Clamping Apparatus

The apparatus relates to a clamping apparatus for use in the selective securing into position of a power tool component and particularly, but not necessarily exclusively, a component in the form of a saw blade or grinding wheel , hereinafter referred to in a non limiting manner as a disc for the purposes of illustration of the invention. Yet further the invention is particularly of use in clamping into position a substantially planar saw disc provided for rotation about a central axis thereof.

Clamping means are conventionally provided to clamp and retain in position a substantially planar, circular disc, on an arbour, said arbour driven to rotate said disc when clamped in position thereon such that a series of teeth or abrasive material at the outer periphery thereof can perform a cutting and/or grinding action on a workpiece to which the disc is presented. This form of operation can be incorporated in many power tools such as chop saws, mitre saws, compound saws, circulars saws and the like.

A common problem with the conventional clamping means is that a tool is required to be used by the user to release a clamping bolt to allow removal of the worn disc, and then to tighten the bolt to again tighten the new disc into position on the arbour.

The requirement for persons to use a tool to remove discs is regarded as being unattractive to potential purchaser's of these products due to the time required to use the tool and the possibility of the tool becoming mislaid and lost.

As a result of this, several attempts have been made to provide a clamping system which allows the clamping and unclamping of a disc without the need of a tool. One such clamping system utilises a clutch mechanism in which two coaxially located plates are brought together in conjunction with a washer keyed to one of the plates and so the clamping of the disc can be effected. However this form of clamp has been found to be relatively complex and represents a relatively expensive component for the power tool.

The aim of the present invention is to provide a clamping mechanism for a disc which provides efficient and effective operation without the need for a tool to be used to do so, while ensuring that the disc can still be effectively clamped in position.

In a first aspect of the invention there is provided a clamping device for use in the clamping of a disc in position for rotation on a power tool, said clamping device including a body having a threaded shaft depending from one side thereof and a handle portion on the opposing side of the body in connection with a cam and biasing means assembly and said device is engaged with the power tool via the threaded shaft and wherein said handle is movable between a first position in which a force is applied to the cam mounted on the body, and a second position to release the force on said cam and when said force is applied to the cam, a clamping action is exerted on the disc via the biasing means.

In one embodiment the device includes a plate which lies between the biasing means and the disc so as to transfer the clamping force from the biasing means onto the disc.

In one embodiment the plate is provided as a means to allow a keying arrangement between the disc and the power tool.

Typically the threaded portion which depends outwardly from the device is received in a threaded aperture in the arbour on which the disc is supported, said arbour rotatable and in turn providing rotation of the disc. Typically the clamping device is screwed into and out of the threaded aperture by the user gripping the handle portion or the body of the device when the handle portion is in the second position.

In one embodiment when the handle is in the first position it lies with its longitudinal axis substantially parallel with the disc and in the second position the handle is in a position other than parallel and may in one embodiment have its longitudinal axis substantially perpendicular to the disc.

In one embodiment the handle is moved to an intermediate position between said first and second positions, in which the handle lies in the same plane as when in the first position but is slid such that one end protrudes from the body of the clamping device and, from that position the same can be moved to the second position.

In one embodiment the handle is normally in the first position when the disc is being rotated and is retained in that position by selective release means which require user operation. Thus the handle can be prevented from moving to the intermediate and second positions until the release means can be operated by the user.

In one embodiment the plate against which the cam exerts a force is located on one face of the disc via a resilient means such as a leaf spring which is biased by the cam onto the plate when the handle is in the first position. When the cam is released and the body removed, the plate can also be removed, and the disc replaced.

In one embodiment the arbour includes a portion which protrudes through a fixing aperture in the disc and the said portion contacts against the plate of the fixing device.

In a further aspect of the invention there is provided a power tool incorporating a disc provided to perform a cutting and/or grinding operation when rotated and wherein said disc is clamped in position on the power tool for use, and selectively releasable therefrom using a clamping device as described herein.

In one embodiment the disc is coated in an abrasive material at least at the periphery to perform a grinding action when rotated.

In one embodiment the disc is provided with teeth at the peripheral edge thereof to perform a cutting action when rotated.

Typically the power tool is any of a circular saw, a mitre saw or a chop saw.

There is therefore provided in accordance with the invention a clamping device for use in the clamping of a disc in position for rotation on a power tool, said clamping device including a body having a threaded shaft depending from one side thereof and a handle portion on the opposing side of the body in connection with a cam, a plate and biasing means assembly and wherein said handle is movable between a first position in which a force is applied to the cam mounted on the body, and a second position to release the force on said cam and when said force is applied to the cam, said cam exerts a clamping action on the disc via the plate and biasing means and said device is operable without the use of a tool.

