Note: Descriptions are shown in the official language in which they were submitted.
CA 02236657 1998-OS-04
SAW TOOTH MOUNTING SYSTEM AND SAW TOOTH
Technical Field
This invention relates to a system for mounting teeth in a
circular saw. The system has particular application in circular saws of the
type used for severing trees in feller bunchers and other tree-felling
machines. Another aspect of the invention relates to a saw tooth for use
in a circular saw equipped with a mounting system according to the
invention.
Background
Some automated tree felling machines, such as the TK series
feller bunchers manufactured by Risley Manufacturing Ltd. of Grande
Prairie, Alberta, Canada incorporate a circular saw for severing trees.
The circular saws in such machines comprise a disc-like blade and a
drive mechanism which can cause the blade to turn rapidly about its axis.
The blade is mounted on a carrier which may be advanced in the plane
of the blade to move the blade into a log. The blade has cutting teeth
around its periphery.
The cutting teeth on such saws experience harsh treatment
and require periodic replacement. In most modern blades of this type, the
cutting teeth are on cutting elements which are removably attached to
holders located around the periphery of the blade. The cutting elements
may be removed and replaced if they become damaged or worn.
Generally, the cutting elements are rotatable in the holders so that a fresh
cutting surface may be exposed by simply rotating the cutting elements
in the holders. The ROTOTOOTH'~ teeth available from Risley
Manufacturing Ltd. of Grande Prairie, Alberta, Canada are an example
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Ltd. of Grande Prairie, Alberta, Canada are an example of replaceable
cutting elements for saws of this general type.
In general, in saws of the nature described above, the cutting
elements are attached to the holders with bolts. While it is much more
convenient to replace the cutting elements of a saw blade, as described
above, than it is to replace permanently mounted cutting elements, it is still
time consuming to change, or even to rotate, the cutting elements on a saw
blade. A saw blade typically has 16 or more cutting elements. Rotating or
removing each cutting element requires a bolt to be loosened and
subsequently re-tightened. Thus, the machine on which the saw blade is
mounted is typically out of service for one hour, or more, each time it
becomes necessary to rotate or replace the cutting elements on the saw
blade. This machinery down time can be expensive.
Some prior cutting elements for use in circular saws include
a shaft extending rearwardly. The shaft is received in a sleeve which is
axially welded on the periphery of the saw blade. An example of a saw
blade having a cutting element of this configuration is shown in United
States Patent No. 4,932,447 to Morin. The Morin design provides locking
pins which must be removed each time a cutting element is to be rotated
or replaced.
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Plante, United States patent No. 5,363,891 discloses a saw
blade having tubular saw teeth which are friction fitted into tubular
mounts. A special tool is required to remove or rotate the hollow teeth.
The Plante tooth provides an axial gap between the tooth and the mount
so that all impact forces on the tooth are transmitted through the friction
fitting between the tooth and the mount. This can be disadvantageous.
Summary of the Invention
One aspect of this invention provides a rotatable saw blade
for a tree felling apparatus. The saw blade comprises: a body adapted to
be drivingly rotated in a direction of rotation; a plurality of holders
affixed at uniformly spaced apart locations around a peripheral edge of
the body and a cutting element received in each of the holders. Each of
the holders comprises a socket facing in the direction of rotation of the
body and a bearing surface adjacent the socket on at least two opposed
sides of the socket. The socket has an inner surface providing a self
holding taper. An aperture extends through the holder from a rear portion
of the socket. The aperture may be used to drive a cutting element out of
the socket or to receive a fastener for drawing the cutting element into
the socket. The cutting elements each comprise a shank received in the
socket and having the same self holding taper as the socket. A front
portion is attached to the shank. The front portion has a cutting edge
facing in the direction of rotation and a rear face in bearing contact with
- the bearing surface on the holder.
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In one embodiment of the invention a threaded fastener
extends through the aperture and holds the shank tightly in the socket.
