GB2214109A - Workpiece clamp - Google Patents

Abstract

A clamp comprises a movable arm (15) carried on a spine (14), the arm having a first member (16) slidably mounted on the spine, a second member (17) pivotally connected to the first member and provided with a jaw (29) and a device (19) for angularly moving the second element relative to the first element, the spine being secured to a base (10) from which it exetnds at 90 DEG , the base (10) extending away from one side of the spine (14). The arm (15) is reversible on the spine so that the jaw can be arranged at either side of the spine, or even inverted. Friction pads (22,23) and a spring (24) allow for sliding movement but mid retention of the member (16) on the spine (14) when clamping. <IMAGE>

Description

CLAMP This invention relates to a clamp and is particularly concerned with a clamp of the type which comprises a movable arm provided with a jaw member and mounted on a spine.

With a known clamp of this type one end of the spine is bent and terminates in a fixed jaw, with the jaw carried by the movable arm being movable and facing the fixed jaw. Whilst this clamp is quite satisfactory for many uses, there are some instances when it cannot achieve the required clamping.

An object of the invention is to provide a clamp which can be used in such instances and is quick and easy to operate.

According to the invention there is provided a clamp comprising a movable arm carried on a spine, the arm having a first member slidably mounted on the spine, a second member pivotally connected to the first member and provided with a jaw member, a device for angularly moving the second member relative to the first member, the spine being carried by a base which extends away from the spine at one side thereof, and the arm being reversible on the spine so that said jaw member can be arranged at either side of the spine.

Preferably the base extends away from the spine at one side only, so that, in use, if the base is secured to a surface, the arm can be used in one position to clamp an object between its jaw member and the base, and in its reversed position to clamp an object between its jaw member and the said surface.

Desirably the device for angularly moving the second member comprises a screw member threadedly mounted on the first member and arranged to engage the second member.

The invention will now be described, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a clamp of the invention; Figure 2 is a cross-section through a screw assembly of the clamp, and Figures 3 to 9 show various possible uses of one or more clamps of the invention.

As shown in Figures 1 and 2, the clamp comprises a metallic, rectangular base 10 having holes 11 for securing it to a surface, such as a work bench 12 or the like. Adjacent one shorter side 13 of the base a spine 14 is secured to the base, an end of the spine being received in an aperture in the base. The spine extends upwardly at 900 to the base upper surface and in use would normally be vertical. The spine has a pair of curved recesses 14a which provide it with a strong but lightweight construction. The recesses are in respective opposite faces of the spine which are parallel to the respective longer sides of the base.

The spine 14 carries an arm 15 comprising first and second members 16, 17 respectively. The first member is slidingly mounted on the spine for up or down adjustment movement, whilst the second member is pivotally mounted to the first member by a rivet 18. A screw assembly 19 is provided for moving the second member angularly relative to the first member.

Referring to Figures 1 and 4 in particular, the first member 16 comprises a pair of plates 20, 21 and a pair of friction pads 22 and 23. The plates 20, 21 are held together by a pair of rivets forming the pads 22, 23 respectively. The pads engage opposite narrower side faces of the spine 14 respectively and are spaced from each other along the length of the spine 14. A leaf spring 24 is attached to pad 22 by a screw 25. A free end of spring 24 engages an edge of spine 14 and functions to keep pads 22 and 23 in firm engagement with spine 14.

The second member 17 comprises a pair of plates 26 and 27 which are held together at one end by a rivet 28 which passes through a movable jaw member in the form of a jaw 29. The rivet 28 is provided with internal shoulders, not shown, which keep the sides of jaw 29 spaced from the inner surfaces of plates 26 and 27.

The rivet 18 passes through a pair of apertures formed in plates 26 and 27. As may be observed in Figure 1, the rivet 18 is located between spine 14 and the movable jaw 29.

Referring to Figures 1 and 2, the screw assembly 19 comprises a screw member 30 having a cross bar 31, a nut 32, which has a cylindrical outer surface, and which nut is received in a pair of apertures in plates 20 and 21, a hexagonal reaction member 33 which is secured to the second member 17 by a rivet 34, and a stiff nut 35. The shank of screw member 30 has a threaded section, preferably a left hand thread, which engages the internal screw thread of nut 32, an unthreaded section which is received in an internal bore of reaction member 33, and a threaded end section in an aperture in the member 33 and which receives the stiff nut 35. The nut 32 and the reaction member 33 are both secured against rotation relative to the first and second members 16, 17 respectively.The reaction member 33 is held between the stiff nut 35 and a shoulder between the threaded and unthreaded parts of the shank of screw member 30.

