Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates generally to power chain saws and more
particularly, to an anti-kickback device for preventing kickback of the saw. -
Chain saws are in widespread use today both by professional lumber-
men in the forestry industry and by non-professionals, such as homeowners,
farmers, ranchers and the like. Considerable research and expense have been
devoted to improving chain saw performance and durability while minimizing
manufacturing costs and reducing the likelihood of accident. When used pro-
perly, the chain saw is quite safe though situations are encountered during
use of the chain saw which present a danger to the saw operator. In this con- -
nection the largest number of chain saw accidents are caused by the phenomenon
known as "throw" or "kickback" which occurs when the saw chain, while travelling
over the nose section of the guide bar, makes initial contact with an object
whereupon the saw is thrown or kicked back towards the operator exposing him :
to very serious injury depending upon the severity of the kickback and the
preparedness of the saw operator for such an occurrence.
It is well recognized in the industry that the occurrence of kick- -
back presents a common hazard and is one of the major causes of chain saw acci-
dents. This is due partly to the inexperience of many chain saw users so that
even minor kickbacks are hazardous if the saw operator is not prepared. On
2~ the other handJ even very experienced professional chain saw operators who are
keenly aware of the kickback hazard are oftentimes unable to cope with it due
to the unpredictability of its occurrence and the high magnitudo of the kick-
back force.
As a result, considerable research and testing has been carried out
to investigate the causes and frequency of kickback occurrences with the hope
of being able to solve and eliminate this problem. For example, in Sweden the
Safety Counsel National Board of Industrial Safety ordered an investigation to
be carried out by Swedish National Machine Testing to determine, among other
factors, the throw frequency of power saw chains. Swedish National Machine
Testing conducted a series of comparative tests and the results of these tests
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were published on February 6, 1974 in a pamphlet entitled "The Throw Tendency
and Cutting Capacity of Power Sa~ Chains". Earlier tests were also run by the
Swedish Forest Products Research Laboratory to determine the magnitude and
frequency of throw in sawing with chains of various types and these results
were published in 1970 in a Forest Products Research Laboratory Report, Series
B, No. 37. The result in these and other tests show that regardless of the
type saw chain used, there always exists the danger of kickback if the saw
chain, while running along the upper part of the nose section of the guide bar,
is brought into contaet with an object.
Various measures have been taken in an attempt to alleviate the
dangers of kickback, though to date, none have eliminated kickback from occurr-
ing. One early approach was to attach a safety guard to the chain saw housing
so as to prevent the upper run of the saw chain from contacting the saw opera-
tor in the event o~ kickback. Safety guards of this type are disadvantageous
primarily in that they do not prevent kickback but rather endeavor to minimize
the resulting danger ~Yhen kickback occurs. Another disadvantage is that safety
guards add additional weight to the chain saw and oftentimes obstruct the view
of the chain saw operator and interfere with the cutting operation.
The introduction of "safety chain" is another measure which has been
taken to cope with the dangers of kickback. Considerable research has been
devoted to devising a type of saw chain which has a reduced tendency to kick-
back and though progress has been made in this area, there has still not been
designed a saw chain which is incapable of kickback during use. The major
disadvantage of the so-called "safety chain" is that the design changes made
to the saw chain to limit kickback detrimentally affect the cutting performance
of the chain. Another drawback is that the kickback tendency of a saw chain
is dependent upon numerous properties of the chain, such as form, set, condi-
tion, filing angle, sharpness, degree of wear and saw chain tension so that
variations in any one of these factors will affect the kickback tendency of
3Q the chain saw.
