Note: Descriptions are shown in the official language in which they were submitted.
CA 02251902 1998-10-28
This invention relates to tree felling heads, particularly those of the type
using circular saw blades for tree felling, and in particular to a head having
a saw blade
with replaceable teeth.
Tree felling disc saws such as first described in United States patent nos.
4,445,552 (Hyde) and 4,491,163 (Kurelek) and later modified by, amongst
others,
United States patent nos. 5,377,731 (Wildey) and 5,085,112 (MacLennan), are
constructed to be unusually sturdy (e.g. 1 inch thick) and to cut an unusually
wide kerf
(e.g. 2-inches thick). The sturdiness is necessary to allow relatively poorly
controlled
machine travel or knuckle boom reach to be used to feed the saw through the
tree.
This requires a thick blade to resist bending from errant feed motion, and
accordingly
a wide kerf to give clearance for the blade in the cut. In addition, after the
tree is cut,
the designs are necessarily such that the butt of the still vertical tree does
not rest on
any top surface of the rotating saw, but on a fixed butt plate which is
recessed into the
saw, as illustrated for example in Fig. 5 (prior art). The saw's kerf must be
wide enough
to allow entrance of the combined thickness of this butt plate and the
rotating blade and
still have some clearance left over on the bottom for head drop, which occurs
as a cut
is completed and the weight of the tree is added to what the machinery is
supporting.
It is because of these greater strength and wider kerf needs on tree felling
applications that thin, commercially available circular crosscut saw blades
such as
those marketed by Simonds, with for example a 1 /4 inch blade and 7/16 inch
kerf, could
not be applied to tree felling. Some early tree felling machines temporarily
solved the
disc strength and wide kerf needs by crudely fabricating saws with integral
teeth, similar
to some inexpensive cross cut saws, but from approximately one-inch thick
steel plate
and with alternate teeth bent up and down to cut a two-inch kerf (see for
example
United States patent no. 4,270,586 (Hyde et al.)).
It was thought that toughness on the job to protect against breakage from
encounters with rocks was a most essential feature and that if the cutting
points dulled
they could be touched up with a grinder or even rebuilt by welding many times
during
the life of the relatively expensive steel disc. However, it soon became
obvious that
loggers tended not to take the time to rebuild and sharpen teeth and were
running with
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CA 02251902 1998-10-28
such dull saws that power consumption was high, productivity was low and blade
stresses so high that cracking at the gullets was occurring.
As it became apparent that loggers would pay more for a saw with
replaceable, keener cutting teeth, various "bolt-on" ideas were devised and
used.
Some examples can be seen in United States patent nos. 4,750,396 (caddis),
4,563,929 (Ringlee), 5,085,112 (MacLennan), 5,303,752 (MacLennan), 4,879,936
(Anderson), 5,211,212 (Carlson et al.), Des. 320,542 (Gilbert), 5,377,731
(Wildey) and
4,932,447 (Morin).
Although these devices sever trees from the stump well and some are
relatively easy to maintain, they all have various drawbacks, including some
which are
safety-related. They all depend on threaded fasteners to retain their teeth
and or tooth
holders. Some have many parts (as many as 6 per tooth) which can potentially
be
thrown if those threaded fasteners wear out, unscrew or break.
Others with fewer parts, such as in United States patent nos. 5,377,731
(Wildey) and 4,932,447 (Morin), have large gaps between teeth where the ends
of
sticks of wood can enter and be thrown. Manufacturing clearance requirements
dictate
the apparently excessive gap of these saws. United States patent no. 4,446,897
(Kurelek) showed a taper-held replaceable tooth in a continuous rim, but an
optimal
method of holding such teeth in place against cutting forces was never
devised. United
States patent no. 5,261,306 (Morey et al.), is exceptional in providing
reduced throw
probability by having a saw blade periphery advantageously contoured with
bumps to
at least effectively reduce the throw gap between teeth at the circumference,
but tooth
retention is very dependent on a threaded fastener.
The bolt and screw parts used on many tooth holding applications present
many chances for errorthat can result in parts being dangerously thrown. For
example,
incorrect installation torque can result in loosening, or unseen fracture; the
fasteners
are vulnerable to poor quality choice or supply during servicing by the user;
the screw
head sockets can fill with tree gum and be difficult to remove, and hence
delay timely
maintenance; and the fasteners, holders and rim can be significantly weakened
by
wear (from wood chips and sand), which is not automatically corrected when
teeth are
replaced.
