GB1580870A - Shears and method of manufacture - Google Patents

Shears and method of manufacture Download PDF

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Publication number
GB1580870A
GB1580870A GB1592478A GB1592478A GB1580870A GB 1580870 A GB1580870 A GB 1580870A GB 1592478 A GB1592478 A GB 1592478A GB 1592478 A GB1592478 A GB 1592478A GB 1580870 A GB1580870 A GB 1580870A
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Prior art keywords
cutting
blade
portion
members
latch
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Expired
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GB1592478A
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Stanley Works
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Stanley Works
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B26HAND CUTTING TOOLS; CUTTING; SEVERING
    • B26BHAND-HELD CUTTING TOOLS NOT OTHERWISE PROVIDED FOR
    • B26B13/00Hand shears; Scissors
    • B26B13/12Hand shears; Scissors characterised by the shape of the handles
    • B26B13/14Hand shears; Scissors characterised by the shape of the handles without gripping bows in the handle
    • B26B13/16Hand shears; Scissors characterised by the shape of the handles without gripping bows in the handle spring loaded, e.g. with provision for locking the blades or the handles
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B26HAND CUTTING TOOLS; CUTTING; SEVERING
    • B26BHAND-HELD CUTTING TOOLS NOT OTHERWISE PROVIDED FOR
    • B26B13/00Hand shears; Scissors
    • B26B13/06Hand shears; Scissors characterised by the shape of the blades

Description

(54) SHEARS AND METHOD OF MANUFACTURE (71) We, THE STANLEY WORKS, of 195 Lake Street, New Britain, Connecticut, United States of America, a corporation organised and existing under the laws of the State of Connecticut, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to shears and to a method of manufacture thereof.

For many years, various configurations for shears have been devised and proposed in an effort to provide effective cutting action on a variety of materials and over a range of thickness. It has been known that, when the cutting angle between the blades is too great, there is a tendency for the object being cut to be pushed outwardly along the blades rather than being cut. In some instances, serrated edges have been employed to minimize this "squirting" tendency.

Moreover, it has been known that providing a rake angle for the cutting edge will improve cutting efficiency and it has also been known that a biasing action at the point of intersection of the cutting edges of the blades will also improve cutting action.

Efforts have been made to provide a level of uniformity in the cutting angle along the length of the blade, as for example, in United States Patent Specification (USPS) No. 2,680,294 (Shoffner). Efforts have also been made to provide some uniformity in the wiping action of the blade edges relative to each other as, for example, in USPS No. 3,376,641 (Usborne). Recently, there has been considerable activity in the fabrication of utility snips by stamping blade members from sheet metal with various elements of the desired configuration as, for example, those shown in USPS No. 3,974,564 (Hough); United States Design Patent Specification (US Des. PS) No. 238,650 (Koblick); and US Des. PS No. 239,080 (Stevenson).

Various hand tools employ operating members which are pivotably assembled, and some of these utilize springs to bias the handles apart so that the user closes the jaws by applying clamping pressure to the handles. In order to maintain the jaws and handles in a closed position for storage and for preventing injury to any of the working surfaces thereof, as well as possible injury to users of the tool during transport or storage thereof, various latches have been devised to maintain the handles in a closed position.

Frequently, such latches employ separate elements which are mounted upon the handles in a manner permitting pivotal movement of one or both thereof. In some instances, a projection may be integrally formed in one of the handles and a separate latch mounted upon the other of the handles for pivoting engagement with the shoulder as, for example:-- in the above-mentioned US Des. PS No. 239,080 (Kloblick); and above-mentioned US Des. PS 239,080 (Stevenson); and USPS No.

803,796 (Streight).

With the advent of synthetic resins such as polypropylene and propylene polyallomers providing integral self-hinging characteristics, there have been recent efforts to provide latches wherein both elements are integrally formed from the synthetic resin of the handle members. Illustrative of such a structure is USPS No.

3,869,793 (Ferguson).

According to a first aspect of the invention there is provided shears comprising: A. a pair of operating members each having a blade portion at one end, a handle portion at the other end and an intermediate pivot portion, said blade portions having opposed convexly curvilinear cutting edges extending longitudinally thereof, and B. pivot means pivotably securing said pivot portions of said operating members together for relative pivotal movement thereof between a closed position wherein the cutting edge of each blade portion overlies the side surface of the blade portion of the other operating member and an open position wherein said cutting edges are spaced apart, the curves defined by said cutting edges being mirror images and, in said open position of said shears, intersecting at a point spaced from said pivot means towards the outer end of said cutting edges, the cutting angle defined by tangents to said curves of said curvilinear cutting edges at the points of intersection along substantially the entire length thereof during closing movement of said shears being substantially constant and within the range of 1230 .

