Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED BRUSH CUTTING BLADE
The present invention relates to a cutter blade for
cutting brush, small trees and like and, more particularly, to a
new and improved arrangement of cutting teeth in such a blade.
Background of the Invention
Circular blades driven by a motor, electric or gas
powered, have been used for a number of years for cutting brush
and small trees. SUCh blades are generally mounted on the end of
a manually supported arm with the blade rotating in a substantlal-
ly horizontal plane to cut upright brush and small trees, although
the blade can cut in any position. Some prior blades were formed
with o~fset teeth formed in the blade much like a handsaw. SUCh
blades are inefficient and slow cutting.
Circular blades for various purposes have been provided
with teeth such as are used in cutting chains for chain saws
secured thereto in evenly spaced relation. Blades of this type
are shown in U.S. Patents Nos. 859,574; 1,988,898; 2,992,664; and
3,425,467; Swedish Patent No. 80,528; and French Patent No.
1,194,641. Other blades had lengths of saw chain secured to their
periphery, e.g. U.S. Patents Nos. 2,958,348; 4,563,929; and
4,627,322. A common problem with such blades was their tendency
occasionally to "kick back," that is, to give a sudden, ~orceful
and uncontrolled reaction that caused the blade and supporting
elements to move suddenly away from the piece being cut. SUCh
"kick backs" have been a source of many injuries. An improved
form of such a blade is shown in my U.S. Patent 4,881,438 which
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issued on Nove~ber 21, 1989. This blade is characterized by
having a plurality of saw chain teeth equally spaced about the
peripher of the
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blade, each of the teeth being formed with a wide ramp
or depth gauge preceding the cutting edge. Such
blades had much reduced kick back as compared to prior
blades and are s~bstantially safer in use.
Nonetheless, it is desirable that a brush cutting
blade evidence as little kick back force as possible
to negate the possibility of an injury producing
reaction.
Su~mary__f the Invention
It is an object of the present invention to
provide an improved circular brush cutting blade.
More particularly, it is an object to provide
a circular brush cutting blade with substantially
negligible kick back reaction.
Another object is to provide a brush cutting
blade with suhstantially less kick back than prior
blades, but with improved cutting efficiency.
Other objects and advantages will become more
apparent hereinafter.
In accordance with the illustrated embodiments
of the invention, the foregoing objects are achi~ved
by providing a brush cutting blade comprising a
circular disc having several pairs of cutting elements
mounted thereon, the cutting elements comprising
cutting edges extending transversely of the disc, the
pairs being of right and left hand configuration. The
cutting elements of each pair are spaced closely
together circumferentially, whereas the pairs of
cutter elements are widely spaced from each other.
Such a blade cuts with a high degree of efficiency,
but exhibits little tendency to kick back.
Drawinqs
Fig. l is a side elevation of a pre~erred form
of cutter blade made in accordance with the invention;
Fig. 2 is an enlarged side elevation of a
portion of the blade of Fig. 1;
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Fig. 3 is a sectional view taken along line
3-3 of Fig. 2;
Fig. 4 is a top view looking in direction of
arrows 4-4 of Fig. 2;
Fig. 5 is a front view of a modified cutter
mounted on a blade;
Fig. 6 is a top view of the cutter of Fig. 5;
Fig. 7 is a front view of another arrangement
of the cutter of Figs. 5 and ~ showing a modi~ication
of the blade structure;
Fig. 8 is a top view of the arrangement of
Fig. 7;
Fig. 9 is a front view of still another
arrangement of the cutter of Figs. 5 and 6 showing a
modification of the blade and mounting of the cutter;
Fig. 10 is a top view of the arrangement of
Fig. g;
Fig. 11 is a side elevation of a portion of a
blade and a pair of cutters showing a modified form of
the invention;
Fig. 12 is a sectional view taken along line
12-12 of Fig. 11; and
Fig. 13 is a top view looking in the direction
of the arrows 13-13 of Fig. 11;
Detail Descri~tion of the Invention
With reference first to Figs. 1-4, the
preferred form or cutter blade 10, made in accordance
with the invention, comprises a circular disc 12
having opposite planar sides 14, 16 and a smooth,
generally continuous periphery 18. Attached to the
disc 12 adjacPnt its periphery are a plurality of
right hand cutter teeth 22 and alternating left hand
cutter teeth 24. The cutter teeth are mounted in
pairs, each pair constituting one right hand and one
left hand cutter. The cutters in each pair are
relatively closely spaced circumferentially, but the
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pairs are relatively widely spaced apart. More will
be said of the spacing subsequently.
