Note: Descriptions are shown in the official language in which they were submitted.
)829
FIELD OF T~IE INVENT~ON
This invention relates to chain saws and more particularly to a new
and improved cutting attachment for use therewith.
BACKGROUND OF THE INVENTION
Conventional chain saws are equipped witll a guide bar having a
rounded nose portion at its outer end. The nose portion may be provided
with an idler sprocket, or roller nose or the chain may run on a
sprocketless but generally hardened nose portion. A groove e~tends along
the edge of the bar, and drive links of the saw chain run in the groove.
The conventional saw chain itself consists of centered drive links joined
by rivets to cutter links, balancing links and tie links, with cutter
links positioned alternatively on opposite sides of the chain. A
balancing link, which may be identical with the tie links is positioned
opposite each cutter link. The drive links run in the groove in the guide
bar, and in turn are driven by a sprocket or ring molmted on the power
take off shaft of a gasoline engine, or other power unit. In order to
reduce the overall weight of the chain saw, two stroke engines operating
at speeds up to fourteen thousand (14,000) RPM are used to drive the
chain. A centrifugal clutch is conventionally included in the saw to
disengage the drive to the chain below a predetermined speed, so that the
saw when idling has a stationary chain. The chain is generally intended
to be run at a lineal speed of 3000 to 4000 feet per minute, and with
approximately eight cutters per foot, each designed to cut approximately
25 thousands of an inch deep. Thus extremely high cutting rates are
obtained with a light weight portable tool.
In normal use, cuts are made with a chain saw by placing the lower
edge of the guide bar on the material to be cut, and as the chain travels
around the bar, each tooth contacts the material and removes a chip or
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chips with each pass througll the saw kerf. The shape and size of the
chips is dependent on many factors including the shape of the cutter, the
height of the depth gauge, the grain of the material, and many other
factors.
Other types of cuts may also be made with a chain saw. Frequently
during limbing of a felled tree, the upper edge of the guide bar is
applied from beneath a limb and the guide bar is urged upwardly to sever
the limb. Boring cuts are also made by pressing the nose of the guide bar
against the material being cut.
It will be appreciated that the speed and power of a modern light
weight chain saw, also creates a potential ha~ard due to accidental or
careless operation of this tool. What is not widely recognized either by
chain saw manufacturers or users, is that seemingly smal] differences in
the design of the cutting attachment can turn a tool referred to as a
"motorized widowmaker" into a safe, dependable, implement.
Aside from careless handling, which can always be fatal, the next
greatest hazard is "kickback".
A kickback is a phenomena which occurs when a cutter of the chain
rounding the nose of the bar strikes an object and the momentum of the
;20 chain is converted into a force, creating a couple around the handle of
the chain saw, causing the chain saw to rotate instead of the chain to
translate. This is analogous to the type of couple created when a load is
hitched too high on a farm tractor, causing the tractor to overturn
backward on top of its driver, instead of drawing the load.
Kickbacks can occur during limbing, buried nose cutting and boring
operations, and result too frequently in the moving saw chain coming in
contact with the head or upper body of the operator. Grievous wounds are
caused which are frequently fatal, and if not, require sophisticated
llZ08Z9
surgical intervention. Plastic surgeons are generally required to repair
such wounds.
The present invention is directed to the improvement in the safety,
versatiLity and efficiency of cutting attachments for chain saws. These
improvements overcome the defects of known prior art cutting attachments
both in cutting efficiency, versatility, safety, and from the users
standpoint, longevity, both of himself and his machine.
The chain saw industry has devoted much time and effort to solve
the problem of kickbacks. One such attempt is the chain brake. This is a
device which is intended to stop the chain if a kickback occurs, and
hopefully before the chain strikes the operator. Chain brakes do not
work! Bloodless corpses have been found in the woods beside an idling
chain saw, and the chain brake was on!
Other attempts to solve the kickback problem have included sprocket
guide bar noses, specially shaped depth gauges, safety links, asymmetrical
guide bars, the so called "banana bar", and others. Possibly the greatest
prior art step in the right direction is the work of Curtis L. Graverson
~ of Milwakie, Oregon, the inventor of the low profile saw chain, for which
'~ he was granted United States Patent No. 3,929,049 on December 30, 1975.
Graverson was concerned with the problem of kickback as may be seen for
example at column 2 line 17 et seq of the above patent.
Because of the risk of kickback, boring operations are difficult
and ha~ardous. It has been found that the portion of the saw chain
entering the cut, during boring operations, becomes slack and the cutters
tend to tilt upwardly on the guide bar, resulting in excessive cut and
vibration. "~ifting" of the chain off the bar as it is carried around the
' nose by means of an idler sprocket imposes severe wedging loads on both
the drive links and the rivets, stretching and loosening the chain, while
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829
lowering of the chain back on to the bar, after passing around the nose,
causes hammering, impactation, wear, and vibration. Further, the cutters
are poorly supported in a relatively unstable condition when the chain is
lifted clear of the bar as contact is only made via the sprocket teeth
insertecl between two pivoting rivets and the drive links in the groove of
the bar.
The contact with the drive links is generally unbalanced because of
the sawdust cleaning feature provided therein, and these factors further
contribute to the hazardous kickback condition. Furthermore, the idler
sprocket teeth tend to jam the chain with wood chips propelled to it by
the chip cleaning device on the drive link. This forces the operator to
work with a loose chain.