According to a second aspect of the invention there is provided a method of making shears, comprising the steps of: A. forming a pair of blade members to provide a blade portion at one end, a handle portion at the other end and a pivot portion therebetween with a pivot aperture therein; B. providing along one edge of said blade portions a curvilinear cutting edge, the curves of said cutting edges being substantially identical and corresponding to the formula set forth hereinafter; and C. assembling said blade members with their cutting edges opposed and with a pivot member extending through said pivot apertures to provide for relative pivotal movement between a closed position wherein the cutting edge of each blade portion overlies the side surface of the blade portion of the other blade member and an open position wherein said cutting edges are spaced apart, the curves of said cutting edges being mirror images and, in said open position of said shears, intersecting at a point spaced from said pivot member towards the outer end of said cutting edges, said cutting edges having a curve corresponding to the following formula:: x=ep . [(y2/x2)+li112 wherein p [tan-'(y/x)/tanTUc]+log8x,; wherein Sc=the cutting angle defined by the tangents to the curvilinear cutting edges at the point of intersection thereof; x=the distance in inches from the centre of the pivot aperture along the imaginary line bisecting the cutting angle (B,); y=the distance in inches to the cutting edge along an imaginary line perpendicular to the imaginary line for x; x,=the distance in inches along the imaginary line for x to the point of initial intersection of the blade edges in the open position and wherein xis within the range of 0.3-2.0; 8,=is within the range of 12--30"; and e=is 2.718282.

The invention will hereinafter be described by way of example of a preferred embodiment of the invention in the form of shears comprising a pair of operating members each having a blade portion at one end, a handle portion at the other end, and an intermediate pivot portion. The blade portions have opposed convexly curvilinear cutting edges extending longitudinally thereof. Pivot means pivotably secure the pivot portions of the operating members together for relative pivotal movement between a closed position wherein the cutting edge of each blade portion overlies the side surface of the blade portion of the other operating member and an open position wherein the cutting edges are spaced apart. The curves defined by the cutting edges are mirror images and, in the open position of the shears, intersect at a point spaced from the pivot means towards the outer end of the cutting edges. The cutting angle defined by tangents to the curves of the curvilinear cutting edges at the points of intersection along substantially the entire length thereof during closing movement of shears is substantially constant and within the range of 12--30".

In the preferred embodiment, the cutting edges have a rake angle of 4--14" and most desirably 5--10"; the cutting angle is desirably within the range of 14- 22". To provide wiping action at the point of intersection along substantially the entire length of the cutting edges, the blade portions of the operating members are inclined towards each other.

Most conveniently, the operating members include sheet metal blade members providing the blade portion, pivot portion and a part of the handle portion, and the blade members are inclined towards each other to provide the desired wiping action at the point of intersection. The blade members also include opposed boss portions about the pivot means to provide the bearing surfaces thereabout.

Synthetic resin handle members are affixed to the handle end of each of the operating members for gripping by the user to effect the desired pivotal movement between open and closed positions, and spring means is operatively connected between the operating members to bias them into the open position. Releasable latch means is integrally formed on the handle members to maintain the operating members in the closed position, and such latch means comprises opposed arm members adjacent the outer ends of the handle members which extend generally perpendicularly to the longitudinal axis of the handle members and into overlying relationship.One of the arm members has a latch aperture extending therethrough which is spaced inwardly from its free end and the other arm member has a latch post which projects from its surface adjacent the first mentioned arm member and into the latch aperture thereof. Either arm member is provided with an integral hinge portion adjacent the body of its handle member which permits pivotal movement of its outer end portion towards and away from the other arm member to permit insertion and removal of the latch post from the latch aperture. The latch post has a laterally extending shoulder spaced inwardly from its outer end which is engaged with a cooperating shoulder surface on the other arm member about its latch aperture. The biasing pressure of the spring means operates to maintain these cooperating shoulder portions in engagement in the closed position of the operating member.

In accordance with the preferred embodiment of the shears, the cooperating shoulder surface on the first mentioned arm member is provided by an enlarged portion in the latch aperture adjacent its outer end. The latch post is configured to provide a camming surface on its face opposite its latching shoulder, and this camming surface is inclined from adjacent the outer end of the post to an increased width adjacent its base; as a result, relative pivotal movement of the latch post into the latch aperture tends to move the latch post towards the cooperating shoulder surface of the other arm member.

As ah alternative to the inclined surface on the latch post, or in combination therewith, the wall defining the latch aperture opposite its cooperating shoulder surface may be inclined from the inner end thereof to the outer end thereof in the direction of the cooperating shoulder surface, and this will tend to move the latch post towards the cooperating shoulder surface upon insertion of the latch post into the latch aperture. As indicated above, the most desirable structures are those in which both camming surfaces are provided and cooperate with each other.

Most conveniently, the blade members may be formed by stamping sheet metal, and the cutting edges may be ground to provide a rake angle in the range of 4--14". The stamped blade members may be formed with their blade portions angularly disposed relative to the pivot and handle portions thereof with the blade portions being inclined oppositely of each other as assembled so as to produce the desired wiping action at the point of intersection.