The holder preferably comprises an elastically deformable U-shaped
member straddling a peripheral edge of the body. The U-shaped member
preferably comprises first and second plates respectively on first and
second sides of the body and two or more fasteners extending between
the side plates through apertures in the body. The socket is dimensioned
to tightly engage the shank. When a cutting element is not present in the
socket, the socket preferably has a maximum diameter slightly smaller
than a maximum diameter of the shank, wherein the side plates of the U-
shaped member are spread slightly when the cutting element is fully
engaged in the socket. The stiff resilient springy nature of the side plates
helps to hold the shank firmly in the socket despite the impacts and
vibrations to which the cutting element must typically endure. The self
holding taper is preferably in the range of 0.45 inches per foot to 0.80
inches per foot.
Another aspect of the invention provides a cutting tooth
assembly for use in a saw. The assembly comprises a holder and a
cutting element which is receivable in the holder. The holder comprises
a member defining a socket, a bearing surface adjacent the socket and an
aperture extending through the holder from a rear portion of the socket.
The bearing surface extends on at least two opposed sides of the socket.
The socket has an inner surface providing a self holding taper. The
cutting element comprises a shank portion dimensioned to be received in
the socket and having the same self holding taper as the socket. A front
portion is attached to the shank portion. The front portion has a cutting
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edge facing forwardly and a rear face. The rear face is in bearing contact
with the bearing surface on the holder when the cutting element is
received in the holder. Preferably the holder comprises an elastically
deformable U-shaped member comprising first and second side plates
connected by a bight portion. Preferably, when the cutting element is not
present in the socket, the socket has a maximum diameter slightly smaller
than a maximum diameter of the shank so that the side plates of the U-
shaped member are spread slightly when the shank is fully engaged in the
socket. This helps to retain the shank in the socket.
Yet another aspect of the invention provides a cutting
element for removable attachment to a saw, the cutting element com-
prises: a solid shank having an outer circularly symmetrical surface, the
outer surface tapered with a taper in the range of 0.45 inches per foot to
0.8 inches per foot; and, a front portion attached to the shank, the front
portion having a cutting edge on its side away from the shank and a flat
rear face surrounding the shank.
Still another aspect of the invention provides a method for
affixing a cutting element to a rotatable saw in a tree felling apparatus.
The method begins by providing a cutting element comprising: a solid
shank having an outer circularly symmetrical surface, the outer surface
tapered with a taper in the range of 0.45 inches per foot to 0.8 inches per
foot; and, a front portion attached to the shank, the front portion having
a cutting edge on its side away from the shank and a flat rear face
surrounding the shank. The method continues with the steps of inserting
the shank into a socket having the same taper as the shank until the shank
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is snug in the socket and the flat rear face is spaced apart from a bearing
surface adjacent the socket; and, resiliently deforming the socket slightly
outwardly by driving the shank farther into the socket until the flat rear
face is bearing against the bearing surface.
Brief Description of Drawings
In drawings which illustrate preferred embodiments of the
invention but which should not be construed so as to limit the scope of
the invention:
Figure 1 is a top plan view of a saw blade having a plurality
of cutting elements mounted according to the invention;
Figure 2A is an expanded fragmentary top plan view of a
portion of the saw of Figure 1 with a single holder and cutting element;
Figure 2B is a section through the holder and cutting element
of Figure 2 in the plane of the saw blade;
Figure 2C is a section through a holder and cutting element
according to an alternative embodiment of the invention in the plane of
a saw blade;
Figure 3 is a sectional view through the holder and cutting
element of Figure 2A in a plane perpendicular to the saw blade;
Figure 4A is a perspective view of a cutting element having
a tapered shank according the embodiment of the invention of Figures 1,
2A and 2B;
Figure 4B is a perspective view of a cutting element having
a tapered shank according the embodiment of the invention of Figure 2C;
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Figures SA, SB and SC are respectively front elevational,
side elevational and isometric views of a U-shaped holder for a cutting
element according to the invention; and,
Figure 6 is a section through a cutting element according to
the invention.
Description
Figure 1 shows a saw blade 10 according to the invention.
