GB2277959A

GB2277959A - Clamping fixtures

Info

Publication number: GB2277959A
Application number: GB9408925A
Authority: GB
Inventors: Edwin Bernard Froggatt
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-05-14
Filing date: 1994-05-05
Publication date: 1994-11-16
Anticipated expiration: 2014-05-05
Also published as: GB2277959B; GB9408925D0; GB9309944D0

Abstract

A clamping fixture (10) for holding a workpiece (11) in position on a base board (12) comprises a guide (13) having a datum face (17) fig 3 (not shown) in which a rebate is formed. A gripping element (19) is located in the rebate and is in the form of a wedge such that, as the gripping element (19) is moved downwardly upon rotation of a shaft (22), a gripping surface of the gripping element (19) is moved transversely to the face (17) to engage the workpiece (11). <IMAGE>

Description

CLAMPING FIXTURES Field of the Invention This invention relates to clamping fixtures such as may be used for clamping a piece of wood in position relative to a base plate while a routing operation is being performed. The invention is, however, applicable to clamping fixtures generally.

The equipment with which the clamping fixtures are used may be as described in Patent Specification No. 2238752, particularly that shown in Figures 9 to 12 of the drawings of Specification No. 2238752.

It is an object of the present invention to provide an improved form of clamping fixture.

Summary of the Invention According to the present invention there is provided a clamping fixture for holding a workpiece in position, said clamping fixture comprising: a) a guide which can be fixed to a supporting base, said guide having a datum face against which a face of the workpiece is located, b) a rebate formed in the datum face, c) a gripping element located within the rebate, d) means for effecting linear movement of the gripping element within the rebate in a direction such that there is a major component of movement of the gripping element in a direction parallel to the plane of the datum face, e) said gripping element having an operative surface which cooperates with a wall of the rebate in such manner that, as said linear movement of the gripping element is effected, a gripping surface of the gripping element is moved in a direction transverse to the plane of the datum face into gripping engagement with the workpiece.

The operative surface of the gripping element and the wall of the rebate are preferably wedge surfaces with a wedge angle of the order of 150.

The guide is preferably held in position on the base by means of one or more fixing screws which pass through an aperture or apertures in the base and engage in a tapped hole or holes in a fixing element or elements located in a slot or slots in the underside of the base.

The means for effecting linear movement of the gripping element preferably comprises a shaft which extends downwardly from the gripping element and has threaded engagement with a nut which bears against the underside of the or a fixing element.

The shaft may be provided at its upper end with a slot in which the blade of a screwdriver can be engaged so that the shaft can be rotated to effect the required linear movement of the gripping element.

The gripping element is preferably in the form of a block which is a free sliding fit in the rebate, the block having upper and lower surfaces, end surfaces which have guiding engagement with the end walls of the rebate, and side surfaces constituted by the operative surface and the gripping surface.

The gripping surface of the gripping element may be serrated, knurled are otherwise formed so as to enhance the grip exerted on a workpiece.

A pair of clamping fixtures may be provided, one acting on one side of a workpiece and the other acting on the other side of the workpiece. Each clamping fixture may include a pair of spaced rebates in each of which a gripping element is located, the rebates being arranged so that the workpiece is gripped symmetrically on both sides.

Each clamping fixture may alternatively include a single rebate and gripping element. In normal use, there will then be two clamping fixtures on either side of the workpiece though, for short workpieces, a single clamping fixture on each side would be used.

Brief Description of the Drawings Figure 1 is a plan view of a first form of clamping fixture in use holding a workpiece in position while a routing operation is being carried out, Figure 2 is a vertical sectional view of the clamping fixture shown in Figure 1, Figure 3 is a plan view of one of the components of the clamping fixture shown in Figure 1, Figure 4 is a plan view of a second form of clamping fixture, and Figure 5 is a vertical sectional view of the clamping fixture shown in Figure 4.

Description of the Preferred Embodiments Figures 1 and 2 show the use of a a clamping fixture 10 for holding a workpiece 11 in position on a base board 12 while a routing operation is being carried out on the workpiece 11 using, for example, a template such as that shown at 82 in Figures 9 to 11 of the drawings of Patent Specification No.

