationally fixedly connected to the hollow drive shaft, whilst on the other hand the inner spindle and the hollow drive shaft are also rotationally fixedly connected to each other. In this known device the effective clamping force between the inner washer and the outer counter washer is applied by a sprinq by which the inner spindle is supported in the axial direction on the outer hollow shaft, so long as the clamping force of said spring is not released by corresponding 1 1 1 actuation of the displacement device. When the inner spindle is freed from load and axially outwardly displaced the counter washer can easily be screwed on or unscrewed manually.

The disadvantage of this known device is its costly construction which is related to the inner spindle being guided through the hollow drive shaft, and the displacement device which has to be of such a design that for the unlocking of the outer counter washer the force of the tension spring can easily be overcome. This complicated design is also very space-consuming which conflicts with the need for a compact construction of electric tools.

is The invention has, therefore, the object of providing a clamping device of known type which is compact and able to operate automatically and where between the inner washer and the outer counter washer high clamping forces are developed, in which nevertheless with the tool unloaded and at rest, the counter washer can be released manually without having to resort to further measures.

Thus according to the invention there is provided device for clamping disc-shaped tools to the main spindle of a hand machine tool having an inner washer and an outer counter washer, which between them accommodate the tool and the outer counter washer thereof being capable of being screwed onto or into the self-locking thread of an axially projecting spindle shaft to tighten the outer washer towards the inner washer in the working direction of rotation wherein by means of a non- self-locking thread the spindle shaft is connectable with the main spindle in an axially displaceable manner in such a way, that due to the load moment the spindle shaft is screwed down towards the main spindle, the spindle shaft being rotationally fixed - 4 with the inner washer as well as being freely guided through it in the axial direction and the inner washer having a free connection with the main spindle in the direction of rotation and a fixed connection with it in the axial direction.

The special advantage of a clamping device according to the invention is that, when the tool is unloaded and at rest, it can be manually rotated in the working direction of rotation, whilst due to being taken along by the inner washer, the axially displaceable spindle shaft rotates out of the main spindle and releases the tool of the contact pressure exerted by the outer counter washer thus resulting in the counter washer being easily removable manually.

On the other hand, when in operation and under load, the spindle shaft locks itself by screwing itself into the main spindle. The connection of the spindle shaft with the main spindle by a nonself-locking thread, ensures that, when not under load and despite existing axial forces on the spindle shaft, the latter cannot be prevented from turning out of the main spindle. The locking and unlocking of the counter washer occurs entirely automatically without having to use a tool or having to operate an auxiliary device for this purpose. Since for its release the counter washer has to be rotated in the same direction as the spindle shaft the new device operates directionally.

Despite the easy release of the clamping device according to the invention the high clamping forces between the inner washer and the counter washer are maintained, thus enabling the usual tools, like sanding discs, to be securely clamped under contact between the plane surfaces of these washers. The thread at the outer end of the spindle shaft, onto which the outer counter washer is placed, has a normal pitch making this thread self-locking.

1 Due to the load moment and the friction drive by the tool the counter washer tightens itself automatically, when in operation, thus producing high clamping forces between the counter washer and the inner washer which guarantee a secure rotational drive of the tool. However, the coarse thread which is not self-locking and by which the spindle shaft is connected to the main spindle, makes an easy release of the clamping device possible, thus achieving the object of easily releasing the clamping device on the one hand and securely clamping the tool in a force fit on the other hand, independently of the two aforementioned threads".

In order to deflect satisfactorily from the inner washer the clamping forces which arise, the spindle shaft is guided loosely through the inner washer in the axial direction, the inner washer being loosely connected with the main spindle in the rotational direction and being fixedly connected with it in the axial direction. The transmission of force in the axial direction occurs, therefore, directly from the inner washer to the main spindle, without impairing the rotation of the spindle shaft in relation to the main spindle due to the rotational drive through the inner washer. Between the main.spindle and the inner washer an axial roller bearing is, therefore, advantageously provided.

The displacement of the spindle shaft is limited inwardly by a stop on the main spindle.