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Another measure taken to cope with the problem of kickback has been
the advent of the chain 6rake. Chain brake mechanisms are normally built into
the chain saw housing and respond to movement of the chain saw during kickback
so as to automatically and rapidly decelerate and stop movement of the saw
chain before it strikes the saw operator. Chain brakes normally require a
stopping time on the order of 100 milliseconds to be effective. The chain
brake mechanisms currently available are generally effective when the chain
saw is new. However, after a short period of use in the field, the mechanism ~ -
becomes fouled with oil, sawdust and other debris thereby increasing the stopp-
ing time to a point where it is too long to be effective. Also, during ex-
tended use of the chain saw, the chain brake mechanism frequently becomes
corroded and rusted and therefore becomes even less effective. Another draw-
back o chain brakes is that the saw operator assumes the chain brake will
automatically safely stop the saw chain in the event of kickback thereby free-
ing and relieving him of danger and consequently the saw operator tends to
become less careful than he otherwise might be. Unfortunately, the chain brake
only stops the travel of the saw chain and has no affect upon the forceful
kickback of the chain saw which can still cause serious harm to the saw opera-
tor. In addition, chain brakes become progressively less effective during use
of the chain saw and there are no practical means by which the saw operator
can periodically test the perormance of the chain brake. A further drawback
of most chain brake mechanisms is that they rely upon a lever or similar device
which is tripped by the saw operator at the initial stage of kickback in order
to actuate the chain brake. However, during some operations, such as making
a elling cut, the operator holds the saw in such a manner as to bypass the
tripping device during kickback thereby rendering the chain brake inefective.
This drawback has been overcome to some extent by the advent of the inertia
chain brake though it still remains a problem with most chain brakes. In some
countries, legislation is under way to make chain brake mechanisms mandatory
3Q on all po~er chain saws and thi~ is undesirable due not only to the ineffective-
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ness of chain brakes in preventing kickback but also because of the addedcost of the chain saw attributed to the chain brake mechanism.
It is therefore a principal objec~ of the present invention to
provide an anti-kickback device which prevents chain saw kickback from
occurring at all as opposed to prior art devices which attempt to control and
compensate for kickback after it occurs.
; Another object of the present invention is to provide an anti-
kickback device which effectively prevents chain saw kickback and which
overcomes the aforementioned drawbacks and disadvantages of the prior art
techniques.
A further object of the present invention is to provide an anti-
kickback device which is inexpensive to manufacture, requires no maintenance,
has a rugged and durable construction, and which is more effective in
preventing injuries due to kickback than prior art devices. The present anti-
kickback device can be removably attached to the guide bar nose section if
desired thereby enabling removal of the devive so that the saw can be used
for boring and other operations which require use of the saw chain while
running over the nose section.
A still further object of the present invention is to provide an
anti-kickback device which is so constructed as to prevent the chain saw
from being pulled out of a cut thereby requiring the saw operator to lift the
saw from the cut thereby preventing leg injuries which might otherwise occur
by pulling the saw out of the cut.
It is a still further object of the present invention to provide an
anti-kickback device which prevents the saw chain during its travel over the
nose section of the guide bar from making contac~ with the ground thereby
enabling objects to be cut while lying lengthwise on the ground.
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According to one aspect of the invention, an anti-kickback device
is attachable to a guide bar of a one-man type portable, hand-held chain saw
for preventing kickback of the saw during use thereof by only one saw
operator and com~rises a platelike member having a connecting portion for
connecting the
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device to one side of the nose section of a guide bar; and a sidewall portion
integral with said connecting portion and having the general configuration of
a circular sector which is dimensioned to extend over a predetermined sector
of the nose section and extend radially outwardly therefrom a distance
greater than the farthest radial extent of a saw chain during its travel over
said nose section so as to prevent the saw chain from making contact with
objects in the region where it travels over said nose section during use of
the chain saw by one saw operator in felling, limbing and bucking trees and
similar sawing operations thereby effectively preventingkickback of the chain
saw; said platelike member being free of any handle or handle-like projection
and being configures so as to be incapable of manual gripping by a second saw
operator during use of the chain saw
According to another aspect of the invention, a guide bar assembly
for a portable, hand-held chain saw of the one-man type comprises a guide
bar having means about its peripheral edge for guiding a saw chain during
use of the guide bar assembly; and kickback preventing means attached to and
extending along the nose section only and not other sections of said guide
bar and operative during use of the chain saw by a sole saw operator in
felling, limbing and bucking trees and similar sawing operations for prevent-
ing the saw chain while running over a predetermined sector of said nose
section from making contact with the object being sawed thereby effectively
preventing kickback of the saw towards the saw operator, said kickback
preventing means being free of any handle or handle-like projections and
being configures so as to be incapable of manual gripping by a second saw
operator during use of the chain saw.
