Trigger switches are typically used in power tools such as electric drills. In such an electric power tool, a trigger switch is arranged in its grip so as to be operated with a single hand, and a trigger member is provided in front of the grip in the manner of a pistol trigger. Typically, the trigger member is provided with a front end which is adapted to be pressed by a finger of the user and a pair of side walls extending rearwardly therefrom. An upper part of the trigger member is pivotally supported by a planar member which is connected to the grip and adapted to be received between the two side walls of the trigger member as it is pulled. To prevent inadvertent activation of the electric switch and to thereby ensure the safety of the switch operation, the trigger member is normally provided with a lock mechanism which is required to be released for the switch to be activated.
The lock mechanism may comprise an arcuate slot provided in the trigger member, having a center of curvature at the pivot center of the trigger member and a locally expanded portion at its rear end. A lock pin is passed laterally through a hole provided in the planar member of the grip and through the arcuate slot of the lock member. The lock pin is provided with a large diameter portion which has a larger diameter than the width of the arcuate slot but can fit into the locally expanded portion of the arcuate slot, and a small diameter portion which can be passed through the arcuate slot. Further, the lock pin can move axially so that either the large diameter portion or the small diameter portion of the lock pin may be selectively placed in the arcuate slot. Typically, the lock pin is biased by a spring member into a position where the large diameter portion of the lock pin is received in the locally expanded portion of the arcuate slot.
Therefore, simply pressing the front end of the trigger member would not cause the pivotal motion of the trigger member because the large diameter portion of the safety catch pin is held in the locally expanded portion of the arcuate slot and cannot move through the arcuate slot. However, when the lock pin is pushed axially against the spring force so that the large diameter portion may be placed out of the arcuate slot, it becomes possible to pivotally move the trigger member by pressing the front end thereof.
In such a trigger switch, the mechanical durability of the slot is important because the lock pin is typically made of metallic material but the trigger member is often made of resin or aluminum alloy material.
It is conceivable to securely attach a metallic lock plate to the trigger member to define the arcuate slot, but the direct contact between the pivot pin and the arcuate slot is not desirable. Even though neither the metallic pivot pin nor the lock plate may be connected to any electric part of the trigger switch, the electric coupling between the pivot pin and the lock plate would not be desirable particularly because the pivot pin is typically exposed to the user.