Bolt cutter

Abstract: Bolt cutter or other tool for cutting or coining of metal, comprising two jaws (13,14) connected to parallel links (15,16) by two jaw joint bolts (17,18), and two handles (11,12) connected to each other by a handle bolt (21) and to the jaws by two middle bolts (19,20), where the distance and parallelness of the jaws can be adjusted by means of one or more of the bolts (15-21) which is provided with one bearing surface (25) eccentrically located relative to one or two other bearing surfaces (24,26), and wherethe angular motion of the jaws is synchronized by a cylindrical roller (22) which is axially retained between the links, and tangentially guided by slots (29) in overlapping shelves (27,28) on the jaws.

Description: Background Bolt cutters are used for cutting metal bars, such as bolts or reinforcement bars, and are normally provided with long handles and leverage. Similar tools are also used for coining or perforation of metal profiles. Two jaws are held together at their centers by parallel links, and the rear ends of the jaws are pressed apart where they are connected by hinges to the front ends of the handles. The handles are connected with each other in such a way that when the cutter is maximally open, a relatively small handle motion is enough to get a certain jaw motion, but when the edges of the jaws almost touch each other at the end of a cutting operation, a greater handle motion is needed for the corresponding jaw motion. In this way one has a strongly variable leverage, with the greatest force at the end of the operation when the jaws have penetrated the work material maximally. The edges of the jaws become worn, and are easily damaged if one tries to cut a hardened bar, and it is therefore a requirement that one shall be able to take the jaws apart for regrinding after some damage. The hinges must thus be disconnectable and have a defined position so that the whole edges rest against each other at the end of the cut. It is thus known to give the jaws a synchronized angular motion by a tangential connection against each other between the parallel links to get a defined closed position, such as shown in patents U S 5,081,769 & 5,101,566 and EP 331 927. In regrinding one must normally grind more at the tips of the jaws to make the edges touch along the whole edge length in a closed position, whereby the rear ends of the jaws get a greater distance from each other. To make the closed position of the handles coincide with the closed position of the jaws, the distance between the hinges of the handles can be made adjustable, such as by changing the handle distance with a screw as shown in U S 5,081,769 & 5,101,566. It is also known to simplify regrinding by making the distance between the joints of the parallel links adjustable by eccentric bolts such as in U S 5,081,769. The present invention concerns a design of the tangential connection between the jaws, which gives less play and a better defined closed position for the jaws compared to previously known designs, and which simplifies adjustment of the parallel position of the edges after regrinding. The invention is described with reference to the figures, where figure 1 shows a bolt cutter according to the invention, figures 2 and 3 different embodiments of a jaw, and figure 4 an eccentric bolt. A bolt cutter according to the invention comprises two handles (11,12), two jaws (13,14) and two parallel links (15,16). The components are held together by two jaw joint bolts (17,18), two middle bolts (19,20) and one handle bolt (21). The relative position of the jaws is determined by a roller (22). According to the invention, the parallel position of the edges of the jaws can be adjusted by shortening the effective length of the links an amount corresponding to the ground-off width of the jaw, in normal cases much less than 1 mm. Shortening of the links is made by rotating one or both jaw joint bolts (17,18) a certain angle. At least one of the jaw joint bolts is provided with a head (23), three cylindrical joint surfaces (24-26) and one thread, where the greatest (24) and the smallest (26) joint surfaces have the same central axis, while the intermediate joint surface (25) is eccentric with a laterally displaced axis. The greatest and smallest joint surfaces fit against holes in the links (15,16) and the intermediate joint surface against holes in the jaws (13,14). By rotation of one jaw joint bolt, the axis of the intermediate joint surface (25) can be displaced at most twice as far as the distance between the axis of the intermediate joint surface (25) and the axis in common for the other joint surfaces (24,26). If that distance is 0.5 mm, the effective length can be adjusted 1 mm with one bolt, and 2 mm with both bolts, which should be sufficient for all regrindings. Since the smallest joint surface (26) and the corresponding hole in one link have a smaller diameter than the intermediate bearing surface (25), further rotation of the bolt is avoided by tightening the bolt against the bolt against the link with a nut (30). To synchronize the angular motion and to give the jaws a defined longitudinal position it is known to make the jaw sides facing each other with gear teeth as in U S 5,101,566, or with a convex cylindrical surface matching a concave as in EP 331 927 or with two concave cylindrical surfaces and one cylindrical roller as in U S 2,382,292. These three designs all have the disadvantage that they suffer from play and lose their precision if the length of the parallel links is changed. It is therefore suggested in U S 5,081,769 to have between two concave cylindrical surfaces an elastically expandable spring roller. That design is only able to compensate a small change in the length of the links, and can only transfer small tangential forces. According to the invention, the jaw are thus provided with shelves (27,28) extending towards each other and overlapping to form slots (29) of even width between them, an a cylindrical roller (22) located in the slots, having a diameter corresponding to the width of the slots and being axially retained by the links (15,16). The shelves can be located in the same plane as in figure 2, or in different planes as in figure 3. In the latter case the jaws (13,14) can be identically shaped. The centerlines of the slots would preferably pass through the centers of the holes for the jaw joint bolts. When the effective length of the parallel links is changed, the distance between the rear ends of the jaws will in general also be changed. Since they are joined to the handles (11,12) by the middle bolts (19,20) this might affect the closed position of the handles. It is desirable to keep the closed position of the handles as defined by the contact between the supporting lugs (31) of the handles, in order not to overstress the cutting edges, and it is thus recommended to adjust the distance between the middle bolt bearing surfaces to fit the distance between the jaw rear ends. This can be done by elastical deformation of part of a handle by means of one or two screws as in U S 5,081,769 and FR 2 744 660, but this has a tendency to make the whole motion too elastic and inexact, and may damage the part of the handle if the deformation is too large. According to the invention this adjustment can be made in the same manner as at the parallel links, by providing one or more of the middle bolts (19,20) and the handle bolt (21) with an eccentric bearing surface (25) as shown in figure 4. When a bolt cutter is assembled after regrinding, one or both jaw joint bolts are first adjusted to make the cutting edges parallel in the closed position. At bolt cutters, this normally is defined as when the cutting edges touch each other. Secondly, one or more among the other bolts is adjusted until the supporting lugs (31) touch each other in the closed position. A bolt cutter according to the invention can be made with integral or replaceable cutting edges. For bolt cutters in special cases, and for coining tools the closed position may be differently defined, as by a certain edge distance, and the aim may be to adjust the tool to this distance. Coining tools may be designed to fasten fittings to cable ends, to join sheet metal parts or similar purposes.