Saw blade 10 comprises a discoid body 12 having a central hub 14
configured for connection to a drive means (not shown) for rotating blade
10 about its axis 16. Blade 10 has a plurality of holders or "mounts" 20
around its periphery. Each holder 20 carries a cutting element 25. Each
cutting element 25 has a hardened sharpened cutting edge 26. Holders 20
may be permanently affixed to body 12. For example, holders 20 may be
welded to body 12. Fourteen of the sixteen holders 20 of blade 10 are not
shown in Figure 1.
Most preferably, each holder 20 comprises a U-shaped
member 21 which straddles the edge of body 12. Member 21 has side
plates 21A on either side of body 12. Side plates 21A are connected by
a bight portion 21B. Suitable fasteners such as bolts 22 equipped with
suitable washers fasten member 21 to body 12. Bolts 22 are recessed so
that they do not project outwardly from side plates 21A. In typical
embodiments U-shaped members 21 are fabricated from 5/8 inch thick
steel plate. The thickness and material of U-shaped members can, of
course, be varied to suit the needs of each specific application according
to standard engineering principles.
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As shown in Figure 2A, each cutting element 25 comprises
a front portion 29 which includes cutting edge 26 and a tapered shank 30
which extends rearwardly from front portion 29. The forward-facing face
of front portion 29 inside cutting edge 26 is typically concave, as is
known to those skilled in the art of designing saws for tree felling
machines.
Shank 30 is received in a correspondingly tapered socket 32
in its holder 20. Shanks 30 are tapered with a self holding or "self
locking" taper such as a Morse taper or a Brown & Sharpe taper. Such
tapers are described, for example in pages 1727 through 1729 of the
Machinery's Handbook, 21st edition. Because shanks 30 have self
locking tapers, there is considerable frictional resistance to any force
tending to turn or rotate shanks 30 when they are engaged in sockets 32.
Shanks 30 have tapers of between about 0.45 inches per foot
(approximately 2 degrees) and 0.8 inches per foot (approximately 4
degrees). Most preferably shanks 30 have tapers in the range of
approximately 2 degrees to approximately 4 degrees. Socket 32 has an
inner surface 33 which has the same taper as the shank 30 which it
receives. The tapered portions of Sockets 32 are deeper than shanks 30
so that shanks 30 cannot "bottom out" in sockets 32. Preferably sockets
32 are dimensioned so that, when shanks 30 are fully engaged in sockets
32 there remains a gap 36 between the rear face of each shank 30 and the
bottom of each socket 32.
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The rear face 40 of front portion 29 of each cutting element
25 provides a bearing surface which contacts the front face 42 of holder
20. Preferably, the rear face 40 of front portion 29 and the front face 42
of holder 20 are generally planar and extend perpendicularly to the
longitudinal axis 44 of cutting element 25. It is an important feature of
the invention that impact forces on cutting edge 26 are borne primarily
by front face 42 of holder 20 and not by socket 32. This does not
preclude a non-preferred embodiment of the invention where a cutting
element 29 with a sufficiently strong shank 30 could locate such that rear
face 40 does not contact front face 42 of holder 20.
Front face 42 of holder 20 provides a bearing surface that
extends on at least opposing sides of socket 32. It is strongly preferable
that front face 42 provides a bearing surface extending around at least 3
sides of socket 32 as shown in Figure SA, SB and SC. Longitudinal axis
44 is generally tangential to body 12.
Socket 32 is preferably dimensioned so that when shank 30
is snugly, but not tightly, engaged in socket 32 there is a slight gap
between rear face 40 and front face 42. That is, the maximum diameter
of socket 32 is slightly less than the maximum diameter of shank 30. As
shank 30 is forced tightly into socket 32, the material of holder 20 yields
sufficiently to allow rear face 40 to bear against front face 42.
When holder 20 comprises a U-shaped member 21 the act of
forcing shank 30 tightly into socket 32 tends to spread side plates 21A
apart slightly. This is advantageous because member 21 acts as a very
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stiff spring which elastically presses against shank 30. This holds shank
30 more tightly in socket 32 than would otherwise be the case. The
inventors believe that the springlike deformation of U-shaped members
21, when combined with the self locking taper of shank 30 and socket 32,
S adds considerably to the ability of holders 20 to hold cutting elements 25
firmly even when cutting elements 25 are exposed to great impacts and
vibration.
