Note: Descriptions are shown in the official language in which they were submitted.
73
This in~ention relates to improvements ~n sheari~g
tools such as shears 9 scissors, tin snipsy secateurs~ and
other hand tools and will be described with particular
reference to hedge shear It is to be under~tood however
that the principles herein exemplified may be applied with
equal ease to scissors and other types of hand-manipulated
instrumentsO
The invention envisions cutting implements in which~
in the cut~ing action, the edges of two cooperating blades,
in sub~tantial con ac~ with each other, move toward and
then past each other as facilitated by a piv~t about which
the blades ro~ate. The novelty lies in the fact that the
operating edge~ of the blades are of arcuate configuration
so tha~ the cutting action is con~tant from the initiation
to termination of the cutting stroke~ a feature aided nd
~betted both ~y the particular arcuate configuration of the
opposing cutting edges of the blades and by a novel
dimensioning of the included ~ngle between the cutting edges
With known prior art shears, particularly hedge shears,
there i~ the aggravating tendency to push or extrude the work
along and relatlve to the cutting edges as the cutting or
closing a¢tion ensues. Such extrusion is in the form of a
~liding of the work along and rela~ive t~ the cutting edges
with the result that a portion of the cutting ac~ion is
obviously wasted.
Any co~ventional shear, particularly a hedge shear~ wlll
exhibit, to some degree, this tendency to extrude. As the
cutting stroke erlsues, the work is pushed away from the apex of
the blades and along the blade edges until some point therealong
is reached where that sliding actlon~ having slowed down~ i~
finally stopped, whereupon the critlcal cutting action in the
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fo~m of the biting of the blades into the work finally
commences. This is seriously disadvantageous as the obvious
desideratum is to obtain not only an optimum cutting ction
in the area of the greatest force (that is~ in the area nearest
the pivot where ~u~h action should be initlated~ but also a
constant and c~ntinuous cutting action throughout tha
cutting s~roke.
To overcome this n~torious tendency to extrude,
serrated blades have been employed, as have notched ~lades ?
either ~pproach constituting an express recognition of the
extruding problem. The serrating of a single blade is shown
in V~S. patent ~3J650,028 to LaPointe, and of both blades
i5 shown in U.SO patent ~2~1~1,236 to McDonald. The notching
of a blade is sh~wn in U.S. patent ~198909355 to Bailey.
The use of serrations represents a sacrifice of one or
both of the blades as far as eficient cutting action is
concerned. The conventional notch9 while it may be helpful
in cutting heavy growth, is actually a drawback when the shear
is used to cut ligh growths, such as grass and the like,
due to the limitations in the shearing action.
We have arrived at a solution which provides a constant
shearing action rom the commencement to termination of the
cutting stroke and defined by the provision of an included
angle between the blades in the cutting stroke which is not so
8mall as to jeopardize the shearing e~ficiency and is yet not
80 large as to ,encourage axtrusion. The solution represents
a strikin~ o an optimum balance between s~earing action and
extruding tendency.
In prior art shears, the blades, in ully-opened
position, may bls generally disposed so as ~o define an
included angle approximating 90 or even more7 sometimes even
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~L~9~ 3
as much as an included angle of 1~5 ~ 130) relative to
each other~ Then, ln the cIosing stroke, they may be moved
in relative positions so that, immediately prior to full
closure, the blades at their outermost points, will have
as~umed, as to each other, an included angle approximating
10 - 12. With the conventional shear9 obviou~ly, the smaller
included angle is found near the ~board extreme and the
larger angle is found near the i.nboard extreme of the
cutting s~roke.
Our prima~y ~bject of providing an i~proved cutting
action ls accomplished with a shear distinguished by a pair
of opposed pivotally-mounted blades~ each having a specific
arcuate curvature along its cutting edge. The cut~ing blades
are each curved tow~rd the other; ~hat is, the blades have
convexly curved edge39 the convexity being toward each other.
In the case of the shear of this inventlon, the included
angle defined between the cutting edges of the blades during
the cutting stro~e is a relatively cons~ant one and ~ignificantly
is maintained at approximately 1? 3.
That angle can be a constant one i.n ~he order of 17
throughout the cutting s~-rnke, or 16, or 18 or comet~ing
else as all~wed by the limitations of the toler~nce. Or the
angle can be an ever increasing one, s~y from 14 or lS in
the pivotal or inboard area to say from 19 or 20 in the
outboard area immediately preceding full blade closure. Or
the angle can be an ever decreasing one, say from 18 or 19
in the inboard area to say from 15 or 16 in the outboard area~
The salient crit:ical feature i8 that the included angle is a
relatively con~t:an~ one approximating 17~ ~ 3.
In our developmental work7 it was recognized that
while to increa~;e the included angle was to increase the
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~8~73
cutting efflciencyi Thi~ was ~o only up to a po;nt; such angle
-- increase also offered the disadvantage that it led to an
extruding of the material when and if a certaill value of
included angle was reached in the absence of course of the
aforemen~ioned serrating or notching feature.
The significant discovery was made that optimum cutting
efficiency as well as work reten~ion c~pabili~y are obtainable
when and ifp in the cutting stroke7 the included angle is
maintained within the all-critical range of 17~ ~ 3 wi~h
that ~ngle remaining con~tant or at least chang;ng only
gradually between the point where the cutting edges irst
contact each other, at stroke initiation7 to the point close
to stroke terminatior~
Should that defined included angle fall bel~w 14,
shearing per~o~mance was seen to deteni~rate rapidly; if
extended above 20, the tendency to ext~ude was seen to
accelerate.
