The invention relates to vacuum securing arrangements particularly; but not exclusively, for securing items such as workpieces to be operated upon, jigs, fixtures and power tools.

In carpentry and general DIY work, it is often necessary to secure a workpiece to a workbench without damaging or marking the workpiece. Clamping of workpieces is often carried out using mechanical clamping devices, such as cramps or G-clamps. However, such devices can be difficult and time consuming to operate, and it is often necessary to use a number of devices in order properly to secure the workpiece to the workbench. Furthermore, such devices are also prone to damage the surface of the workpiece, particularly if over-tightened or used without suitable padding material. Such devices can also impede the free passage of hand and power tools.

The invention has arisen from attempts to overcome the disadvantages of the prior art.

According to the invention there is provided a vacuum securing arrangement for securing items such as workpieces to be operated upon, jigs, fixtures and power tools, comprising a substantially flat work surface formed with a plurality of openings which are defined by apertures, or which are in fluid communication with apertures, adapted to be connected to a vacuum source so that the item may be held against the

work surface by means of reduced pressure within the openings, each aperture being provided with a valve for opening and closing the aperture so that the number of openings which are exposed to the vacuum source can be varied in accordance with the size and shape of the item.

Such an arrangement removes the need for mechanical clamping devices, and has been found to be particularly effective at securing flat workpieces, such as cupboard doors.

Preferably, the openings are in the form of recesses or grooves. Where the openings are in the form of recesses, preferably there is one said aperture in the base of each recess. Where the openings are in the form of grooves, preferably at least some of the grooves extend outwardly from said apertures in the plane of the work surface.

The valves are preferably automatic valves which automatically move to an open position when covered by a portion of the item, and automatically move to a closed position when uncovered.

This arrangement is particularly quick and simple to use since the item is automatically held against the work surface when placed on the work surface, irrespective of the particular size and shape of the item.

For example, each valve may be provided with biasing means for biasing

the valve towards its closed position, and a part which protrudes above the work surface when the valve is in its closed position, and which is adapted to open the valve when depressed by an item placed on the work surface.

Conveniently, the apertures communicate with a common gallery which

extends beneath the work surface and which is connected to the vacuum source.

In order to allow an item to be released from the work surface without the need to switch off the vacuum source, it is preferable for the vacuum securing arrangement to be provided with a release valve which can be opened to admit air directly to the vacuum source in order to raise the air pressure in those openings which are exposed to the vacuum source.

The release valve could, for example, be provided on the gallery.

The invention is particularly suitable for use in general DIY tasks and in carpentry, and the work surface may form the upper surface of a workbench.

The work surface may be provided with a blade-receiving slot or groove extending along the work surface and having at least one said opening on each of its

sides.

It will be appreciated that such an arrangement allows a workpiece to be cut while it is secured to the work surface. This arrangement has been found to be

particularly effective since the workpiece is secured on both sides of the cutting blade.

Furthermore, the workpiece remains secured to the work surface even if the workpiece is cut into two separate parts. In conventional arrangements this would have required the use of at least two separate mechanical clamping devices on opposite

sides of the line of cut.

Conveniently, the vacuum securing arrangement comprises a downwardly projecting clamping member adapted to be clamped between the jaws of a portable workbench .

This allows a portable workbench to be converted to a highly efficient and portable vacuum securing arrangement.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a first embodiment of a vacuum securing arrangement according to the invention;

Figure 2 is a cross-section taken along A-A in Figure 1 ;

Figure 3 is a cross-sectional view through a first embodiment of a valve of

the vacuum securing arrangement;

Figure 4 is a cross-sectional view through a second embodiment of a valve of the vacuum securing arrangement;

Figure 5 is a plan view of the valve shown in Figure 4;

Figure 6 is a cross-sectional view through a third embodiment of a valve of the vacuum securing arrangement;

Figure 7 is a plan view of the valve shown in Figure 6;

Figure 8 is a plan view of a second embodiment of a vacuum securing arrangement according to the invention;

Figure 9 is a side view of a portable workbench attached to the vacuum securing arrangement shown in Figure 6;

Figure 10 is a sectional view of a portable workbench having two work surfaces and a single integral vacuum source;

Figure 11 is a section taken along line B-B of Figure 10, and

Figures 12 to 15 shown alternative openings in the work surface, on an enlarged scale.

Referring to Figure 1 , the vacuum securing arrangement 2 comprises a flat work surface 4 provided with a plurality of openings in the form of elongate upper recesses 6. The recesses 6 communicate with a gallery 8 located below the work surface 4 via apertures 10 as shown in Figure 2.