The cutter teeth 22, 24 are substantially
identical, other than being opposite hand, and in
numerous respects, particularly in the cutter
configuration, resemble teeth commonly used in saw
chain. Because of this identity, only a left hand
tooth 24 will be described in detail. The cutter
tooth 24 comprises a flat plate portion 26 which abuts
the left disc side surface 16, the tooth b~ing rigidly
secured to the disc by suitable fastener means, such
as rivets 28. The tooth 24 is formed with a single
cutter element 30 consisting of a kerf side wall
cutting portion 32 and a kerf bottom cutting or flange
portion 34. As hest shown in Fig. 3, the side wall
cutting portion 32 is laterally offset from the plate
portion ~6, the offset decreasing from thP forward to
the rearward end thereof to provide clearance for the
following portions of the tooth. The flange portion
34 extends from the side wall cutting portion 32
substantially at a right angle to the disc side
surfaces 14, 16 so as to extend beyond the right disc
side surface 14. The forward edge ~f the side wall
portion 32 and flange 34 is formed with a beveled
surface 36 defining a continuous cutting edge 38.
Each cutter tooth 24 is provided with a ramp
or depth gauge 40 integral with the forward end of th~
plate portion 26 and positioned forwardly of the
cutter element 30 to define a gullet 42 between the
cutter element and depth gauge 40. The depth gauge 40
comprises a shank portion 42 and top plate portion 44
which extends across the blade from said shank portion
substantially perpendicularly to the blade side
surface. The top plate portion 44 defines an upwardly
facing flat surface 46 which slopes upwardly from its
forward edge toward the cutting sdge 38.
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While the illustrated tooth i5 of so-called
chipper tooth design, such as shown in U.S. Patent
No. 2,508,784, such a tooth having a rounded side wall
kerf cutting portion 32, the configuration of the
sidewall cutting portion is not critical and other
commonly used con~igurations could be used so long as
the tooth top plate or flange portion 44 forms a kerf
bottom cutting element. For example, the tooth could
be of chisel bit design as shown in U.S. Patent
No. 2,622,634 or semichisel design as shown in U.S.
Patent No. 3,144,891 or any of the other commonly used
saw chain tooth configurations.
Referring more particularly to Fig. 2~ the
periphery of the disc 12 is formed with a cutaway 50
opposite each tooth so that the teeth may be mounted
on the disc with certain portions of the teeth
recessed below the periphery of the disc. Thus, the
right hand tooth 22 is mounted opposite a cutaway 50
including a forward portion 52 receiving the depth
gauge top plate 44, the forward portion 52 being
shaped so that the bottom surface of the depth gauge
top plate engages a cooperatively inclined surface 54
which supports the depth gauge. The cutaway 50
includes a rear portion 56 opposite the tooth
gullet 42 and cutter 30, the portion 56 being
sufficiently deep that the tooth cutting edge 38 may
be sharpened with a file or grinding element extending
across the tooth and blade. The r~ar cutaway
portion 56 preferably extends beyond the rearmost
portion of the tooth flange 34 so as to provide
clearance for wood chips cut by the cutting edge 38.
The teeth 22, 24 are each mounted to the blade
preferably so that the depth gauge surface 46 slopes
upwardly at an angle of between twenty-five and
thirty-five degrees with respect to a plane parallel
to the axis of the disc and normal to a radius of the
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disc intersecting the trailing edge 58 of the depth
gauge top plate 44, and with said trailing edge
positioned above the arc of the blade periphery 18
hetween about 0.025 and 0.035 inch.