The blades9 at all relative positions9 are deslrably
in contact at the point-contact intersection of their cutting
edges so as to define an included angle which is never less
than 14 or more than 20~
Additional to the desirability for an arcuate curvature
in the cutting edge of each of the blades from pivot to outer
extremity and wherein the lncluded angle defined therebetween
as the cutting ~troke ensues is held within certain limits,
our investigati~e work led us to the further discovery that
optimum results ~re obtained when the total included angle
~efined by the t:wo opposed cutting edges is desirably
between 80 and 120.
If the total included angle is less than 80, the edges
te~d to self distruct. If it exceads 120, the slippage
fe~ture is disadvantageously accelerated.
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In sumrnary7 the scissor~like device may be said to consist
of a pair of pivotally~secured blades and a pair of handles with
a pivotal connaction providing a pivot axis for interconnecting
the ~lades and handles so that the movement of the handles in
closing stroke t~ward and in opening stroke away from e~ch other
generates a corresponding movement of the blades in facial
engagement with each other such that the size of the work-
receiving space is reduced and increased respectively~ same
being singularized by the work engaging edges of the blades each
being of arcuate conf iguration and of cour~e disposed in opposed
facing relationship. In the clo~ing stroke" they offer a work~
receiving-opening defining a relatively constant in~-luded angle
having a value of 17 ~ 3~. The cut ing edge of one blade
will have a combination holding edge and blunt edge, which
preferentially will be in the range of 60 and the cutting
edge of the other blade will preferentially be in the
range of 45O
A certain embodiment of shear, in accordance with
the invention7 will now be described7 b~ way of example~
with reference to the accompanying drawingsg
in which~
Figs. 1 - 3 are views in top plan of a hedge shear
of the invention in an openedg partially
closed, and nearly fully closed positions
respectively;
Fig. 4 is an exaggera~ed sectional view on the
line 4-4 of Fig. l; and
Fig. 5 is a schematic representation showing the
arcuate curvature of the cutting edges of
3~ the blades and the relationship thereof to
lines tangent to the respective lines of
curvature.
2~73
The shear includes an upper blade 10 and a lower blade
12 disposed in the us~al criss-cross relation and pivotally
int rconnected by a pivot bolt 14 or other suit~ble
fastening device, Pxtended, in known manner, at their point
of intersection through strategically-located9 ver~ically~
aligned blade apertures~
A nu~ ~not sh~wn) may be ~hreadedly engaged with the
outboard ~r lower end of ~he pivot holt and a spring washer
of dished form may be sleeved on the pivot bolt to provide
a desired permanent force between the blades. Alternative
pivotal me~n~ are conceivable,
The blades have suita~le handle p~rti~ns 20 and 22
for grasping the ~hear and swinging the respective blades 10
and 12 abou~ ~he pivot means 14 in the cutting functio~.
The blades 10 and 12 will have confron'cable inner
aces 30 and 32 respectively and oppositely facing outer
faces 40 and 42 respec~ively.
The inner faces 30 and 32 upon assembly wlll be disposed
in generally the same plane so that ~hey will slide in facial
engagement when the ~lades are swung about the pivot means.
The desired arcuate configuration of the blade cutting
is generated ma~hematically so as to allow the definition~
cooperantly with the identical arcuate configuration of the
edge of the complemental blade, of an included angle in the
order of 17 ~ 3 at any point of intersection of the
opposed ~lades when plvotally interrelated.
The upper and lower blades have generally-convex
work-engaging cutting edges 15 and 19 respectively, which edges
oppose each other in facing relationship.
In Fig. 5, we have shown a schematic representation
illustrating the arcuate curvature o~ the cutting edges of the
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Z'~3
upper and 1i3wer blades ~d the relationship thereof to
respectiva lines x-x tangent to the respective lines of
curvature. When assembled, the cutting edges are so disposed
that the tangent lines thereo~ bisect each other and are
generally normal to an imaginary line subtending the con~ex
edges of the blades adjacent the pivotally~linked blades.
The work engaging dges in the closing stroke define
an opening having an:included angle of the ~alue of
~7 ~ 3
Upper blade 10 will be provided with a first beveled
so~called "blun~' surace 11 disposed at an angle ~f 45
relative to its outer face 40 and with a second beveled
so-called ~Iholding~ surface 13 disposed at ~n angle of
60 relative to its outer face 40 in the defining of what
is known as the cutting edge 15 of the upper blade.
Lower bl~de 12 is provided with a beveled so-called
"cutting" surface 17 disposed at an angle of 45~ relative
to its ou~er face 42 in the defining of what is known as the
cutting edge 19 of the lower blade.
The beveled surfaces extend ~ver ~he ma30r or shearing
portion of the blade lengths and aGross the blade thicknesses
from their outer faces to their inner faces.
Judicious experimentation showed that the totality of
the bQvels in the case of the confronting cutting edges should
not be less than 80 in value or more than 120 in value.
In the exemplification delineated above, the upper blade
bevel of 60 and the lower blade bevel of 45 offers an ideal
arr~ngement with optimum shearing eficiency and wherein t~e
totaliky Qf the included angle i~ in the order of 105 ~ Various
changes in the angularlzation o~ the respective cutting edges
could conceivably be made 30 long as the totality of the
included angle is not less than 80 or not greater than 120.
1~9~ 73
For example~ typical alternate arrangements could exploit
angles of 40 and 50~ or 45 and 65 , etc. Each offers
an excellent combination of reten~ion means and positive
cutting means and is well within the 80 - 120
parametersO
The holding surface ~f one bl~de provides an effective
retaining means for holding the work against movement along
the longitudinal extent of the blades as their cutting edges
are being brought together for the cutting action~
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