The invention will be further described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a perspective view of shears embodying the invention; Figure 2 is a top plane view thereof; Figure 3 is a bottom view thereof; Figure 4 is a side elevational view thereof; Figure 5 is an end elevational view of the blade end thereof; Figure 6 is an end elevational view of the handle end thereof; Figure 7 is a plan view with the blades and handles in the biased open position; Figure 8 is a fragmentary plan view of one of the operating members with a portion of the handle in section to reveal internal construction; Figure 9 is a fragmentary sectional view to an enlarged scale along the line 9 9 of Figure 7; Figure 10 is a sectional view to an enlarged scale along the line 10--10 of Figure 8;; Figure 11 is a side elevational view to an enlarged scale of one of the blade members with construction lines included to indicate the angular disposition of the blade portion; Figure 12 is a fragmentary exploded view to a greatly enlarged scale of the latch portion of the handles; Figure 13 is a fragmentary sectional view to the same scale showing the handles as latched; Figure 14 is a fragmentary diagrammatic illustration of a prior art type of shears using a linear cutting edge and indicating the cutting angle when the blades are in the fully opened position; Figure 15 is a similar diagrammatic view of the shears of Figure 14 with the blades approaching the end of the closing movement thereof;; Figure 16 is a fragmentary diagrammatic view of shears embodying arcuate cutting edges with reference designations of various constructional features required for proper design thereof; Figure 17 is a similar view further showing the effect of the thickness of the material being cut upon the cutting action; Figure 18 is a graphic plot of the curve of a blade fabricated in accordance with the present invention; Figure 19 is a diagrammatic view showing the rake angle of the arcuate blade; and Figure 20 is a diagrammatic view along the line 2020 of Figure 19.

Turning now in detail to the accompanying drawings, shears embodying the present invention are illustrated in Figures 1--7 and comprise operating members generally indicated by number 10, 12 which are pivotable relative to each other about a pivot pin or rivet 14. A compression spring 16 normally biases the operating members apart into the position shown in Figure 7 and the operating members 10, 12 may be secured in the closed position of Figures 1--3 by means of a latch assembly including a latch member on the operating member 12 generally designated by numeral 18 and a latch post member on the operating member 10 generally designated by numeral 20.

In Figure 8 there is illustrated one of the operating members 10, 12 since the two members are identical with the exception of the latch members 18, 20. Each operating member 10, 12 is comprised of a sheet metal blade member generally designated by numeral 22 and a synthetic resin handle member generally designated by numeral 44.

Turning first in detail to the construction of the blade member 22, it is conveniently stamped from sheet metal so as to provide at one end a blade portion 24 tapering to a reduced width at its outer end, an intermediate pivot portion 26, and a handle portion or tang 28 extending from the pivot portion 26 to the side of the pivot aperture 37 therein opposite from the blade portion 24. The blade portion 24 is provided with an arcuate cutting edge 32 and a reinforcing rib or boss 34 of generally L-shaped configuration is formed in the metal somewhat inwardly from the cutting edge 32 and the adjacent edge surface of the pivot portion 26. In the assembled structure, the bosses 34 of the cooperating blade members 22 project oppositely away from each other so as not to interfere with the cutting action of the blade portions 24.

A circular boss 36 is provided about the pivot aperture 37 and extends in the opposite direction from the reinforcing boss 34 so that, in the assembled structure, the raised bosses 36 of the two cooperating blade members 22 will function as the bearing surfaces therefor. In addition, the pivot portion 26 is provided with a stop boss along the same side as the cutting edge 32 and which limits pivotal movement of the other operating member 10, 12 to the blade open position in response to the biasing action of the spring 16. The stop boss 38 projects in the same direction as the reinforcing boss 34, and the outer edge of the other operating member 10, 12 will abut the edge of the upstanding stop boss 38.

Along the edge of the handle portion on the opposite side from the blade cutting edge 32, there is provided a spring guide projection 40 adjacent the pivot portion 26 and a recess adjacent the end thereof providing a locking shoulder 42 for a purpose to be described more fully hereinafter. This edge of the handle portion 28 extends substantially in alignment with the cutting edge 32, and the configuration of the handle portion 28 is such that the opposite edge thereof initially extends to a substantial spacing from the first mentioned edge and then tapers inwardly to provide an abutment shoulder 43 and a terminal handle portion of substantially lesser width.

The synthetic resin handles 44 are generally L-shaped configuration and have cavities 46 therein of generally rectangular cross section to seat the handle portions 28 of the blade members 22. As seen in Figure 8, the cavities 46 have an outwardly tapering portion adjacent the opening therein to provide a surface abutting the abutment shoulder 43 of the blade member 22 when the blade members 22 are driven into the cavities 46. Moreover, locking shoulder 42 on the handle portion 28 of the blade members 22 will tend to embed itself in the synthetic resin of the handle 44 so as to prevent disengagement after assembly. As seen in Figures 1--3, the handles 44 are of greater thickness along their outer side margins to provide ribs 50 of increased surface area for gripping by the hand of the user.On the adjacent edges of the handles 44 are laterally projecting and aligned projections or stops 48 which limit closing movement thereof.

