GB2118896A

GB2118896A - Workpiece clamping device

Info

Publication number: GB2118896A
Application number: GB08206632A
Authority: GB
Inventors: Osbourne Malcolm Sweatman
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-05
Filing date: 1982-03-05
Publication date: 1983-11-09
Also published as: GB2118896B

Abstract

A workpiece such as a log (20) is clamped to a bed (19) by means of a clamp arm (9) which is movable into clamping engagement with the log by a spring-loaded manually operable toggle lever (12). When released, the toggle lever (12) is urged upwards by its loading spring (17). <IMAGE>

Description

SPECIFICATION Workpiece clamping device This invention relates to a workpiece clamping device.

The invention is particularly, but not exclusively, applicable to the clamping of wooden logs, for example trunks or branches of trees, during chain sawing operations.

The use of a portable chain saw for cutting a log is potentially dangerous, since the operator normally holds a chain saw in both hands and a problem arises in clamping the log to be sawn.

Some chain saw manufacturers provide accessories in the form of clamping vices which have to be adjusted, normally by a screw adjustment, to the size of the work being sawn.

Such clamping arrangements generally suffer from the disadvantage that they are time consuming to use, particularly if the work clamp has to be readjusted each time a fresh log is introduced.

The present invention seeks to provide a quickrelease workpiece clamping device suitable for use in clamping logs during chain sawing, or for clamping workpieces generally.

According to the present invention there is provided a workpiece clamping device, comprising a support upstanding from a bed on which a workpiece to be clamped is located, a clamp arm pivoted to the support about a horizontal axis, and a spring-loaded toggle lever pivoted to the support, the toggle lever having an engaged position in which it exerts a downward force on the clamp arm for clamping a workpiece to the bed, and a released position in which it allows the clamp arm to be swung upwardly.

The use of a toggle lever to engage and disengage the clamp arm facilitates the clamping and release of a workpiece, and moreover the clamp arm, being pivoted to the support, can readily swing into a clamping position, effectively adjusting itself to the size of the workpiece without requiring time consuming pre-setting or adjustment.

In a preferred embodiment the toggle lever is loaded by a thrust spring which bears at one end against the clamp arm, the line of action of the thrust spring being below the toggle neutral axis when the toggle lever is in its engaged position and above the said neutral axis when the toggle lever is in its released position.

The upstanding support may comprise an upright post upon which a lever carrier is mounted for vertical adjustment on the post, the carrier supporting respective pivotal connections for the clamp arm and the toggle lever. The lever carrier is preferably slidable along the post and engages the latter at two points, spaced apart vertically, on opposite sides of the post, such that the moment due to the spring loaded toggle lever and the clamp arm acting upon the lever carrier in the engaged position of the lever exerts clamping forces on the post at the said two points.

In a preferred embodiment of the invention the bed includes a base member to which the post is connected, and the base member extends horizontally from the post directly below the clamp arm, so that in the engaged position of the toggle lever the workpiece is clamped between the clamp arm and the base member. The bed may, for example, include a wooden base block into which the post is driven.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic partly sectioned side elevation of a workpiece clamping device according to one embodiment of the invention, shown in its workpiece clamping position; Figure 2 is a diagrammatic side elevation corresponding to Figure 1, showing the workpiece clamping device in its released position: and Figure 3 is a plan view in the direction of arrow III in Figure 1.

The illustrated workpiece clamping device is intended for the clamping of wooden logs, for example true trunks or branches, to be sawn using a portable chain saw (not shown). The device is mounted on a wooden base block 1 and has an upstanding support in the form of a square section steel post 2 having a spiked end 3 which is driven vertically into the base block 1. A lever carrier 4 is slidable vertically along the post 2 and engages the latter at two points, spaced apart vertically, on opposite sides of the post. These two points are defined by two square-section ties 5, 6 which interconnect parallel plates 7, 8 arranged on opposite sides of the post 2, as shown in Figure 3.

The lever carrier 4 supports a clamp arm 9 which is pivoted to the carrier 4 about a horizontal pivot pin 10. An endplate 11 is welded onto the free end of the clamp arm 9 and projects above and below the arm 9.

A toggle lever 12 is pivotally mounted on the lever carrier 4 about a horizontal pivot pin 1 3 arranged above the pivot pin 10. The toggle lever 1 2 has a slightly cranked shape, with a downwardly projecting nose 14 intermediate its ends which rests on the clamp arm 9. A manually operating knob 1 5 is provided at the free end of the toggle lever 12.

