Note: Descriptions are shown in the official language in which they were submitted.
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POWER SAW INCLUDING REMOVABLE
CIRCULAR CUTTING ELEMENT AND HOLDER
Field of the Invention
This invention pertains to power saws for
falling tree~. In particular, the invention provides a
power saw having a rotatable cutting disc with a plura-
lity of removable cutting elements disposed around the
outer rim of the disc. The cutting elements have circu-
lar, conical or concave cutting faces and circumferen-
cial cutting edges.
Background of the Invention
Manipulable powered apparatus termed "tree
falling heads" are used in tree falling operations.
Conventional tree falling heads include grapple arms for
holding the tree while it is cut and a power saw for
cutting the tree. The present application is particu-
larly concerned with tree falling heads having circular
power saws which can be designed to provide a platform
upon which the tree is supported while it is cut and
upon which the tree may be transported after cutting.
Such an arrangement is shown in United States patent No.
3,915,209 issued 28 October, 1975 for an invention of
8ernard Denis, in which a cutter-bearing ring is driv-
ingly rotated around the periphery of a support plat-
form. Denis provides a drive gear which is offset to
one side of the circular platform/ring assembly and
which engages gear teeth provided around the inner cir-
cumference o the cutter-bearing ring. A cutter ring
suffers a number of disadvantages as compared with a
cutter disc. For example, the ring must be precision
machined to minimize wear on the drive gear. In prac-
tice, because it is difficult to provide adequate sup-
port for a cutter ring, the loads to which the ring is
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subjected affect the ring/drive gear tolerance and cause
premature wearing of the drive gear. It is also diffi-
cult to lubricate a cutter ring adequately, which fur-
ther accelerates wear.
United States patent ~o. 3,494,389 issued 10
Februry, 1970 for an invention of John L. Thibodeau
illustrates a ring saw which is rotated by a drive gear
offset to one side of the ring to mesh with gear teeth
disposed around the inner circumference of the ring.
The offset drive mechanism leaves the ring saw unob-
structed over most of its diameter, thereby increasing
the size of tree which may be cut with a saw of a given
diameter. Unlike Denis, Thibodeau provides no support
platform - presumably because his apparatus does not
appear to be intended for use in cutting trees, but
rather is used for slashing and loading small bundles of
timber which apparently do not have to be supported away
from the rotating saw while they are cut, as does a tree
which would pinch and stall the saw if allowed to rest
on the saw during the cutting operation. Since
Thibodeau provides no platform to support the tree, his
apparatus is unsuited to use in tree falling opera-
tions.
A particular problem with prior art power saws
concerns the saw cutting elements which must be kept
sharp in order to produce an even, clean cut. If the
saw cutting elements are dull, they tend to leave a rag-
ged edge and may cause splintering at the severed buttof the tree, seriously degrading the quality of the lum-
ber subsequently produced from the tree and reducing its
value, particularly in foreign markets.
Saws having fixed saw teeth of the type shown
in the Thibodeau patent are particularly difficult to
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keep sharp. An experienced saw filer must be engaged to
sharpen the saw teeth at regular intervals. If any of
the saw teeth are broken or damaged to the point that
they cannot be sharpened (a common occurrence, since
tree falling heads are operated close to the ground by
an operator who may be more than twenty feet away from
the saw, thereby significantly increasing the likelihood
that the saw may strike a rock or other object and
damage the saw teeth), then the remains of the damaged
teeth must be removed and new teeth silver-soldered in
their place. Thus, Thibodeau's arrangement is undesira-
ble because of the costly labor-intensive process re-
quired to sharpen and/or repair the saw teeth. Further-
more, unless an expensive inventory of sharpened saws is
maintained, significant down time may be experienced in
view of the time required to disassemble the saw and
transport it from a remote site of operation to a faci-
lity having apparatus and personnel capable of sharpen-
ing and/or repairing the saw (or conversely, down time
may be experienced in view of the time and cost inherent
in transporting such apparatus and personnel to the
remote operation site). Although Denis overcomes some
of the disadvantages of Thibodeau's arrangement by pro-
viding individually replacable cutting teeth with a
rather elaborate mechanism for locking each tooth in
place around the rim of the saw, his arrangement is
undesirable in view of its relative complexity, which
increases the overall cost of the saw.