One of the handles 44 is formed to provide the latch post member 20 which is best seen in Figures 6, 7, 12 and 13. The latch post member 20 extends laterally from the outer end of the handle 44 perpendicularly to the longitudinal axis of the handle 44 and includes at its free end a relatively thick body portion 52 connected to the body of the handle 44 by a reduced thickness hinge portion 54. Projecting upwardly from the body portion 52 is a latch post generally comprised of a cylindrical post portion 56 and a buttress portion 60 which is inclined from adjacent the upper end of the cylindrical post portion 56 to the free edge of the body portion 52. The cylindrical portion 56 is undercut on its surface opposite the buttress 60 to provide a shoulder 58.

The other handle 44 is configured to provide the latch member 18 which comprises a lateral arm extending perpendicularly to the longitudinal axis of the handle to overlie the body portion 52 of the latch post member 20 and having a keyhole shaped aperture 62 adjacent its free end. The linear portion of the aperture 62 is dimensioned and configured to cooperate with the buttress portion 60 of the latch post and has a cooperatively tapering surface 64. The circular portion of the aperture 62 opposite the linear portion has an enlarged portion adjacent the outer surface to provide a shoulder 66 which cooperates with the shoulder 58 on the cylindrical post 56 for effecting latching action as seen in Figure 13.

As seen in Figure 10, the cutting edge 32 is ground so as to provide a rake angle beta which is highly desirable to provide clearance to facilitate cutting by the edge 32 through various materials. As seen in Figure 11, the tendency for the relatively flexible blade portions 24 to deflect apart during cutting action is compensated by inclining the blade portions 24 from the plane of the pivot portion 26 and handle portion 28 in the direction of the cooperating blade member 22. The angle of incline from the point X representing the inner end of the cutting edge 32 to the outer end of the blade portion 24 is represented by the angle alpha.Since the two blade portions 24 are inclined towards each other, there is a constant biasing pressure operating at the point of contact of the cutting edges 32 which ensures the desired wiping action of the blade portions adjacent the point of cutting.

The configuration of the cutting edge 32 is critical to achieving the desired cutting action over substantially the entire length thereof. In Figure 14 and Figure 15 are illustrated prior art shears having a rectilinear cutting edge between which is defined a cutting angle theta. In the blade full open position of Figure 14, the cutting angle theta is quite large which will tend to push the material to be cut outwardly (the "squirting effect"). In Figure 15, the cutting angle theta is much smaller so that there will be little tendency to push the material out. Thus, the cutting angle theta will vary from very large to very small as the point of intersection of the blade edges moves outwardly from the pivot.

In Figure 16, there are diagrammatically represented two cutting blade edges f(x) and f'(x) having a pivot point defined by the intersection of the X and Y grid lines, i.e. the "origin" [the cutting angle Oc is defined by the tangents to the point of intersection of the curved edges and it is desired to maintain this angle constant as the point of intersection of the cutting edges moves outwardly along the blade edges] .

The point x, y is spaced further out along the blade edges from the point of intersection shown and the tangent at that point is shown by the line T. The line from the pivot to that point is defined as y=mx and the angle of elevation of the line from the X grid is defined as tan-1m If the curved edges were to be pivoted (through tan-'m) to bring the points x, y and x', y' onto the X grid line, the cutting angle is still required to be Oc. Thus, the angle between the line y=mx and the tangent thereto to any point along the curve is C.

The slope of the blade curve at point (x, y), better known as the derivative of the curve, can then be expressed as: dy/dx=tanT0c+tan-' y/x where y/x is substituted for m. Solving this differential equation results in the blade curve as defined by the formula: x=e, . [(y21x2)+l]-112 wherein P= [tan-1(y/x)/tan#]+logex1 wherein #c=the cutting angle defined by the tangents to the curvilinear cutting edges at the point of intersection thereof; x=the distance in inches from the centre of the pivot aperture along the imaginary line bisecting the cutting angle (0c); y=the distance in inches to the cutting edge along an imaginary line perpendicular to imaginary line for x;; x,=the distance in inches along the imaginary line for x to the point of initial intersection of the blade edges in the open position; Turning now to Figure 17, the blade curves f(x) and r(x) are similarly constructed with the initial point of intersection of the cutting edges in the open position being a distance x1, from the pivot. Here can be seen the basis for the method of calculating the length of cut xc and the total angular stroke s as well as the effect of the thickness of the material being cut t.The length of the blade to the tip is defined by the point x2, y2 and the angular cutting stroke O is defined by the angle between the imaginary lines drawn from the pivot point to those points in the open position of the blades.Since y=[tan(Os12s] . x and values of OS can be empirically selected, it can be derived that Xc=(X+y)1/2-1 Several calculations can be used to derive the optimum combination of values for XC and Us As seen in Figure 17, the thickness of the stock being cut twill define an angle between the tangent at the point of contact with the blade and a parallel line to the X grid of SCT/2. It is important that Oc be less than oCT for the bulk of the materials to be cut to get good cutting action.

