GB2164877A - Work gripping device - Google Patents

Abstract

A work gripping device in the form of a bench vice comprises a fixed jaw or bench stop 12 and a movable jaw having two parts 27 with means for moving the two parts together at right angles or at least transverse to the direction the movable jaw approaches the fixed jaw. The parts of the movable jaw can be carried slidably on a transverse arm and cammed together or apart by a camming arrangement including slots 28 in a base plate 11. The transverse arm can be a rocker arm so that the two parts of the movable jaw can grip irregular objects against the fixed jaw. A mitre block can be fitted to the end of the base plate remote from the fixed jaw and this mitre block has resilient projections so when the movable jaw parts are backed away from the fixed jaw against work-pieces against the mitre block the work-pieces move together to form a tightly held mitre joint. <IMAGE>

Description

SPECIFICATION Work gripping devices FIELD OF THE INVENTION The present invention concerns work gripping devices such as vices and jigs especially for light woodwork.

BACKGROUND OF THE INVENTION Various ways of holding workpieces have been proposed. The most common way is a vice consisting of two joints which are drawn together by means of a tead screw to grip the work. This is very effective for holding a single workpiece or for holding parallel workpieces but is not very versatile. For example, it is often desired to join two workpieces which are at right angles to form a T join.

Here the workpiece to be joined at a right angle (in the manner of the upright of the T) to the other piece has to be pushed lengthwise against the other piece. This means a large jaw motion since the upright will be long and also there is a tendency for the workpieces to buckle. The present invention aims at providing a more versatile vice.

SUMMARY OF THE INVENTION The present invention provides a work piece gripping device having two jaws with means for drawing them together in which one of the jaws is in two parts with means for drawing them together in a direction at right angles drawing together direction.

Thus a workpiece can be gripped between the two parts and then moved lengthwise at right angles to another workpiece to form a T join. Whilst the two means could be indepent of each other and have separate operating handles, it is preferred to have the two parts as the movable jaw and to have the two parts cammed together by movement of the movable jaw. If the two parts are cammed together, some adjustment may be desirable for different workpiece widths to augment the camming motion and this is possibly accomplished by having the two parts in the form of blocks which can be twisted to increase or reduce the distance between the gripping faces of the two blocks which co-operate.

It would be possible to join the workpiece at other than right angles by tilting the fixed jaw to the required angle or having a fitment to tilt the gripping surface of the fixed jaw provided that the gripping surface of the fixed jaw gripped the work piece in contact with it frictionally or otherwise to prevent it being slid along the surface by the pressure of the other workpiece.

It has been said that the movable jaw preferably consists of two twistable blocks. This enables the moveable jaw to conform to shapes of irregular workpieces to be clamped either as a single workpiece to be firmly located or when an irregular workpiece has to be clamped side-by-side to another workpiece.

This conformability can be increased by having the two blocks mounted on a rocker arm from the means for drawing the jaws together. This rocker arm could be spring biassed or held by a spring-loaded indexing device in a direction transverse to the jaw drawing direction. Alternatively the rocker arm could have mechanical provisions to hold the rocker arm transverse when desired but with the provisions being releasable when the rocker arm is to be free to rock; for example the rocker arm could be mounted on a spindle with a flat on it with the arm having a keyhole slot so that sliding the rocker arm along its length would engage the spindle with either the smaller width of the slot to lock the rocker arm transversely by engagement with the flat or the larger width to enable the rocker arm to turn freely.

In a preferred embodiment, the workpieces are supported on a base plate with a fixed jaw at one end and a lead screw (rotated by a handle at that end) below the base plate. A nut on the lead screw carries the rocker arm.

The blocks forming the movable jaw are mounted on shafts passing through slots in the base plate and slots in the rocker arm.

The slots in the base plate converge to the fixed jaw end. Thus drawing the movable jaw to that end brings the blocks together since the slots in the base plate cam them together and the shafts slide along the rocker arm. The workpieces are loosely clamped together and then pushed into the desired position with a finger-tight abutment. Tightening up forces the workpieces together and tightens up the grip on the workpieces. The use of slots in the base plate permits a further use of the gripping device. The slots remote from the fixed jaw are made to converge with an included angle of 90 or slightly more say 120" on a position adapted to receive a mitre block.

Thus pushing the movable jaw away from the fixed jaw causes the rear faces of the blocks to move into the inclined faces of the mitre block with any excess of the included angle over 90' acting to push the mitre corner firmly together.