To overcome the foregoing disadvantages, the
present invention provides disposable, replacable, self-
sharpening cutting elements which are cheap to make and
which may be rapidly installed by inexperienced person-
- nel. The teeth are removably attached around the peri-
phery of the cutting disc by holders which have a rela-
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tively simple design yet provide massive support capableof withstanding and transmitting to the cutting disc
forces imparted to the cutting elements during cutting
operations.
Summary of the Invention
The invention provides a saw cutting element
comprising an indented, circular cutting face having a
circumferencial cutting edge. Preferably, the cutting
face i~ conical or concave. Advantageously, the cutting
element has a tapered rim which narrows the element in
the direction away from the cutting face at an angle of
about 10 with respect to a line perpendicular to the
plane of the cutting edge.
The invention also provides a saw cutting
assembly comprising a cutting element having a circular
cutting face and a holder for removably holding the cut-
ting element. The holder preferably comprises an anvil
for supporting the cutting element opposite the cutting
; face. Advantageously, the holder also has a recessed
shoulder for supporting the cutting element around at
least 1/4 and preferably about 1/2 of the circumference
of its cylindrically tapered rim. Releasable attaching
means are provided for releasably attaching the cutting
element to the holder.
The invention further provides a saw compri-
sing an upper, stationary platform disc; a lower, rota-
table cutting disc; a plurality of cutting elements dis-
- posed around the outer rim of the cutting disc; and,
drive means for rotating the cutting disc.
Brief Description of the Drawings
Figure 1 is a side view of a powered exca-
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vator-type apparatus having an arm with a tree falling
head supported at the end of the arm.
Figure 2 is a side view of a tree falling head
with the power saw thereof in the retracted position.
Figure 3 is similar to Figure 2, but shows the
power saw fully extended.
Figures 4A through 4D show how the tree fall-
ing head is moved into position to grapple a tree and
then operated to sever the tree.
Figure 5 is a top plan view of the base of the
tree falling head of Figures 1 through 4D, showing the
disc saw thereof.
Figure 6 is a side view of the tree falling
head base portion shown in Figure 5 and includes a sec-
tional side view of the disc saw of Figure 5 (the scale
of Figure 6 has been enlarged in comparison to the scale
of Figure 5).
Figure 7 is an exploded illustration of a cut-
ting assembly according to the invention.
Figure 8 is a partial cross-sectional side
view of the cutting assembly of Figure 7, showing how
the components thereof are assembled.
Detailed Description of a
Preferred Embodiment of the Invention
(a) Cutting Element
Figures 7 and 8 depict a cylindrically tapered
cutting element 10 having an indented (preferably
conical or concave) circular cutting face 12 surrounded
by a circumferencial cutting edge 14. Element 10 has a
rim 16 which is tapered to narrow element 10 in the
direction away from cutting face 12 (that is, element 10
becomes narrower in the direction of arrow 18 shown in
Figure 7). Preferably, rim 16 is tapered at an angle 20
of about 10 with respect to a line 22 perpendicular to
the plane of cutting edge 14.
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An aperture 24 having a counter-bored or
coun~er-sunk face 26 is provided in cutting element 10
to receive bolt 36 which is for removably attaching cut-
ting elemen~ 10 to holder 30 as hereinafter described.
Cutting element 10 is preferably machined from
low alloy steel and then case hardened so that element
10 has a hard exterior and a soft core. The inventor
has found it preferable not to completely temper element
10 since such elements have exhibited a tendency to
shatter during use. The inventor has also found that
carbide materials are not well suited for producing
element 10 since they are quite brittle and tend to chip
if a rock is struck (a common occurrence in tree falling
operations)-
b) Cutting Assembly
Figures 7 and 8 also show a cutting assemblycomprising cutting element 10 as described above and a
holder 30 for removably holding element 10. Holder 30
has a relatively massive anvil 32 for supporting element
10 over the face of element 10 which is opposite to cut-
ting face 12. Holder 30 also has a recessed shoulder 34
having the same shape as cylindrically tapered rim 16.