Secondary (grease gun) lubrication of the sprocket at the nose
portion of the bar is relatively difficult and further contributes to the
wear problem. It should be appreciated that uninterrupted and effective
lubrication of the saw chain as it slides around the guide bar is by far
the major contributor to control chain wear and kickback.
OBJECTS OF THE INVENTION
~; It is an object of the present invention to provide a cutting
attachment which substantially reduces the risk of kickback, and which has
a substantially increased life.
It is also an ob~ect of the invention to improve the lubrication of
the saw chain and guide bar to decrease wear and improve operation.
It is a further object of the invention to improve the cutting
efficiency and versatility of a chain saw by controlling the flow of chips
from the saw chain, and preventing chips from re-entering the kerf
entrained in the chain, and to keep the guide bar groove and interstices
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~'Z~)8:29
of the chain from beoming clogged with power robbing build up of chips
absorbing oil.
It is a further object of the invention to provide a cutting
attachment which requires less frequent maintenance.
SUMMARY OF T~IE INVENTION
These and other objects of this invention are achieved by providing
a cutting attachment for a chain saw, said attachment comprising a saw
chain, a guide bar and a drive sprocket. The guide bar is provided with a
generally elongated symmetrical shape; both long edges are curved
outwardly away from each other, and have a relatively large radius of
curvature, as defined hereinafter. The nose of the guide bar has a
relatively small radius of curvature as discussed below. The groove in
the guide bar is of substantially the same depth as the depth to which the
drive links extend below the edges of the guide bar. An oil injection
hole is positioned in the bottom of the groove and connects to an oil
passage which is directed in the direction of travel of the chain. The
chain is a chisel or semi-chisel low profile type chain, having an equal
number of left and right hand cutters, and with the lower edge of each
link modified to run continuously against the rails of the guide bar. The
~20 drive sprocket and the guide bar are adapted to be mounted on the chain
saw powerhead so that the chain passes around the drive sprocket on a path
complimentary to the path around the nose of the guide bar. Whether the
drive sprocket is of large of small diameter, it is essential that the top
; of each tooth of the sprocket have the same radius of curvature as the
guide bar nose. That is, the top of each sprocket tooth is a circular
segment of the same radius as the nose.
The radius of curvature of the guide bar upper and lower edges
(rails) is chosen so that at the design operating linear velocity of the
08Z9
chain, the curved path of the chain causes the centrifugal force exerted
on the chain, the oil entrained with the chain, and the cuttings to be
such that the guide bar is continuously lubricated, and the groove in the
bar is also maintained free of cuttings.
The radius of curvature of the guide bar nose, and correspondingly
the drive sprocket tooth top radius is chosen to ensure that for the pitch
of the chain, that not more than one cutter is at any time within an arc
of approximately 70 on either side o~ the longitudinal axis of symmetry
of the guide bar. This is achieved when the nose radius is approximately
twice the chain pitch. The minimum practical pitch is 3/8 in.
The lower edges of the cutter links and the balancing links are
provided with a pair of curved surfaces. The first curved surface extends
from end to end of the link and has a curvature not less tllan the
curvature of the upper and lower edges of the guide bar. The second
curved surface is centrally positioned on the link and interrupts the
first curved surface. The curvature of the second curved surface is
choosen to match the curvature of the guide bar nose. On the tie links,
; only the second curved surface is provided. Thus the links of the chain
maintain a maximum effective surface-to-surface contact with the rails of
~20 the guide bar. 8ecause of this the temperature of the chain, which
normally runs much higher than the bar, is held similar to the bar
temperature, since a high rate of heat transfer from the chain to the bar
is obtained. Because the chain and bar are at closely similar
,
temperatures the chain does not tend to elongate and sag during use.
The cutter links of the chain are preferably so proportioned that
the height of the cutting edge above the lower edge of the link is not
more than approximately 50% of the distance between the ends of the cutter
link.
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I)ESCRIPTION OF THE DRAWINGS
~ .
The invention will be described in more detail hereinafter with
reference to the accompanying drawings in which:
Fig. 1 is a side elevation of a chain saw carrying a cutting
attachment in accordance with the present invention;
Fig. 2 is a similar view partly broken away of the proximal end of
the cutter attachment illustrating the drive sprocket;
Fig. 3 is a plan view of a portion of chain on the cutter bar in
accordance with the present invention;
Fig. 4 is a side elevation of the chain of Fig. 3;
Fig. 5 is a view partly broken away showing the outer end of the
cutter attachment of Fig. l;
Fig. 6 is a side view of a balancing link, or tie link, constructed
in accordance with the invention;
Fig. 7 is a side view of a cutter link in accordance with the
present invention;
Fig. 8 is a side view partly broken away illustrating the
construction of the guide bar of the present invention;
Fig. 9 is a view illustrating schematically the forces operating on
a cutter on the long edge of the guide bar;
Fig. 10 is a figure similar to Fig. 9 illustrating the forces
acting on a cutter link as it is carried around the nose of the guide bar;
Fig. ll is a graph illustrating reduction o~ kickback energy using
the cutter attachment of the present invention;
Fig. 12 is graph similar to Fig. 11 at a higher approach velocity.
