Pliers and similar hand tools, such as shears and secateurs, which in use are repeatedly opened and closed several times are often made with a return spring for automatic opening when the gripping force on the handles is reduced (see for instance GB-A-762740). The return spring is often linear, requiring an increasing force as the jaws are progressively closed. In order not to tire the hand and to provide the best control of the force used for holding, shearing or deforming the workpiece, it would be preferable that the return force would remain constant or decrease.

It is also desirable that the return force when the jaws are closed is adjustable to suit different tasks and the strength of different persons, and that the equilibrium opening when there is no more return force can be adjusted independent of the maximum opening allowed by the joint.

The present invention provides for a pliers type tool as defined in claim 1, dependant claims 2 and 3 defining prefered embodiments. The pliers type tool according to the invention is provided with a return spring which is adjustable to provide different return forces and different equilibrium openings to suit the user and the task.

The invention is described with reference to the figures, where figure 1 shows a tool with the spring located in a position with low return force and large equilibrium opening, figure 2 shows a tool with with the spring located in a position with large return force and small euilibrium opening, and figure 3 is a graph of how the return force can depend on the opening with different spring locations.

The pliers type tool comprises two shanks held together by a joint (10). Between the handle parts (11,12) of the shanks is a leaf spring (13) which when unstressed is basically straight, but when mounted is S-shaped, with its ends inserted in slots or recesses in the handles (11,12). A first end (14) of the spring is located closer to the joint (10) and is inserted in one of a plurality of recesses in a first handle (11), where a recess (15) at greater distance from the joint (10) results in a greater return force and a recess (16) at a lesser distance from the joint (10) results in a lesser return force. The second end (17) of the spring is located farther from the joint (10) and is inserted in one of a plurality of recesses in the second handle (12), where a recess (18) at a greater distance from the joint (10) results in a lesser equilibrium opening and a recess (19) at a lesser distance from the joint (10) results in a greater equilibium opening.

Since the recesses of the first handle (11) are located so close to the joint, the choice of recess (15,16) will have as its main effect a variation of the leverage of the spring force, directly affecting the return force. When the tool is open, however, the recesses (15,16) of the first handle are almost at the same distance from whichever recess in the second handle has been utilized. The recesses (18,19) of the second handle (12) are so close that they result in roughly the same return force, especially if there is some angular difference, but they have a strong influence on the euilibrium opening.

The recesses can be shaped and adapted to the ends of the spring in different ways. Slots with a narrow opening combined with thickened ends (14,17) of the spring allow insertion of the spring from the side and prevent accidental dislodging of the spring when the tool is maximally opened. The slots need not be parallel to each other. The spring can also be made from round spring wire, and in such case the recesses can be drilled holes.

Figure 3 shows how the return force F on the handles depends on the opening D between the jaws with two different locations of the spring. The first graph (21) shows the dependence for a tool with the spring placed as in figure 1, with a small return force (24) when the jaws are closed, since the spring force against the first handle (11) has little leverage, and with a great equilibrium opening (23) since the recess (19) in the second handle (12) is rather close to the joint (10). The second graph (22) shows the dependence for a tool where the spring is placed as in figure 2, where the return force (24) with closed jaws is larger due to larger leverage for the spring force against the first handle (11), and the equilibrium opening (23) is smaller since the recess (18) in the second handle is farther from the joint (10).

The choice of recess (15,16) for attaching the inner first end (14) of the spring will mainly influence the return force (24) for closed jaws, and the choice of recess (18,19) for attaching the outer second end (17) will mainly influence the equilibrium opening (23). Due to the S-shape of the spring the return force will be relatively constant except near the equilibrium opening, which is an advantage in itself. Unused recesses can be blocked or unfinished.