Note: Descriptions are shown in the official language in which they were submitted.
362
BACKGROUND OF THE INVENTION
Field of the Invention `
The invention relates to a tree shear blade or
cross-cut blade as used in a mechanical tree felling device.
Prior Art
Tree felling devices using shear or cross-cut
blades are old and can be divided into two main typesO One -~
type is a "feller buncher" in which two similar blades are
mou~ted on a scissor-like mechanism used primarily by a
carrler wi~h a hydraulically operated boom, The two blades
close simultaneously by hinging about a pivot point and sever
th~ ~ree which is held by clamps or grapples. The second
type is a single blade cutter which is commonl~ mounted on a
crawler- or loader-type carrier. The single blade is generally
thicker than the scissor type blade and is commonly designed
to cause a tree to fall in a particular direction for later
gathering.
Both types of shear blades as above identified i
commonly cause splitting or crushing damage to severed trees
far in excess of what would be anticipated by normal falling
when using an ax or chain saw. The splitting tends to run
longitudinally from the cut and up the butt of the tree,
sometimes extending six to ten feet up the butt, depending
on the species and condition of the tree. This splitting
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tendency of the tree is well known and many attempts have
been made to reduce the spli-tting. To reduce the amount of
wood that is compressed when the blade severs the tree, blades
have been made thinner but such blades are mechanically weak.
Sometimes the thin blades are strengthened by ribs on a s-urface
of the blade but, to the inventor's knowledge, these ribbed
thin blades have not reduced the splitting tendency appreciably.
One such attempt to strengthen thin blades is disclosed in
Canadian Patent 9~0,66~, inventor Thomas A. McLaughlan, and, ~ -
whilst this blade has a tendency to reduce splitting when
compared with earlier shear blades, according to some author-
itiesJ this blade still causes more damage to trees than ~!; ''
would be expected with chain saw or ax felling techniques.
S~MARY OF THE INV~NTION
'`,~
The present invention reduces some of the diffi~
2~ culties and disadvantages of the prior art by providing a thinblade stiffened with ribs on both upper and lower surfaces.
The ribs are staggered along the blade to attempt to reduce
displacement of wood as the blade enters the tree, and the
blade has an assymmetrical cutting edge to direct the fall of
the tree.
',`.' : '
A tree shear blade according to the invention is -~
characterized by a web portion and a plurality of upper and
low0r rib portions. The web portion has upper and lower web
faces, a datum plane, a lower bevelled face and a cutting edge,
the cutting edge being defined by intersection of the lower
r'~
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bevelled face with the upper web face at the datum plane of
the web portion. The upper rib portions a.e similar and are
spaced along the blade and extend upwardly from the upper web
face and rearwardly from the cutting edge. Each upper rib
S portion is generall~ rectangular in cross-section and has a
leading end having an inclined rib leading face extending
rearwardly from the cutting edge. The lower rib portions are
similar and are spaced along the blade and extend downwardly
from the lower web face and rearwardly from the lower bevelled
face. Each lower rib portion is generally rectangular in ~ -
cross-section and has a leading end having an inclined rib -~ ;
leading face extending rearwardly from, and being coplanar
with, the lower bevelled face. The lower rib portions are
generally staggered relative to the upper rib portions along
thé blade.
A detailed disclosure following, related to the
drawin~s, describes a preferred embodiment of the invention
which is capable o~ expression in structure other than that
particularly described and illustrated.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top plan of a shear blade according to the
invention9
Fig. 2 is a front elevation looking at a cutting edge,
Fig. 3 is a bottom plan of the blade of Fig. 1,
.
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Fig. ~ is a fragmented staggered section following sweep
of blade, substantially according to line 4 ~ of
Fig. 1, and as shown generally by line 4~4 of
Fig. ~,
~ Fig. 5 is a simplified fragmented isometric sketch of an
; upper portion of a leading edge of the blade 7 .'~
'"`'
Fig. 6 is a simplified fragmented isometric sketch of a
lower portion of the leading edge of the blade,
'.`.
Fig. 7 is a detailed fragmented top plan o~ the upper
portion of the leading edge of the blade
`` '
Fig. ~ is a detailed front elevation o~ a portion of the ~
leading edge of the blade, some portions being omitted, `; -
''~:, "'
Fig.;~ is a detailed fragmented bottom plan of a portionof the leading edge of the blade.
,.~.: ,
DETAILED DISCLOSURE
Fi~s. 1 through 3
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A tree shear blade 10 according to the invention ;~
has a web portion 12 having a plurality of slots 13 ~or
securing to a felling apparatus (not shown), which moves the
blade through an arc for shearing a tree. The web portion
has upper and lower web faces 15 and 16, a lower bevelled
face 1~, and a cutting edge 20, the structure adjacent the
cutting edge being particularized with reference to Figs. 4
through 9. The blade has a length 21J usually between about
50 cms and 90 cms and a width 22 ~ usually between about 2 5 cms
and 45 cms.
.