Although the cutting angle theta may be greater than 30 for soft materials or when a large rake angle is employed, it has been found that a uniform cutting angle of 12--300 is desirable for most materials and the range of thicknesses that will normally be encountered. Preferably, this angle is in the range of 14--22".

Although the distance from the pivot to the initial point of intersection (x,) may be larger, generally it will fall within the range of 0.3-2.0 inches and preferably 0.4- 0.8 inch.

In Figure 18, there is graphically presented the preferred curve configuration for the shears of Figures 1--13, drawn to twice the scale and using for the equation the following values: x,=0.6; Oc=20 To provide improved cutting action, the cutting edges are desirably hollow ground to provide the rake angle as shown in Figures 19 and 20. The rake angle may range from as little as 40 to 14" and even higher albeit. with a tendency for more rapid wear or fragility. Preferably, the rake angle is within the range of 5 10 .

In operation of the shears, the latch post member 20 is disengaged from the latch member 18 by pressing the handles 44 towards each other which causes the sloping surface of the buttress portion 60 of the latch post to bear against the tapered surface 64 of the latch aperture 62 as operating members 10, 12 are pivoted somewhat about the pivot 14. This produces a camming action causing the latch post to be cammed outwardly and downwardly relative to the latch aperture 62.

Thus, when the clamping pressure on the handles 44 is released, the operating members 10, 12 will spring apart towards the open position shown in Figure 7.

The material to be cut (not shown) is introduced into the space between the cutting edges 32, and the user then applies closing pressure to the handles 44 which concurrently brings the blade portions 24 towards each other. Because of the configuration of the cutting edges 32 and the wiping action produced by the angular offset of the blade portion 24, the material will be cut at the point of contact without any substantial tendency for the material to be pushed outwardly by the cutting action. Moreover, the rake angle of the cutting edge 32 will provide the clearance necessary for effective cutting action of substantially all materials.

Upon completion of the cutting stroke, the user releases the clamping pressure upon the handles 44 and the blade portions 24 again spring into a position to effect the next cut.

When the cutting has been completed and it is desired to latch the handles 44, they are moved towards each other until the stops 48 abut or substantially abut, at which point the latch post member 20 overrides the latch member 18. The user may then press downwardly upon the latch post member 20 while at the same time releasing some of the closing pressure, and this will cause pivoting of the post member 20 about the hinge portion 54 and entry of the cylindrical post 56 into the keyhole aperture 62. As the cylindrical post 56 moves downwardly into the aperture 62, the camming action produced by the tapered surface 64 of the aperture and the tapered surface of the buttress portion 60 causes the post 56 to move in the opposite direction until the shoulder 58 and shoulder 66 enter into the latching engagement, at which point all closing pressure may be removed from the handles 44.

In fabricating and assembling the above-described the blade members 22 are conveniently stamped and punched from sheet metal into the desired configuration, heat treated and then subjected to a grinding operation to provide the rake angle beta along the cutting edge 32. The handles 44 are moulded into the desired configuration and affixed to the blade members 22 by inserting and driving the handle portions 28 thereof into the cavities 46 of the handles 44. As previously indicated, the locking shoulder 42 will tend to embed itself in the synthetic resin of the handle 44 defining the wall of the cavity 46 to prevent subsequent disengagement.If so desired, adhesive engagement may also be provided by an adhesive coating, heat sealing or other means, or physical interlocking may be increased by providing recesses or apertures in the handle portion 28 into which synthetic resin from the handles 44 may be caused to flow. Moreover, an alternate method of assembly may involve the forming of the handles 44 from molten resin about the previously formed handle portions 28.

Following assembly of the handles 44 to the blade members 32 to form the operating members 10, 12, these members are then pivotably engaged by inserting the pivot pin or rivet 14 through the aligned apertures 37 and staking the shank thereof as seen in Figure 9. The compression spring 16 is seated about the spring guide 40 of one of the handle portions 28, compressed, and then slipped over the spring guide of the other handle portion 28. For shipping purposes, the latch post member 20 is engaged in the latch member 18 to complete the assembly as shown in Figures 1--6.

The synthetic resin employed for the handles should be one providing selfhinging properties such as polypropylene or ethylene/propylene polyallomers. The handles may be fabricated by injection moulding, centrifugal moulding, or any other suitable technique. The blade members are most desirably fabricated from stainless steel to permit their use for many cutting applications including foods and the like.