If a roller bearing is advantageously provided between the opposite stop faces of the main spindle and the spindle shaft, no locking friction forces can thus occur between the spindle shaft and the main spindle. Outwardly the displacement of the spindle shaft is limited by being stopped on the inner washer, which is fixedly positioned in the axial direction. A pressure on the surfaces, thereby occurring, is not damaging since in any case the spindle shaft and the inner washer are rotationally connected to each other.

The roller bearing between the inner washer and the main spindle is advantageously disposed in such a way that additionally it guides the inner washer in the radial direction, if radial locking elements have been provided thereon to prevent a falling off of the inner washer, when the tool and the counter washer have been removed.

Furthermore, a further advantageous feature of the invention is to have one or several springs engage directly or indirectly on the spindle shaft via the inner washer, said sorinqs acting unon the spindle shaft in the peripheral direction by rotating it into the main spindle through the coarse thread and keeping the stop shoulder of the spindle shaft in contact with the axial bearing and thus with the face of the main spindle. This measure ensures that in idling and deceleration the flywheel effect of the tool does not open the clamping device. automatically. it is, therefore, necessary that the springs exert with their forces a torque on the spindle shaft which is greater than the moment of reaction which occurs when the machine is deceleratinq. However, when opening the clamping device manually via the tool or the counter washer the force of these springs has to be overcome, but this is possible without difficulties. with respect to the pitch of the coarse thread between the spindle shaft and the main spindle the displacement of the springs has been chosen to be sufficient that the clamping device can be reliably freed from load.

Further advantageous features of the invention will be apparent from-the following description and claims.

t z 7 - The invention is hereinafter more fully explained by way of example with reference to the drawings which illustrate two preferred embodiments thereof. In the drawings:- Fig. 1 is a section of the spindle head of an angle grinder, Fig. 2 is an illustration as in Figure 1 of a slightly different embodiment and Fig. 3 is a section of the spindle head of an angle sander along the line III-III of Figure 2.

Figure 1 shows in detail the outer portion of a gearbox 1 onto which a qearbox cover 2 is fixed. A main spindle 3 penetrates the gearbox cover 2, said main spindle being guided by a ball bearing 4 in the gearbox cover 2. The main spindle 3 has an axial blind tapped hole 5 open on its outer face in which a spindle shaft 6 is mounted axially displaceable by rotation. An inner washer 7 and an outer counter washer 8 are disposed on the spindle shaft 6, a sanding disc 9 being accommodated between the washers. In the usual manner the sanding disc 9 is partially covered by a protective hood 10 which is fixed to the gearbox cover 2.

The spindle shaft 6 has an inner rear section 12 with an external thread, which engages in a respective internal thread of the main spindle 3. This thread connection is marked by 11. It is a free-action coarse thread which is not selflocking, so that even with an axial load transmitted via thread 11 the spindle shaft 6 is still rotatable in relation to the main spindle 3.

The displacement of the spindle shaft 6 is limited by a stop shoulder 13 which is supported in the inner end position of the spindle shaft 6 on the outer face of the main spindle 3. In order to prevent any friction between said face and the stop shoulder 13, which might hinder the 1 rotation of the spindle shaft 6, roller bearings 14 are provided between the stop faces of both parts facing each other.

The right-hand side of the drawing shows the inner end position of the spindle shaft 6 and the left-hand side the outer end ppsition of same, the play 15, by which the spindle shaft 6 is movable in the axial direction, being clearly indicated in the corresponding positions. In the outer end position the spindle bolt 6 abuts with its stop shoulder 13 on the inner face of the inner washer 7 which is again indicated in the left-hand side of the drawing, whilst the play 15 of the spindle shaft 6 between the stop shoulder 13 and the facing inner face of the inner washer 7 is indicated in the right-hand drawing.

The inner washer 7 is cup-shaped, thus having an inwards facing, cylindrical peripheral wall 16 which surrounds the outer end of the main spindle -3. Pins 17 or screws projecting inwardly are provided in the peripheral wall 16, which engage in a circumferential groove 18 of the main spindle 3, in order to prevent the inner washer 7 falling off the spindle head, when the counter washer 8 and the sanding disc 9 have been removed. On its outer end face the main spindle 3 has a collar 19, which is radially inwardly offset and axially projecting, in order to accommodate roller members 20 of a diagonal bearing, which on the one hand guides the inner washer 7 in the peripheral direction and on the other hand, by removing the load from the pins 17 and so far as possible without friction directs the axial forces acting inwardly upon the inner washer 7 to the main spindle.