Fig. 13 is a side view of a modified tie strap;
Fig. 14 is a side view of a modified extended cutter of the present
invention;
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11~08;~9
Fig. 15 is a side view o a modified balancing link for the cutter
Of Fig. 14, and
Fig. 16 is a side view of a modified drive link of the present
invention.
DETAILED DESCRIPTION OF T~IE DRAWINGS
Referring to Fig. 1 of the drawings, there is shown a chain saw 10
consisting of a power head 11 and a cutting attachment 12. Conventionally
the power head 11 is provided with a control throttle 13 for controlling
the speed of the motor which is normally a two stroke gasoline engine.
Such engines have the virtue of a large power output for a small size and
are relatively light in weight when made of the usual aluminum and
magnesium alloys.
The cutting attachment of the present invention as illustrated in
Fig. 1 consists of a guide bar 14, a saw chain 15, and a drive sprocket,
not shown. In accordance with the present invention, the guide bar 14 has
upper and lower edges or rails 16, and 17 symmetrically convexly curved
about the longitudinal axis of the bar and with a sharply reduced
curvature of the nose portion 18.
As illustrated in Fig. 2, the chain 15 of the cutting attachment is
~driven by a drive sprocket 19 mounted to the shaft of the power head 11.
~20 The power head 11 is also provided with an oil dispensing mechanism, not
shown, which consists of an oil reservoir and a pump for supplying oil to
the cutting attachment. Details of the oil supply in the cutting
attachment will be provided below.
:
Fig. 3 is a plan view of the cutting attachment of Fig. 2 showing
the saw chain 15, and showing partly broken away the upper rails of the
guide bar 14. As illustrated in Fig. 4 the chain 15 is provided with a
series of drive links 20 connected by rivets to tie straps 22 balancing
)829
links 21 and cutter links 23. Each of the bala~cing and tle links 22 and
each of tlle cutLer links 23 is provlded with a lower surface 27 which is
in sliding contact with the guide bar rails. The drive links run in the
groove of the guide bar and contact the sprocket 19 to propel the chain.
The lower surface 27 of the balancing links 22 and cutter links 23 is
specially shaped to conform with the shape of the guide bar as the chain
moves around the rails of the guide bar, and will be discussed in more
detail in relation to Fig. 6 and 7 of the drawings.
Referring again to Fig. 4, it should be noted that the upper
surfaces of the balancing or tie links 22, may of course be completely
flat, or for the sake of manufacturing convenience these links may be so
formed that both the upper and lower surfaces of the balancing or tie
links are similarly shaped. Also with respect to the drive links, these
are shown as having a symmetrical shape, although the prior art drive
links such as for example shown in Graverson U.S. Patent No. 3,929,049 are
provided with a notch the function of which is to scoop chips from the
slot of the guide bar. There is no necessity for such a notch in the
drive link in accordance with the present invention since chips do not
tend to collect in the slot.
Referring to Fig. 5, there is shown a portion of the cutting
attachment of the present invention illustrating the nose of the guide bar
18, around which the chain 15 travels. It will be noted that the groove
1~ .
in the guide bar ~ is of a depth corresponding exactly with the depth of
the drive links 20 below the upper and lower rails of the guide bar. A
significant feature of the invention that may be noted at the nose 18 of
the guide bar is that the curvature of the portion 27 of the cutter links,
balancing links and tie links conforms exactly to the radius of the nose
18 and that the chain links maintain continuous contact with the rails of
11~0829
the bar 18 as they traverse around the rails of the bar. A second feature
of the invention may also be noted in that as illustrated in Fig. 5, there
is only one cutter link 23 located at the critical nose portion of the bar
18 at any one time. It should also be noted that because of the shape of
the cutter, that is the long curved depth gauge, and the heel, the
effective depth of cut of the cutter is substantially reduced as the
cutter moves around the nose of the bar. This reduced "bite" of the
cutter substantially reduces the reaction force that the chain can
generate, and as a result a kickback cannot occur. Moreover, I believe
that if not more than one cutter is within a zone of approximately 70
either side of the longitudinal axis of the guide bar at the nose portion
at any one time, that tlle likelihood of uncontrolled kickback is virtually
totally removed. This is achieved when the nose radius is approximately
twice the chain pitch, and the length of the cutters is approximately 1
and 1/2 to 2 times height of the cutters above the rails.
The critical dimensions of the cutter links of the present
invention are more clearly illustrated in Figs. 6 and 7. Fig. 6
illustrates a balancing link 22 of the invention which has a shape closely
resembling the side link of Graverson U.S. Patent No. 3,929,049, with
;20 critical differences. As usual the balancing link 22 is provided with a
pair of rivet holes 30 and 31 through which rivets are intended to be
inserted in order to connect the side links with the drive links 20 of the
chain. This is all in accordance with the well known techniques of the
prior art.
In accordance with my invention the lower surface 27 of the
balancing link is provided with a pair of surfaces the first being the
surface 33 which is interrupted by the surface of higher curvature 34.