In one preferred embodiment the platelike member terminates in an
inturned lip which is turned inwardly towards the guide bar so as to effect-
ively enclose the saw chain during its travel over the nose section. The
device may be permanently or removably attached to the guide bar. In another
embodiment, two complementary platelike members are attached to opposite
sides of the guide bar and each member may terminate in an inturned lip which
is turned inwardly towards the other inturned lip so as to enclose the saw
chain during its traversal over the nose section. The two platelike members
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may be permanently or removably attached to the guide bar. In thc event the
guide bar is formed of laminated construction, the anti-kickback device may
comprise an extension of the guide bar outer side plates and this construction
can be used whether the anti-kickback device is composed of one or two plate-
like members.
In the drawings, Figure 1 is a perpsective view showing a power
chain saw equipped with an anti-kickback device constructed according to the
principles of the present invention;
Figure 2 is an explanatory diagram useful in explaining the
phenomenon of kickback;
Figure 3 is a side elevational view of one embodiment of chain saw
guide bar equipped with an anti-kickback device according to the present
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invention;
Figure 4 is a cross-sectional view taken along the line 4-4 of
Figure 3;
Figure 5 is a side elevational view of another embodiment of chain
saw guide bar equipped with an anti-kickback device according to the presen~ . :
invention;
Figure 6 is a cross-sectional view taken along the line 6-6 of
Figure 5;
Figure 7 is a side elevational view of another embodiment of chain
saw guide bar equipped with an anti-kickback device according to the present
invention;
Figure 8 is a cross-sectional view taken along the line 8-8 of
Figure 7;
Figure 9 is a side elevational view of a further embodiment of
chain saw guide bar equipped with an anti-kickback device according to the
present invention;
Figure 10 is a cross-sectional view taken along the line 10-10 of
Figure 9;
Figure 11 is a side elevational view of another embodiment of chain : -
saw guide bar equipped with an an~i-kickback device according to the present
invention; and
Figure 12 is a cross-sectional view taken along the line 12-12 of
Figure 11.
One embodiment of a power chain saw equipped with an anti-kickback
device according to the invention is shown by way of example in Figure 1 of
the drawings. The chain saw is of the one-man type and comprises a power
unit including an engine 10 mounted on the chassis of the chain saw and
connected to drive a saw chain 11 running on a guide bar 12. The engine 10
is shown as a single-cylinder internal combustion engine and is of known
construction. A front handle 14 and a rear handle 15 are connected to the
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chassis as shown to enable holding and manipulation of the chain saw by a
sole operator. An anti-kickback device or kickback preventing means 20 is
attached to the nose section of the guide bar 12 and has a radial extent
sufficient to project beyond the outermost radial extent of the saw chain 11
thereby preventing the chain from contacting any object while running over
the nose section,
Before discussing in detail the various embodiments of the invented
anti-kickback device, it will be helpful to discuss the kickback phenomenon
so as to better understand and appreciate the present invention, Figure 2 is
an explanatory diagram showing how kickback forces are developed during use
of a power chain saw, The saw chain and its direction of travel around the
guide bar are represented by a broken arrow and for purposes of explanation,
it is assumed that the saw chain is brought into contact with a stationary
object at the point shown in the drawing, At the instant of contact, the
object applies a reaction force to the saw, the force being applied tangen-
tially to the arcuate path of travel of the saw chain, This reaction force
is referred to as a kick force or kickback force and is represented by a
dashed arrow,
The kick force may be broken down into its horizontal and vertical
components and as seen in Figure 2, the horizontal component is directed
axially along the guide bar and tends to move the chain saw backwardly towards
the saw operator, The vertical component is known as a spin component and
tends to move the chain saw upwardly and spin it about the center of gravity
of the saw, Thus the spin force is the upward force originating at the nose
section of the guide bar and causing the saw to spin around the center of
gravity of the saw and the axial force is that force directed through the
- guide bar in a backward direction along the axis of the bar, It is the
combination of these two forces that cause the chain saw to move upwardly and
backw OEdly towards the saw operator and this type movement of the chain saw
is the phenol~enon known in the art as chain saw "kickback" or "throw". During
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kickback the tremendous kinetic energy possessed by the rotating parts of
the chain saw is abruptly transferred into an upward and backward movement
of the saw towards the saw operator creating an extremely dangerous condition.