In one mode of operation, the arm 15 is slid along the spine 14 until the jaw 29 lightly engages a workpiece disposed on the bench 12 adjacent the side 13 of the base 10. The screw member 30 is then rotated by engaging the cross bar 31 so as to cause the second member 17 to rotate relative to the first member 16. This causes the workpiece to be clamped between the jaw 29 and the bench and the pads 22 and 23 to lock onto spine 11. The screw member 30 is rotated until a desired clamping force is achieved. With a left hand thread on the screw member 30 the rotation thereof to produce clamping is clockwise, with the member 33 being placed under tension.

The leaf spring 24 ensures that there is no backlash to be taken up during initial rotation of screw member 30 and also prevents the movable arm 15 from sliding along spine 14 under its own weight.

It is to be noted that the screw member 30 is located on the opposite side of spine 14 from the jaw 29 and that the axis of the screw member 30 is inclined relative to spine 11. The screw assembly 19 is arranged so that the cross bar 31 and the stiff nut 35 never touch the spine 14.

As stated above, when clamping a workpiece, the pads 22 and 23 lock onto spine 14. The ability of the movable arm to grip the spine 14 with sufficient force depends upon the correct spacing of pads 22 and 23. The force exerted on jaw 29 by a workpiece both rotates the movable arm about pad 23 and produces a tendency for the movable arm 15 to slide away from the workpiece.

It can be shown that the movable arm will lock onto the spine 14 with sufficient force to overcome the tendency to slide providing the following condition is fulfilled:

where x is the distance between the jaw 29 and the spine, y is the separation between the friction pads in the direction of the spine axis, and f is the coefficient of friction between the pads and the spine.

Where the pads 22 and 23 are firmly rivetted to the first member 16, y is the distance between the outermost parts of the engagement surfaces between pads 22 and 23 on spine 14. The coefficient of friction must allow for accidental lubrication by the user. For greasy steel the coefficient of friction is approximately 0.1 and so the ratio y/x must be less than or equal to 0.2 for satisfactory operation of the clamp, As may be readily appreciated, the inner most parts of the surfaces of engagement between the pads 22 and 23 must be spaced from each other in the direction of the axis of the spine 11. In other words, the surfaces of engagement between pads 22 and 23 and spine 14 must not overlap each other in the axial direction.

These constraints on the design of pads 22 and 23 mean that the axial length of the surface of each of the pads 22 and 23 which engages spine 14 is inevitably short. The choice of hexagonal cross sections for pads 22 and 23 ensures that this dimension is sufficiently short and at the same time provides a sufficiently large cross-section to enable the pads to be rivettea to the first member 16.

If the screw member 30 becomes worn or damaged, it may readily be replaced by removing the stiff nut 35 and then disengaging screw member 30 from nut 32.

Similarly the nut 32 can readily be replaced if damaged or its thread worn.

As shown in Figure 1, and in the mode of operation described, the arm 15 is arranged on the spine 14 with its jaw 29 disposed over the surface on which the base 10 rests, rather than over the base 10 itself. However the arm 15 is sufficiently symmetrical for its orientation on the spine to be reversed so that the jaw is over and facing the base, as shown in Figure 4. All that is required is a sliding of the arm 15 upwardly from its Figure 1 position until it disengages from the spine, followed by a turning of the arm 180O in a vertical plane, and replacement on the spine.

The provision of the base for the clamp, the reversibility of the arm and the absence of a fixed jaw at the upper end of the spine all contribute to the increased versatility of the clamp of the invention, some of the possible modes of operation of the clamp being shown in Figures 3 to 9 and illustrating this versatility.

Figure 3 shows the arm 15 positioned as in Figure 1 with a clamped workpiece up against the side 13 of the base 10 for a drilling or boring operation.

