GB2172823A - Fastening assemblies for grinding or cutting discs - Google Patents

Abstract

A fastening assembly includes an abutment member (4) which can be locked onto the rotary drive shaft (6) of a machine and provides an abutment surface against which a grinding or cutting disc (8) can be clamped. A clamping member (2) has a clamping disc portion (2A) and an annular support portion (26) supporting a pressure washer (10). A spring clip (12) engages a groove (2C) in the support portion (2B) to imprison the washer (10) loosely on the support portion (2B). The clamping member (2) has a screwthreaded bore to enable it to screwthreadedly engage the screwthreaded end of the shaft (6) and urge the disc (8) into clamping engagement with the abutment surface of the clamping member (4). The mating surfaces of the disc portion (2A) and the pressure washer (10) are of low coefficient of friction to ease the initial release of the clamping action of the assembly. The disc portion (2A) is thus allowed to distance itself from the pressure washer (10) before the spring clip (12) engages the washer (10) to pull the washer (10) axially away from the disc (8). <IMAGE>

Description

SPECIFICATION Fastening assemblies The present invention relates to fastening assemblies, for example, for fastening work discs such as grinding or cutting discs to the shafts of motor driven tools.

Portable angle grinders and bench mounted cutting or grinding tools are provided with a rotary shaft having a reduced diameter end portion, which end portion is screw threaded. Grinding discs having a central opening are mounted on the shaft sandwiched between a two part fastening assembly.

Such assemblies, once secured on the shaft with the disc clamped between them, are often difficult to release due to various faactors such as faces of the two parts of the assembly and the onset of corrosion.

It is an object of the present invention to provide an improved fastening assembly.

According to the present invention there is provided a fastening assembly for fastening a work disc to a rotary screw-threaded shaft, the assembly comprising an abutment member arranged to be locked onto the shaft for rotation therewith and to present an abutment surface for engagement by a work disc subsequently mounted on the shaft, and a clamping member comprising a clamping disc having an annular support portion projecting therefrom supporting a pressure washer loosely imprisoned thereon, the clamping member having a screwthreaded through-hole to screwthreadedly engage the screwthreaded shaft to bring the pressure washer into engagement with the work disc when mounted on the shaft and so clamp the work disc against the abutment surface.

A fastening assembly embodying the invention will now be described by way of example, with reference to the accompanying diagrammatic drawing in which Figure 1 is an exploded perspective view of the fastening assembly; and Figure 2 is an exploded perspective view of a clamping member of the fastening assembly of Figure 1.

As shown in Figure 1 the fastening assembly comprises an abutment member 4 and a co-operating clamping member 2.

The abutment member 4 comprises a hollow cylindrical member having one axial end portion 4A of greater external and internal diameter than the external and internal diameters of the other axial end portion 4B.

The smaller diameter end portion 4B is provided with a diagrammatically extending slot 4C in the axial end face thereof. The internal diameter of the end portion 4B is sized to accommodate the reduced diameter end portion 6A of a shaft 6 of a motor driven tool (not shown). An enlarged diameter portion 6B of the shaft 6 is provided with diametrically opposed flats extending tangential to the outer circumference of the reduced diameter end portion 6A of the shaft 6. These flats are arranged to engage the opposite walls of the slot 4C when the abutment number 4 is displaced along the shaft 6 until the step in the shaft 6 engages the base of the slot 4C. In this position the abutment member 4 is locked to the shaft 6 for rotation therewith.

The clamping member 2 as more clearly shown in Figure 2 comprises a disc portion 2A provided with two 'pin' holes 2D or engagement by a pin spanner (not shown) and an axially aligned annular support portion 2B integral therewith. A common bore through the disc portion 2A and the annular support portion 2B is screwthreaded to screwthreadedly engage the screwthreaded shaft 6. A pressure washer 10 has a central opening which receives and is slidably supported on the annular support portion 2B.

The annular portion 2B has a circumferential groove 2C which is arranged to accommodate a generally circular spring clip 12 to imprison the washer 20 loosely on the annular portion 2B.

The central opening of the pressure washer 10 is of enlarged diameter at one axial end to accommodate that portion of the spring clip 12 which projects from the groove 2C when the spring clip 12 is accommodated in the groove 2C. The pressure washer 10 is allowed a limited degree of movement axially of the annular support portion 2B between the disc portion 2A and the spring clip 12.

The face of the disc portion 2A which is arranged to be engaged by the pressure disc 10 is provided with an annular slot or recess in the area immediately surrounding the annular portion 2B. In a modification the annular slot may be omitted.

The facing surfaces of the pressure disc 10 and the disc portion 2A are coated with a material having a low coefficient of friction for example PTFE.

In operation to secure the grinding disc 8 to the shaft 6 using the fastener assembly described, the abutment member 4 is first mounted on the shaft 6 in a position in which the flats on the enlarged portion 6B of the shaft 6 are located between the walls of the slot 4C.

The grinding disc 8 is then mounted on the annular portion 2B of the clamping member 2 (with the pressure disc 10 on the clamping member 2 being located between the grinding disc 8 and the disc portion 2A) and the whole is then caused to screwthreadedly engage the screwthreaded reduced diameter portion 6A of the shaft. As the clamping portion 2A is rotated it will move along the shaft 6 until the annular portion 2B enters the enlarged diameter portion 4A of the abutment member 4. Continued rotation of the clamping member 2 may now need to be effected by means of pin spanner engaging the pin holes 2D as greater effort will be required for the disc portion to displace the washer 10 and the grinding disc 8 into clamping engagement with the abutment face of the enlarged axial end portion 4A of the abutment member 4.

Once a sufficient degree of tightness has been achieved the grinder is ready for action.

To release the grinding disc 8 from the shaft the clamping portion 2 is rotated in the opposite sense. Because the mating surfaces of the disc portion 2A and the washer 10 are of low friction material, relative sliding between them will readily be achieved whereas relative angular movement between the washer 10 and the grinding disc 8 will not readily take place. As the disc portion 2A begins to distance itself from the washer 10, the spring clip 12 will be drawn against the rear face of the washer 10 and pull the washer 10 axially away from the grinding disc 8, the action of the screwthread provides the necessary mechanical advantage to exert a significantly high pulling action in response to the relatively low turning action provided by an operator using a pin spanner to turn the clamping member 2.

Also because the mating surfaces of the disc portion and the washer 10 are coated with plastics the possibility of corrosion occuring between these surfaces is significantly reduced.

Claims (6)

1. A fastening assembly for fastening a work disc to a rotary screwthreaded shaft, the assembly comprising an abutment member arranged to be locked onto the shaft for rotation therewith and to present an abutment surface for engagement by a work disc subsequently mounted on the shaft, and a clamping member comprising a clamping disc having an annular support portion projecting therefrom supporting a pressure washer loosely imprisoned thereon, the clamping member having a screwthreaded through hole to screwthreadedly engage the screwthreaded shaft to bring the pessure washer into engagement with the work disc when mounted on the shaft and so clamp the work disc against the abutment surface.

2. A fastening assembly according to Claim 1 wherein the abutting surfaces of the clamping disc and the pressure washer are coated with material having a low coefficient of friction.

3. A fastening assembly according to Claim 2 wherein said material comprises PTFE.

4. A fastening assembly according to any preceding Claim wherein said annular portion is provided with a circumferential groove accommodating a spring clip to imprison the pressure washer on the annular portion but allowing limited degree of axial movement relative to the annular portion.

5. A fastening assembly according to Claim 4 wherein the pressure washer has an annular recess for accommodating the spring clip.

6. A fastening assembly substantially as hereinbefore described with reference to the accompanying drawings.