IE47995B1 - Improvements in or relating to pressure assemblies - Google Patents

Abstract

The device comprises a base plate 11, a ram 12 and a wedge 25, 26 located between the base plate and the ram, the wedge having at least one inclined face facing the base plate or ram, the facing surface 22 of the base plate or ram being inclined at the same angle and a screw 31 adapted to move the wedge at right angles to the separation of the ram and base plate to alter the separation of the ram and base plate. Preferably a pair of wedges 25 and 26 are provided, and preferably their inclined faces are oppositely-inclined. The base plate 11 may be connected to a support member 13 adapted to be secured to a firm foundation, for example by bolts passing through bores 41. The device can be used to clamp a workpiece between the ram 12 and a fixed member 14 by engagement of the base plate 11 with the fixed member 13 and by increasing the separation of the ram from the base plate by rotating the screw 31.

Description

This invention relates to a pressure assembly comprising · a base plate and a ram and means for moving the plate relative to the ram. In a screw clamp, the screy acts as the moving means and one tum of the screw cause's the base plate and the ram to change their separation by the pitch of the screw. The pressure which can be exerted by the base plate and the ram is limited hy the strength of the screw.

According to the invention, there is provided a pressure assembly comprising a base plate, a ram and a pair of wedges located between the base plate and the ram, each said wsdge having at least one inclined face facing the base plate or the ram, the facing surface of the base plate or ram being inclined at the same angle, said wedges having oppositely-inclined faces, and a screw adapted to move the wedges in opposite directiansat right angles to the separate icn of the ram and base plate to alter the separation of the ram, and babe plate. In this arrangement, the screw acts indirectly on the base plate and the ram, through the medium of the wedges. The wedges can be provided with large surface areas to resist the forces between the ram and the base plate and the angle of the wedges can he selected to give a suitable multiplication factor between the axial movement of the screw 47895 relative to the base plate and the separation of the base plate from the ram.

Preferably means are provided for securing the ram and the ba§e plate to the wedges to prevent relative movement between the' wedges an the one hand and the ram and base plate on the other hand in the direction of the separation of the ram and base plate.

The pressure assembly may be used in conjunction with a support member against which the base plate or the ram may be placed so that pressure may be exerted on a workpiece placed against the other of the base plate and ram on movement of the wedge in the pressure assembly.

An example of the invention will now be described with reference to the accompanying figure, which is an isometric partially exploded view of a pressure assembly, support casting and face plate.

The pressure assembly shown in the figure comprises a base plate 11 and a ram 12 having outwardly facing parallel surfaces whose separation can be adjusted. If fixed members 13 and 14 are provided with inwardly facing parallel surfaces, the pressure assembly can be placed for example with the surface of base plate 11 engaging the fixed member 13 and the separation between the base plate and the ram can be increased to clamp a workpiece between the surface of the ram 12 and the fixed member 14.

The base plate 11 is a parallel-sided member with a dovetail-shaped groove 21 on the side facing the ram 12.

The ram 12 has a pair of inclined surfaces 22 and 23 arranged symmetrically facing the base plate 11 and each surface 22 and 23 has a dovetail-shaped groove 24 formed therein.

A pair of wedges 25 and 26 are arranged between the base plate 11 and the ram 12, the wedges having^surfaces inclined at the same angle as the surfaces 22 ahd 23 and facing those surfaces. The wedges 25 and 26 have dovetail-shaped projections (not visible) on both sides for running in the grooves 21 and 24 so that the facing surfaces of the wedges with the base plate 11 and with the ram 12 are kept in engagement although the wedges can 15 move at right angles to the separation of the base plate 11 from the ram 12.

Movement of the wedges 25 and 26 at right angles to the separation of the base plate 11 from the ram 12 is controlled by a shaft 31 provided with oppositely directed 2o threaded portions passing through threaded bores in the wedges 25 and 26 so that rotation of the shaft 31 in one direction will cause the wedges to move towards each other and thus increase the separation of the base plate 11 from the ram 12 and rotation of the shaft 31 in the opposite direction will retract the ram 12 towards the base plate 11 47998 through the action of the grooves 21 and 24 with the lugs on the wedges 25 and 26.

Along the upper edge of the dovetail-shaped grooves 21 and 24 there is provided a gib or bearing strip 32 which is secured by a number of adjusting screws 33 provided with locking nuts 34.