The gallery 8 is connected to a vacuum source, such as an ordinary domestic vacuum cleaner (not shown), via an aperture 12 located on the underside of the gallery 8.

When a flat object 14 (see Figure 2), such as a cupboard door, is placed on the work surface 4 it is secured firmly against the work surface 4 by means of reduced air pressure within the recesses 6.

Figure 3 shows a simple cylindrical peg 16 which can be inserted into an aperture 10 in order to isolate the associated recess 6 from the gallery 8. It will be appreciated that the user can use a number of such pegs 16 in order to select which recesses he wishes to use. The choice of which recesses to use will of course depend on the particular size and shape of the workpiece 14 which is to be operated upon. For example, if it is required to secure a narrow plank of wood to the work surface 4, the user may choose to use only the three recesses 6 which are arranged end to end along one side of the work surface 4.

In order to simplify and speed up use of the vacuum securing arrangement, the cylindrical pegs 16 can be replaced by automatic valves 18, shown in Figures 4

and 5 or by automatic valves 58, shown in Figures 6 and 7.

The automatic valves 18, shown in Figures 4 and 5, comprise -a valve member 20, a valve guide 22, and a spring 24 for biasing the valve member 20 towards its closed position. The valve member 20 comprises an upright stem portion 26 which protrudes above the work surface 4 and a lower closure portion 28.

The valve guide 22 comprises a hollow cylindrical portion 30 adapted to receive the upright stem portion 26 of the valve member 20, and four radial support members 32 for supporting the cylindrical portion 30 within the aperture 10. When

the valve 18 is not covered by the workpiece 14 the spring 24 biases the valve member 20 upwards so that the closure portion 28 seals the bottom of the aperture 10. The associated recess 6 is therefore not exposed to the vacuum source which ensures that the air pressure within the gallery 8 is not raised unnecessarily. However, when the workpiece 14 is placed over the valve the upright stem portion 26 is depressed downwardly so that the recess 6 communicates with the gallery 8, and hence with the vacuum source.

The automatic valves 58, shown in Figures 6 and 7, comprise a valve member in the form of a ball 59 mounted in a cup 60 which is press fitted in the

aperture 10. The cup 60 has an upstanding cylindrical wall 61, a base 62 with a central opening 63 therein to allow air to pass therethrough, an outwardly extending flange 64 at its upper end which rests on the base of the recess 6 and an inwardly extending flange 65 at its upper end which defines a sharp edged seat for the ball 59.

A compression spring 66 is disposed between the base 62 of the cup 60 and the ball

59 to urge the ball against the seat. When the ball 59 is urged against the seat, it projects above the work surface 4, typically by about 1.25 mm. The urging force of the spring 66 is such that it can close the valve 58 against atmospheric pressure when the ball 59 is free to rise, but it cannot dislodge the workpiece when in place on the work surface.

It will be appreciated that the automatic valves 18, 58 ensure that the correct recesses 6 are exposed to the vacuum source, in dependence on the size and shape of the workpiece 14. The apertures 10 may be located towards the outside edges of the recesses 6 (as shown in Figure 1) or in the centre of the recesses 6 (as shown in

Figure 7).

The elongate recesses 6 shown in Figures 1 and 6 are of generally

rectangular shape with radiused ends. The recessed area occupies about 50% of the area of the work surface 4. Indeed, experiments have shown that a recessed area of 47% of the area of the work surface is near an optimum value. Typically, the recesses 6 have a depth of the order of 3 mm, a length of between about 10 and 15 cms, and a width of about 4 cms.

Initially it was thought that the vacuum clamping mechanism was "hydrostatic". Thus, holding power was thought to be solely related to the fraction of the work surface area which was recessed compared with the overall area, and that reduced pressure applied only to the recesses 6. However, measurements of pressure

have been made on the lands of the work surface between the recesses and these show intermediate levels of pressure. Therefore, the system appears to be dynamic with air moving within the interface between the work piece 14 and the work surface 4.

In order to allow the workpiece 14 to be quickly and easily released from the work surface 4 a simple release valve (not shown) is provided on the gallery 8. When the release valve is opened, air rushes into the gallery 8 causing the air pressure therein to increase and thus allowing the workpiece 14 to be lifted from, or

repositioned on, the work surface 4.