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CA 02251902 1998-10-28
Figs. 15 and 16 (prior art) illustrate the throw gap which results from
several typical prior art shank and bolt tooth attachment methods. Fig. 15
shows the
blade from above, and Fig. 16 shows the blade edge-on. It is known that a
tangentially
oriented wooden stick, somehow accidentally and rapidly fed at the saw rim of
teeth,
can be dangerously thrown if a radial face of a moving saw tooth can contact
sufficient
of the stick end grain area to instantly accelerate it to tooth tip velocity
without cutting
or fracturing out a relatively harmless chip of wood. The exact values of such
numbers
as saw rpm, tooth velocity, stick size, stick density and weight and the
engagement
area at which throwing rather than cutting occurs are virtually impossible to
calculate
and design against. However, it is reasonable to predict that for any given
saw speed,
the greater the gap between the face of a tooth and the back of the previous
passing
tooth, the more likely it is that a stick end will occasionally enter the gap
sufficiently to
be thrown. A stick might enter a gap from either the top or the bottom or the
circumference of a saw toothed rim. It is also evident that near horizontal or
tangential
stick angles would most likely result in a spear-like throw if the saw does
not break a
chip out of the stick. A continuous smooth rim which would not be able to
throw cannot
be used because at least enough gap needs to be provided as a gullet to accept
the
wood chips being cut loose and to carry them out of the cut for expulsion.
There has thus been a need for a felling saw blade that would have a
relatively smooth circumference with only enough tooth protrusion to do its
share of
cutting and enough gullet gap to carry its wood chips out of the kerf in the
tree. I n such
a blade, the tooth retention method should not depend on threaded fasteners,
and wear
in excess of normal such as might occur on poorly maintained machines should
not
result in tooth parts or tooth holders being thrown, but rather the saw should
cease to
cut at a sufficiently productive rate, so that new teeth will have to be
installed.
For the work of cross-cutting already-felled trees into logs, the saw mill
industry has long known the art of using arcuate (C-shaped) replaceable teeth
in
circular sockets. In United States patent nos. 67,682 (Strange), 80,929
(Disston),
81,811 (Miller), 108,059 (Smith), 142,258 (Miller), and 488,336 (Kendall), we
see very
early examples of single piece arcuate shaped teeth that are rotated into
their sockets
and held there by developing some press fit. In United States patent nos.
289,715
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(Risdon), 313,427 (Johnson), and 368,999 (Emerson), we see examples where an
additional non-threaded fastener is used to retain the one-piece tooth against
rotation
in the removal direction, but not to stop rotation caused by the impact of
cutting (which
always rotates the tooth further into its socket). This very old art showed
that rotation
of the tooth in its socket from cutting forces could be stopped by providing
stops in the
socket to contact the tooth either at its tail or at the back of its head or
both. More
recent related United States patent nos. 4,955,273 and 5,092,212 (both
Pawlosky) are
to the same effect.
It was thought by logging saw designers that this existing saw technology
for freely cross-cutting already felled trees and logs would not stand up to
the abusive
job of cutting trees and brush in the woods. The saw blade with its axis
vertical would
have to be strong enough to, at certain times of use, support a tree bearing
down on
it near its circumference. At other times the weight of the felling head and
part of the
supporting boom would push the blade down on a stump. A much thicker blade
would
therefore be needed. The thickness would depend on the saw head design and the
working conditions, but generally whereas cross-cut teeth are a maximum of
0.18
inches thick, various tree felling, stump clearing and brush cutting work
would require
tooth thicknesses mainly in the range of 1" to 2-1/2" thick, although other
thicknesses
are possible.
Merely scaling up the prior art crosscut blades and their teeth, however,
is not usable in practice. There are some problems associated with attempting
to do
so, which the present invention overcomes.