A member 1 6 supporting a compression spring 1 7 is pivotally connected to the toggle lever 1 2 adjacent the nose 1 4 and extends through a hole 1 A in the end plate 11 of the clamp arm 9. The compression spring 1 7 bears at one end against an adjustable stop nut 1 8 on a screw-threaded part of the member 16 and at its other end against the end plate 11.

The action of the spring 1 7 on the toggle lever 1 2 is such that the lever has two static positions, namely an engaged position, illustrated in Figure 1, in which the line of action of the spring 1 7 passes below the toggle neutral axis X-X, and a released position, illustrated in Figure 2, in which the line of action of the spring 1 7 passes above the said axis X-X. In the engaged position of the toggle lever 12 the spring 1 7 urges the lever 12 downwards, that is, clockwise about its pivot pin 13, pressing the nose 14 into engagement with the clamp arm 9, and pressing the clamp arm 9 downwardly towards the base block 1. In the released position the toggle lever 12 is free to move upwards, carrying with it the clamp arm 9.

A baseplate 1 9 rests on the base block 1 and is anchored to the latter by the post 2. The baseplate 19 extends horizontally from the post 2 on the same side of the latter as the pivoted clamp arm 9.

Figure 1 shows the device in use for the clamping of a wooden log 20. The log 20 is placed on the baseplate 19 and against the support post 2. The clamp arm assembly is then moved downwards by simple sliding of the lever carrier 4 downwards on the post 2, with the toggle lever 12 in its released position (Figure 2) until the clamp arm 9 is close to or touching the log 20. The toggle lever 12 is then depressed by pushing downwards on the knob 15, causing the lever 12 to pass through its overcentre position and into the locking position, illustrated in Figure 1.In this position the action of the spring 1 7 urges the clamp arm 9 downwardly into positive clamping engagement with the log 20, and the anticlockwise (as viewed in Figure 1) moment exerted on the carrier 4 by the reaction force of the toggle lever 12 urges the ties 5, 6 into engagement with the post 2, effectively clamping the carrier 4 to the post 2.

In the engaged position of the device, therefore, the log 20 is firmly clamped by the force of the spring 17 acting upon the clamp arm 9 and holding the log 20 firmly in engagement with the baseplate 19 and the post 2, while at the same time the force of the clamping spring 1 7 also locks the lever carrier 4 in position on the post 2.

Release of the clamped log 20 is easily effected by upward movement of the knob 15 of the toggle lever 12 to move the latter into the release position illustrated in Figure 2. In this position the toggle lever 12 can easily be raised together with the clamp arm 9, to enable the log 20 to be removed.

Since the lever carrier 4 can be positioned at any point along the post 2 the device according to the invention is extremely versatile in its ability to clamp workpieces of different shapes and sizes within a wide range. Thus the device may be used on building sites for the clamping of timber to be sawn, for example roof joists and the like.

Claims

1. A workpiece clamping device comprising a support upstanding from a bed on which a workpiece to be clamped is located, a clamp arm pivoted to the support about a horizontal axis, and a spring-loaded toggle lever pivoted to the support, the toggle lever having an engaged position in which it exerts a downward force on the clamp arm for clamping a workpiece to the bed, and a released position in which it allows the clamp arm to be swung upwardiy.

2. A device according to Claim 1, in which the toggle lever is loaded by a thrust spring which bears at one end against the clamp arm, the line of action of the thrust spring being below the toggle neutral axis when the toggle lever is in its engaged position and above the said neutral axis when the toggle lever is in its released position.

3. A device according to Claim 1 or Claim 2, in which the upstanding support comprises an upright post upon which a lever carrier is mounted for vertical adjustment on the post, the carrier supporting respective pivotal connections for the clamp arm and the toggle lever.

4. A device according to Claim 3, in which the lever carrier is slidable along the post and engages the latter at two points, spaced apart vertically, on opposite sides of the post, such that the moment due to the spring loaded toggle lever and the clamp arm acting upon the lever carrier in the engaged position of the lever exerts clamping forces on the post of the said two points.

5. A device according to any one of the preceding claims, in which the bed includes a base member to which the post is connected, the base member extending horizontally from the post directly below the clamp arm, so that in the engaged position of the toggle lever the workpiece is clamped between the clamp arm and the base member.

6. A device according to any one of the preceding claims, in which the bed includes a wooden base block into which the post is driven.

7. A workpiece clamping device substantially as herein described with reference to and as shown in the accompanving drawings.