A specific embodiment of the invention is now described with reference to the accompanying drawings wherein

Figures l a-d illustrate an embodiment of the clamping device of the invention in use; and

Figures 2a and b illustrate the clamping device in cross section in open and closed positions; and

Figure 3 illustrates in schematic fashion one form of power tool with which the clamping device can be used.

Referring firstly, for illustrative purposes, there is shown a power tool 50 with which a clamping device 2 in accordance with the invention can be used.

The power tool in this case is a mitre saw which has a base 52 on which a workpiece to be cut is placed. At the rear of the base there is provided a pivot arm 54 and at the free end of the same is mounted the disc 4 mounted to rotate around an axis 56 when mounted on an arbour at the axis. The drive for rotation is typically provided by a motor 57 in connection therewith. With the disc clamped in position, and the disc rotating, the arm can be lowered down as indicated by arrow 58 to perform a cutting action on the workpiece on the base 52. It will be appreciated that the disc needs to be securely clamped in position, but also needs to be releasable from time to time to allow the same to be replaced, for example when the same becomes worn. The present invention provides a clamping device 2 which allows this clamping and removal to be achieved without the conventional requirement to use a spanner or similar tool to remove a bolt which conventionally was used to clamp the disc in position.

Referring now to Figures I a there is illustrate a clamping device 2 in use to exert a clamping force on a disc 4, only part of which is shown for illustration purposes. The clamping device has a body 6 with a handle portion 8.

Turning now to Figures 2a and b the device is shown in more detail. The body and handle 6, 8 are shown as is a threaded shaft 10 which passes into a threaded aperture 12 to secure the device to the arbour 14 of the power tool.

The clamping device also includes a plate 16 which acts on the side 4' of the disc 4 under the influence of biasing means in the form of a leaf spring 18 when the handle is in a first, closed clamping position as shown in Figure 2a. The leaf spring is influenced by control portion, hereonin referred to as a cam 20. The cam is moved between a position shown in Figure 2a when the handle is closed in which the same exerts a downward force on the biasing means which in turn exerts a force on the plate, and an open position shown in Figure 2b where the handle is in an open, second, release position and in which the biasing means are not forced towards the plate. The plate 16 can be provided as part of a keying assembly to ensure that the rotation of the disc is achieved by providing a keyed location with the disc.

Turning back to Figures l a-d a preferred operation of the device between a closed clamping condition and an open condition can now be described.

In Figure I a the device 2 is shown in a clamping position in which the handle 8 is substantially parallel with the blade and is effectively locked in position via a release mechanism incorporating a spring plate 22 which acts to force the handle

against a protrusion 24. This in turn, retains the cam 20 in position, the resilient spring 18 against the plate 16 and hence the disc 4 is clamped and located on the arbour 14.

In order to remove the disc 4 the handle is first slid as indicated by arrow 30 in Figure I b to an intermediate position so that a portion of the handle protrudes from the side of the body. In order to achieve this the spring release means 22 is first required to be pressed down by the user to disengage the protrusion 24. The movement of the handle to the position shown increases the mechanical advantage which can be achieved by the user.

With the handle moved to the position shown in Figure Ib the protruding portion can be gripped and moved to pivot the same about axis 35, as indicated by arrow 34 in Figure I c to move the handle to the second open release position which in this case is substantially perpendicular plane with respect to the disc surface 4'. This action releases the force on the cam 20, spring 18 and plate 16 and hence the clamping force on the disc 4' against the arbour 14 is released.

Once the clamping force is released, the handle and or body can be gripped and rotated as indicated by arrow 36 to unscrew the device 2 threaded shaft 10 from the threaded aperture 12 in the arbour 14 and releases the plate of the clamping device from the disc and allows the disc to be removed and replaced.

To engage the new disc in position the reverse procedure is followed in that the new disc is placed in position, the plate 16 is placed against the side 4' of the disc, the clamping device shaft 10 is screwed into the threaded aperture 12 and this is performed with the handle 8 in the second open position. When the clamping device is screwed into the arbour, the handle is then pivotally moved to the intermediate position from which

position the same is slid towards the first clamping position to cause the cam and biasing means 18 to exert the clamping force on the plate 16. The handle is then also engaged with the release means so as to maintain the position of the same during rotation of the disc when operated as part of the power tool.

The present invention therefore provides a tool free disc clamping device which is effective and easy to use by the user of the power tool.