Although the hinged portion has been provided upon the pivot post member in the illustrated embodiment, it may be provided on the apertured latch member if so desired.

It may be appreciated that the overall configuration and dimensioning of the blade members may vary considerably from that illustrated in the drawings and that multiple corrugations or ribs may be employed to provide the desired stiffness in the sheet metal blade members.

As will be appreciated, the latch mechanism of the illustrated shears may be used in connection with hand tools which are other than shears and which employ pivotable operating members wherein the handles and jaws are normally biased apart by spring means. Exemplary of such other tools are pliers, tool retrieving clamps, and the like.

Thus, it can be seen from the foregoing detailed specification and attached drawings that the cutting angle defined between the cutting edges is substantially constant throughout the effective cutting length of the blade to afford highly effective cutting action. Moreover, the efficacy of the shears is augmented by blade edges which have a desirable rake angle and which are biased together over substantially their entire length to provide the desired wiping action at the point of cutting. The operating members or blades may be readily and economically fabricated from sheet metal to provide a durable and versatile tool, and the method for fabricating the shears is one which is convenient and economical.

The latch assembly is integrally formed with the synthetic resin handles and is rugged and durable and yet easily operable for both closing and opening thereof.

The dimensions of the latch components may be varied as required to increase the strength or holding capabilities of the latch assembly depending upon the size of the tool for which employed and the opening pressures to be resisted.

WHAT WE CLAIM IS: 1. Shears comprising: A. a pair of operating members each having a blade portion at one end, a handle portion at the other end, and an intermediate pivot portion, said blade portions having opposed convexly curvilinear cutting edges extending longitudinally thereof; and B. pivot means pivotally securing said pivot portions of said operating members together for relative pivotal movement thereof between a closed position wherein the cutting edge of each blade portion overlies the side surface of the blade portion of the other operating member and an open position wherein said cutting edges are spaced apart, the curves defined by said cutting edges being mirror images and, in said said open position of said shears, intersecting at a point spaced from said pivot means towards the outer end of said cutting edges, the cutting angle defined by tangents to said curves of said curvilinear cutting edges at the points of intersection along substantially the entire length thereof during closing movement of said shears being substantially constant and within the range of 12--30".

2. Shears as claimed in Claim 1, wherein said cutting edges have a rake angle in the range of 4--14".

3. Shears as claimed in Claim 1, wherein said cutting angle defined by the curves of said cutting edges is within the range of 14--22" and wherein the rake angle provided by said cutting edges is in the range of 5--10".

4. Shears as claimed in Claim 1, 2 or 3, wherein said blade portions of said operating members are inclined towards each other to provide wiping action at the point of intersection along substantially the entire length of said cutting edges.

5. Shears as claimed in any preceding Claim, wherein said operating members include sheet metal blade members providing said blade portion, pivot portion and a part of said handle portion, the blade portions of said blade members being inclined towards each other to provide wiping action at the point of intersection along substantially the entire length of the cutting edges.

6. Shears as claimed in Claim 5, wherein said blade members include opposed boss portions about said pivot means to provide the bearing surfaces at said pivot means.

7. The shears in accordance with Claim 1, wherein the curves defining said cutting edges conform over substantially their entire length to the formula: x=ep . [(y2/x2)+1]-112; wherein p [tan1(}VxYtan+Ocl+Thgex1; wherein 8,=the cutting angle defined by the tangents to the curvilinear cutting edges at the point of intersection thereof;

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (22)