On the outside and abutting outwardly on the stop shoulder 13 the spindle shaft 6 has a collar 21 with drive surface faces 24 through 1 which the spindle shaft 6 has an axially free but rotationally fixed connection with the inner washer 7.

Finally, the spindle shaft 6 has an outer section 22 with a thread 23, onto which the outer counter washer 8 in the form of a nut may be screwed. The thread 23 has to be self-locking, having a considerably smaller pitch compared to the thread 11 between the inner bolt section 12 and the blind tapped hole 5 of the main spindle 3.

The clamping of the sanding disc 9 in operation is carried out as follows: firstly, the counter washer 8 is screwed onto the thread 23 of the spindle shaft 6 to such an extent that the sanding disc 9 is slightly braced between the inner washer 7 and the counter washer 8. In so doing, the spindle shaft 6 can also be rotated, unless it is braked by the contact of the grinding wheel 9 with the inner washer 7. It is irrelevant, whether the spindle shaft 6 has thereby already reached its inner end iDosition because the design of the thread 23 for the counter washer 8 is such, that due to the reaction moment of the sanding disc 9, when the machine is switched on, and the load moment transmitted via the sanding disc 9 by friction forces to the counter washer 8, the counter washer 8 is further braced against the inner washer 7. In this way, during operation, the rotation of the sanding disc 9 is sufficiently ensured. Furthermore, the aforementioned moments cause the spindle shaft 6 to be held in its inner end position, supported on the main spindle 3. In a load-free, standstill condition, in order to be released, the counter washer 8 has to be slightly turned in the original working direction of operation, possibly by means of the sanding disc 9, thus causing the inner washer 7 and the spindle shaft 6 to rotate in this direction as well. However, the main spindle 3, normilly having a heavy action because of its coupling to the drive motor and the associated gear partsr remains stationary, so that the spindle shaft 6 comes out of the main spindle 3 and releasing the 5 clamping forces moves the outer counter washer 8 away from the inner washer 7. Thereafter the counter flange can easily be removed by further turning about the thread 23 in relation to the snindle shaft 6.

Figure 2 illustrates a different locking mechanism between the cup-shaped inner washer 7 and the main s-pindle 3. Here adjacent to the inwardly directed free end of the peripheral wall 106 of the inner washer 7 a retaining ring 25 is inserted into a circumferential inner groove. which engages over a radially projecting shoulder 27 of the main spindle 3.

It can be seen from Figure 3 that springs 26 can be effective between the spindle shaft 6 and the main spindle 3, said springs acting upon the spindle shaft 6 in the rotational direction in which it rotates through the coarse thread 11 into the m.ain spindle 3. Except when it is intended to release the clamping device, the spindle shaft 6 is thus constantly kept in contact with the thrust bearing 14 (Figure 1 and 2) and thus in contact with the end face of the main spindle 3, thereby relieving the coarse thread 11 of the clamping action and merely permitting an axial displacement of the spindle shaft 6 for the release of the tool 9. The automatic clamping of the tool 9 takes place here only via the self-locking thread 23 by which the counter washer 8 is screwed onto the spindle shaft 6. The force of the springs 26 is thereby so determined, that when the apparatus is braked the moment of gyration of the tool 9 cannot open the clamping device. A jerking of %i a 7.

the tool 9, caused by vibrations, can sometimes also occur in free running with high speed angle sanders, which periodically reverses the direction of the resulting load moment acting on the spindle 5 shaft 6. Due to the counter force of the springs 26, however, not even such jerking can cause the clamping device to be released unintentionally.