Numerous studies have been conducted to determine those factors
principally responsible for kickback and to determine the zone at which
maximum kickback occurs, It is generally recognized that the zone of maximum
kickback occurs between 10 and 40 above the centerline of the guide bar
nose section and this area has been represented by cross-hatching in Figure 2
and identified as the kick area. Throughout this disclosure, all references
to kickback or throw pertain to reactions occurring at the nose section of
the guide bar. The kickback phenomenon is to be distinguished from other
reactions and in particular, those reactions caused when the upper or lower
run of the saw chain is brought into contact with an object. When the upper
run of the saw chain is brought into contact with an object, this condition
is known as undercutting and the reaction force is directed axially back-
wardly towards the saw operator and this condition is not too dangerous in
that there is no vertical or spin component so that the only movement of the
chain saw is backwardly towards the operator, In a similar manner, when the
lower run of the saw chain is brought into contact with an object, the
reaction force is applied axially forwardly so that the chain saw is urged
forwardly towards the object and this is the customary manner in which chain
saws are used.
An outline of the anti-kickback device 20 is superposed on the
guide bar shown in Figure 2 from which it can be readily seen that the device
effectively eliminates and prevents kickback in that it prevents contact of
the saw chain with the object while the chain is travelling over the nose
section of the guide bar, As maximum kickback occurs in the region from 10
to 40 above the centerline of the guide bar, the anti-kickback device can be
formed with an included angle of 90 thereby preventing kickback within a
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~egion 45 above and below the guide bar centerline. The preferred included
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angle is between 90 and 120 though if desirable, the included angle can be
as much as 180 . Most guide bars are designed so as to have no distinct top
or bottom thereby enabling the bars to be connected in a reverse manner to
the saw chassisso that the top in one orientation becomes the bottom in the ~ -~
reverse orientation This enables the guide bar to be reversed after an
extended period of use so that the worn bottom edge can be positioned as ~he
top edge and the relatively unworn top edge becomes the bottom edge thereby
extending the useful life of the guide bar. For this reason, the included
angle extends equally above and below the centerline so that the device is
effective regardless of the orientation of the guide bar. From the foregoing,
it can be appreciated that the anti-kickback device of the invention completely
prevents kickback irrespective of the speed at which the saw chain is
travelling and regardless of the angle relative to the centerline at which
the object makes contact with the nose section. Unlike the prior art devices
which attempt to minimize the effects of kickback once it occurs, the anti-
kickback device according to the invention prevents the occurrence of kick-
back and is therefore superior.
One embodiment of anti-kickback device will now be described in
detail with reference to Figures 3 and 4. The anti-kickback device or kick-
back preventing means 20 comprises a generally platelike member having a
sidewall portion 21 which is in the form of a sector of a circle, and a
connecting portion 22 for connecting the device to a chain saw guide bar, The
sidewall portion 21 has two radial edges 23 and 24 which lie along radial
lines of the sector, as indicated by dashed lines in Figure 3. The included
angle between the radial edges 23 and 24 is preferab]y within the range of
from 90 to 120 thereby adequately preventing kickback throughout the
region where kickback would otherwise occur. If desired, the included angle
could be increased up to 180. The sidewall portion 21 has a circumferential
edge 25 which interconnects the outermost tips of the radial edges 23 and 24.