End plates 35 are provided at each end of the base plate 11 and formed with bearing housings 36 for supporting the shaft 31 for rotation. The ends of the ram 12 slide between the facing surfaces of the end plates 35· The housings 36 are provided with a flat portion 37 marked with an index mark for use with a vernier indicator, which indicates the separation of the ram 12 from the base plate 11 from the rotation of the shaft 31.

The fixed member 13 Is provided by a support casting having three bores 41 to receive fixing bolts. The centre bore is formed directly in the casting, but the two outer bores are formed eccentrically in plugs 42 received in larger bores 43 in the casting. Locking screws may be screwed into threaded apertures 44 in the casting to secure the plugs 42 in their desired position. Rotation of the plugs in tne same direction will cause the member 13 to be inclined to the line of the fixing bolts, and movement of the plugs in the opposite directions allows the bolts to be arranged in a triangle. Base plate 11 is provided with threaded bores 45 for securing the base plate 11 to the fixed member 13. 7 9 9 3 The fixed member 13 may be secured in a conventional ' mode to the bed of a machine tool, which bed has an underside recess with slots extending from the bed face to the recess. The slots are dimensioned to receive the shanks of securing bolts which pass through the bores 41 and are enlarged at one end for insertion of the securing bolt heads. Securing nuts are screwed onto the ends of the bolts which protrude from the top of the bores 41 to hold the fixed member 13 securely on the bed of the machine tool. Fixed member 13 is cast with rearwardly extending webs 46 for strength.

The positioning of the ram 12 relative to the base plate 11 can be achieved in a variety of ways using the sliding wedges 25, 26. The inclined faces can be between 15 the base plate 11 and the wedges instead of or as well as between the ram 12 and the wedges, as illustrated. When both sides of the wedges are inclined, the inclinations are of course at different angles.

The illustrated arrangement of the wedges with their 20 narrower ends facing each other puts the shaft 31 under tension when the wedge assembly is being expanded, but the reverse arrangement (with the wider ends of the wedges facing) may be used.

In place of a shaft with oppositely-handed threads for the two wedges, it is possible to form the shaft with three differently pitched threaded sections all of the same sense, the threaded section of intermediate pitch co-operating with a hearing on the base or ram or end plates, and the extreme threaded sections co-operating with respective wedges. If the intervals between the pitches are equal, there will be an equal and opposite movement of the wedges relative to the component co-operating with the section of intermediate pitch on rotation of the shaft.

Claims (9)

1. A pressure assembly comprising a base plate, a ram and a pair of wedges located between the base plate and the ram each said wedge having at least one inclined face facing 5 the base plate or the ram, the facing surface of the base plate or ram being inclined at the same angle, said wedges having oppositely-inclined faces, and a screw adapted to move the wedges in opposite directions, at right angles to the separation of the ram and base plate to alter the separation 10 of the ram and base plate.

2. An assembly as claimed in Claim 1 wherein said screw has portions of oppositely-directed threads for moving said wedges in opposite directions.

3. An assembly as claimed in Claim 1 wherein said screw 15 has three threaded portions of different pitches, the portion of intermediate pitch engaging a threaded bore in said base member and the other portions engaging respective wedges, the difference between the pitches being equal.

4. An assembly as claimed in any ofte of the preceding 20 claims comprising means to secure the ram and the base plate to the wedges to prevent relative movement between the wedges on the one hand and the ram and the base plate on the other hand in the direction of the separation of the 47885 ram and base plate.

5. An assembly as claimed in Claim 4 wherein said securing means comprises lugs and grooves which engage each other and which run longitudinally on said base plate, wedge and 5 ram parallel to the axis of the screw. ό. An assembly as claimed in Claim 5 wherein said lugs and grooves are dovetail-shaped.

6. 7. An assembly as claimed in Claims and Claim 6 wherein said grooves are provided with replaceable bearing plates 10 along a surface engaging said lugs.

7. 8. A pressure assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

8. 9. A clamping device comprising a support member adapted to 15 be secured fixedly to a firm foundation and a pressure assembly as claimed in any one of the preceding claims, said base plate being secured against a face of said support member.

9. 10· A device as claimed in Claim 9 wherein said support 20 member is formed with fixing holes through which bolts may pass to secure the support member to a firm foundation, and means on said support member for adjusting the inclination of the line joining the fixing holes to said face of said support member. 25 11. A device as claimed in Claim 10 wherein said support member is formed with three fixing holes, said inclination adjusting means being arranged to adjust two of the holes independently relative to the third so that the holes lie either in a single line of variable inclination to said face or at the comers of a triangle.