With reference to Fig. 5 of the drawing, it will be seen that the surfaces
33 maintain intimate contact with the upper and lower rails 16 and 17 of
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11~08Z9~
the guide bar 14 and that tlle surface 34 maintains intimate contact with
the raiLs at the guide bar nose 18 as the link i9 dra~ around the nose 18
during operation. Similarly with the cutter 23, the lower surface 27 i5
provided ~ith curved surfaces 33 and 34. The cutter 23 of Fig. 7 will
also be seen to have the usual configuration of a chisel or semi-chisel
cutter, being provided with a depth gauge 35 and a cutting edge 36 which
is sharpened in the usual way to maintain the efficiency of cutting. It
may be noted that the portion 34 having the radius of curvature
corresponding to the nose 18 of the guide bar 16, subtends approximately
an angle of 30 to 40, and it has been found that the minimum angle
subtended by the area 34 in both the cutter and in the balancing and tie
links should be not less than 30 in order for stable operation of the
cutter to occur around the nose of the guide bar. The most critical part
of the rail for maintaining lubrication is at the nose. If there is only
a small area of link-to-rail contact at the nose, the lubricating film
will break down and extreme heating and wear will occur. The nose of the
bar will be greatly overheated and annealed, resulting in excessive wear
and destruction of the bar. It is thus extremely critical to prevent
metal-to-metal contact and heating. Indeed it is more important to
~20 provide a long link to rail contact at the nose than at the any other part
of the rails.
It should be noted that as illustrated in Fig. 7 the height of the
cutter, Reference A, in relation to the length of the cutter, Reference B,
should be in a ratio of approximately 1:1.6, and possibly as great as
l:2. In this regard it has been found by the applicant that the chain
disclosed in Graverson U.S. Patent Wo. 3,929,049 may be modified, in
accordance with the present invention to provide the dimensions specified
in relation to Figs. 6 and 7. In particular, by altering the lower
l:lZV8Z9
portion of the side Links and cutter links oE ~raverson, to provide the
curved surfaces 33 and 34, it is possible to produce a chain which meets
the requirements of the present invention. This modified chain
possesses vastly superior properties when combined with the guide bar of
the present invention to provide a cutting attachment which overcomes all
of the problems associated with prior art devices.
Fig. 8 illustrates a segment of the guide bar 14 of the present
invention constructed in accordance with the applicant's teachings. In
particular, the bar consists of the usual upper and lower rails 16 and 17,
the bar being symmetrical about its longitudinal axis. As will be
apparent to those skilled in the art, one of the virtues of having a
symmetrical bar is that it may be mounted to the saw with either edge
upward, and provided appropriate oiling connections are made to the power
head of the saw, adequate oiling of the chain will occur. In this regard,
the present invention provides a novel and improved oil system for the
guide bar of a chain saw cutting attachment which substantially improves
the operation of the chain saw, thereby significantly reducing wear on the
components, the generation of heat during operation particularly in the
critical nose portion of the guide bar, and thereby improving the
longevity of the chain, and other benefits as noted above.
One might wonder what relevance there is in the way a chain is
lubricated as it travels around the guide bar to the problems of cutting
efficiency and kickback. Everyone appreciates the necessity for oiling a
chain. Up to now however, no one has appreciated the possibility of
maintaining continuous, positive lubrication around the entire guide bar,
and the benefits of being able to run the chain in continuous sliding
contact with the bar. Unless the chain/bar interface is continuously
separated by a layer of lubricant overheating and annealing of the chain
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11i~0829
and bar occurs. To avoid ehis, it is common to run the chain with slack
in it, and to file down the depth gauges to achieve a satisfactory cutting
rate. This is a very dangerous practice, since it greatly increases the
chance of a kickback occurring.
In the absence of continuous positive lubrication, the chain
temperature rises faster and to a higher temperature than the bar.
Therefore the chain will expand more rapidly than the bar, causing slack
in the chain, and permitting the cutters to rear up, or tilt around the
nose of the bar, causing a kickback.
I have discovered that the chain can be rlm in sliding contact with
the rails of the guide bar, even around the nose, by ~ollowing the
procedures set out below. The edge of the guide bar 14 is provided with a
groove 28 in which the drive links 20 of the chain 15 slide. In
accordance with the invention the depth of the groove 28 is made to
correspond exactly with the depth of the drive links 20 so that there is a
~ero clearance between the bottoms of the drive links 20 and the bottom 41
of the groove 28. By ensuring that there is zero clearance between the
bottom of the drive links 20 and the bottom of the groove 41, the
applicant ensures that all oil which enters the groove 28 is propelled
~20 around the slot by the drive links 20. In accordance with a further
feature of the invention, the oil from the chain saw is injected into the
groove 28 through a passageway 42 which terminates at the bottom 41 of the
groove 28. The passageway 42 communicates between the bottom 41 of the
groove 28 and a small blind hole 43 bored into one face of the guide bar
; 14, but not completly through the bar. Thus by providing a blind hole 43,
with the passage 42 communicating therebetween and fhe bottom surface 41
of the guide bar groove 40, oil is directly injected in a jet through the
passageway 42 into the groove 28. Because the passage 42 is the same
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11;~0829
diameter as the width of the groove, for e~ample approximately
fifty-thousandths of an inch, and because the passaKeway 42 is angled in
the direction of motion of the chain, the oi]ing passages will not become
clogged with debris from the saw but will remain clear at all times and
oil wil] be continuously and immediately delivered to the chain during
operation.
