Bar clamp

Abstract: A hand tool or clamp (10) which locks itself to a workpiece (8) to thereby free the hands of the user, includes a fixed jaw (12) secured to one end of a slide bar (14) and a movable jaw (16) mounted on the slide bar (14) for movement there-along towards and away from the fixed jaw (12). The movable jaw (16) is normally spring biased toward the fixed jaw (12) by a flat coil spring (46) supported on the fixed jaw (12) and connected at its free end (46a) to the movable jaw (16). The spring (46) is uncoiled as the jaws (12, 16) are pulled apart to receive a workpiece (8), and when either jaw (12, 16) is released, re-winds and rapidly advances the movable jaw (16) along the slide bar (14) into clamping engagement with the workpiece (8). Additional clamping pressure is provided by a screw mechanism (60) associated with the movable jaw (16) which co-operates with the slide bar (14) to advance the movable jaw (16) towards the fixed jaw (12) and increase the clamping pressure between them.

Description: This invention relates generally to bar clamps of the type used to temporarily clamp two articles together, for example, for gluing, or to hold a workpiece for welding or other operation, and more particularly to a quick-action bar clamp wherein the moving jaw can be rapidly moved to accommodate a workpiece. Bar clamps of the various configurations are old and well-known. A relatively recent entry into the prior art is the quick-action bar clamp disclosed in U.S. Patents Nos. 4,926,722 and 5,005,449 and marketed by Peterson Manufacturing Co., Inc. as its "Quick-Grip" clamp. The clamp has a movable jaw which is rapidly movable over both short and long distances to clamp against a workpiece, and is operable with one hand. The movable jaw is connected to one end of a movable slide bar and a stationary jaw is supported on the slide bar by a support structure including a trigger handle grip which releasably engages the slide bar and advances the movable jaw toward the fixed jaw. The trigger mechanism provides a one-way drive which normally precludes moving the slide bar and movable jaw away from the fixed jaw; the movable jaw can be moved in the opposite direction only when the one-way drive mechanism is disengaged. A disadvantage in the "Quick-Grip" clamp lies in the fact that once the jaws are initially clamped against a work-piece the construction of the lever mechanism is such that the hand cannot exert sufficient force on the trigger handle to advance the movable jaw by another increment, with the consequence that the clamp lacks the power to adequately clamp two articles together. In other known forms of bar clamps the moving jaw is entirely disengaged and free to move on one or more slide bars until the final tightening of an object between the movable and fixed jaws is accomplished, making its use cumbersome and imprecise. Thus, there is a need for a bar clamp having a movable jaw which is rapidly movable from any point on a slide bar to clamp a workpiece against a fixed jaw and is capable of providing large clamping forces. Document DE-A-1,301,762 discloses a bar clamp having an elongate slide bar, a fixed jaw supported to one end of the slide bar, and a moveable jaw supported on the slide bar for movement towards and away from the fixed jaw. Document DE-A-2,413,816 which is considered forming the closest prior art and forming the base of the preamble of claim 1, discloses an extensible tension spring which serves to draw a moveable jaw in the direction of a fixed jaw. According to the present invention, a self powered quick acting clamp comprises: an elongate hollow slide bar having a U-shaped cross section; a fixed jaw having a clamping surface secured to one end of said slide bar; and, a movable jaw having a clamping surface slidably mounted on said slide bar for movement there-along towards and away from said fixed jaw, and is characterised in that it further comprises a partially unwound flat coil spring supported at one of said jaws which extends interiorly of said slide bar and has a free end connected to the other of said jaws for normally pulling the clamping surface of said movable jaw toward the clamping surface of said fixed jaw, wherein the tension of said spring is substantially uniform over the maximum range of movement of said movable jaw whereby upon release of either jaw after having been pulled apart against the tension of said spring a distance sufficient to receive a workpiece said spring advances said movable jaw toward said fixed jaw to clamp the workpiece between their respective clamping surfaces with a pressure corresponding only to the tension of said spring; and, means supported on said movable jaw for releasably engaging said moveable jaw with said slide bar, said means being user-operated following initial clamping of a workpiece by only the tension of said coil spring and which, when operated, increases the clamping pressure over that exerted