GB2035181A - Hand shears - Google Patents

Abstract

Hand shears 1 for cutting steel rods and the like comprise two blades 4, 5 which are accommodated and pivoted in respective supporting side pieces, and have their ends remote from the cutting edges cooperating with respective actuating handle bars 6, 7 that also pivot in the side pieces. Connection of each blade 4, 5 to its associated actuating handle bar 6, 7 is by a shaped seat 15 in the blade engaging a correspondingly-shaped lug 16 on the respective handle bar 6. Upon rotation of the actuating handle bars 6, 7 the lugs 16 cause the blades 4, 5 to move, the position of maximum expansion of the shears being determined by the geometrical engagement of the lugs 16 in the respective shaped seats 17. <IMAGE>

Description

SPECIFICATION Hand shears This invention relates to hand shears for cutting steel rods and the like.

Hand shears of this type are generally utilized to cut, or shear off, high strength metal parts, such as screws, bolts, threaded bars, sectional metal, cables, concrete reinforcement rods, and the like. Thus, the majority of shears of this type are subjected in operation to very high stresses, and require a specially robust and wear-resisting construction.

It is recognized that prior art shears of this type exhibit a very low force amplification ratio, thereby the operator is required to exert a very high force.

Furthermore, it has been found that when encountering high strength workpieces the operator, upon starting the cut, is to overcome a considerably high initial resistance, thereafter before the workpiece actually parts off, he has to apply a force which is close to the upper limit of his muscular power or even exceeds it. Thus, the shears operator is practically encouraged to apply, during the cutting operation, a reciprocating rotary movement to the tool, back and forth or up and down in a transverse plane to the work-piece. Obviously, this results in premature wear of the shears cutting edges, and occasionally in the destruction thereof as well as of the force transmitting linkage.

Also, known, from the German published patent application No OS 2 5 06 448, are shears having two blades carried on a common holder, the holder also supporting two handles as well as means for transmitting the forces and movements involved between the cutting edges and handles. According to the teachings of that invention, the ends of the shears handles next to the cutting edges are individually journalled, and such ends are located internally between the rear ends of the shears cutting edges. The knuckle connection of one handle and to its related cutting edge end is implemented through the use of an articulation lever, the ends whereof are connected in a swing-oscillable manner, on one side, to the associated cutting edge, and on the other side, to the associated handle end.

According to the proposed solution, moreover, the longitudinal axes of the levers take each time an inclined position with respect to the shears centreline, this inclined position remaining approximately the same for all the positions that the shears can assume.

This invention sets out to provide hand shears for cutting steel rods and the like, to the general design indicated in the preamble, which additionally to obviating the cited prior art drawbacks, further affords the following advantages: -achievement of a high applied force amplification coefficient; -component parts designed for direct transmission of forces, without intervening complementary parts; -automatically synchronized movement of the cutting edges; -possibility of utilizing identical moulded blanks, by suitably dimensioning the machining allowance; -simple construction and assembly procedure; -possibility of using parts having the same thickness dimensions, thus simplifying their manufacture.

In order to achieve the above objects and advantages, the present invention prqvides hand shears for cutting steel rods and the like, comprising two oppositely arranged supporting side pieces, two blades pivotally secured therein and cooperating, at the ends thereof remote from the cutting edges, with respective actuating handle bars which are also pivotally secured in the side pieces, wherein each blade has a seat directly cooperating with a lug provided at the hinged end of the associated handle bar, each pair of seats and lugs being shaped such that rotation of the handle bars about a respective pivot pin forces the associated blade to rotate about the respective pivot pin.

Furtherfeatures, advantages and details of the hand shears according to the invention will become apparent from the following exemplary description thereof, in conjunction with the accompanying drawings in which: Figure lisa top plan view of the front or working end of hand shears, a portion thereof being omitted from view, and specifically part of a side piece, for clarity of illustration; Figure 2 is a side elevation view of the shears of Figure 1; Figure 3 is a top plan view, similar to Figure 1, but showing the blades in their open positions; Figure 4 is a much enlarged representation of the seats provided in the blades; Figure 5 are actual test plotted graphs showing the relationship which exists between the applied force P and the range angle y of the blades, in prior art shears versus the inventive shears;; Figure 6 is a diagram illustrating the movement ratios existing between the individual parts of the inventive shears; and Figure 7 is a theoretically plotted graph showing the relationships existing between the force amplification coefficientnl and the range angle y of the blades of conventional design versus the inventive shears.

With reference to the drawings, wherein similar parts are denoted throughout with the same reference characters, hand shears for cutting steel rods, screws, bolts, threaded bars, and the like stock are generally indicated at 1. They comprise two supporting side pieces 2 and 3, which are arranged opposite each other, and two blades 4 and 5, as well as two actuating handle bars or arms 6 and 7. In the example shown the handle bars are divided in two knuckle members, as illustrated, and two extension handles (not shown). The blades 4, 5 are pivotally connected or hinged at 8,9 to the side pieces 2,3 with the interposition of spacers 8a, knownperse.The handle bars, or knuckle members, 6, 7. are independently hinge connected at 10, 11 to the side pieces 2, 3, the hinge or pivotal connections being implemented through the use of suitable bolts. In this particular instance, no spacers have been used owing the dimensional requirements. The reference numeral 12 denotes an additional bolt member provided at the lower side of the assembled side pieces 2, 3 with the interposition of a space 12a.