The flange portion 34 of a tooth inclines
downwardly at a small acute angle, preferably between
about seven and ten degrees, with respect to a
perpendicular to a radius of said disc intersecting
the forward edge of the flange portion, the cutting
edge of the flange portion projecting beyond the arc
of the disc periphery 18 by between about 0.020 and
0.045 inch beyond the depth gauge projection. The
tooth is preferably mounted so that the trailing edge
of the top surface of the flange portion 44 is flush
with the arc of the disc periphery 18.
The foregoing arrangement of clearance of the
cutting edge of the flange portion 34 and the depth
gauge allows a tooth to be sharpened repeatedly, at
each sharpening lowering the depth gauge by the same
amount as the cutting edge on the flange portion 34 is
lowered by filing down the depth gauge at its trailing
edge 58 in the customary manner of sharpening a saw
chain tooth to maintain the desired cutting edge
clearance, until the depth gauge has been lowered to
the point where its top surface is flush with the arc
of the blade periphery 18. At this point the cutting
edge 38 will have a clearance of at least 0.020 inch
above the periphery of the blade 18 which will permit
it to cut material effectively.
The purpose of providing the teeth in pairs of
right and left configuration with the substankial
spacing between the pairs is to provide smoothness in
the cutting operation, reduce the drag imposed upon
the saw blada as it progresses through the wood,
reduce kick back, and improve the blade cutting
efficiency.
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When the teeth are evenly and relatively
closely spaced around the edge of a blade as has been
the practice in the past, there is not enough space
between teeth to permit the smaller engines to recover
engine speed after it slows during the progress of a
tooth through the brush that is being cut. Thusl the
engines labor. Spacing separate cutters widely also
provides either a hard left or a hard right pull on
the individual cutters, thus deflecting the blade so
that the blade is out of a centered position for the
following cutter. This creates a vibration or
"chatter" that can be detected by the operator, and
can cause a blade to wander, increasing kerf width and
decreasing the blade's efficiency. However, when the
teeth are in pairs, there is an almost instant
left-right pull on the blade, minimizing its
deflection and leaving the blade in a relatively
balanced position for the next set o~ cutters. As a
result, a blade with widely spaced cutter pairs
operates more smoothly and efficiently.
Traditional blade technology was to provide a
blade so that there was at least one and preferably
two teeth in a cut at all times. I have found that
providing a blade having teeth in widely spaced apart
pairs, there are brief periods with no teeth in the
cut. The pause period provided between the cuts
enables the small, high speed motors used with brush
cutters to recover their lost speed and the motoxs
operate more smoothly and efficiently. The space
between teeth pairs needs to be longer for smaller
motors than for larger more powerful motors~ For
example, a 20 cc. gas engine would successfully
operate a nine inch blade with three equidistantly
spaced pairs of teeth, but would not operate well with
a nine inch blade with our equidistantly spaced pairs
of teeth. By contrast, a large gasoline engine of
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64 cc. could successfully function in a brush cutter
with a ten inch blade with six equidistantly spaced
pairs of teeth. Thus, the optimum spacing between
pairs of teeth will depend upon the horsepower of the
engine propelling the blade and the blade diameter,
but, in any case, the spacing between pairs should be
several times the length of a tooth or the spacing
between teeth. Ordinarily, saw chain teeth are of the
order of 3/4 to 1" in length. Thus, a brush cutting
machine powered by an engine of small horsepower and
driving a 12'1 blade may accommodate only three pairs
of teeth on the blade. On the other hand, an 8~' blade
driven by an engine of large horsepower, may be able
to accommodate six pairs of teath.
With respect to the spacing between the cutter
teeth of a pair, that is the left and xight cutters of
a pair, the closer such teeth are spaced peripherally
the less chatter and drag will occur and the higher
the cutting efficiency. However, from a practical
standpoint, it is preferable that a trailing tooth of
a pair be spaced from the leading tooth so as to
provide a segmental portion of the disc periphery,
indicated at 57, between such tooth. The segmental
portion 57 will protect the trailing tooth of a pair
if a lsading tooth is damaged or broken. The
preferred spacing between individual cutter teeth of a
pair is about 0.250 inch, but may vary between 0.150
to greater than one inch in some instances.