As depicted in Figures 3 and 4, the anti-kickback device 20 is
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shown attached to a guide bar of laminated construction and it is, of cou-se,
understood that the device may be attached to and is equally applicable with
guide bars of solid construction. As well known in the art, guide bars may
be of either solid or laminated construction and a solid guide bar is
typically formed of a single steel plate the peripheral edge of which is
machined to provide a peripheral groove for guiding the saw chain. A
laminated guide bar may be formed of three steel plates the combined thickness
of which is equal to the thickness of the desired guide bar and in this case,
the two outer plates are of like size and shape while the middle plate which
is sandwiched between the two outer plates is of similar shape but smaller
size so that when the plates are assembled, the peripheral edge of the center
plate is spaced inwardly from the peripheral edges of the two outer plates
thereby providing a peripheral groove for guiding the saw chain.
In the laminated guide bar construction shown, a sprocket wheel or
nose roller is rotatably mounted at the guide bar nose section between the
two outboard plates of the guide bar and as indicated by dashed lines, the
middle plate is shortened so as to leave room for housing the sprocket wheel.
Such sprocket wheels are well known in the art and are provided to assist in
guiding the saw chain around the curved nose section thereby reducing friction
and chain stress and prolonging the life of the guide bar and saw chain.
In accordance with one aspect of the invention, the anti-kickback
device 20 may be either permanently or removably attached to the guide bar
nose section and in either case, the device is rigidly colmected to and
immovable with respect to the guide bar. In the embodiment shown in Figures
3 and 4, the device is permanently at~ached. The attaching means comprises
four rivets which, in this case, are the same rivets used to mount the
sprocket wheel on the guide bar. The rivets are inserted through holes in the
connecting portion 22 and in this manner, the anti-kickback device 20 is
permanently attached to the guide bar nose section. The permanent attachment
is the preferred construction in that it prevents removal of the device by the
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saw operator thereby ensuring that the anti-kickback device will be attached
to the chain saw whenever the saw is used. However, in some applications it
may be desirable to remove the anti-kickback device and, for example, the
professional lumbermen may wish to remove the device so that the nose section
of the saw chain can be used for boring. To this end, it may be practical in
some situations to removably attach the device.
According to another aspect of the invention, and as best seen in
Figure 4, that part of the sidewall portion 21 which extends beyond the guide
bar nose section is flared outwardly so as to accommodate the saw chain ll
and to provide sufficient clearance so as not to interfere with the cutting
operation of the chain saw. The flared section may be formed by bending the
platelike member outwardly to form a flared wall part 21a followed by a
further radially extending flat wall part 21b which extends beyond the outer-
most tip of the saw chain. The marginal edge of the wall part 21b is bent
inwardly to form an inturned wall part in the form of an inturned lip 21c.
The wall parts 21a-21c of the sidewall portion 21 define an annular cavity
for receiving and accommodating the saw chain. During normal use of the saw,
it is improbable that an object capable of causing kickback will come into
contact with the saw chain from the side as opposed to head-on. Therefore it
is normally not necessary to completely enclose the saw chain in order to
prevent kickback so that the annular cavity can be left open on one side. It
is important, however, that the sidewall portion 21 extend radially at least
farther than the outermost extension of the saw chain during its traversal
over the nose section so that if the saw operator attempts to move the nose
section of the guide bar into contact with an object, the end of the sidewall
portion 21 will abut the object and prevent contact between the object and
saw chain.
One advantage of this embodiment is that the anti-kickback device
is formed as a one-piece, unitary construction thereby simplifying its
3Q manufacture and attachment to the guide bar. Moreover, in view of the fact
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the anti-kickback device does not completely enclose the nose section of the
guide bar, the saw chain may be easily replaced without the necessity of re-
moving the device. In all embodiments, the anti-kickback device is formed of -:
lightweight material such as solid or perforated steel plate, plastic, aluminum
or other materials having similar strength so as not to unduly increase the
weight of the saw.