One such problem is that the arcuate teeth of prior art cross-cut saws are
designed to be installed at the required snap-in or holding press fit by a
single person
with a reasonable manual effort. Obviously, it would be equally desirable for
the teeth
of felling type saws to be installable by a single person with only reasonable
manual
effort. However, if with no other modifications the width of prior art teeth
was increased
to cut the kerf width that would be needed for tree felling, the insertion
torque required
would increase exponentially to unmanageable values.
Another problem is that all of the above prior art arcuate tooth inventions
show that the teeth are held in their sockets against axial or twisting-out
movement by
CA 02251902 1998-10-28
a relatively steep-angled V-groove at their circumference, which engages over
a V-
pointed ridge which takes up the entire bore of the socket. With some
modifications to
arc shaping and a switch to a two piece tooth design, arcuate teeth in
circular sockets
are to this day held against axial movement by such steep angle V grooves.
Tooth
rotation torque is dependent on the forces normal to the V surfaces.
If a felling saw tooth was to be 1.8 inches thick instead of 0.18 as in a
typical cross-cut saw, a simple calculation warns that the radial force to
collapse the C-
shape of the tooth into its socket would be ten times as great as for the
cross-cut saw
tooth, and that if the same V-angle was maintained, the normal forces and
hence
rotational torque would also be so increased, making manual tooth replacement
virtually
impossible.
It is thus an object of the invention to provide an improved tree felling
head, using a saw with a saw blade with teeth which are readily replaceable
but
securely installed.
In particular, it is an object of the invention to modify the cross-cut type
of circular socket and tooth insertion and retention methods, so that it
becomes usable
for thick disc saws, with reduced risk of tooth parts and wood pieces being
thrown
during tree and brush cutting.
It is a further object, of the preferred embodiment, to avoid the use of
threaded fasteners or the like to secure the teeth.
It is a further object, of the preferred embodiment, for the teeth to
constitute the only significant early wear elements, so that replacement of
the teeth
restores the blade to nearly-new condition, for a longer safe service life
than in the prior
art.
The invention uses replaceable teeth which are arcuate, i.e. generally C-
shaped, combined with novel insertion and retention means. As discussed above,
arcuate teeth are known in the prior art of cross-cutting saws, but were
thought to be
unsuitable for tree felling, or at least were never adapted to tree felling.
In the invention,
it was realized that with suitable modifications and adaptations, the circular
socket type
of cross-cut tooth insertion and retention could be used to great advantage
for tree
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CA 02251902 1998-10-28
felling disc saws, and that among other advantages, this would reduce the risk
of tooth
parts and wood pieces being thrown during tree felling operations in the
forest.
The invention provides a robust circular saw blade for cutting a wide kerf
as is necessary in high-speed tree felling, by providing a disc with arcuate
sockets in
its rim, to accommodate arcuate teeth which project only a minimal distance
from the
circumference of the disc. This reduces the probability of sticks or chunks of
wood
being thrown during tree felling and brush cutting operations. The teeth are
of a width
sufficient to cut a kerf of sufficient width to accommodate the rim with only
a small
clearance as the blade advances. The teeth are rotated into the sockets and
held in
place by a combination of dimensional entrapment and a press fit, so as to
avoid
dependence on threaded fasteners or the like.
Furtherfeatures of the invention will be described orwill become apparent
in the course of the following detailed description.