Another aspect of the present invention provides a mitre block wherein the faces at 90 have resilient means for spacing workpieces away from their fully clamped positions so that the workpieces can be positioned fingertight and on clamping the workpieces move inwardly to tighten up the mitre joint.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a workpiece gripping device according to the present invention, Figure 2 is a side view of the device, Figure 3 is a worm's eye view of the device, and Figure 4 is a plan view of a mitre block.

BEST MODE OF PERFORMING THE INVENTION The invention will now be described, by way of example, with reference to the drawings. The drawings do show a host of optional features.

The device consists of a base plate 11 at one end of which is a fixed jaw 12 or bench stop. A lead screw 14 is supported in journals in downturned flanges 15 of the base plate to extend underneath the base plate at right angles to the fixed jaw and is operatable by means of a handle 16. At least one of the flanges 15, preferably that adjacent the fixed jaw, has a mounting flange 17 by means of which the device can be secured to a work table by means of screws in holes 18 in the base plate and flange 17.

A nut or traveller 19 on the lead screw is generally cylindrical with the threaded bore diametrically placed and with a coaxial spigot on its top end journalling a rocker arm 20. It would be possible to use a traveller which can be disengaged from the lead screw and slide along to a position where it is desired to reengage it with the lead screw. The rocker arm has a slot along its length or two slots 21 one at each end along which shafts 22 can slide. Whilst the rocker arm can be held transversely to the lead screw permanently, it is preferred to use a rocker arm to increase the versatility of the device but even so it is better to hold lightly the rocker arm transverse to the screw. This can be done by a spring or a springy detent.As illustrated a washer 23 has an upturned tab 24 engaging in one of the slots 21 and a downturned tab 25 extending down and inwardly to engage a flat 26 on the nut 19 in a manner somewhat similar to the type of locking washer with a tab turned up to engage a flat on a hexagonal nut but without a positive lock but merely a springy detent.

A movable jaw of the device consists of two parts 27 mounted on the shafts 22 which shafts are arranged so as not to tilt. These shafts penetrate the base plate by means of slots 28. Each part can be in the form of a rectangular block 29 twistable about a shaft 22 which is either central giving two different spacings, or off-centre giving up to four different spacings, between confronting faces of the blocks. Alternatively each part can be in the form of an irregular prism 30 with a combination of flat and curved sides to conform to a range of workpiece shapes. It would be possible to have one of each type of part but this would be unusual.The slots 28 converge inwardly towards the fixed jaw or bench stop so as the nut or traveller is drawn by the lead screw towards the fixed jaw or bench stop, the parts 27 move not only towards the fixed jaw or bench stop but also approach each other. The idea is that for making a T join the upright of the T is first lightly clamped anywhere along its length between the two parts 27 and then slid into finger-tight engagement with the cross piece of the T, both workpieces being supported on the base plate, whereupon further tightening of the device firmly clamps the upright and pushes it against the crosspiece thus clamping the cross piece.

A window 31 can be cut in the base plate to allow for all-round inspection of the join. Since the slots converge and it is largely immaterial where along the slots the parts 27 are when clamping occurs, various widths of upright are catered for and this range of widths can be increased by twisting the parts.

If it is desired to make a modified T join with the upright at other than 90" to the cross piece, a false fixed jaw 32 can be hinged at one end 33 to the fixed jaw or to the base plate with the other end secured by a screw 34 sliding in a slot 35 at the desired departure from 90", the crosspiece would be secured to this false jaw by cramps or by friction with the face of the false jaw roughened as by having a strip of fine abrasive attached to it. For small departures from the 90" it should not be necessary to secure the crosspiece. This false jaw can be a permanent bit of the device or can be a removable accessory. If a permanent bit it would be arranged to fold down flat against the main jaw and would act as the clamping face of the main jaw.

The baseplate slots 28 in their simplest form are straight and at an angle of about 11' to the lead screw, this may not be the optimal orientation but has been found to be effective with hardwood parts 27 and softwood workpieces. However it is possible to increase the range of upright widths that can be gripped by having a succession of parallel slots joined by interconnecting slots. As illustrated, the straight slots are staggered with the interconnecting slots blending the straight slots into one another to form continuous slots. The centre lines of the straight slots in the illustrate version are preferably spaced by less than half the difference between the longer and shorter sides of a block 29; thus if the block is 4X6 cm. the centre lines could be spaced by 8 mm without leaving an upright width that could not be gripped. For each transition the width that can be gripped is increased by 1.6 cm and a number of transitions can be used. Another arrangement would be to have the straight slots side-byside joined by interconnecting slots so wide uprights would be gripped using the outer slots and narrow uprights using the inner slots; this effectively nearly doubles the length of the slots for a given device depth.