Another embodiment of anti-kickback device is shown in Figures 5 and
6 and in this embodiment, the device is shown attached to a guide bar of solid
construction. The anti-kickback device or kickback preventing means 30 com-
prises two complementary sections 31 and 32 which are respectively attached to
opposite sides of the guide bar nose section. The section 31 has a sidewall
portion 33 and a connecting portion 35, both portions being integral and pre-
ferably formed from the same piece of platelike stock. The sidewall portion
33 has a flared wall part 33a which has a curvature similar to and overlies
that of the curved nose section. The flared wall part 33a terminates in and
~; is connected to a flat wall part 33b which is integral with an inturned wall
part or lip 33c. In like manner, the other section 32 has a sidewall portion
34 connected to a connecting portion 36 and the sidewall portion includes a
flared wall part 34a, a flat wall part 34b and an inturned wall part 34c.
In this embodiment, the two sections 31 and 32 are removably attached
to the guide bar nose section by a set of nuts and bolts. As shown, two thread-
ed bolts 37 extend through openings in both sections as well as through holes
in the guide bar and the sections are secured in place by lock washers 38 and
nuts 39 which are threaded on the ends of the bolts. Though a nut-and-bolt
connection has been shown for purposes of explanation, it is understood that
any equivalent connecting or attaching means can be employed to removably con-
nect or attach the anti-kickback device to the guide bar. It is also under-
stood that the device may be removably connected to a laminated guide bar in
the same fashion.
3Q As best seen in Figure 6, the anti-kickback device or kickback
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preventing means 30~ when attached to the guide bar nose section, defines an
annular cavity which substantially encloses the saw chain during its
traversal around the nose section. Sufficient clearance is provided so that
the device does not interfere with the travel of the saw chain and in this
embodiment, the radial extent of the two sidewall portions 33 and 34 together
with their inturned lips 33c and 34c effectively prevent the saw chain from
making contact with any object while it is travelling over the guide bar nose
section Thus kickback of the chain saw cannot occur when the saw is equipped
with the anti-kickback device.
If desired, the anti-kickback device 30 can be quickly removed by
simply unthreading the nuts 39 and withdrawing the threaded bolts 37
Because in this embodiment the saw chain is completely encased by the anti-
kickback device, it is necessary to have the device removable to enable
replacement of the saw chain.
Figures 7 and 8 show another embodiment of anti-kickback device
constructed according to the invention and in this embodiment, the anti-
kickback device or kickback preventing means 40 is shown permanently attached
to a guide bar of laminated construction. In other respects, the device 40
is similar to that shown in Figures 5 and 6 with the exception that the
device 40 omits the inturned wall parts or lips which exist in the other
embodiment. More particularly, the device 40 includes two complementary
sections 41 and 42, each section having respective sidewall portions 43 and
44 and connecting portions 45 and 46 and further details thereof will not be
given as they correspond to those shown in Figures 5 and 6. The device 40
is permanently attached to the laminated guide bar by means of rivets which
are used to mount the sprocket wheel.
According to this embodiment, the outer peripheral edge of each
section 41 and 42 contains no inturned lip so that each sidewall portion
comprises a simple circular sector of stepped configuration. Moreover, the
spacing bet~een the two sections 41 and 42 is close enough so that it is
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extremely unlikely an object capable of causing kickback can be inserted
therebetween during use of the saw. Thus it is not necessary to inturn the
peripheral edges of the sections 41 and 42 in order to prevent kickback and
all that is necessary is to space the two sections sufficientlya part so as to
avoid interference with the saw chain and to extend the two sections radially
beyond the farthest radial extent of the saw chain during its traversal over
the nose section.