The blade has a plurality of similar upper rib `
portions 23 spaced along the blade and extending upwardly from
the upper web face 15 and rearwardly from the cutting edge,
The blade also has a plurality of similar lower rib portions
2~ spaced along the blade and extending downwardly from the
lower web face and rearwardly from the lower bevelled face~
The rib portions are arcuate in plan so as to be concentric
abou~ a center (not shown) about which the blade swqngs to
~ff~ct severing of a tree. Thus each rib portion has a rib
arc radiu~, e.g. 25~ which differs sligh-tly ~rom adjacent rib
radii. Thu~ as the blade swings, each rib portion follows
~b~p 0~ the blade at its particular arc radius~ Apart from
th~ arc r~dil, the rib portions on a particular face of the
web are es~entially equal and thus one rib on each face only
will be described in detail
Figs. ~ through 9
Referring particularly to Figs. 4 through 6, the
blade has a datum plane 2~ within the blade positioned so
that the cutting edge 20 is defined by intersection of the
lower bevelled face 1~ with the upper web face 15 at the datum
plane of the web. The web portion is forwardly tapered and
the upper and lower faces are inclined to the datum plane of
the web portion at angles 31 and 32 respectively. The angle
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31 is shown as approximately 3 degrees but can be between 1
and 10 degrees depending on parameters as will be discus~sed.
The angle 32 is shown as approximately 1 degree but can be
between 0.5 and 5 degrees. The lower bevelled face 1~ is
inclined to the datum plane 2~ of the web portion at an angle
34 which is shown as 15 degrees but can be between about 10
and 30 degrees.
'',-
The upper rib portion 23 has a leading end 35 having .
a plane rearwardly inclined rib leading face 37 inclined to the
datum plane at an angle 3~. The angle 3~ is shown as 24 degrees -
but can be between 15 and 30 degrees9 The lower rib portion
24 has a leading end 40 having a rearwardly inclined rib lead~
in~ face 41 extending rearwardly from and being coplanar with .
the lower bevelled face 1~ and is also inclined to the datum :
plane at the angle 34. The angles specified above depend `
mainly on cutting parameters, wood condition and species, and . :
in some circumstances angles outside the ranges specified may .~.
be practical.
The upper rib portion 23 extends from the leading
end 35 to a rear end 45 adjacent a rear portion 47 of the web
portion 12. The rear end 45 of the portion ~3 is bevelled
and merges smoothly with a rear upper face ~9 of the web,
which face is parallel to the datum plane 2~. The rib has ~.
an upper surface 51 and, for a major portion 46 of its length
from the leading face 37 to an upper bevelled face 4~, the rib .
23 has a substantially constant thickness 4~, defined as
spacing of the rib upper face 51 from the web upper face 15
Thus the rib upper surface 51 is spaced an equal distance
from the web face 15 for the length of the ribs extending : .
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from the cutting edge 20 to -the face 44 adjacent the rear ~ -
portion ~7. The thickness Lr~ is typically about h. 7 mms but
can vary between 2 mms and 7 mms.
The lower rib portion 2L~ has a rib lower face 5h -;
disposed para]lel to the datum plane 2~ of the web. The
inclination of the lower web face results in the rib portion
2~ converging rearwardly from the relatively thick leading
end 40 to merge with the lower face o:E the web portion at a
position approximately beneath the upper bevelled face 44 of
the upper rib portion 23. The leading end ~0 can have a
thickness 56 of about ~ mms~ but this can vary between 2 mms
and 6 mms depending on the value of the angle 32 of the lower
web face, the width of the blade~ and other factors.
Referring to Figs. 7, ~ and 9, the upper rib
port.ion 23 has generally parallel side faces 59 and 60 when
viewed in cross-section with fillets 61 and 62 blending
smoothly from the side faces into adjacent portions of the
upper web face 15. Similarly the lower rib portion 2~ has
generally parallel side faces 63 and 6l~ with fillets 65 and
66 blending smoothly from the side faces into adjacent portions
of the lower web face 16. For both upper and lower rib
portions, the fillets are shown to have fillet radii substan-
tially equal to respective thicknesses of the rib portions,
but a reasonable range of fille-t radii would be practical.
.
The upper rib portion 23 has a first width 69
defined as space between the side edges 59 and 60, and is spaced
laterally along the blade from adjacent upper rib portions at
a first spacin~ 71 which is equal to the first width. All the
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upper rib portions have equal first widths and are spaced -
laterally ~rom each other along ~he blade at the first spacing.
The first width 69 and first spacing 71 are both about 19 mms
but can be between 15 mms and 25 mms.