Claims: Tool for cutting or coining of metal, comprising two jaws (13,14) connected to two parallel links (15,16) by two jaw joint bolts (17,18), and two handles (11,12) connected to each other by a handle bolt (21) and connected to the rear ends of the jaws by two middle bolts (19,20), at least one jaw joint bolt having concentric bearing surfaces (24,26) against said two links, and one in relation to them eccentric bearing surface (25) against one jaw, characterised by each jaw being provided with at least two shelves (27,28) facing and overlapping those of the other jaw, separated by a slot of even width, and by a cylindrical roller (22) located in the slots with a diameter corresponding to the width of the slots. Tool according to claim 1, characterized by at least one of the middle bolts (19,20) having concentric bearing surfaces (24,26) against the handle and one in relation to them eccentric bearing surface (25) against the jaw. Tool according to claim 1, characterized by the handle bolt (21) having a bearing surface (25) against one handle which is eccentric relative to one or two bearing surfaces (24,26) against the other handle. Tool according to any of claims 1-3, characterized by the jaws having edges for cutting of metal bars. Tool according to any of claims 1-3, characterized by the jaws being provided with coining shape elements.

Inventors: JANSSON CONNY, JANSSON, CONNY
Applicants: KAPMAN AB
Application year: 2000
Main classification: B26B17
IPC codes: B26B17, B23D29