1)ismantling of tlle cutting attachment from the powerhead to clean
the groove and oil hole is permanently eliminated. This cleaning
procedure is insisted on by all chainsaw manufacturers, but never
practised by the chainsaw user. The importance of adequately oiling the
chain cannot be over-emphasized, since without proper lubrication, the
chain cannot cut properly, nor can it be prevented from binding and
overheating the guide bar causing premature breakdown of heat-treated
surfaces and destruction of the cutting attachment.
In accordance with one aspect of my invention, I have found that
the guide bar which has a groove deeper than required to provide adequate
clearance for the drive links of the chain, may be made suitable for
operation by filling the groove of the guide bar with an aluminum filled
epoxy, which while still in the liquid stage, can be removed to a depth
20~ corrèsponding to the depth of the drive links. Indeed if the depth of the
; ~ epoxy layer is too great, such that the groove is too shallow, the drive
links will quickly abraid the aluminum filled epoxy to provide a precise
zero clearance fit for the drive links in the bottom of the groove. By
this means, the lubrication of the chain i9 greatly enhanced and the
optimum zero clearance depth of the slot is permanently maintained
throughout the life of the guide bar.
Fig. 9 is a magnified drawing illustrating a single cutter 23 as it
travels on a guide bar 14. It will be appreciated that the cutter 23 is
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0~3Z9
moving in the direction of the arrow 50, and that the cutting edge 36 will
thus conne in contact with the material to be cut, creating a force
illustrated by the arrow 60 in the direction opposite to the direction of
motion 50. This force 60 creates a couple around the point 37 of the
cutter 23 which is in contact with the guide bar 14 which couple seeks to
cause rotation about the point 37. This couple is resisted by the
downward force 61 drawing the chain in the direction of the arrow 50. The
force 61 creates a couple acting in the opposite direction to the force
60. The closer the point 36 to thc guide bar 14, in relation to the
distance between the point 36 and the point 37, the lower the couple will
be tending to cause rotation of the cutter 23 about the point 37. Indeed
in accordance with the invention, if the shape of the tooth is modified,
to extend the cutter substantially to the rear, in the direction of
travel, such as illustrated in 37' of Fig. 9, substantial improvements can
be obtained in the longevity of the ^hain, and in the resistance of the
cutters to llfting during cutting operation. I consider that lifting of
the cutters about the point 37 during operation is one of the major
problems which gives rise to kickbacks, and as well causes damage and
premature wear to the guide bar 14 due to rocker-like cutter surface and
~20 small effecive contact area which is unable to retain lubricant between
the heel and rails of the guide bar.
; ~ Extensive experimentation and testing has established that kickback
in chain saws is largely a function of contact between the bar and the
chain as its passes over the critical nose area of the bar, particularly
in boring operations. As pointed out hereinabove, wedging loads on the
chain as it passes over a sprocket guide bar nose causes elongation wear
and wear of the chain rivets and drive link holes. Return of the chain
causes hammering and impact wear of the bar rails. Further, while the
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chain is "lifted" away from the bar it is mstable since it is dependent
for its stability solely on the depending drive link flange engaging in
the slot in the guide bar. Such engagement can cause considerable side
loading on the cutter links and the chain is consequently relatively
unstable. The problem is therefore one of designing a saw chain in which
all links maintain constant lineal contact with the bar throughout its
travel around the bar, including during the critical transition between
the longitudinal edge and the nose portion of the bar.
; It has been found that elimination of the wedging loads from small
diameter sprockets and hammering by maintaining constant lineal contact
between the chain and bar has important side effects. Firstly chain oil
is more easily carried with the chain around the nose of the bar and a
lubrication layer is maintained between the chain and the bar rails at all
points. Thus wear and overheating are avoided. Chain jamming with
sawdust is eliminated; chain stretching is eliminated; chain and bar noise
is reduced and pitch is not altered. Kickback is avoided.
It is of primary importance to the present invention that the chain
be carefully and closely matched to the bar with which it is used.
Heretofore straight and curved bars have both been proposed. Even
~20 asymmetrically curved bars, the so-called "banana bars", have been
proposed. Straight bars with corresponding straight edge chain links
provide excellent lineal contact during longitudinal travel therealong,
but only limited point contact and hence loss of lubrication at the noæe
of the bar. Further, straight edge guide bars of course have no
self-cleaning feature nor do they have the capability of forcing the chain
oil to engage the wear surfaces of the chain as does the bar of the
present invention. Similarly asymmetrically curved bars cannot provide
large area lineal contact. Because of the asymmetry of the bar the
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11~0829
effective contact area between bar and chain is extremely small and
consequently heat and wear is excessive.
In carrying out the present invention therefore, a symmetrically
curved bar as set out above is essentlal.
(`urved bars are not new to the art, but heretofore have only been
employed with straight sided chain links so that only point contact is
achieved on the longitudinal edges and at the nose. Parabolically curved
bars have also been used but these vary in curvature along their length.
It has been found essential that the chain length be so selected
and the chain so constructed as to have an equal number of cutter links
extending left and right so as to neutralize side thrust and consequent
wear of the chain drive links and the bar groove sides.
A typical 18-inch bar constructed in accordance with the present
invention is provided with a curved nose portion having a radius of
curvature of approximately 0.71 inch (36 mm), and a longitudinal curved
surface having a radius of curvature of approximately 72 inch tl925 mm).