by the tension of said spring alone. With the quick action bar clamp in accordance with this invention the movable jaw may be rapidly moved in either direction along the slide bar. The movable jaw may be rapidly and precisely advanced from any position toward a fixed jaw and holds itself on a workpiece regardless of orientation of the clamp. This enables the quick action clamp to be initially self-holding so as to free both hands of the user. A particular embodiment of a quick acting clamp in accordance with this invention will now be described with reference to the accompanying drawings, in which:- FIG. 1 is a perspective view of a quick action bar clamp constructed in accordance with the invention shown in clamping engagement with a workpiece; FIG. 2 is a side view of the clamp of FIG 1; FIG. 3 is a sectional view taken along line 3-3 of FIG. 1; FIG. 3A is a sectional view taken along line 3A-3A of FIG. 1; FIG. 4 is an enlarged view, partially in section, which shows the angular position of the movable jaw relative to the slide bar when the drive means is not engaged; and FIG. 5 is an enlarged view, partially in section, which shows the angular position of the movable jaw relative to the slide bar when the drive means is engaged. Referring to the drawings, the quick-acting clamp 10 according to the invention, shown in FIG. 1 clamping two work-pieces 8A and 8B together, has a fixed jaw 12 secured to one end of a slide bar 14, and a movable jaw 16 mounted to the slide bar for movement therealong toward and away from the fixed jaw. The fixed jaw 12 includes a support member 18 having formed therein a rectangular cavity 20 in which one end of the slide bar is received with a press fit. The support member 18 is secured to the slide bar by one or more pins 22 which pass through openings in the member 18 and the slide bar. The longitudinal axis of support member 18, and also the plane of the clamping surface 24 of the fixed jaw, are disposed at right angles to the longitudinal axis of slide bar 14. The movable jaw 16 includes a support member 26 having a rectangular opening 28 therethrough dimensioned to receive slide bar 14 with a sliding fit. The longitudinal axis of support member 26 extends generally perpendicularly with respect to the longitudinal axis of the slide bar and has a bifurcate outer end for receiving a jaw member 30 between its spaced apart arms 26a and 26b. The jaw member 30, which is free to swivel about a pivot pin 33, has a clamping surface 32 which opposes the clamping surface 24 of the fixed jaw. If desired, the clamping surfaces 24 and 32 may have protective pads 34 and 36 attached thereto or, alternatively, pads shaped to grip a specially-shaped work-piece may be substituted for the protective pads. The slide bar 14 is shown as a hollow tubular steel bar of square cross-section having a top wall 14a and adjacent sidewalls 14b and 14c and an elongated slot 14d in the wall opposite the top wall. Alternatively, the bar 14 may have an inverted-U cross-section and is preferred because of its relatively low fabrication cost while still providing adequate strength and stiffness. The slide bar may be any of several different lengths depending on the desired gripping capacity of the clamp, being approximately three inches longer than the gripping capacity. That is, a bar nine inches long is needed for a clamp having a maximum spacing of 152 mm (six inches) between the clamping surfaces 24 and 32, and a 305 mm (12-inch) capacity clamp would require a 381 mm (fifteen-inch) bar. As best seen in FIGS. 3 and 3A, the rectangular opening 28 through which slide bar 14 extends is defined by the sidewalls of support member 26, a block formed of metal 42 encased within support member and forming the bottom of the opening, and a hardened steel bar 44 which extends transversely of the bar, between the arms 26a and 26b of support member 26 and secured in place by a pair of pins 46 which extend through aligned openings in support member 26 and bar 44. The opening 28 is dimensioned so that the movable jaw moves freely on the bar 14. In accordance with an important feature of the invention, the movable jaw structure is normally spring-biased toward the fixed jaw structure by a flat coil spring 46 which is supported on a dowel 50 which, in turn, is supported on a pin 52 extending transversely across a cavity 48 formed in the support structure 18. The spring passes through a slot 54 formed in the upper wall of bar 14, extends along the interior of the bar and its free end 46a is secured to the movable jaw structure by a screw 56 threaded into the metal member 42 of the movable jaw structure. The spring 46 is a coil of flat steel ribbon which has been heat-treated to a spring temper so that when it is unwound, as by pulling the movable jaw away from the fixed jaw, it wants to return to its original coiled condition. Springs of this type, known as negator springs, are widely used in roll-up steel