**WARNING** start of CLMS field may overlap end of DESC **. multiple corrugations or ribs may be employed to provide the desired stiffness in the sheet metal blade members. As will be appreciated, the latch mechanism of the illustrated shears may be used in connection with hand tools which are other than shears and which employ pivotable operating members wherein the handles and jaws are normally biased apart by spring means. Exemplary of such other tools are pliers, tool retrieving clamps, and the like. Thus, it can be seen from the foregoing detailed specification and attached drawings that the cutting angle defined between the cutting edges is substantially constant throughout the effective cutting length of the blade to afford highly effective cutting action. Moreover, the efficacy of the shears is augmented by blade edges which have a desirable rake angle and which are biased together over substantially their entire length to provide the desired wiping action at the point of cutting. The operating members or blades may be readily and economically fabricated from sheet metal to provide a durable and versatile tool, and the method for fabricating the shears is one which is convenient and economical. The latch assembly is integrally formed with the synthetic resin handles and is rugged and durable and yet easily operable for both closing and opening thereof. The dimensions of the latch components may be varied as required to increase the strength or holding capabilities of the latch assembly depending upon the size of the tool for which employed and the opening pressures to be resisted. WHAT WE CLAIM IS:
1. Shears comprising: A. a pair of operating members each having a blade portion at one end, a handle portion at the other end, and an intermediate pivot portion, said blade portions having opposed convexly curvilinear cutting edges extending longitudinally thereof; and B. pivot means pivotally securing said pivot portions of said operating members together for relative pivotal movement thereof between a closed position wherein the cutting edge of each blade portion overlies the side surface of the blade portion of the other operating member and an open position wherein said cutting edges are spaced apart, the curves defined by said cutting edges being mirror images and, in said said open position of said shears, intersecting at a point spaced from said pivot means towards the outer end of said cutting edges, the cutting angle defined by tangents to said curves of said curvilinear cutting edges at the points of intersection along substantially the entire length thereof during closing movement of said shears being substantially constant and within the range of 12--30".
2. Shears as claimed in Claim 1, wherein said cutting edges have a rake angle in the range of 4--14".
3. Shears as claimed in Claim 1, wherein said cutting angle defined by the curves of said cutting edges is within the range of 14--22" and wherein the rake angle provided by said cutting edges is in the range of 5--10".
4. Shears as claimed in Claim 1, 2 or 3, wherein said blade portions of said operating members are inclined towards each other to provide wiping action at the point of intersection along substantially the entire length of said cutting edges.
5. Shears as claimed in any preceding Claim, wherein said operating members include sheet metal blade members providing said blade portion, pivot portion and a part of said handle portion, the blade portions of said blade members being inclined towards each other to provide wiping action at the point of intersection along substantially the entire length of the cutting edges.
6. Shears as claimed in Claim 5, wherein said blade members include opposed boss portions about said pivot means to provide the bearing surfaces at said pivot means.
7. The shears in accordance with Claim 1, wherein the curves defining said cutting edges conform over substantially their entire length to the formula: x=ep . [(y2/x2)+1]-112; wherein p [tan1(}VxYtan+Ocl+Thgex1; wherein 8,=the cutting angle defined by the tangents to the curvilinear cutting edges at the point of intersection thereof;
x=the distance in inches from the centre of the pivot aperture along the imaginary line bisecting the cutting angle (0c); y=the distance in inches to the cutting edge along an imaginary line perpendicular to imaginary line for x; x,=the distance in inches along the imaginary line for x to the point of initial intersection of the blade edges in the open position and wherein x, is within the range of 0.3-2.0; Oc is within the range of 12--30"C; and e is 2.71828.
8. Shears as claimed in Claim 7, wherein the cutting angle is within the range of 14--22" and wherein said cutting edges have a rake angle in the range of 4--14".
9. Shears as claimed in any preceding Claim wherein synthetic resin handle members are affixed to the other end of said operating member for gripping by a user to effect said pivotal movement thereof; spring means are operatively connected between said operating members and biasing said operating members into the open position thereof; and releasable latch means are integrally formed on said handle members to maintain said operating members in said closed position, said latch means comprising opposed arm members adjacent the outer ends of said handle members extending generally perpendicularly to the longitudinal axis of said handle members into overlying relationship, one arm member having a latch aperture therethrough spaced inwardly from the free end thereof and the other of said arm members having a latch post projecting from the surface thereof adjacent said one arm member and into said latch aperture thereof, either one of said arm members having an integral hinge portion adjacent the body of the handle member thereof permitting pivotal movement of the outer end portion thereof towards and away from the other one of said arm members for insertion and removal of said latch post from said-latch aperture, said latch post having a laterally extending shoulder spaced inwardly from the outer end thereof engaged with a cooperating shoulder surface of said one arm member about said latch aperture, said biasing pressure of said spring means operating to maintain said cooperating shoulders in engagement in the closed position of said operating members.
10. Shears as claimed in Claim 9, wherein said cooperating shoulder surface of said one arm member is provided by an enlarged portion of said latch aperture adjacent the outer end thereof.
11. Shears as claimed in Claim 9 or 10, wherein said latch post is configured to provide a camming surface on the face thereof opposite said shoulder and tapering from adjacent the outer end of said post to an increased width adjacent the base thereof, said camming surface tending to move said latch post towards the cooperating shoulder surface of said one arm member upon relative movement of said latch post into said latch aperture.
12. Shears as claimed in any one of Claims 9 to 11, wherein the wall defining said latch aperture in said one arm member opposite said cooperating shoulder surface is inclined from the inner end thereof to the outer end thereof in the direction of said cooperating shoulder surface to move said latch post towards the cooperating shoulder surface of said one arm member upon relative movement of said latch post into said latch aperture.
13. Shears as claimed in any one of Claims 9 to'12, wherein said latch post is configured to provide a camming surface on the face thereof opposite said shoulder tapering from adjacent the outer end of said post to an increased width adjacent the base thereof, and wherein said latch aperture has a cooperatively dimensioned and configured inclined surface, whereby said cooperating surface function to cam the latch post towards the cooperating shoulder surface of said one latch member upon relative pivotal movement of said latch post into said latch aperture, said cooperating surfaces also serving to cam said latch post outwardly of said latch aperture upon movement of said handle members towards each other.
14. Shears as claimed in Claim 11, wherein said camming surface on said latch post is provided by a tapered buttress portion extending towards the free end of said arm member to provide a substantially key-shaped cross section.
15. Shears as claimed in Claim 13, wherein said camming surface on said latch post is provided by a tapered buttress portion extending towards the free end of said other arm member to provide a substantially key-shaped cross section and wherein said latch aperture has a cooperatively dimensioned and configured inclined surface to provide a generally keyhole cross section.
16. Shears as claimed in Claim 15, wherein said cooperating shoulder surface of said latch member is provided by an enlarged portion of said latch aperture adjacent the outer end thereof.
17. Shears as claimed in any one of Claims 9 to 16, wherein the arm member having said integral hinge portion is said other arm member having said latch post.
18. A method of making shears, comprising the steps of: A. forming a pair of blade members to provide a blade portion at one end, a handle portion at the other end and a pivot portion therebetween with a pivot aperture therein; B. providing along one edge of said blade portions a curvilinear cutting edge, the curves of said cutting blade being substantially identical and corresponding to the formula set forth hereinafter; and C. assembling said blade members with their cutting edges opposed and with a pivot member extending through said pivot apertures to provide for relative pivotal movement between a closed position wherein the cutting edge of each blade portion overlies the side surface of the blade portion of the other blade member and an open position wherein said cutting edges are spaced apart, the curves of said cutting edges being mirror images and, in said open position of said shears, intersecting at a point spaced from said pivot member towards the outer end of said cutting edges, said cutting edges having a curve corresponding to the following formula:: x=eP, [(y2/x2)+ 1 ]-1/2 wherein P [tan-'(y/x)/tanT0c]+logex,; wherein 8,=the cutting angle defined by the tangents to the curvilinear cutting edges at the point of intersection thereof; x=the distance in inches from the centre of the pivot aperture along the imaginary line bisecting the cutting angle ( c); y=the distance in inches to the cutting edge along an imaginary line perpendicular to imaginary line for x; x1=the distance in inches along the imaginary line for x to the point of initial intersection of the blade edges in the open position and wherein x,=is within the x, is within the range of 0.3-2.0; Oc is within the range of 12--30"; and e is 2.71828.
19. A method as claimed in Claim 18, wherein said blade members are formed by stamping sheet metal.
20. A method as claimed in Claim 18 or 19, wherein the cutting edges of said blade members are ground to provide a rake angle in the range of 4--14".
21. A method as claimed in Claim 18, 19 or 20, wherein said blade members are formed with their blade portions angularly disposed relative to the pivot and handle portions thereof with the blade portions being inclined oppositely of each other as assembled so as to produce a wiping action at the point of intersection along substantially the entire length of the cutting edges.
22. A method as claimed in any one of Claims 18 to 21, wherein xl is in the range of 0.4--0.8 and Or is in the range of 14--22" and wherein the cutting edges of said blade members are ground to provide a rake angle in the range of 4--14".
GB1592478A 1977-11-02 1978-04-21 Shears and method of manufacture Expired GB1580870A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US05847698 US4114268A (en) 1977-11-02 1977-11-02 Shears with improved latch for handles
US05847697 US4150484A (en) 1977-11-02 1977-11-02 Shears with improved cutting action and method of making same

