This invention relates to staple driving tools. More particularly, it relates to staple driving tools which are hand-held and where the power for driving the staple is derived from a non-manual source, such as electricity.
Hand-held staple driving tools powered by electricity are well known. Typically, such staplers are powered by an electromagnetic solenoid coil which, when energized by electricity causes a moveable plunger made out of a magnetizable material such as iron or steel to be pulled into the center of the solenoid by virtue of the magnetic field created by energizing the coil. The staples typically are held on a staple rack in a magazine and delivered to the shearing region of a staple driving chute near the front of tool where they are sheared off and driven into the workpiece by means of a staple driving knife attached to the bottom of the plunger.
This knife, which shears off and drives the staples, typically extends down from the center of the bottom of the plunger through the center of the solenoid and is commonly attached to the plunger by insertion into a slot cut in the bottom center of the plunger and secured with a horizontal pin. The staple driving knife is, thus, generally aligned with and directly below the central axis of the plunger.
While this construction of a staple driving tool has proven generally satisfactory for many purposes, the placement of the staple driving knife at the bottom of the plunger so that it passes through the center of the solenoid makes it difficult or impossible to drive staples close to obstructions or into corners, because of the space taken up by the solenoid.
Staple driving tools powered by compressed air delivered to a pneumatic cylinder with a movable piston are typically similarly constructed, the piston taking the place of the magnetizable plunger as the primary drive member. Pneumatically driven staple driving tools have similar problems of only limited ability to drive staples in tight places or near to obstructions.
Previous attempts to build a staple driving tool that would have the ability to drive staples near obstructions have not been entirely successful. One construction uses a curved staple driving knife centrally extending from the bottom of the plunger, with the solenoid positioned above and to the rear. This arrangement allows the solenoid to be located rearwardly enough to avoid obstructions near the staple driving chute, from which the staples emerge, but the curved knife may jam and its position also tends to increase the vertical height of the tool, limiting the use of the tool where vertical clearance may be restricted.
Current staple driving tools commonly have housings constructed of medially split, complementary sides molded of a durable plastic, such as polypropylene. In mass production of such molded plastic housings, it is possible for different batches of housings to have slight variations in color. In order to avoid the cosmetically unacceptable appearance caused by housing sides which have noticeably varying color, it is common to attach complementary mold sides together which are molded from the same batch of plastic, after molding but before final assembly, by such temporary means as rubber bands or string. This ensures color uniformity of the assembled product, but the need to keep matched housing sides attached with rubber bands or strings prior to the final assembling process is cumbersome and interferes with efficient mass production assembly.
Countersunk holes for attachment screws are also typically molded into the sides around the periphery of the housing so that the sides can be attached together by means of the housing attachment screws. Due to the fact that the sides are separate, and a large proportion of the stress on the housing occurs at the front end of the tool where the primary driving means, such as the solenoid, is located, attachment screws must generally be placed along the front end of the housing of the stapler in order to assure sturdy construction. This need for screws at the front end of the stapler tends to further exacerbate the clearance between the staple driving knife and the front of the stapler, making it even more difficult to drive staples near obstructions.
Electrically powered staple driving tools typically have a metal, usually steel, staple magazine assembly. The magazine assembly includes a staple magazine, which holds and delivers staples to a position for driving, and a mainframe assembly, which supports and contains the staple magazine. The mainframe assembly has a frame or channel which forms the main horizontal structural member for the staple driving tool, and a front cover attached at the front end of the mainframe channel which forms a wall of the staple driving chute to guide the staples, and the staple driving knife. The mainframe channel is typically mounted to the bottom of the housing of the tool. The mainframe assembly, including both the front cover and the mainframe channel, is typically metal and is typically exposed to the user. To minimize the risk of electrical shock to the user, the mainframe channel is preferably connected to ground by means of a ground wire. Typically, connection of a ground wire to the mainframe channel is made independently of any mounting means of the housing of the tool to the mainframe channel. Although this satisfactorily insures grounding of the mainframe channel, and the other metal parts of the magazine assembly which are connected together, the use of separate fasteners for the ground wire, and for the mounting of the mainframe to the housing causes additional expense in manufacturing.