rules and other devices, and are commercially available in a variety of lengths, widths, thicknesses and tensions. Such springs characteristically exhibit a substantially constant tension force irrespective of the length of the uncoiled portion, whereby to provide in a 152 mm (6-inch) clamp, for example, substantially the same clamping force on a 127 mm (5-inch) thick work-piece as on a work-piece that is 12,7 mm (1/2-inch) thick, or less. By way of example, the steel ribbon of the spring may be 12,7 mm (1/2-inch) wide and of a thickness to provide sufficient tension to hold the clamp on a work-piece however oriented, including clamped to an overhead beam, and of sufficient length that the movable jaw can be moved to the extreme end of the slide bar, limited only by a transverse pin 57 extending across the bar. In use, an operator grasps the fixed jaw structure in one hand, the curved cutout formed in the front of support structure 18 being provided to facilitate grasping it when the clamp is closed, and the movable jaw in the other, and pulls them apart against the tension of the spring a distance sufficient to receive a work-piece between them. When the clamping surfaces have been oriented as desired relative to the work-piece and the movable jaw released, the spring, wanting to return to its original coiled condition, precisely advances it into firmer engagement with the work-piece and provides sufficient clamping pressure between the jaws 24 and 32 to self-hold the clamp in place on the work-piece. This frees both hands of the operator to adjust, if necessary, the relative positions of the clamp and work-piece, and to actuate drive means embodied in the movable jaw structure (to be described presently) for increasing the clamping pressure of the clamp over that provided by spring 46. As best seen in FIGS. 3A, 4 and 5, the metal member 42 is secured within the lower end of support structure 18 with a screw 58, and has an inverted-U-shaped cavity formed therein; the spring securing screw 56 is threaded into the upper wall of the cavity, and the inner end of a screw 60, threadably engaging a plate 62 which closes the lower end of support structure 26, when turned by a suitable handle, such as the screwdriver handle 64, is forced into engagement with the under surface of the upper wall. The location of screw 60 at the underside of slide bar 14, together with the transverse steel member 44 located above the slide bar and rearwardly of the point of connection of the spring to the movable jaw structure, provide drive means which, when engaged with the slide bar, precisely advances the movable jaw toward the fixed jaw and increases the clamping pressure between them over that provided by spring 46 acting alone. More particularly, because spring 46 is connected towards the front of the movable jaw structure 26, when it pulls the movable jaw against a work-piece held between it and the fixed jaw, the longitudinal axis of the movable jaw structure 26 is tilted slightly to the left (as viewed in FIG. 4) which causes sharp teeth 44a and 44b formed at opposite sides of the back edge of transverse member 44 to dig into the upper surface of slide bar 14 to a sufficient depth as to temporarily lock the movable jaw to the slide bar at the position to which it was pulled by spring 46. Upon tightening screw 60, which preferably has square threads and typically may be 9,5 mm (3/8-inch) in diameter and have 24 threads per 25,4 mm (inch) so as to provide extremely high leverage advantage, its inner end pressing on the underside of the upper wall of structure 42 causes the entire movable jaw structure to be tilted toward the work-piece and the teeth on transverse bar 44 to dig even deeper into the upper surface of the slide bar. Tightening screw 60 by two or three turns tilts the movable jaw structure and moves its clamping member 30 toward the right from the position shown in FIG. 4, and by dotted lines in FIG. 5, to the solid-line position shown in FIG. 5; because of the small angle of incline of the screw thread the clamping surface 32 exerts tremendous force, on the order of 2224 to 4448 N (500 to 1,000 pounds), on the clamped work-piece. Loosening of screw 60 uncocks and releases the movable support structure to allow it to move freely back along the slide bar for release of the work-piece. Because the clamping member 32 of the movable jaw structure is free to swivel about pin 33, the plane of its clamping face always assumes a position parallel to the plane of the opposing face 24 of the stationary jaw structure for all situations that might be encountered; namely, when the tool is not in use; when a work-piece is initially held by spring action alone; and for all angles of tilt of the movable jaw structure. While in the illustrated embodiment the slide bar 14 is formed of steel and has a rectangular cross-section, alternatively the slide bar may be formed of high-strength plastic material and may have