It will of course be appreciated that differently sized bars will have
correspondingly different radii of curvature. It is of course
conventional in guide bar design to provide hardened inserts at the nose
of the bar to assist in resisting wear.
; As set forth above, the essential relationship of the curvature of
the bar to the saw chain is such that a sufficient centrifugal force will
be generated by the chain as it travels along the curved long edges of the
bar to ensure that chain oil is constantly present at all sliding and
rotating joints of the chain on the guide bar and all chips are expelled
outwardly from the chain at the first opportunity. At the same time, the
radius of curvature at the nose of the guide bar must also be related to
the top plate angle of the cutter and to the depth gauge shape, and the
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~ ch of the chain in such a way that not more than one cutter is
within the critical zone of the nose as set forth above at anyone time.
Fig. 10 illustrates this important point in more detail. The
cutter 23 is shown passing around the nose 18, with the cutting edge 36
in contact with the material to be cut, generating a force 60 as shown.
This force which tends to lift the cutter is balanced by the downward
component of the force 61 to maintain the curved surface 34 in contact
with the nose 18. It will be noticed that the surface 34 in contact
with the nose 18 subtends an angle of approximately 30' so that a high
proportion of the lower surface of the cutter 23 is in contact with the
nose, thereby maintaining the lubricant layer between the nose 18 and
cutter 23. It may also be noted that only one cutter at a time is in
the critical zone of about 70- either side of the long axis of the bar 14.
Referring to Figures 13 to 15, in one preferred form of chain
in accordance with the present invention, the shape of the tie straps 22'
may be reduced to a minimum length, for a given pitch of the chain, and
the length of the cutter links 23' and their respective balancing links
21' increased correspondingly so as to provide a longer length on the
cutter link and hence increased weight and stability thereof to preventing
lifting of the cutter link from the bar.
The radius of curvature of the nose portion 18 is a function
of the top plate angle and depth gauge shape as discussed above. It
will b:e appreciated that the length of the bar, must be such that there
will be an equal number of left and right hand cutters.
The minimum practical pitch of the chain in this concept
begins at about 0.375". It is a particularly preferred feature of this
invention that the radius of curvature of the nose portion of the bar
shall be as
-18-
B
~.Z~)829
small as possible whiLe still permittlng the chain to pass smoothly there
around without liftlnP or binding or otherwise hammering or chattering.
In practice the radius of curvature of the nose is identical to the
diameter of the dri~ sprocket but may be varied between 5/8"-1". It is
also preferred that the diameter of the nose portion be equal to the
diameter of the drive sprocket at the other end of the bar so that the
path travelled by the chain is symmetrical on both edge of the bar.
The size of the drive sprocket is a function of the power of the
head driving the chain. Generally a 6 or 7 tooth drive sprocket is
employed. Small saws for the casual or domestic user generally have
electric motors or gasoline engines with a displacement of 40 cc, or less,
which provides sufficient power to drive the chain.
The radius of curvature of the longitudinal surface 16 and 17 of
bar 14 is also strictly controlled as discussed above. For bars up to
about 19" long, it has been found that the radius of curvature should be
about 72" (1925 mm). Note, in the short bar the 1925 mm delivers 2G at
clutch engaging speed. The longer bars do not need such high acceleration
because the force acts upon the chain oil for a longer time and for bars
in excess of this length the radius of curvature should be increased
~20 somewhat to perhaps about 96" maximum. A chain designed for use with a
;~ 72" radiuF bar can be used on a bar having a larger radius as it will
eventually wear-in to fit from the outside edges inwards, ensuring lineal
contact at all times, but the converse does not apply. That is, a chain
designed for a 96" radius bar cannot be used on a 72" radius bar. As the
links of the chain slide along the guide bar, with a chain which is
provided with curvatures 33 (Figs. 6 and 7) intended for use for example
with a bar having a radius on the long edges of 72' on a bar of 96
radius, it will be appreciated that the fore and aft corners of the side
19
. _ , ... . . . .
` li;~)t329
links and cuttLng links will be in contact with the sur~ace of the bar,
rather than the inner corners at the junction with the curved surface 34.
If, however, a chain intended for use on a bar having a large radius of
curvature for the long edges is used on a bar having a smaller radius of
curvature, then the cutter teeth will be supported only at the inside
corners constituting the junction between the surfaces 33 and 34, and this
will permit the cutter links to rock back and forth since they are only
supported at an inner point rather than at the extreme end of the cutter
link. Thus, wear must take place from the outside in to obtain lineal
contact. It is important that the longitudinal curved surfaces 14 and 15
shall be a continous segment of a circle, and not a curved noncircular
shape, in order to ensure maximum lineal contact between the links and the
bar throughout travel of the chain. This is believed to be a major
distinction over the curved bars, or bars not having a constant circular
shape. The continuous curve is important in order to ensure chip removal,
proper lubrication of the chain during its travel and rapid heat transfer
from chain to bar hinders other benefits discussed above.
The constant radius of curvature of the bar ensures that oil is
carried to all parts of the chain by centrifugal force and that wood chips
;~ 20 are also removed cleanly by centrifugal force as soon as the chain exits
the kerf. If the radius of curvature is too small, for the lineal chain
~ velocity, the lubricating oil is thrown outwardly from the point of
; introduction and does not lubricate the chain, and if the radius of
curvature is too large, then there is insufficient force to throw the oil
outwardly to the chain links and insufficient lubrication occurs.