In one embodiment of the invention cutting elements 25 are
equipped with threaded fasteners. The threaded fasteners may be used to
draw shanks 30 into tight engagement in sockets 32. The threaded
fasteners may be left in place during use of saw blade 10 to help to hold
cutting elements 25 in place. In the embodiment of Figure 2B, the
threaded fastener comprises a threaded bolt 28. A cutting element 25
according to this embodiment may be fixed in a holder 20 by cleaning
socket 32, pushing cutting element 25 into socket 32, threading a bolt 28
and a washer 28A into a threaded axially extending hole in the cutting
element 25 and then tightening bolt 28 until rear face 40 of front portion
29 contacts front face 42 of holder 20. Cutting element 25 may be
removed by loosening bolt 28 and hitting the projecting end of bolt 28
with a hammer.
In another embodiment of the invention cutting elements 125
(Figures 2C and 4B) have no threaded fasteners. A cutting element 125
may be engaged in a socket 32 by cleaning socket 32, pushing cutting
element 125 snugly into socket 32 and then hammering on the front face
of cutting element 125 until rear face 40 of front portion 29 contacts front
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face 42 of holder 20. Impacts on cutting edges 26, as will occur when
saw 10 is used, will tend to tighten cutting elements 125 in holders 20.
Cutting element 25 may be easily and quickly removed by
hitting the rear face of shank 30 with a drift. The embodiment of Figures
2B and 4B is advantageous because it allows cutting elements 125 to be
rotated to use a new portion of cutting edge 26 or replaced much more
quickly than is possible with cutting elements 25 which are attached with
threaded fasteners. This can be accomplished with only a hammer and a
drift, both of which would be found in almost any mechanic's tool box.
No specialized tools are required to rotate or replace cutting elements
125.
Cutting elements 25 (or 125) should be hardened and
tempered as is understood to those skilled in the art. Preferably cutting
elements 25 (or 125) have a hardness in the range of about 50-55 on the
Rockwell C scale.
The mounting system of the invention may be used with
various configurations of cutting edges 26. Cutting edges 26 may be
circular as described, for example, in Isley, United States Patent No.
4,738,291 or may be square, as described for example, in Morin, U.S.
patent No. 4,932,447 or may have some other shape. The mounting
system of the invention is particularly advantageous for use with round
cutting elements because the self holding interfit of shank 30 in socket 32
prevents rotation of cutting elements 25 (or 125). The symmetrical nature
of round cutting elements means that they cannot be held against rotation
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by providing an abutment in the holder as is often done, for example,
with square cutting elements. An advantage of the invention is that a
single holder can be made to accommodate variously shaped cutting
elements.
A feature of the invention is that holders 20 are capable
without modification of allowing cutting elements 25 (or 125) to be
rotated about axis 44 through any desired angle. The same holder 20 will
allow a cutting element 25 having a square cutting edge 26 to be rotated
about axis 44 in increments of ninety degrees to expose fresh cutting
edges and will also allow a cutting element 25 having a round cutting
edge 26 to be rotated about axis 44 in smaller increments, if desired.
It can be appreciated that a mounting system according to the
invention can make it possible to quickly replace or rotate cutting
elements in a saw with common hand tools. At the same time the use of
a self holding taper to receive cutting elements holds the cutting elements
against rotation during use.
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 practice of this invention without departing from the spirit or scope
thereof. By way of example only, the cutting elements 25 or 125 and
holders 20 are not limited to use only on a blade 10 comprising a flat
circular discoid body 12. Holders 20 may be attached to blades having
other configurations. It is convenient to make faces 40 and 42 flat.
However, while faces 40 and 42 should have complementary configura-
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tions so that the area of contact between faces 40 and 42 is reasonably
large, faces 40 and 42 are not necessarily flat. While the threaded
fastener used to draw cutting elements 25 into engagement in sockets 32
has been described as a bolt 28, bolt 28 could be replaced with a stud
projecting outward from shank 30 or a bolt passing through a central bore
in cutting element 25 and fastened with a nut, or the like without
departing from the invention.
Accordingly, the scope of the invention is to be construed in
accordance with the substance defined by the following claims.