The invention will now be described in detail with reference to the
accompanying drawings of the preferred embodiment by way of example. In these
drawings:
Fig. 1 is a plan view of the preferred embodiment of the blade in the
invention;
Fig. 2 is a side cross-sectional view of the blade, at A-A of Fig. 1;
Fig. 3 is an exploded perspective showing one of the teeth, the
corresponding socket in the rim of the blade, and a pin to prevent out-
rotation;
Fig. 4 is a perspective view corresponding to Fig. 6, showing the tooth
installed in the rim;
Fig. 5 (prior art) is a schematic side view showing a saw cutting a tree;
Figs. 6A-6D are illustrations of alternative key means between the tooth
and its socket in the rim;
Figs. 7-11 are consecutive views showing the sequence of installation of
a tooth;
Fig. 12 is a plan view showing one of the teeth in its socket;
Fig. 13 is a cross-section at B-B of Fig. 12, showing a pin which prevents
out-rotation of the tooth;
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CA 02251902 1998-10-28
Fig. 14 is a cross-section at C-C of Fig. 13, showing the pin in more detail;
Fig. 15 (prior art) is a plan view showing a typical "throw gap" in the prior
art;
Fig. 16 (prior art) is a side view showing the throw gap;
Fig. 17 is a plan view showing the reduced throw gap in the present
invention;
Fig. 18 is a side view showing the reduced throw gap in the present
invention;
Fig. 19 (prior art) is a plan view showing prior art gullet wear;
Fig. 20 is a plan view showing a blade with view showing gullet wear in
the present invention;
Figs. 21 A and 21 B are side and plan views respectively of an alternative
rim configuration with swellings or "pods" for the teeth;
Fig. 22 is a side cross-sectional view of an alternative tapered rim and
tooth;
Fig. 23 is a front view of an adapter for use with a wrench for installation
of a tooth;
Fig. 24 is a side view of the adapter;
Fig. 25 is a front view of an alternative adapter, having a hex drive instead
of a square drive as in the Fig. 23 adapter;
Fig. 26 is a side view of the Fig. 25 adapter;
Fig. 27 is a front view of a special wrench for installation of a tooth,
integrating the features of the adapter of Fig. 23;
Fig. 28 is a side view of the special wrench of Fig. 27; and
Figs. 29-31 show, in sequence, the installation of a tooth using the wrench
of Figs. 27-28.
The saw blade 1 comprises a disk 2 and multiple removable teeth 3. The
disc has an integral hub 4, web 5, and rim 6. The teeth are arcuate, i.e.
generally C-
shaped, with an open gullet 7, and are installed in correspondingly-shaped
sockets 8
in the rim 6. In the preferred embodiment, the rim 6 is substantially thicker
than the web
5, at least in the area of the teeth. The hub 4 is a mounting means for
bolting the blade
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CA 02251902 1998-10-28
to the drive means (not shown, but similar for example to that shown in Fig. 5
(prior
art)).
Because of the robust equipment needs for tree felling, the rim 6 at least
in the region of the teeth is preferably at least about 1-1/4 thick and
preferably closer
to 2 inches thick, i.e. approximately in the range of 30-50 mm. The teeth
accordingly
are sized to cut a kerf which is even thicker, e.g. about 2-1 /8 or 2-1 /4
inches for a 1-7/8
inch rim. This distinguishes this type of saw from the much flimsier type of
crosscut saw
mentioned above, where the thickness of the blade around the teeth typically
may be
only 3/16 to 1/4 inches.
In the flimsiest version of the invention for harvesting small trees, the rim
at least in the area around the teeth would still typically be at least 3/4
inch thick and
the kerf would typically be at least 1-1/4 inches thick to allow room for a
butt plate in
cases where a butt plate is used, or typically at least 1 inch thick with no
butt plate.
Most applications of the invention will require tree gathering and hence
a butt plate will be used, but for some applications such as clearing brush or
cutting
stumps, i.e. applications other than tree harvesting, there is no need for
tree gathering.
Such applications may not have a butt plate, so narrower kerfs and thinner
teeth than
customary for tree felling may be used. In other applications, smaller and
larger
diameter saws will require an even greater range of tooth thicknesses. For
example,
a very large diameter saw might be used for clearing stumps from previously-
logged
sites. Such a saw might have a 120-inch diameter, and although no butt plate
would
be required to support the weight of a tree, the disc thickness and kerf could
be say 2
and 3 inches respectively. At the other extreme, for limb and brush clearing,
again with
no butt plate required, the saw may be only 20 inches in diameter, with a 1/2
inch blade
and rim and a 3/4 inch kerf. In such saws, the rim is not necessarily thicker
than the
web or main body of the blade, i.e. there may be no distinction between the
"rim" and
the web, in which case "rim" simply means an outer portion of the blade
adjacent the
circumference. For greater clarity, the expression "rim portion" is used in
the claims,
to indicate the area adjacent the circumference, regardless of whether or not
there is
in fact a discrete "rim".
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CA 02251902 1998-10-28
Returning to the preferred embodiment, however, the web 5 is made
thinner both for weight reduction and in order to accommodate a butt plate 9,
as known
in the prior art and as shown in Fig. 5 (prior art). Preferably but not
necessarily, this is
accomplished by machining the disc to reduce the height of its upper surface
inward
from the rim, sufficiently to allow room for the relatively thick butt plate.