Figure 4 shows an arrangement where the arm 15 is reversed compared to Figures 1 and 3 with the jaw 29 over the base 10. At the end of the base remote from the spine 14 is arranged a V-block 36 and a cylindrical workpiece is supported by the block 36 and clamped by the jaw 29. The screw assembly has been omitted for clarity. Supports other than a V-block could of course be used as appropriate.

Figure 5 illustrates the use of the clamp to hold a first workpiece on top of a second, larger workpiece during their welding together. As with the arrangement & Figure 3, the arm 15 is directed to the opposite side of the spine from the base, with the workpieces abutting the side 13 of the base.

Figure 6 shows a mode of operation where two arms 15 are mounted on the spine 14, both extending away from the base 10, with the jaws 29 facing one another to clamp between them one end of an elongated workpiece, which is being welded at its other end to a further component. Naturally with a sufficient length of spine a multiplicity of arms 15 can be engaged on the spine, with some arms possibly being reversed relative to the others and the jaws inverted relative to some others, as required.

Figure 7 illustrates the use of two single-armed clamps at right angles to hold a rectangular piece of sheet metal, so that a part of the sheet protruding over a side of a work bench can be cut off.

Finally, Figures 8 and 9 each show the use of two clamps at opposite sides respectively of a workpiece received on the work bench, the clamp jaw of each clamp engaging the top workpiece surface. In Figure 8 the workpiece is relatively high and could be of composite form. The respective sides 13 of the bases of the clamps are spaced slightly from the workpiece. In Figure 9 the workpiece is abutted by the bases 10 and a drilling operation is carried out on the upper surface of the clamped workpiece.

In a further arrangement, not illustrated, the screw member could be arranged to be rotated by a hydraulic motor.

The clamp of the invention is intended primarily for use with light machining, such as with polymers, aluminium and light steel, although it could be used with heavy machining on a machine table, provided side thrusts were relatively low. It is designed for quick and easy operation and is advantageous over known clamps with bases in being reversible, allowing stepless adjustment and requiring no tools for its operation.

In an alternative embodiment, the spring 24 is omitted and instead there is provided a spring, formed from a single piece of wire, which has a coiled part around rivet 18 and has a looped blade-like part engaging the spine 14 below the pad 23. Two free ends of the spring bear on the top of the pad 23, so that like the spring 24, this spring biases the arm to hold the pads in firm engagement with the spine.

Although the jaw 29 normally satisfactorily holds a workpiece firmly, in use, it has been found that if the workpiece is particularly smooth and/or oily, clamping of the jaw onto the workpiece may cause movement of the workpiece towards the base 10, thus altering any precise set up position of the workpiece. It has been found that if an alternative jaw member, in the form of a cylindrical roller, is substituted for the jaw, the rivet 28 passing through the roller axis, such workpiece movement does not occur.

Claims (8)

1. A clamp comprising a movable arm carried on a spine, the arm having a first member slidably mounted on the spine, a second member pivotally connected to the first member and provided with a jaw member, a device for angularly moving the second member relative to the first member, the spine being carried by a base which extends away from the spine at one side thereof, and the arm being reversible on the spine so that said jaw member can be arranged at either side of the spine.

2. A clamp as claimed in claim 1, wherein the base extends away from the spine at one side only of the spine, so that, in use, if the base is secured to a surface, the arm can be used in one position to clamp an object between its jaw member and the base, and in its reversed position to clamp an object between its jaw member and the said surface.

3. A clamp as claimed in claim 1 or claim 2, wherein the device for angularly moving the second member comprises a screw member threadedly mounted on the first member and arranged to engage the second member.

4. A clamp as claimed in claim 3, wherein the device for angularly moving the second member comprises a reaction member which is secured to the second member and receives an end of said screw member, the reaction member being placed under tension, in use, when the screw member is rotated in a direction to cause clamping.

5. A clamp as claimed in any one of claims 1 to 4, wherein spring means carried by an element pivotally connecting the first and second members bears at one end against a friction pad for gripping the spine and at its opposite end against the spine below said friction pad.

6. A clamp as claimed in claim 5, wherein said element is between the spine and said jaw member.

7. A clamp as claimed in any one of claims 1 to 6, wherein the jaw member is a cylindrical roller.

8. A clamp substantially as hereinbefore described with reference to and as shown in the accompanying drawings.