GB2338913A - Jig assembly - Google Patents

Description

2338913' JIG ASSEMBLY This invention relates to jig assemblies of the kind

comprising at least one jaw which is mounted on a carriage capable of translational movement with respect to a base for clamping and unclamping the jaw, and a releasable connecting pin providing the force path between the carriage and the jaw.

Such jig assemblies enable the jaw to be replaced when the jaw becomes worn or when a different jaw is required to clamp workpieces of a different shape. Often the jaws are sacrificial jaws which are machined to fit the workpieces to be clamped.

According to a first aspect of the present invention there is provided a jig assembly of the kind set forth, in which the pinned connection comprises camming means, the camming means being so arranged that a workpiece which is acted on by the jaw is subjected to a clamping force component which is substantially perpendicular to the direction of movement of the carriage.

Such a clamping force component provides improved positioning of a clamped workpiece to enable an operation, such as a machining operation, to be performed on the clamped workpiece.

Preferably the jaw comprises at least two clamping faces on substantially opposite sides of the jaw, to enable the jaw to be double-acting.

Preferably the camming means comprises a camming pin releasably connected to the jaw or to the carriage, and a camming pin receiving means provided on the carriage or jaw respectively.

For ease of assembly it is preferred that the camming pin is releasably connected to the jaw, and the camming pin receiving means is provided on the carriage.

Preferably the underside of the jaw, that side which is towards the base, is recessed to receive the camming pin, rather than housing the camming pin in a bore machined in the jaw. This facilitates accurate positioning of the pin but with ease of machining.

Preferably opposite ends of the camming pin are secured to the jaw by screws to provide said releasable connection between the pin and jaw, and the camming pin ends are desirably each provided with a flat abutment face to abut with a complementary abutment face in the jaw recess.

The camming pin and camming pin receiving means are most preferably provided with forward and reverse pairs of camming surfaces that are operative to urge the double-acting jaw in the direction towards the base for both directions of clamping of the jaw.

Preferably said hole is defined by at least two adjacent surfaces which together form a substantially V-shaped outline, said adjacent surfaces being inclined in opposite directions to the direction of movement of the carriage.

Although the jig assembly may be provided with only one jaw which is capable of moving relative to the base, preferably there are at least two such jaws, and the two jaws are connected to respective carriages by respective camming means.

When the jig assembly comprises two such jaws the associated carriages can be urged together or apart in well-known manner by a clamping screw engaging with both carriages.

The assembly may comprise a third jaw which is fixed or adapted to be 5 fixed to the slide in a position between two jaws.

According to a second aspect of the invention, a jig assembly comprises first and second jaws, the first jaw being carried by a jaw carriage working in a slide, an operating screw arranged to cause relative movement of the jaw carriage towards and away from the second jaw, camming means connecting the first jaw with the first carriage, the camming means comprising a pin fast with first jaw and extending through a profiled hole in a spigot portion of the jaw carriage, the crosssectional shape of the pin, and the cross-sectional shape of the profiled hole being chosen such that the pin and walls of the profiled hole cam together to cause the first jaw to be urged towards the slide when the first jaw is exerting an axial clamping force acting towards the second jaw, and also when the first jaw is exerting an axial clamping force away from the second jaw.

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

Figure I shows an exploded view of a jig assembly in accordance with the invention, Figures 2a and 2b show side elevations of the carriages of the jig assembly of Figure 1, Figures 3a, 3b, 4a and 4b show front and rear elevations of the carriages shown in Figures 2a and 2b, Figure 5 shows a plan view of one of the jaws shown in Figure 1, Figure 6 shows a side elevation of the jaw shown in Figure 5, Figure 7 shows a plan view of a camming pin shown in Figure 1, Figure 8 shows an end elevation of the camming pin shown in Figure 7.

Figure 9 is a side elevation of the jig assembly of Figure 1 when provided with a central, fixed jaw; Figure 10 is a plan view of the three jaw assembly of Figure 9; Figure 11 is a longitudinal cross-section on the line 12-12 of Figure 10; Figure 12 is an end view of the assembly looking from the left in Figure 11; and Figure 13 is an end view looking from the right in Figure 11.

Figure 1 shows a jig assembly 1, comprising a pair of jaws 6a and 6b connected by camming means 5a, 5b, 7a, 7b to respective carriages 3a and 3b working in a slide 14, which provides a base of the jig assembly.

The carriages 3a and 3b comprise elongate blocks and integral upstanding 20 spigots 15a and 15b, the blocks being provided with longitudinal through- bores 16a and 16b respectively. Said spigots project outwards from the slide 14. Each spigot 15a and 15b is provided with a respective profiled through-hole 7a and 7b extending transversely through each spigot 15a and 15b relative to the axis of bores 16a and l6b. The cross-sectional shape of each through-hole 7a, 7b is that of a square with rounded comers, as is clear from Figures 1, 2a and 2b.