Preferably, means are provided on the blade to
deflect the blade towards the central plane of the
blade as the blade rotates into the kerf. Blades tend
to wander, particularly blades of larger diameter
using larger cutters, that is having greater than 3/8"
spacing between rivet openings. This wandering of the
blade makes it difficult to start into a cut since the
blade will tend to walk up or down the face of the
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material being cut. The wandering sf the blade will
also cause the blade to cut a wider kerf, greatly
reducing cutting efficiency.
In the embodiment of the invention illustrated
in Figs. 1-4, a deflecting means is embodied in the
depth gauge 40. As will be seen in Figs. 3 and 4, the
shank portion of the depth gauge is reversely curved
portion and outwardly from the plate 42 and thence
back over the center line of the tooth wherein it
forms the depth gauge top plate 44. As best shown in
Fig~ 4, the shank portion 42 is inclined outwardly
from the *orward edge of tha tooth so as to provide an
inclined planing surface. The slope of this surface
should be between about 4 to 12~, preferably about
8, with respect to the blade surfaces 14, 16. The
trailing edge of the reversely curved depth gauge~
portion 60 should provide at least between about ~*
to 0.035 inches clearance îor the cutting edge 38
formed on the kerf sidewall cutting portion 32.
While the configuration of the depth gauge
described above is preferred, other configurations may
be utilized. For example, a standard depth ~au~s~c~
as shown in U.S. Patents Nos. 2,508,784 and *~4,
or the more sloping depth gauge of U.S. Patent
No. 3,929,049 may be used. Referring to Figs. 5 and
6, there is therein illustrated a left hand cutter
tooth 24' having a depth gauge 40l thereon of the
width of the sheet material from which the tooth is
formed. While such depth gauge 40l may be co-planar
with the flat plate portion 26' of the tooth,
preferably the depth gauge is canted outwardly from
its front to the trailing edge 55 thereof as best
shown in Fig. 6 to provide a deflecting means to
deflect the blade toward the central plane of the
blade as it enters a kerf. Use of single width depth
gauges will, however, give rise to increased kickback
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forcP, but because of the recessing of the teeth and
their arrangement in widely spaced apart pairs, the
kickback will be substantially less than for blades
with evenly and closely spaced teeth.
The width of the depth gauge can be
effectively increased also by providiny a ramp 40'' on
the periphery of the disc as shown in Figs. 7 and 8
matching the ramp or slope o~ the cutter link depth
gauge 40'. In addition, an opposing side plate 57
with a matching ramp 40''' can be positioned on the
disc so that the depth gauge in effect is made up of
three adjacent members as shown in Figs. 9 and 10. In
both of these embodiments, the depth gauge 40' on the
cutter element is preferably canted outwardly as
described in connection with Fi~s. 5 and 6. Because
of the greater width of the depth gauge surface
provided by the double and triple ramps, they will
have greater effectiveness in reducing kickback force
than the single width depth gauge but will not be as
satisfactory as the embodiment of Figs. 1 to 4.
Alternatively, a deflecting means may be
provided by wings 62, 64 on the disc 12 of right and
left configuration, respectively, as shown in Figs. 11
to 13, positioned in front of a pair of teeth 22',
24'. The wings 62, 64 are formed on the disc 12
immediately preceding each pair of teeth such as by
forming a pair of L-shaped cuts 66, 68 to permit the
wings 62, 64, respectively, to be bent outwardly from
the blade. The teeth 22', 24~ are provided with depth
gauges 90 which in this instance comprise a planar
shanX 92 and an inclined top plate portion 94.
As indicated earlier, blades made in
accordance with the described embodiments run more
smoothly, have less tendency to kick back and cut more
effectively than prior blades of which I am familiar.
Having illustrated and described a preferred
embodiment of the invention and certain modifications
thereof, it will become apparent to those of skill in
the art that the invention permits further
modification in arrangement and detail. I claim all
such modifications as come within the purview of the
appended claims.