This is as shown
in Fig. 5 or in Figs. 6A-6D.
In the preferred embodiment, as shown best in Figs. 3, 4 and 6A, each
socket 8 has a square male key portion 10 preferably but not necessarily
centered on
the plane of the rim, and each tooth 3 has a corresponding female recess 11 to
receive
the male portion, to ensure and maintain the proper alignment of the tooth
relative to
the plane of the disc. As illustrated in Figs. 6B-6D, alternative keying means
clearly
could be employed. For example, the sockets could have female portions with
the teeth
having the male portions (Fig. 6B), although this would rule out the preferred
type of
retainer pin 30. Alternatively, one could use a shallow V-shaped key (Fig.
6C), although
this would not be as stable for thick teeth and would certainly not be
preferred, for the
reasons stated above in the Background of the Invention. As yet another
alternative,
multiple grooves could be used (Fig. 6D), although that would be somewhat
complicated. It should be clear that the scope of the invention encompasses
any and
all suitable keying means, not just the preceding. The essence of the
invention does
not reside in the keying means.
Using the preferred keying means avoids the above-mentioned difficulties
which would make manual tooth replacement virtually impossible with a V-shape.
The
preferred keying means provides easier size control, a smaller outer diameter
and a
parallel bore, achieving manageable insertion rotation torques.
Existing felling saw art uses different shaped cutting tips to suit various
tree and ground conditions. Similarly, the teeth in this invention may be
variously tipped
as desired. Figs. 6A-6D, for example, shows just one of many possible angled
surface
variations, by contrast to the preferred curved configuration of Fig. 3. It
should be
understood that for the purposes of this description a tooth that has a
relatively small
and light carbide tip brazed into a seat is still considered a one-piece
tooth. Even
though this does add another piece that can be thrown if not carefully
attached, the
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CA 02251902 1998-10-28
requirement for such carbide tips depends on the soil conditions of the
logging site and
not on the type of saw being used.
Figs. 7-11 show the sequence and the principle of installation of a tooth
in its socket. Essentially, the tooth is rotated into place. Fig. 7 shows the
tooth 3 being
hooked into the socket 8. Fig. 8 shows it being rotated freely about its tail
into its
socket. It rotates freely until reaching the position of Fig. 9. Fig. 9 shows
a special
wrench 20 having protruding pins 19 which are applied to the holes 21 (one of
which
holes is also used for the pin 30 described later) to produce about 40°
of initial rotation
from the Fig. 9 position to the Fig. 10 position, during which the arcuate
outside
diameter is being pressed in to match the inside diameter of the socket.
Preferably, the teeth and their sockets are concentric circles, with the
inside diameter of the socket being slightly smaller than the outside diameter
of the
tooth. The slightly smaller diameter ensures a press fit during an additional
approximately 40° of tooth rotation, from the position of Fig. 10 to
the position of Fig.
11, developing a dimensional entrapment for the tooth. This last 40°
requires
considerable continuous torque, say 300 ft Ib..
Obviously, the specific angles of rotation in the preceding are not critical
to the invention. What is important is that the teeth fit tightly against
rotation, e.g. by
use of a slightly smaller diameter socket, and that a final additional angle
of rotation
after 180 degrees of socket contact is sufficient to create a dimensional
entrapment for
the tooth in the socket.
After the last 40 degrees or so of rotation, in the preferred embodiment
a tail portion 24 of the female recess 11 of the tooth butts against a
complementary-
shaped tail stop 26 machined into the rim so as to project inwardly within the
socket,
to provide a transverse stop surface. This completely prevents any further
rotation of
the tooth in its socket from cutting forces, i.e. forces at the tooth tip
resulting from
whatever the tooth is contacting.
Alternatively, it may be possible to make both the socket and the tooth
slightly elliptical, such that the major axes of the ellipses coincide when
the tooth is fully
rotated into its installed position, for a possibly somewhat relaxed fit, and
such that
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CA 02251902 1998-10-28
there is a very tight press fit otherwise, i.e. when the tooth is rotated away
from the fully-
installed position.