The bores 16a and l6b extend through the entire length of each carriage 3a and 3b. The bore 16a comprises two bore portions 20 and 22. The bore portion 20 is of greater diameter and co-axial with the bore portion 22, an annular shoulder 12 being defined at the junction between bore portions 20 and 22. The bore l6b comprises two bore portions 18 and 19, bore portion 18 being provided with a thread 21. Bore 19 is co-axial with the bore portion 18, and is of greater diameter than that of the bore portion 18. The slide 14 comprises two lips 40 and 41, said lips co operating with shoulders 42a, 42b and 43a, 43b (see Figures 3a, 3b, 4a and 4b) so as to hold each carriage in the slide 14.

A slide cover plate 2 protects the slide against ingress of dirt and swarf.

The jig assembly shown in Figure 1 also comprises two camming pins 5a and 5b. Referring to Figure 7 and Figure 8, each camming pin comprises two end portions 27 and 28 and an intermediate portion 29. Each end portion has formed therein threaded bores 30 and 31. The outline of the intermediate portion 29 is quasi-octagonal in which alternate surfaces 32, 34, 36 and 38 are flat, and intermediate surfaces 33, 35, 37 and 39 are part-circular about the axis of the camming pin. The camming pins 5a and 5b and the through-holes 7a and 7b are formed such that the distance D1 between opposing flat surfaces which define each through-hole 7a and 7b is slightly greater that the distance, D2, between opposing flat surfaces of each camming pin 5a and 5b, so that when each camming pin is inserted into the respective through-hole there is a small amount of play.

The end portions 27 and 28 comprise half sections of the inner portion 29, to define diametral locating faces 271, 281.

Turning now to the jaws 6a and 6b shown in Figures 5 and Figure 6, each jaw 6a and 6b is machined in the underside thereof with a main square recess 46 and with opposed subsidiary recesses 44, 45 of shallower depth than main recess 46. The recess 46 receives the respective spigot 15a or 15b, and the subsidiary recesses 44 and 45 receive the end portions 27 and 28 of the camming pins which have been inserted into the respective through-holes 7a and 7b.

Screw holes 47 and 48 are provided in each jaw to extend into recesses 44, 45 respectively and are so arranged that said screw holes 47 and 48 will be aligned with the threaded bores 30 and 31 in the camming pins when the camming pins 5a and 5b are correctly positioned in the spigots 15a and 15b. Thus each jaw 6a, 6b can be rigidly secured to the respective camming pins 5a, 5b by screws 23. Thus when screws 23 are inserted into screw holes 47 and 48 and the screws are subsequently tightened, the camming pins will be pulled up inside the respective through-holes 7a, 7b to clamp surfaces 271, 281 against the bases 441, 451 of subsidiary recesses 44, 45.

Further screw holes 49 and 50 are also provided in each jaw. Screw holes 49 and 50 extend through the entire depth of each jaw to allow either jaw to be attached when required to the slide 14 by a pair of jaw fixing screws 491, 501 (Figure 1). It should be noted that the screw hole pairs 47 and 48, and 49 and 50 are not shown in Figures 6 and 11 for reasons of clarity.

Slide cover plate 2 is provided with three pairs of screw holes 55a, 56a; 55b, 56b; 55c, 56c which allow the jaw fixing screws 491 and 50' to be secured in holes 90a or 90b (or 90c) according to which of the jaws 6a, 6b (or a third jaw 6c, described later with reference to Figures 9 to 11) is to be fixed to the slide 14. The cover plate 2 is further provided with apertures 17a and l7b to accommodate the range of available movement of the carriages 3a, 3b in the slide 14.

A jaw-operating screw 9 (Figure 1) comprises a threaded end portion 70 which co-operates with the thread 21 of the bore 18. The plain shank 91 of screw 9 extends through the bore portion 16a of jaw carriage 3a.

Screw 9 is held axially relative to the carriage 3a by a securing pin 25 and ring 8, and by stop end 58, the pin 25 extending through a transverse hole 60 in screw 9. The stop end 58 abuts a washer 13 and the washer 13 abuts the shoulder 12. Thus rotation of the screw 9 varies the separation between the carriages 3a and 3b.

In use, the jig assembly 1 operates as follows. When a workpiece is placed between the faces 61a and 61b of the jaws 6a and 6b, as the jaws are urged together by turning the screw 9, the reaction exerted by the workpiece on the jaws urges the jaws axially apart relative to the carriage spigots 15a and 15b. The vertical positions of the camming pins 5a, 5b relative to slide 14 as determined by the position of face 441, and the vertical positions of the through-holes 7a and 7b in spigots 15a, 15b determine which of the flat faces 32, 34, 36, 38 engage with the corresponding flat faces bounding through-holes 7a, 7b. The tolerances are chosen such that a face 32, 38 of each camming pin will engage the respective forward surface Ila and 11b bounding the through-holes 7a and 7b and thus the camming pins 5a and 5b will move down the forward surfaces Ila and 11b respectively to urge the jaws 3a, 3b downwards towards slide 14, thereby subjecting the workpiece to a clamping force component which is directed towards the slide 14.