Prior art guide bars have a groove generally twice the depth of the
drive link. This prior art bar coupled with existing lubrication
practices prevents the chain oil from reaching the chain until the groove
; ~ 20 -
11'~0829
has become saturated with oil. Also, such grooves tend to become filled
with chips and sawdust, and due to the shape of the notched drive link, it
tends to press the chain oil into the sawdust rather than causing the oil
to flow through the chain. It is, therefore, an important aspect of the
present invention that oil should be transferred away from the channel 42
immediately upon introduction, thus avoiding the notorious problem of
oiling passages blocking and sawdust build-up in the groove. Transfer of
oil from the oil feed hole to the chain is facilitated by angular
introduction of oil along the oil passage 42 into the groove and by the
zero clearance between the drive links and the bottom of the groove.
Preferably the oil passage is at an angle between 45 and 90 to the
direction of movement of the chain, and more particularly it has been
found that an angle of 60 yields superior results. Further, there should
be no clearance between the bottom of the groove and the drive links to
eliminate oil draining from the chain into the space between drive links
and the bottom of the groove during stops between cutting. In order to
prevent wear of the drive links on the bottom of the groove, as the bar
rails wear, it is preferable that the zero clearance be obtained by
partially filling the groove with a relatively soft and easily abraded
~ 20 material, such as an aluminum filled epoxy resin, which will adhere firmly
-~ to the walls of the groove and resist chemical reaction with the oil, even
` at elevated temperatures. It will be appreciated that as the rails and
chains wear, the drive links abrade the relatively soft epoxy resin and
maintain a zero clearance. Figure 16 shows a slightly modified form of
drive link 20' provided with one or more serrations 50 to assist in
abradeing the bottom of the groove during operation, to maintain zero
; clearance. Oil in~ected through the oil passage is picked up by the drive
links and is pressurized by centrifugal force throughout all of the links
; - 21 -
0~329
and rivets as the chain travels along the smoothly curved longitudinal
path created by the bar. Oil is also held between the links and the bar
during rest periods and wear of the bar is thus substantially eliminated.
As oil is carried by the chain itself and is not dependent upon transport
along a partially clogged groove to reach the nose of the bar, heating and
wear at the nose of the bar is also markedly reduced as the time taken for
oil to reach the nose is much reduced. ~pid transport of oil to the nose
is, of course, particularly important when the saw is operated under
extreme load conditions. 60% of cutter surface is in effective contact
with the bar rails at the nose, while 10% on large radius. The effective
heat transfer to the large heat sink of th bar is achieved. At 1:2 ratio
this would be 50/50. At low ambient temperatures the somewhat viscous and
flows less readily along the channel, resulting in a relatively long delay
before oil reaches the tip. At high temperatures, although the oil is
relatively fluid, it is easily retained
in the large effective contact area which must be maintained for cooling
the chain. (The oil conducts the heat to the bar).
In order to demonstrate the advantages of a chain and bar of the
present invention relative to a conventional chain and bar a series of
~-20 comparative kickback tests were conducted using standard chain saw
manufacturers' tests in which an operating chain saw is freely suspended
~ .
about its point of balance over a log carriage track along which a log
carriage and log can be propelled at controlled speed, acceleratlon and at
a specified angle to the saw bar. Upon impact with a moving log the chain
bites into the log and kicks back or rotates. The angle of rotation is
determined as a measurement of the kickback energy of the saw under test.
I do not agree with this test! While this testing procedure
produces so~e angular velocity, this velocity cannot be duplicated when
; - 22 -
'
0829
the same chainsaw is handheld and rammed against the same piece o~ wood.
And that is the reality! But that's all the industry has.
EXAMPLE 1
-
A Pioneer P28S portable chain saw equipped with a SW16001-DS bar
and a 375 Procut chain was tested at 0, 10, 20, and 30 degrees to the
perpendicular at impact speeds of about 18 and 28 in/sec, under the
influence of acceleration weights of 2 and 5 lbs. respectively, falling
over the end of te track, into the end grain of hemlock logs. The results
are tabulated below in Table I.
; - 23 -
11;~0829
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u~ ~ cr~ ~ ~ o~ _, oO I~
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~Z _ O~ o~ ~ r~
o o~o __ _ _ _
~ ~3 _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ o ~ o o ~ o o o U~ C~l U~ U~
~ ~ ~ ~ ~ ,` . ~ U~
Z--~' o ~ ~ ~ u) ~ u~ O ~ I_ ~ In u~ 0
~Z~X- ~ ~ C~ ~ ~ ~ ~
~ .. __
Z~ _ O O ~D ~ ~ ~ O ~ ~ _ ~ I~
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::- H ~ _ _ _ ~.7 ~1 (~ _ _ _ C~l ~ ~`I ~ ~')
~! _ _ __ __ _
g oO 8 g o 8 8 8 8 0 8 8 o 8 o 8 8 8 8 8 8 8 8 8 8 8 8 g
o ~ o~ S a~ ~ a~ ~ o~ $~ o ~ ~o ~ o~ ~ o~ $~ a~ ~ ~o $~ o~ ~ ~o ~ c~ ~
_ _ _
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_ _ _ _ _ _ _ _ H
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llZ0829
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_ _ _ _ _
~ ~ ~ 0~ ~ 0~ 00 0~ 0~ 00 00 ~O 0~ 00 0~
_ __ _ _ _
z ~ ~ ~ o 8 o 8 g g 8 8 g g 8 8 8 g 8 8 g 8 3 8 8 8 g g o 8
~ ~ 0~ ~ ~ 0~ G~ ~ æ~ ~ ~ ,~ a~ ~ ~
-- A -- -- _ _ _ _
~ ,0,~ 01 01 0 01 O O ~ O O O
__ __ _ _ _ _
a ~ _ _ __ _ _ _ _
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V8;~9
EXAMPLE 2
The procedure of Example 1 was repeated using a Pioneer P28S
portable chain saw equipped with an 18" bar modified in accordance with
the present invention to have symmetrical longitudinal convexly curved
surfaces having a radius of 72`' and a Stellite hardened nose portion
having a radius of 71" and an Oregon 91S low profile semi-chisel 3/8"
pitch chain modified in accordance Jith the present invention to fit
precisely on the mofified bar described herein. The results of this
series of tests is tabulated below in Table II.