other shapes, with the cavities in the support structures for the fixed and movable jaws appropriately shaped for attachment to and movement along the bar, respectively. The support structures may be formed of any suitable material including metal and plastic and, in alternative embodiments may have a different profile, and means other than the curved cutouts may be provided for facilitating grasping of the jaws to pull them apart. It will have become apparent from the foregoing description that the clamping tool in accordance with the invention is compact, it closes very rapidly from an open to a clamping position, it has the ability to hold itself on a work-piece so as to free both hands of the operator, and provides extremely high clamping forces. The components of the tool are relatively thin and the overall length of the clamp is only approximately three inches longer than the capacity of the clamp over a range of different sizes. That is to say, clamps having differing maximum openings between the jaws can be provided simply by changing the length of the slide bar, and in all cases the overall length is no more than about three inches greater than the maximum opening. It will now be evident to ones skilled in the art that certain modifications and changes, in addition to the alternatives already mentioned, may be made in the described construction without departing from the scope of the invention. For example, the locking screw may be positioned on the movable jaw structure at a location to engage the top wall of the slide bar. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims: A self powered quick acting clamp comprising: an elongate hollow slide bar (14) having a U-shaped cross section; a fixed jaw (12) having a clamping surface (34) secured to one end of said slide bar (14); and, a movable jaw (16) having a clamping surface (36) slidably mounted on said slide bar (14) for movement there-along towards and away from said fixed jaw (12), characterised in that it further comprises a partially unwound flat coil spring (46) supported at one of said jaws (12,16) which extends interiorly of said slide bar (14) and has a free end (46a) connected to the other of said jaws (16,12) for normally pulling the clamping surface (36) of said movable jaw (16) toward the clamping surface (34) of said fixed jaw (12), wherein the tension of said spring (46) is substantially uniform over the maximum range of movement of said movable jaw (26) whereby upon release of either jaw after having been pulled apart against the tension of said spring (46) a distance sufficient to receive a workpiece (8) said spring (46) advances said movable jaw (16) toward said fixed jaw (12) to clamp the workpiece (8) between their respective clamping surfaces (34, 36) with a pressure corresponding only to the tension of said spring (46); and, means (60) supported on said movable jaw (16) for releasably engaging said moveable jaw with said slide bar (14), said means (60) being user-operated following initial clamping of a workpiece (8) by only the tension of said coil spring (46) and which, when operated, increases the clamping pressure over that exerted by the tension of said spring (46) alone. A quick acting clamp according to claim 1, wherein said flat coil spring (46) is supported at said fixed jaw (12) and its said free end (46a) is connected to said movable jaw (16). A quick acting clamp according to claim 1 or claim 2, in which said means (60), when operated, tilts said movable jaw (16) toward said fixed jaw (12), and wherein said movable jaw (16) is pivotally supported for maintaining parallelism between its clamping surface (36) and the clamping surface (34) of said fixed jaw (12). A quick acting clamp according to any preceding claim, in which said fixed jaw (12) is secured to said one end of said bar (14) by first support means (18); said movable jaw (16) is mounted for movement along said bar (14) on second support means (26); said spring (46) is mounted o a pin passing through said first support means (18) transversely of said slide bar (14); and, wherein the free end (46a) of said spring (46) is connected to said second support means (26). A quick acting clamp according to claim 4, further comprising a bar (42) extending transversely of a rear portion of said second support means (26) for engaging a top wall of said slide bar (14) when said second support means (20) is tilted away from a clamped workpiece (8), and means including a screw (60) threadably engaged in said second support means which, when tightened, tilts said second support means (26) and said movable jaw (16) toward said clamped workpiece (8) for increasing the clamping pressure between said fixed (12) and movable (16) jaws over the pressure exerted by said spring (46).

Inventors: WHITEFORD CARLTON L, WHITEFORD, CARLTON L.
Applicants: WHITEFORD CARLTON L, WHITEFORD, CARLTON L.
Application year: 1993
Main classification: B25B5
IPC codes: B25B5