The arrangement described so far is already a highly versatile vice capable of making T joints, modified T joins, normal vice grips for holding a single workpiece or two workpieces side-by-side, and coping by virtue of the rota tion of the blocks and of the rocker arm with holding irregular shapes. However it is possible to have a mitre block 36 engageable with the rear of the base plate by mushroom head studs (not shown) fitting in keyholes 37 either to form a straight back fence or presenting a right angle 38 to the fixed jaw. A mitre block is in plan a right-angied isosceles triangle with a slight gap at the right angle and arranged so that a saw blade can be passed through the gap to to cut any workpieces held against the short sides of the mitre block to correct any errors in the precut mitring angles.The device according to the present in invention is adapted to co-operate with a mitre block by having the slots 28 curve inwardly to the back and converge with an included angle of 90" so they are normal to the short edges of the mitre block or with an included angle slightly more than 90 so as to push workpieces against the short sides but with a component tending to feed the workpieces towards the right angle to tighten up on a finger-tight abutment of the workpieces. The short sides of the mitre block according to a feature of the present invention are provided with resilient spacers to hold the workpieces away from the short sides. Resilient ball catches 40 are used in the illustrated embodiment in Fig. 4. When the blocks 29 push on the work pieces these catches move back into the short sides and thus the mitre joint is pushed together.The blocks 29 engage the workpieces away from the rightangle corner allowing the mitre joint to be pinned.

Fig. 5 illustrates a possible further embodiment. Each jaw is in two parts 41 with two 42 at right angles with an access space 43 between the faces. Each part is joined by a flexible member 44 to a capstan-like device 45 disposed equidistant from the jaw parts. In use each jaw part is engaged with a corner of a mitred frame and tightening up one the capstan-like device draws in each flexible member by a similar amount so gripping the mitred frame and forcing the corners tightly together.

To avoid the device 45 twisting under the tension of the members 44 to relax that tension, the device 45 should be heavy or otherwise frictionally engage the work surface or the members must enter the device 45 radially and be frictionally or otherwise gripped in the manner of jamming cleats before they enter the tangential run in the device.

Claims (12)

1. A workpiece gripping device having two jaws with means for drawing them together in which one of the jaws is in two parts with means for drawing the parts together in a direction transverse to the jaw drawing together direction.

2. A device according to claim 1 wherein the part drawing together means is a camming arrangement so as the jaws are drawn together the parts are also moved together.

3. A device according to claim 2 wherein the parts are carried on pins slidable along a cross-arm which pins also pass through slots in a base plate which converge towards each other in the direction of the jaw drawing together movement.

4. A device according to claim 3 wherein the cross-arm can tilt so one part can be closer to the other jaw.

5. A device according to claim 4 wherein the cross-arm is resiliently locked transversely of the jaw drawing together movement.

6. A device according to any one of the preceding claims wherein the parts are rectangular or other prismatic shape so they can be twisted to bring the parts closer together for initial adjustment.

7. A device according to any one of the preceding claims as dependent on claim 2 wherein when the jaws are separated by more than a certain amount, the camming direction is reversed so further separation again causes the parts to approach each other.

8. A device according to claim 7 having provision for mounting a mitre block so that on separation of the jaws the parts will engage work-pieces against the mitre block and push the work-pieces against the mitre block with the parts moving in the separation direction with a convergence of about 90 included angle.

9. A mitre block as used in claim 8 wherein the operative faces of the mitre block have means for resiliently spacing the workpieces from those faces.

10. A device according to claim 1 wherein each jaw is in two parts, each part being designed to fit over a corner of a picture frame and wherein the means for drawing the parts together consist of flexible members which can be drawn in by means of a capstan-like device.

11. A device substantially as herein described with reference to Figs. 1 to 3 of the accompanying drawings, with or without a mitre block substantially as herein described with reference to Fig. 4.

12. A device substantially as herein described with reference to Fig. 5 of the accompanying drawings.