- 26 -
,
~ ;~0829
- .LZ -
. ~ ~ ~ U~ _ ~ U~ U~ ~ oo ~ ~ , _
~ E-~ ~ G C~ ~1 ~ ~:t ~j? ~ _ ~ O a~ I~ ~) ~ ~
_ ~ _ . __ _ _ _ ;~i ~2
~ ~ G ~, ~ C~ ,~ a~ 1/~ _ _ O ~I ~ ~ ~1
Z _ __ ___ _ _ _
~g~^ `D ~ ~O ~ ~O `D ~D ~D `D ~ `D ~ `D ~O
.~ _ _ __
X ~ ~ CO ~ U~ _ ~ ~ ~ ~ ~ ~ O O _
Z ~_ _ _ _
H OZ ~ Z O O O O O O ~ ~) 1~ O O O O O
o o o o o o ~ a~, ~ ~ o o o 0-
~ ~1 _ _ _ _ _ _~ ~
3 æ ~ ~ ~o o~ CD o~ o~ o~ cr~ o ~ ~ ~ ~ oo ~o
_ _ _ _ _
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__ _ _ __
o o o o o o ~o ol ~o o ~o ol ~o ~o
_ _ _ _ .
.
_ _ __ _ _
æ~ O ~ ~ ~ u ~ r _ a o
~7
x~ -
11'~0829
.
~D ~, _ _ ~ 0~ l ~ l ~, ~ C`l
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z ~ ~ o8 og g8 o$ 8o o8 8g o8 88 80 80 o8
~ ~ ~ ~0 ~ æ ~ æ ~ ~0 ~ æ ~ æ ~ æ ~ æ ~ ~0 ~ c~ ~ ~ ~ æ ~
_ _ _
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2~
--`` llZ08Z9
Following the tests the results shown in Tables I and II were analysed
and summarized in Tables III and IV below.
Example 1 Example 2
_ AVERAGE AVERAGE _ AVERAGE AVERAGE _ _
NET TOTAL NET TOTAL
APP. WOOD ROTARY DEVIA- NET IN. DEVIA- ROTARY DEVIA- NET IN. DEVIA-
ANGLE GRAIN IN.LBS. TION LBS. TION IN. LBS. TION LBS. TION
O E 36.3 3~4 36.3 3.4
_ 23.1 1.3 23.1 1.3
. _ _
-10 86.7 3.7 89.3 3.2 _
_ _ _ 44.5 5.2 44.8 5.2
-20 _ _ 99.1 15.7 119.1 15.7
= = = = = = 1.8 1.2 3.8 2
-30 0 0 0 0
= = = = 3 .4.3 .4
_
TA8LE III
Example 1 Example 2
AVERAGE _ AVERAGE AVERAGE AVERAGE
NET TOTAL NET TOTAL
APP. WOOD ROTARY DEVIA- NET IN. DEVIA- ROTARY DEVIA- NET IN. DEVIA-
ANGLE GRAIN IN.LBS. 1 TION LBS. TION IN. LBS. TION LBS. TION
G E 57.214.557.2 14.5 _
~;~ 48.7 .9248.7 92
~ _1o 109.43.0112.4 2.2 _ _ _
- _ ~ 66.6 3.166.6 3.1
-20 87.612.4112.4 11
26.965.6 26.1
_ .. _
30 ~ 2.Z .98 7.7 2.4
91 .2991 29
TABLE IV
,
- 29 -
0829
Table III summarizes the results at an approach velocity of about
18 2 in/sec and Table IV summarizes the results at an approach velocity
of 28 2 in/sec. In eacll case the average net rotary and total reaction
energy in pounds is shown, together with the standard deviation. The
reduction kin kickback energy in the case of the bar and chain of Example
2 is considerable over mos~ approach angles, and is most clearly seen
graphically in Figs. 6 and 7 which are graphica] representations of the
data presented in Tables III and IV respectively.
It will be appreciated that the considerably reduced kickback
energy levels exhibited by the chain and bar of the present invention
represents a considerable advance in safety of chain saws in that a major
hazard has been considerably reduced.
- 30 -
, . , ,, _ . _ .. .. .. , .. . . . ,, , ~