As shown in the embodiment, it is not necessary for the springs 26 to engage directly on the spindle shaft 6, on the contrary they can also be provided between the shoulder 27 of the Tnain spindle 3 and the peripheral wall 16 of the inner washer 7 surrounding the shoulder. Pockets 28 and 29 are made in the shoulder 27 of the main spindle 3 and the peripheral wall 16 of the inner washer 7, so that, when the pockets 28 and 29 are in line with each other, the springs 26 accommodated therein as compression springs engage tangentially on the shoulder 27 of the main spindle 3. Since the inner washr 7 is rotationally fixedly connected to the spindle shaft 6, the adjusting moment of the springs 26 is transmitted through the inner washer 7 to the spindle shaft 6. In embodiments other than the one shown the springs can also be formed as tension springs, torsion springs or spiral springs, whereby a suitable accommodation for these springs between the main spindle 3 and the spindle shaft 6 must be chosen.

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Claims

Claims:

1. Device for clamping disc-shaped tools to the main spindle of a hand machine tool having an inner washer and an outer counter washer, which between them accommodate the tool and the outer counter washer thereof being capable of being screwed onto or into the self-locking thread of an axially projecting spindle shaft to tighten the outer washer towards the inner washer in the working direction of rotation wherein by means of a non-self-locking thread the spindle shaft is connectable with the main spindle in an axially displaceable manner in such a way, that due to the load moment the spindle shaft is screwed down towards the main spindle, the spindle shaft being rotationally fixed with the inner washer as well as being freely guided through it in the axial direction and the inner washer having a free connection with the main spindle in the direction of rotation and a fixed connection with it in the axial direction.

2. Device according to claim 1 wherein between the inner face of the inner washer and the opposite outer face of the main spindle a bearing ig disposed as axial support for the inner washer on the main spindle.

3. Device according to claim 1 or 2 wherein the inner washer is cupshaped and with its peripheral wall facing inwards, engages over the main spindle, whilst on the peripheral wall locking means are provided projecting inwardly which engage in a circumferential groove of the main spindle or engage over a shoulder of the main spindle.

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4. Device according to claims 2 and 3 wherein at its end the main spindle has a radially inwardly offset axially projecting collar and between the collar and the spindle face outwardly adjacent to it the bearing is disposed on which the inner washer abuts both with its inner face and the internal side of its peripheral wall.

5. Device according to any one of claims 1 to 4 wherein the spindle shaft has a radially projecting stop shoulder, between which and an inwardly lying opposite face of the main spindle a thrust bearing is disposed.

6. Device according to claim 5 wherein the spindle shaft has an axial play relative to the inner washer which is limited outwardly by its shoulder abutting on the inner face of the inner washer.

7. Device according to any of claims 1 to 6 wherein the counter-washer is formed as a nut with an internal thread and correspondingly the spindle shaft has an outer end section with an external thread projecting acros's the inner washer.

8. Device according to any of claims 1 to 7 wherein the spindle shaft has an inner end section with an external thread and that correspondingly the main spindle has an axial blind tapped hole at its outer end.

9. Device according to any of claims 1 to 8 wherein the thread between the spindle shaft and the main spindle is a coarse thread, the pitch thereof being greater than that of the thread between the spindle shaft and the counter washer.

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10. Device according to claim 5 wherein one or several springs engage indirectly or directly on the spindle shaft, said springs acting upon the spindle shaft in the peripheral direction to screw 5 It into the main spindle through the thread, and keepin 9 the stop shoulder of the spindle shaft in contact with the thrust bearing and thus with the face of the main spindle.

11. Device according to claim 10 wherein the springs are disposed between the main spindle and the inner washer which is rotationally fixedly connected to the spindle shaft.

12. Device according to claim 11 wherein the springs are approximately tangentially arranged as compression springs in pockets on the inner side of the peripheral wall of the inner washer and the opposed peripheral side of the shoulder 20 of the main spindle.

13. Device for clamping disc-shaped tools to the main spindle of a hand machine tool substantially as described with reference to Fig. 1 of the accompany25 ing drawings.

14. Device for clamping disc-shaped tools to the main spindle of a hand machine tool substantially as described with reference to Figs. 2 and 3 of 30 the accompanying drawings.

Published 1988 at The Patent Office. State House. 66 71 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. V87.

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