While Figs. 7 - 11 explain the theory of tooth insertion and removal in a
simplified manner, it is found in practice that during insertion, at the
position shown in
Fig. 9 or slightly later, as the tooth begins to be squeezed by virtue of the
slightly
smaller socket diameter, the resultant of forces on the tooth may choose to
rotate its
tail end out of contact with the socket and abort the installation, even when
the bent
handle in the Fig. 10 position is used. Although a solution to this is to have
an assistant
tap the wrench and tooth radially in with a plastic maul as it is being
rotated, this cannot
be accepted as practical forthe industry. Preferably, therefore, an adapter as
illustrated
in Figs. 23-24 or Figs. 25-26 is used instead. The adapter has a square drive
socket
34 as shown in Figs. 23-24, or a hex drive peg 35 for a hex wrench, as shown
in Figs.
25-26, so that it can be readily driven manually or with power tools. It has
dowel pins
19 pressed into its body 36, protruding therefrom to engage the holes 21. The
tooth is
kept centered as it rotates, by virtue of a tongue 33 which is integral with
the adapter
and which rides in the arcuate socket as the tooth rotates, as can be seen
from Figs.
23 and 25 (or better still from Figs. 29-31 referred to below). The tongue 33
is a circle
segment 33 which in effect sufficiently completes an arc of a circle to ensure
at least
180 degrees of contact with the socket. Otherwise, ignoring friction which
tends to keep
it in place, the tooth could pop out during the rotation leading up to the
final 40 degrees
or so of rotation. After the final 40 degrees of rotation, a total of about
220 degrees of
contact is obtained, so that the tooth can only be removed by out-rotation.
As shown in Figs. 27-28, the tongue 33 could be made integral with a
wrench 20 such as the one described earlier above, although providing this
functionality
via an adapter such as the ones of Figs. 23-26 is simpler. In such a wrench,
there may
be provided a square drive socket hole 15, a rubber bumper 16 which can double
as
a rubber hammer, and a support 17 for the rubber bumper. Figs. 29-31 show, in
sequence, the installation of a tooth using the wrench.
Although Figs. 9 -11 show a handle on the wrench so that tooth changes
could be made remote from power tools, it is expected that air wrenches will
often be
used, with drive adapters such as shown in Figs. 23-26.
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CA 02251902 1998-10-28
In other tree felling saws such as Morin, Wildey, MacLennan and Gilbert,
the teeth are attached in such ways that the force of cutting at the tooth
tips has a
tendency to tip or rotate the cutting part of the tooth in such a direction
that bending
stress concentrations can occur at a reduced section shank or at a fastener.
In the
invention, by contrast, the cutting forces on the tooth tend mainly to further
rotate the
tooth into its socket in compression against the tail stop 26, avoiding all
section change
stress concentrations.
As an alternative to such a tail stop 26, clearly other stop means could be
used to prevent further rotation. For example, though not illustrated, a
transverse pin
or a transverse or radial or tangential bolt could be used to provide the stop
surface.
However, this is considerably less desirable than the preferred embodiment,
since it
creates dependency on the pin or bolt to withstand the forces transmitted from
tooth
collisions with wood or other material, with the attendant maintenance and
safety
concerns referred to earlier above. The inventor would not recommend or choose
such
alternative embodiments, but it should be clearly understood that they are
intended to
be included within the scope of the invention, should someone choose to adopt
such
an inferior stop means as a way of attempting to circumvent the patent.