A further embodiment of the invention is shown in Figures 9 and 10
and in this embodiment, the anti-kickback device or kickback preventing means
50 is formed as an extension of the guide bar side plates. This form of the
invention is suitable only for guide bars of laminated construction as the
guide bars of solid construction do not contain separate side plates. As
seen in Figures 9 and 10, the two outer side plates are formed with extensions
which are shaped into and form the anti-kickback device 50. The left outer
side plate 51 is formed with an extension 52, the extension having a flared
wall part 52a and a flat wall part 52b. In like manner, the right outer
side plate 54 is formed with an extension 55 which includes a flared wall
part 55a and a flat wall part 55b. The flared parts 52a and 55a are flared
outwardly a sufficient amount to accommodate the width of the saw chain and
the flat wall parts 52b and 55b have sufficient radial extent to prevent the
saw chain from striking an object while travelling over the guide bar nose
section. Thus the anti-kickback device 50 is permanently attached to and
forms part of the guide bar itself and no additional parts are needed.
In this embodiment, the peripheral edges of the guide bar extensions
are not inturned thereby enabling ready removal and replacement of the saw
chain. If desired, one of the two flat wall parts 52b or 55b can be inturned
or both can be inturned a small amount so long as sufficient clearance exists
to enable removal of the saw chain. As explained hereinabove, it is
unnecessary to turn in the edges in order to prevent kickback during normal
use of the saw as it is extremely unlikely an object capable of causing kick-
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back can fit between the two extensions 52 and 55.
A further embodiment of anti~kickback device according to the
invention is shown in Figures 11 and 12 and in this embodiment, the anti-
kickback device or kickback preventing means 60 is formed as an extension of
only one of the outer side plates of the laminated guide bar As shown, the
right outer side plate 61 is provided with an extension 62 which is configured
into the anti-kickback device 60. The extension 62 has a flared wall part
62a which flares outwardly from the guide bar and terminates in a flat wall
part 62b which has a radial extent greater than that of the saw chain. An
inturned wall part or lip 62c is connected to the flat wall part 62b and the
wall parts 62a, 62b and 62c define an annular cavity for accommodating the
saw chain. By such a construction, the anti-kickback device 60 effectively
prevents the saw chain from being brought into contact with an object while
travelling over the nose section.
In all of the embodiments, the anti-kickback device extends over a
predetermined angular sector of the nose section and extends radially out-
wardly of the nose section an amount greater than the radial extent of the
saw chain thereby preventing the saw chain from striking an object during its
traversal around the predetermined sector of the nose section In this
manner, kickback of the chain saw cannot occur since in the region where
kickback could occur, the anti-kickback device prevents the saw chain from
being brought into contact with the object. Consequently, during use of a
chain saw equipped with the anti-kickback device of the invention, it is not
possible for the saw operator to create a kickback condition since the
operator cannot bring the saw chain, while travelling over the nose section,
into contact with an object due to the presence of the anti-kickback device.
The anti-kickback device also has other secondary advantages aside
from preventing kickback For example, if during the course of cutting a
log or like object the saw becomes pinched in the log, the saw operator can-
not pull the chain saw backwardly out of the cut due to the presence of the
lO~iS~32
anti-kickback device attached to the guide bar. Instead, the operator must
lift the saw out and this is advantageous in that it prevents leg injuries
which might otherwise occur if the chain saw is pulled out of the cut while
running. Another advantage is that the anti-kickback device effectively
prevents the nose section of the guide bar from contacting the ground. It is
known that dirt and other debris cause rapid dulling of the cutting edges of
the saw chain and that such invariably happens when the saw operator cuts
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objects whichare lying on the ground, A chain saw equipped with the anti-
kickback device prevents the chain from striking the ground while travelling
over the nose section thereby eliminating one of the chief causes of chain
saw dulling,
The various features and advantages of the present invention have
been described with reference to preferred embodiments thereof and obvious
changes and modifications thereto will be apparent to those of ordinary skill
in the art and the present invention is intended to cover all such obvious
changes and modifications which fall within the spirit and scope of the
invention as defined in the appended claims.
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