Figure 8 shows how two of the vacuum securing arrangements shown in Figure 1 can be connected together in order to form a single work surface having a

blade receiving slot. The work surfaces 4 are connected together by means of two bridging members 36 (only one of which is shown in Figure 8) at opposite ends of the work surfaces 4. The blade-receiving slot 34 allows the workpiece 14 to be cut into two separate pieces while ensuring that each piece remains properly secured to the work surfaces 4. The slot 34 may also be used to drill holes through the workpiece 14 without causing air leaks, which would arise if a drill bit were to pass into one of

the recesses 6.

Figure 9 shows the embodiment of Figure 8 attached to the top of a portable workbench. Downwardly projecting members 38 are secured to the bottom of the bridging members 36, and the downwardly projecting members 38 are gripped between jaws 40 of the portable workbench 37. Figure 9 also shows two tubes 42

which are used to connect the galleries 8 of the work surfaces 4 to a suitable vacuum source. It will therefore be seen that the invention allows an ordinary portable workbench having only mechanical securing means to be converted into a highly efficient and portable vacuum securing arrangement.

The portable vacuum securing arrangement shown in Figure 9 uses a

separate vacuum source connected to the work surfaces by flexible tubes. This may be improved by making the vacuum source integral with the two work surfaces 4.

The unit so formed may be placed onto a portable work bench 37 and then plugged in for immediate use. Figures 10 and 11 show such an arrangement. A vacuum source 43 is diaphragm mounted within a plenum chamber 48 which is directly connected to suction galleries 8 by short ducts. Two isolation valves 45a and 45)2 are fitted in the ducts. The valve 45a is shown open, and the valve 45b is shown closed. This enables a single work surface to be used when a small part is to be held. When in operation, air is drawn from galleries 8 past valves 45 through the vacuum source 43 and expelled through vent 44. To facilitate the rapid release of work pieces, a pressure release valve 46 of the lever slide valve type connects with the plenum chamber admitting an inrush of air at near atmospheric pressure to release the work piece without switching off the vacuum unit.

The ends of the work surfaces 4 remote from the plenum chamber 48 are bridged by a transversely mounted member 47. This member 47 and that of the plenum chamber attachment system are arranged so that a blade receiving channel 34 is formed between the two work surfaces 4.

The vacuum unit may have a power cable storage facility and also a switch for motor control.

Figures 12 to 15 shown alternative openings in the work surface 4.

The opening shown in Figure 12 comprises two intersecting grooves 50 arranged in the shape of a St. Andrew's cross. The grooves 50 are typically 23cm in length, 4 mm in width and 3 mm in depth. An aperture 51 (which is preferably fitted with an automatic valve) is provided at the intersection of the grooves 50. Typically the aperture has a diameter of 1.2 cm. The grooves 50 communicate with a gallery, similar to gallery 8, located below the work surface via the aperture 51.

The opening shown in Figure 13 is similar to the opening shown in Figure 12 but a plurality of microgrooves 52 (of substantially smaller width and depth than the grooves 51) communicate with, and extend transversely from, the grooves 51.

The opening shown in Figure 14 comprises a single groove 53 and an aperture 54 midway between the ends of the groove 53. Tests made with an aperture 54 having a diameter of 1.2 cm and a groove 53 having a width of about 4 mm and a depth of about 3 mm have shown that the clamping efficiency increases as the length of the groove is increased to about 15 cm, above which length no further increase in clamping efficiency is obtained.

The opening shown in Figure 15 is defined solely by an aperture 55. The

aperture is not located in the base of a recess and has no grooves communicating with it.

Tests have been carried out to measure the clamping efficiency of the different openings described above. A test rig was set up and a test pressure of 6.89 kN/m ² (1.5 lb/in ² negative gauge) was selected. The horizontal force necessary to just move a workpiece was measured using a spring balance and the clamping efficiency of each opening was derived from these measurements.

The opening shown in Figure 13 was found to be the most efficient and the opening shown in Figure 15 was shown to be the least efficient. The clamping efficiency of the opening 6 shown in Figure 1 was found to be comparable with the clamping efficiency of the opening shown in Figure 12 and second only to the clamping efficiency of the opening shown in Figure 13. Each of the openings shown in Figures 12 and 13 occupies a larger discrete area of the work surface than each opening of Figure 6. Therefore, the size of the working area influenced by a single opening is smaller in the case of Figure 6 than those areas of Figures 12 and 13, allowing the opening array of Figure 6 to accommodate a greater range of size and configuration of workpiece than that achievable with those of Figures 12 and 13. Taking this factor into account the array of openings 6 (shown in Figure 1) is thought to provide the best overall results of design so far tested.

The vacuum securing arrangements disclosed above may be used to support items other than workpieces. For example, they could be used to support jigs,

fixtures or power tools.