This downward clamping force component ensures improved clamping of the workpiece.

It will be noted that the forward camming surfaces Ila, l1b and adjacent reverse camming surfaces 13a, 13b are inclined in opposite directions to the longitudinal axes of the carriages 3a, 3b.

If outwardly facing clamping faces 62a and 62b are used to clamp a workpiece internally, such as a ring-shaped workpiece, then as the jaws are separated and the clamping faces 62a and 62b come into contact with the workpiece a flat face 32 or 38 of each camming pin will engage with a reverse surface 13a, l3b respectively around the through-holes 7a and 7b. Thus the workpiece is also subjected to a force which is directed towards the slide 14. The clamping faces 61a and 61b and 62a and 62b are generally formed from a suitable 'soft' material so that the jaws are 'sacrificial' in nature.

As just mentioned the height of face 441 relative to the base 71 of the jaw 6a, 6b controls whether an upper flat face 32 or a lower flat face 34 engages with a corresponding flat wall of the relevant through-hole 7a, 7b, and it is essential to ensure that engagement is with the upper wall 13a, 13b, rather than with a lower wall of the through-hole. This condition can be relatively easily achieved since in a milling operation it is relatively easy to control the position of face 44' when machining the subsidiary recesses 44, 45.

It will be appreciated that the symmetrical arrangement of faces lla, 13a, faces 11b, 13b, and faces 32, 38, together with a suitable choice of tolerances in the machining of those faces, causes both camming pins 5a, 5b and, accordingly, the jaws 6a, 6b, to be urged downwards towards slide 14 for both external and internal clamping actions, thereby providing a very robust clamping action.

Figures 9, 10 and 11 show how an additional third jaw 6c can be fixedly 10 mounted to the slide 14, between jaws 6a and 6b which can then both be allowed to move axially relative to slide 14.

In this configuration the pair of jaw fixing screws 491, 501 are employed to secure the third jaw 6c to slide 14, by being located in bores 79c, 80c respectively of jaw 6c to extend through holes 55c, 56c respectively in cover plate 2 into threaded holes 90c in slide 14.

Claims (11)

1. A jig assembly of the kind comprising at least one jaw which is mounted on a carriage capable of translational movement with respect to a base for clamping and unclamping the jaw, and a releasable connecting pin providing the force path between the carriage and the jaw, in which the pinned connection comprises camming means, the camming means being so arranged that a workpiece which is acted on by the jaw is subjected to a clamping force component which is substantially perpendicular to the direction of movement of the carriage.

2. A jig assembly as claimed in claim 1 in which the jaw comprises at least two clamping faces on substantially opposite sides of the jaw, to enable the jaw to be double-acting.

3. A jig assembly as claimed in claim 1 or claim 2 in which the camming means comprises a camming pin releasably connected to the jaw or, to the carriage, and a camming pin receiving means provided on the carriage or jaw respectively.

4. A jig assembly as claimed in claim 3 in which the camming pin is releasably connected to the jaw, and the camming pin receiving means is provided on the carriage.

5. A jig assembly as claimed in claim 3 or claim 4 in which the underside of the jaw, that side which is towards the base, is recessed to receive the camming pin.

6. A jig assembly as claimed in claim 5 in which opposite ends of the camming pin are secured to the jaw by screws to provide said releasable connection between the pin and jaw.

7. A jig assembly as claimed in any of claims 3 to 6 in which the camming pin and camming pin receiving means are provided with forward and reverse pairs of camming surfaces that are operative to urge the double-acting jaw in the direction towards the base for both directions 5 of clamping of the jaw.

8. A jig assembly as claimed in claim 7 in which said hole is defined by at least two adjacent surfaces which together form a substantially Vshaped outline, said adjacent surfaces being inclined in opposite directions to the direction of movement of the carriage.

9. A jig assembly as claimed in any of the preceding claims in which there are at least two such jaws, and the two jaws are connected to respective carriages by respective camming means.

10. A jig assembly comprising first and second jaws, the first jaw being carried by a jaw carriage working in a slide, an operating screw arranged to cause relative movement of the jaw carriage towards and away from the second jaw, camming means connecting the first jaw with the first carriage, the camming means comprising a pin fast with first jaw and extending through a profiled hole in a spigot portion of the jaw carriage, the cross-sectional shape of the pin, and the cross-sectional shape of the profiled hole being chosen such that the pin and walls of the profiled hole cam together to cause the first jaw to be urged towards the slide when the first jaw is exerting an axial clamping force acting towards the second jaw, and also when the first jaw is exerting an axial clamping force away from the second jaw.

11. A jig assembly substantially as described herein with reference to the accompanying drawings.