Shoulder 34 supports element 10 around at least 1/4 and
preferably about 1/2 of the circumference of rim 16.
A releasable attaching means such as bolt 36
and nut 38 are provided for releasably attaching cutting
element 10 to holder 30.
In use, the cutting assembly is rigidly af-
fixed to a saw by welding or otherwise firmly attaching
face 40 of holder 30 to the saw cutting edge. Anvil 32
and shoulder 34 provide massive support for cutting
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element 10 capabLe of widthstanding the forces imparted
to element 10 during cutting operations and transmitting
the forces to the body of the saw.
If cutting element 10 is dulled or damaged, it
can easily be replaced by an unskilled person who need
only remove bolt 36 and nut 38 to free the dulled or da-
maged cutting element and insert a fresh cutting element
in its place. It is expected that the cost of producing
cutting element 10 may be held low enough that the most
economic alternative will be to discard dulled or dama-
ged cutting elements rather than attempt to sharpen or
repair them. It should however be noted that cutting
element 10 has a self-sharpening feature. Woodchips cut
by element 10 tend to curl across cutting face 12 as
they travel from the portion of edge 14 which does the
cutting to the opposite portion of edge 14. In the pre-
ferred saw hereinafter described, when cutting element
10 and holder 30 are fastened to the saw, only about 1/4
of circumferencial cutting edge 14 does any cutting and
thus only that portion is dulled. As the chips roll
across the opposite portion of edge 14, they tend to
erode that portion, thereby sharpening it somewhat. ~y
periodically rotating cutting element 10 by about 1/4
turn, one may sequentially expose fresh, sharp portions
of cutting edge 14 to perform the cutting operation.
Such periodic rotation of element 10 eventually posi-
tions previously dulled portions of edge 14 opposite the
cutting portion of the edge, thereby facilitating self-
sharpening of those previously dulled portions in themanner aforesaid.
As mentioned above, woodchips cut by element
10 tend to curl across the surface of cutting face 12.
Since large quantities of chips are produced in tree
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falling operations, every effort should be ~ade ~o avoid
obstructing the movement of the chips and to ensure that
they can be rapidly removed from the vicinity of cutting
element 10 so as to prevent jamming. For this reason,
the head of bolt 36 is recessed beneath the surface of
cutting face 12 by counter-boring or counter-sinking
face 26 as aforesaid so that the bolt head will not ob-
struct the chips as they curl across face 12. The manu-
facturing of element 10 may be simplified if cutting
face 12 is made conical, rather than concave. In parti-
cular, the conical taper of cutting face 12 may be the
same as the taper of counter-bored or counter-sunk face
26, thereby facilitating production of faces 12 and 26
in a single operation yielding a single tapered face.
c) Saw
Figure 1 illustrates a powered excavator-type
apparatus 50 having an arm 52 at the end of which a
tree falling head 54 is removably coupled. Tree falling
head 54 (shown in greater detail in Figures 2 and 3) in-
cludes a pair of grapple arms 56, 58 for grappling a
tree 200 (Figure 1) and a circular saw 60 which may be
advanced across the base of tree falling head 54 to
sever tree 200. In Figure 2, saw 60 is shown in its
fully retracted position. Figure 3 shows saw 60 fully
extended.
Figures 4A through 4D illustrate the tree
falling operation. In Figure 4A, the operator of appa-
ratus 50 has opened grapple arms 56, 58, retracted saw60 and manipulated arm 52 to position tree falling head
54 at the base of tree 200. In Figure 4B, the operator
has moved arm 52 forward and has closed grapple arms 56,
58 around tree 200. The base of tree 200 is centred
within a "U" shaped yoke 53 (best seen in Figure 5) in
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the base of tree falling head 54. In Figure 4C, the
operator has actuated a drive motor which rotates saw 60
in the manner hereinafter described in greater detail
and has actuated a pair of hydraulic rams (not shown)
S which gradually advance rotating saw 60 across the base
of tree falling head 54 and into tree 200. In Figure
4D, saw 60 has been fully advanced to completely sever
tree 200 from stump 202 and the operator has manipulated
arm 52 to lift tree 200 free of stump 202. Saw 60 in-
cludes a stationary platform which supports the severedtree. After the tree has been severed, the operator
manipulates arm 52 to deposit the tree ~t any desired
location.