The lower rib portion 24 has a second width 74
defined as space between the side faces 63 and 6~J and is `'
spaced laterally from adjacent lower rib portions at a second
spacing 76. A11 the lower rib portions have equal second ,;,
widths and are spaced laterally from each other along the blade
at the second spacing. The second width 74 is about 22 mms "'
but can be between 17 mms and 30 mms depending on the first
width. The second spacing 76 is about 16 mms but can be bet- ''
ween 12 mms and 22 mms depending on the first widthu A major '-"'
factor determining the relative differences between the first
and second spacings and widths is that the second width 74 of ~ '
the lower rib portions is greater than the first width 69 of
the upper rib portions, and that the second spacing 76 is less ~,
than the first spacing 71, so that the side faces of the upper
rib portions are displaced laterally relative to the side faces
of the adjacent lower rib portions. Thus outer margins of
adjacent upper and lower rib portions overlap slightly so
that at particular locations along the shear blade the shear ; ,'
blade has an overall thickness 7~ of combined thicknesses of " '~
the web and the upper and lower rib portions. When used as a '"-
single shear blade, the blade has,a root thickness 79 of 19
mms, adjacent the rear portion of the blade and in such a -, ''
blade the datum plane 2~ is spaced from the rear upper face !'~
49 at a plane spacing ~1 of about 15 mms, but the spacing ~1 "
can be between 12 mms and 16 mms. `;
362
It can be seen that the rib leading face 37 of the
upper rib portion 23 cooperates with an immediately adjacent
portion of the cutting edge 20, thus forming a double facetted
chisel point, one of the facets being the face 37 and the
other facet being a portion of the bevelled face li~. This
contrasts with the rib leading :face 41 of the lower rib portion
2h, because the face ~1 forms a coplanar continuation of the
bevelled face 1~, and thus the leading ends of the lower rib
portions are remote from the cutting edge 200
It has been found that, when using the present
invention, splitting and compression damage to the portion
of the tree immediately above the cut, i.e. the butt of the
tree, is considerably less than that with prior art tree
she~rs. Whilst the underlying causes of tree damage using
any type of shear blade are not fully understood, the reduction
in damage resulting from use of the present invention is
attributed in part to the chiselled edged rib portions which
have rc]atively short length ~acets on the upper surfaces
thereof, and longer length facets on the lower surfaces.
That is, relative to the datum plane 2~ passing through the
cutting edge 20, the lower portion of the blade below the
datum plane is thicker than an upper portion, and the inclined
bevelled face 1~ appears to direct damage into the stump,
rather than into the butt of the tree. Furthermore, the rib
portions are integral stiffening bars which increase stiffness
of the total shear blade to resist bending of the shear blade
out of the datum plane 2~. This permits the web to be thinner ~-
than otherwise would be practical without rib por-tions, thus
reducing volume of steel forced into the tree. The upper
and lower rib portions are generally rectangular in cross-
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section which provides greatest sectional modulus relative
to bending for a given depth of bar with similar thickness,
which increases sti~fness of the blade when compared to a
blade having a V-shaped or semi-cylindrical rib portions. -
; The present invention also reduces sharpening
problems associated with many conventional shear blades.
To sharpen the present inventlon, usually the bevelled face
1~ and adjacent coplanar inclined lower rib leading faces ~1 {-
only are ground, thus sharpening the edge 20 formed at the
intersectlon of the face 1~ with the web upper face 15~
After a while it may become necessary to grind back the rib
leading faces 37 on the upper rib portions so as to maintain
the cutting edge as a straight line.
;~
OPERATION
.
The blades can be fitted to a conventional felling
machine to which the trees are clamped prior to felling. The
shear blade is secured to a scissor-lilce mechanism used ~;
primarily by a carrier with a hydraulically operated boomg
such mechanism being referred to as a feller buncher. In
such an arrangement, two similar blades are pivoted together
, ;,
so that arcs of the rib portions are concentric with the
plvot point of the scissors. Thus as the blade sweeps through
the arcs, each rib portion tracts in a groove in -the end face
of the butt or tree stump produced by the leading end face of
that particular rib portion. Thus operation of the feller
buncher follows normal procedure with a reduction of tree
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S362
damage and simplification of sharpening.
ALTERNATIVES AND EQUIVAIENTS
The blade as disclosed has a thickness adequate
for a shear blade for felling soft wood trees of up ~o about ~0
cms in diameter. Alternatively, a stronger embodimen-t of
-the same basic type of blade can be fitted to a tree cut-ter
mechanism or tree shear which is commonly used as a single
blade and is mounted on a crawler or loader type carrier.
Such a blade is generally thicker, perhaps between about
2.5 cms and 3 cms, but nevertheless this blade alternative
has a similar angle and spacings as described.
In the embodiment described, the upper rib portions and
spa~es between the rib portions are equal, and the lower rib
portions are wider t;han the upper rib portions and spaces bet-
ween the lower ribs are narrower than the width of the upper
rib por-~ion~. This results in the staggering of the upper and
lower rib portions causing the limited overlapping of the rib
portions to strengthen the blade, which is of importance. In
an alternative blade (not shown) the lower rib portions and
spaces between the lower rib portions can be equal and the
upper rib portions can be wider than the lower rib portions, and
spaces between the upper rib portions can be narrower than the
width of the lower rib portions. ~his alternative also results
in limited overlapping of the rib portions and thus comes
within the invention. Other alternative structures to produce
the required overlapping can be devised. Clearly if the blade
were to be used in a motion other than sweeping through an arc,
the ribs would be of different shape compatible with the motionO
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