As is clearly shown in Figures 2 and 3, the ends of the blades 2,3 located away from the cutting edges proper, 13, 14, are formed with respective contoured seats 15, adapted for engaging a contoured lug 16 provided at the pivoted ends of the handle bars 6, 7.

As can be observed in Figures 1 and 3, the contours of the seats 15 and lugs 16 comprise arcs of circumferences having the same diameters and their centers a and b spaced apart by a distanced. Furthermore, a line led through said centers a, b would be offset to one side with respect to the center c of the associated pivot pin 10 or 11, for the handle bars 6,7 in the side pieces 2, 3. Thus, a rotational movement imparted to the handle bars, or knuckle members, 6, 7 abouttheir related pivotaxesc would coercively cause rotation of the blades 4,5 about their pivot pins 8, 9, the force applied to the handle bars being transmitted to the blades through the movements of the lugs 1 in their respective seats 15.

The reference numeral 17 denotes generally mating profiles formed in the blades 4, 5, the same being effective to ensure a perfectly true movement of the blades 4, 5 and, accordingly, of the handle bars 6, 7.

By providing such mating profiles, constant mutual engagement of the blades 4,5 is accomplished regardless of the expansion angle thereof or of the cutting edges 13, 14.

From the experimentally plotted graph of Figure 5, the relationship of the force P as applied to the shears handle bars, or arms, to the range or expansion angler of the cutting edges thereof can be observed. The area included between the curvea' and curve b' incorporates the various curves determined for shears of conventional designs. The curve relative to the shears according to this inventon is the curvec'. The test was carried out on a round bar having a diameter of 6mm and a braking point of about 85 kg/mm2.

The graph of Figure 7, illustrating the relationship between the force amplification coefficient al and the range or expansion angley of the blades, also shows at a" andb"two curves incorporating several curves relating to prior art shears, whereas the curve relating to the inventive shears is indicated at c".

By inspection of the graphs in Figures 5 and 7, it will be apparent that the theoretical diagram of Figure 7 is fully confirmed by the experimental one of Figure 5, as obtained by actual testing.

From the foregoing, it will be evident how the shears according to this invention effectively achieve the objects mentioned in the preamble and afford the advantages cited hereinabove.

From a practical standpoint, the novel shears proposed herein provide a very high force amplification ratio, thereby less power is required for the cutting or shearing operation than with equivalent shears of conventional design.

In practising the invention, individual parts may be replaced with other, technically and function-wise equivalent parts, such as, for example, substituting for the contours herein proposed for the blade seats and the handle bar knuckle joints, other contours or profiles which, rather than having a circular pattern, are conferred other curvilinear mating patterns; or providing a holder which instead of two opposite side pieces could comprise a box-like holer having a U-like, or similar, cross-sectional configuration; or changing the blade geometry; or even providing lightening slots in the blades and in the supporting side pieces; and so forth, without departing from the scope of this invention.

Claims (12)

1. Hand shears for cutting steel rods and the like, comprising two oppositely arranged supporting side pieces, two blades pivotally supporting side pieces, two blades pivotally secured therein and cooperating, at the ends thereof remote from the cutting edges, with respective actuating handle bars which are also pivotally secured in the side pieces, wherein each blade has a seat directly cooperating with a lug provided at the hinged end of the associated handle bar, each pair of seats and lugs being shaped such that rotation of the handle bars about a respective pivot pin forces the associated blade to rotate about the respective pivot pin.

2. Hand shears according to claim 1 comprising means for reducing frictional resistances and for securing the side pieces.

3. Hand shears according to claim 1 or 2, wherein the shape of the seat in each blade and the shape of the lug of each actuating handle bar comprise mating sectors spaced apart from each other and lying on a line which is offset to one side with respect to the centre of the adjacent pivot pin for the respective handle bar.

4. Hand shears according to claim 1,2 or 3, wherein the shape of the seat provided in each blade and the shape of the lug of each actuating handle bar comprise arcs of a circumference spaced apart from each other and lying on a line which is offset to one side with respect to the centre of the adjacent pivot pin of the respective handle bar.

5. Hand shears according to any of claims 2 to 4, wherein said frictional resistance reducing means are in the form of spacers.

6. Hand shears according to any of claims 2 to 5, wherein said side piece securing means comprise a bolt-type fastening connection.

7. Hand shears according to claim 6, wherein the bolt is provided at the lower middle portion of the side pieces.

8. Hand shears according to any preceding claim comprising a spacer located intermediate the side pieces.

9. Hand shears according to any preceding claim, wherein the shaped lug cooperation with the shaped seat in the associated blade is formed on a knuckle member, which is removably connected to a respective handle bar.

10. Hand shears according to claim 9, wherein the knuckle member is removably connected to a respective handle bar by positive engagement means.

11. Hand shears according to any preceding claim, wherein the maximum expansion of the blades of the hand shears is determined by an end portion of each blade cooperating and engaging with a respective knuckle member.

12. Hand shears substantially as hereinbefore described with reference to the accompanying drawings.