2238752, to which reference should be made. A second clamping fixture (not shown) may be provided at the other end of the workpiece 11 and, if the workpiece 11 is of significant width, two clamping fixtures may be provided at each end of the workpiece 11.

The clamping fixture 10 comprises a generally rectangular guide 13 which rests on top of the base board 12 and is held in position by means of a fixing screw 14 which passes through an opening in the guide 13 and has threaded engagement in a tapped hole in a fixing element 15 located beneath the underside of the base plate 14.

The guide 13 is in the form of a flat plate having a downwardly extending rib which sits in a slot in the upper surface of the base board 12 and the fixing element 15 has a corresponding upwardly extending rib which sits in a slot in the under surface of the base board 12. The upper surface of the guide 13 includes a recess 16 to receive the head of the fixing screw 14.

The guide 13 has a planar vertical datum face 17 which engages the adjacent side of the workpiece 11 to provide location for the workpiece 11. A rebate 18 is formed in the datum face 17, said rebate 18 being of generally rectangular form in plan view, as shown in Figure 3. A gripping element 19 is located in the rebate 18.

The gripping element 19 is in the form of a wedge and has flat upper and lower surfaces and planar end surfaces which have free sliding engagement with the end walls 20 of the rebate 18. As shown in Figure 2, the wall 21 of the rebate 18 remote from the workpiece 11 is inclined to the vertical at an angle of the order of 15 and the gripping element 19 has an operative surface which engages this inclined wall 21 of the rebate 18 and is inclined at the same angle to the vertical.

The surface of the gripping element 19 opposite to the inclined operative surface is a gripping surface which faces towards the workpiece 11. The gripping surface can be serrated, knurled or otherwise formed so as to have an enhanced gripping action and the arrangement is such that, as the gripping element 19 is moved downwardly, the interaction between the inclined operative surface and the inclined wall 21 of the rebate 18 causes the gripping element 19 to be displaced bodily towards the workpiece and the formations on the gripping surface "bite" into the workpiece 11 exerting a positive downward thrust on the workpiece 11 thereby gripping it and causing it to lie flat against the base board 12.

A shaft 22 extends downwardly from the gripping element 19 and has threaded engagement in an inclined bore formed in the gripping element 19. The shaft 22 is slotted at its upper end so that it can be rotated by means of the blade of a screwdriver or similar tool and it passes through a correspondingly inclined opening in the fixing element 15. The shaft 22 has an externally threaded lower end portion on which a nut 23 is received. A spring 24 surrounds the shaft 22 and acts between the lower surface of the gripping element 19 and the upper surface of the fixing element 15.

As can be seen from Figure 2, the axis of the shaft 22 is inclined at an angle of 150 to the vertical, and thus at an angle of 150 to the plane of the datum face 17. The axis of the shaft 22 is thus parallel to the inclined face 21 of the rebate 18. The threaded engagements between the shaft 22 and the gripping element 19 on the one hand and between the shaft 22 and the nut 23 on the other hand are such that, as the shaft 22 is rotated, the gripping element 19 will be displaced downwardly in the direction of the axis of the shaft 22.

Such movement of the gripping element 19 will be at an angle of 150 to the vertical so that, as the gripping element 19 moves downwardly, it will be displaced towards the adjacent face of the workpiece 11 and it will exert a gripping action on the workpiece 11.

When, however, the shaft 22 is rotated in the opposite direction, the gripping element 19 will be free to move upwardly under the action of the spring 24 and the gripping action exerted on the workpiece 11 will be released.

As shown, the inclined surface 21 of the rebate 18 is at an angle of 150 to the vertical and the axis of the shaft 22 is also at an angle of 150 to the vertical. Thus, as the gripping element 19 is moved downwardly, it will move in a linear direction at 150 to the vertical and at 150 to the plane of the datum face 17. The gripping element 19 will thus move linearly with a major component of movement parallel to the plane of the datum face 17. The gripping surface of element 19 will remain vertical during its downward movement but will be displaced towards the workpiece 11 to effect a gripping action on the workpiece 11.