Saw 60 (which is shown in greater detail in
Figures 5 and 6) comprises an upper, stationary platform
disc 70 and a lower, rotatable cutting disc 72. A plur-
ality of cutting assemblies of the type described above
and each comprising a cutting element 10 and a holder 30
are welded around the outer rim of cutting disc 72. As
may be seen in Figure 6, the cutting assemblies are ar-
ranged to protrude alternately above the plane of plat-
form diqc 70 and beneath the plane of cutting disc 72.
The shaded portions 74 of cutting elements 10 do the
actual cutting when saw 60 is rotated. Preferably, no
more than about ten to fifteen percent of each of cut-
ting elements 10 (i.e. shaded portions 74) protrude
above platform disc 70 or below cutting disc 72 so as to
present as little resistance as possible, should the
operator wish to withdraw saw 60 from a partially
severed tree.
Cutting disc 72 rotates around a bearing 76
which is supported by a steel bearing retainer 78. A
non-metallic wear ring 80 separates cutting disc 72 from
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stationary platform disc 70 and absorbs frictional
forces therebetween, as well as impact loads imparted to
either disc.
Support arms 82, 84, 86 having non-ferrous
(i.e. brass) wear pads 88, 90, 92 are suspended from
yoke 53 to slidably support the underside of disc 72 as
the disc is advanced and retracted with respect to yoXe
53. Support arms 82, 84, 86 resist forces which might
distort the shape of discs 70, 72 during the tree cut-
ting operation, (such distortion is undesirable because
it might allow the saw drive motors to disengage) and
also relieve the load on bearing 76. Wear pads 88, 90,
92 must be periodically adjusted by extending them up-
wards from arms 82, 84, 86 to close the gap between pads88, 90, 92 and disc 72 caused by wearing of the pads.
Cutting disc 72 is rotated by a pair of
hydraulic drive motors 94, 96 having drive gears 98
which mesh with an internal spur gear 100 around the
internal circumference of a ring 102 set into and rigid-
ly affixed to cutting disc 72.
Drive motors 94, 96 preferably rotate cutting
disc 72 at a relatively slow speed of about 1,300 feet
per minute. This permits the application of a relati-
vely high drive torque (approximately 4,000 foot-pounds)
to cutting disc 72, which in turn tends to limit the
wearing abrasion of cutting elements 10 as compared with
conventional circular saws rotated at speeds in the
15,000 to 18,000 foot per minute range. The slower cut-
ting speed also reduces significantly the stresses
imparted to saw 60 in overcoming the rotational inertia
of the saw (which increases with the saw speed) as the
rotational plane of the saw is displaced.
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Cutting element sharpness is not particularly
critical at high drive speeds since the high inertia of
the rotating saw usually suffices to cut the tree,
although a relatively poor quality cut often results
which limits the saleability of the lumber, particularly
in foreign markets. A further disadvantage of high
speed saws is that vibration problems are often
encountered, necessitating careful balancing of the saw.
Furthermore, it is usually necessary to continually
power a high speed saw, since it can take ten seconds or
longer to bring the saw rotation speed up to the 15,000
to 18,000 foot per minute range. By contrast, drive
power need only be applied to the saw of the preferred
embodiment just prior to commencement of the cutting
operation since the saw can very quickly be brought up
to the preferred 1,300 foot per minute speed.
Lubricating oil is injected between the
rotating discs 70, 72 in the region between drive motors
94, 96. The oil flows from the central disc area toward
the outer rim of the discs, thereby tending to flush
foreign matter from between the discs.
As will be apparent to those skilled in the
art in the light of the foregoing disclosure, many
alterations and modifications are possible in the prac-
tice of this invention without departing from the spirit
or scope thereof. Accordingly, the scope of the inven-
tion is to be construed in accordance with the substance
defined by the following claims.
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