The press fit of the tooth in its socket in itself is sufficient to prevent
any
possible unintentional out-rotation of the teeth once installed, especially
since cutting
forces are in the opposite direction. However, as an added precaution against
improper
(reverse rotation) operation, for discouragement of tooth theft in the field,
and for
greater psychological reassurance in some sensitive operating locations, a pin
may be
provided, such as a roll pin 30 as shown in Figs. 12-14. The arrangement is
dimensioned in such a way that the pin is pressed only into its hole in the
tooth and thus
remains tight in the tooth. When a tooth is fully installed, there is a
clearance space 31
for the pin in the blade, so that it does not received any of the forces from
cutting. Nor
does the pin hold the tooth with its tail portion 24 tightly against stopping
means as in
the prior art such as the above-mentioned MacLennan, Wildey, Morin and Gilbert
patents. The pin comes into play only if out-rotation begins, i.e. it must be
removed if
out-rotation is desired for replacement of a tooth. The pin would however
prevent
accidental out-rotation of teeth should the hydraulics of the machinery be
inadvertently
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CA 02251902 1998-10-28
connected to turn the motor in the "wrong" direction, and should tree cutting
then be
attempted. It is known that a capscrew or a bolt might also be used in this
same
location if head and nut space are provided, but this is not recommended,
since that
would introduce a threaded fastener with its inherent drawbacks. The fact that
the pin
is installed in the tooth and not in the blade means that repeated
installation and
removal of the pin does not cause any accumulated wear on the blade, such as
might
cause a loose pin over time. If rivets were used, as on some old crosscut
saws,
special machinery would be required to install and remove them, given the
relatively
large size that would be needed. Clearly, this would be bad for in-field
maintenance.
A particular advantage of the invention is that it provides a highly effective
solution to the previously described problem of sticks potentially being
thrown. As can
be seen from Figs. 17 and 18, a very short throw entry gap can be achieved,
and with
it an end grain engagement chance that is very substantially less than the
engagement
chance in felling saw prior art. Comparing Fig. 15 (prior art) with Fig. 17,
and
comparing Fig. 16 (prior art) with Fig. 18, shows greatly reduced throw entry
gaps in
both planes, e.g. from an inch or more of engagement x (Fig. 15) to possibly
less than
half an inch engagement (Fig. 17) with a stick 40 oriented more or less
tangentially, in
the plane of the saw or at a small angle a thereto (Figs. 16 and 18). In the
invention,
the throw gap y can be less than two inches, and easily less than 3 inches.
A small engagement means that the tooth tends to take a harmless chip
out of a stick, without accelerating the stick, whereas a larger engagement
can provide
enough end grain in compression to transmit sufficient acceleration force to
the stick
to accelerate it.
As shown in Fig. 19 (prior art), the flow of wood chips from the cutting tips
in felling saw prior art tooth and blade systems severely wears the gullet
area radially
inwardly from the tooth tips, resulting in a worn section 45. This gullet area
is part of
the blade disc or rim proper or in some designs part of a tooth holder. Thus
replacing
worn teeth does not remedy this wear, and after several tooth changes it
sometimes
becomes necessary for safety to replace the blade or holder as well. By
contrast, as
shown in Fig. 20, the gullet 7 in the present invention is part of the tooth
itself, so that
most of the wear, as shown in the worn middle tooth of Fig. 20, is on the
replaceable
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CA 02251902 1998-10-28
tooth itself, although the socket adjacent the tail stop will wear slightly as
well. The
right-hand tooth of Fig. 20 is a replacement tooth. Note that the socket
immediately
adjacent its tail stop has eroded somewhat. However, further wear is partially
prevented by the fact that the new tooth juts out slightly from it. The
overall result, in
any event, is that the disc does not receive wear to the same degree as in the
prior art,
and therefore can be expected to have a much longer life.
Many variations on the preferred embodiment of the invention are
possible, within the scope of the invention, in addition to those already
mentioned
above. As just one example, it should be clear that the rim need not have a
continuous
thickness around the circumference of the disk, and need not have the same
cross-
section as in the preferred embodiment. All that is required is that the rim
be thick
enough in the area of the tooth to accommodate the tooth. Thus there could be
a
relatively thin rim 6, 1 inch for example instead of the preferred 1-1/4 to 2
inches, with
tooth mounting swellings or "pods" 50, i.e. bulged out areas which are
suitably radiused
and tapered so as not to provide an exposed surface which could engage and
throw
a stick, as illustrated in Figs. 21A and 218. Such a configuration, although
more
expensive to manufacture, would be somewhat lighter and would allow a little
extra
space for air and chips to flow, thus improving self cleaning.
For some uses the rim could be tapered inwardly, possibly with teeth
tapering similarly, as illustrated in Fig. 22. This configuration might reduce
weight and
friction while retaining the advantage of a small throw gap, but air and chip
flow might
not be as improved. Thus throughout this specification, it should be clearly
understood
that the word "rim" is not intended to denote necessarily a continuous rim or
a rim of
constant cross-section.
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