Publications (1)

Publication Number Publication Date
GB1580870A true true GB1580870A (en) 1980-12-03

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ID=27126728

Family Applications (1)

Application Number Title Priority Date Filing Date
GB1592478A Expired GB1580870A (en) 1977-11-02 1978-04-21 Shears and method of manufacture

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DE (1) DE2818913A1 (en)
FR (1) FR2407798B1 (en)
GB (1) GB1580870A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2147534A (en) * 1983-10-07 1985-05-15 Wallace Mfg Cutting device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19517654C1 (en) * 1995-05-13 1996-10-17 Jaguar Stahlwarenfabrik Gmbh barber scissors

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Publication number Priority date Publication date Assignee Title
US2269587A (en) * 1940-08-12 1942-01-13 Hardin Ernest Scissors or the like
FR1001351A (en) * 1946-04-24 1952-02-22 Development scissor blades, shears and other tools of the same kind
US2511187A (en) * 1946-10-16 1950-06-13 Philbeck Corp Shears
FR1049603A (en) * 1950-12-06 1953-12-30 Scissors
GB729308A (en) * 1950-12-06 1955-05-04 Erwin Krusius Improvements in or relating to scissors
GB1377418A (en) * 1971-06-16 1974-12-18 Hough J A Cutting tools
US3869793A (en) * 1974-02-19 1975-03-11 Wiss & Sons Co J Latch for hand tool

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2147534A (en) * 1983-10-07 1985-05-15 Wallace Mfg Cutting device

Also Published As

Publication number Publication date Type
FR2407798A1 (en) 1979-06-01 application
DE2818913A1 (en) 1979-05-03 application
FR2407798B1 (en) 1982-07-30 grant

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