The guide 13, the fixing element 15 and the gripping element 19 may be formed as plastic mouldings. In particulare, they may be formed as mouldings of Nylon 66 containing 30% by weight glass fibre as a filler to give added strength. The use of plastic mouldings, as opposed to metal components has the advantage that, if a routing cutter should inadvertently be moved into contact with one of the plastic components, no damage will be caused to the cutter.

Turning next to the embodiment shown in Figures 4 and 5, this is used in a similar way to the embodiment of Figures 1 to 3 and differs therefrom primarily in the way in which rotary movement of the shaft 22 is effected. The same reference numerals as have been used in relation to the parts shown in Figures 1 to 3 indicate corresponding parts of the embodiment shown in Figures 4 and 5.

The shaft 22 is fixed at its lower end to a knob 30 access to which is obtained from beneath the base 12. When the knob 30 is rotated in one direction, the gripping element 19 will be moved downwardly and towards the workpiece 11. When, however, the knob 30 is rotated in the opposite direction, the downward force acting on the gripping element 19 will be released and the gripping element 19 will be free to move upwardly under the action of the spring 24 to release the grip exerted on the workpiece 11.

The shaft 22 of the embodiment of Figures 4 and 5 is again inclined at an angle of 150 to the vertical so that the gripping element 19 will be moved linearly downwardly at an angle of 150 to the vertical to effect the4 required gripping action on the workpiece 11.

As compared to the embodiment of Figures 4 and 5, the embodiment of Figures 1 to 3 has the advantage that the required movements of the gripping element can be obtained by access from above whereas, with the embodiment of Figures 4 and 5, the user has to reach beneath the base 12 to affect the required clamping or release actions.

Claims

Claims:

1. A clamping fixture for holding a workpiece in position, said clamping fixture comprising: a) a guide which can be fixed to a supporting base, said guide having a datum face against which a face of the workpiece is located, b) a rebate formed in the datum face, c) a gripping element located within the rebate, and d) means for effecting linear movement of the gripping element within the rebate in a direction such that there is a major component of movement of the gripping element in a direction parallel to the plane of the datum face, e) said gripping element having an operative surface which cooperates with a wall of the rebate in such manner that, as said linear movement of the gripping element is effected, a gripping surface of the gripping element is moved in a direction transverse to the plane of the datum face into gripping engagement with the workpiece.

2. A clamping fixture according to Claim 1, in which the operative surface of the gripping element and the wall of the rebate are wedge surfaces with a wedge angle of the order of 150.

3. A clamping fixture according to Claim 1, in which the guide is held in position on the base by a fixing screw which passes through an aperture in the base and engages in a tapped hole in a fixing element located beneath the base.

4. A clamping fixture according to Claim 1, in which the means for effecting linear movement of the gripping element comprises a rotatable shaft which extends downwardly from the gripping element.

5. A clamping fixture according to Claim 4, in which the shaft has threaded engagement with a nut which bears against the underside of a fixing element.

6. A clamping fixture according to Claim 4, in which a knob is fixed to the lower end of the shaft and is manually accessible for effecting rotation of the shaft.

7. A clamping fixture according to Claim 5, in which the shaft is provided at its upper end with a slot in which the blade of a screwdriver can be engaged so that the shaft can be rotated.

8. A clamping fixture according to any one of the preceding claims, in which the gripping element is in the form of a block which is a free sliding fit in the rebate.

9. A clamping fixture according to Claim 8, in which the block has upper and lower surfaces, end surfaces which have guiding engagement with the end walls of the rebate, and side surfaces constituted by the operative surface and the gripping surface.

10. A clamping fixture according to any one of the preceding claims, in which the gripping surface of the gripping element is serrated, knurled or otherwise formed so as to enhance the grip exerted on a workpiece.

11. A clamping fixture substantially as hereinbefore described with reference to and as shown in Figures 1 to 3 of the accompanying drawings.

12. A clamping fixture substantially as hereinbefore described with reference to and as shown in Figures 4 and 5 of the accompanying drawings.

13. A method of routing which includes the use of a clamping fixture according to any one of the preceding claims to hold a workpiece in position.

14. A method of holding a workpiece in position which includes the use of a pair of clamping fixtures, each according to any one of Claims 1 to 12, one at each end of the workpiece.