Information
-
Patent Grant
-
6748840
-
Patent Number
6,748,840
-
Date Filed
Wednesday, August 7, 200221 years ago
-
Date Issued
Tuesday, June 15, 200420 years ago
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Inventors
-
Original Assignees
-
Examiners
- Shoap; Allan N.
- Prone; Jason
Agents
- Schwabe, Williamson & Wyatt, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 083 830
- 083 831
- 083 832
- 083 833
- 083 834
-
International Classifications
-
Abstract
A saw chain for a chain saw including alternating center and side link pairs with certain of said side links being cutting links and certain of said center links preceding said cutting links having guard portions to inhibit kick back. Said guard portions including a forward and rearward guard portion, the rearward guard portion in overlapping relation with a depth guide of the cutting link. A relief spacing between the guard portions facilitates chip carriage and the guard portions cooperatively form a ramp to guide wood being cut over and onto the depth gauge for controlling the depth of cut taken by the cutting link.
Description
FIELD OF THE INVENTION
This invention relates to a saw chain for cutting wood, e.g. trees and logs, which saw chain includes a guard feature that inhibits the occurrence of kickback, and more particularly wherein the guard feature is provided on the center links of the saw chain preceding the saw chain cutters or cutting links.
BACKGROUND OF THE INVENTION
A popular saw chain used on consumer-type chain saws is a ⅜″ pitch chain having a low profile and provided with side links having a guard feature. The guard feature is provided above the body portion of certain of the side links and extends substantially the length of the body portion and somewhat rearwardly of the body portion. Thus, a following side link cutter is substantially protected from taking an excessive bite or penetration into the wood, particularly when there is contact between the chain at the upper quadrant of the bar nose and the material being cut (when cutting with the nose) or accidental contact with nearby branch or the like. Such contact may induce kickback.
Although popular, this chain is perceived to cut less efficiently due to the presence of the guard feature and, from the manufacturer's point of view, is more costly to produce than is desired.
BRIEF DESCRIPTION OF THE INVENTION
A cost issue results from the significant number of parts that have to be produced and assembled for the prior chain. The parts include: 1. a left-hand cutter; 2. a right-hand cutter; 3. a standard center drive link; 4. a standard tie strap (that fits on either side of the chain); 5. a right-hand guard side link; and 6. a left-hand guard side link. It is desirable to provide a center drive link with a guard portion rather than a side link in that this reduces the number of parts from six to five (the center guard link replacing both left and right-hand side guard links).
Cutting speed is believed to be affected by the length and height of the guard portion, in that the gaps between the cutting teeth of the cutting links carry the chips that have been cut and when this space fills up (partially due to the presence of the guard portion), the cutting teeth are forced away from the kerf bottom, i.e. out of the cutting mode. However, it is known that a reduced, e.g., shortened guard portion for the side link (front to back) is not as effective in preventing kickback. Particularly during a nose cut, the depth gauge of the cutting link as well as a shortened guard portion will be pressed into the kerf bottom, thereby compressing the wood which allows the following cutting tooth to penetrate further into the kerf and take the undesired excessive bite that can cause kickback. The longer guard portion requires a greater pressure to compress the wood and, thus, more effectively guards against the undesired excessive bite problem.
The present invention provides a guard portion at least at the trailing portion of the center link and because the cutting link and center link are overlapped (they share a common pivotal connection), the upwardly extended trailing guard portion is positioned alongside the depth gauge of the cutting link. This double thickness of depth gauge and guard portion is believed to more effectively resist penetration into the wood fibers of the kerf bottom (as compared to an elongated single thickness) and substantially enhances the resistance to excessive penetration of the following cutting tooth. In the preferred embodiment, the guard portion is relieved in the center area forward of the trailing guard portion to provide added chip carrying capacity, and then the center link is provided with a leading guard portion formed to provide a ramping effect that assists in resisting cutting tooth penetration but without unduly restricting chip-carrying capacity.
In the preferred embodiment, the configuration of the leading and trailing portions of the center link are cooperatively formed so that the ramp of the leading portion ramps the wood being cut in a direction that projects above the leading edge of the trailing portion, the leading edge of the trailing portion being itself shaped to avoid presenting a corner that might dig into the kerf.
The invention will be more fully appreciated upon reference to the following detailed description of the preferred embodiment having reference to the accompanying drawings. The cutting chain therein described has been found to be a lower-cost chain construction while providing improved cutting performance and without sacrificing safety.
A prior art patent that discloses a guard portion overlapping with the depth gauge is U.S. Pat. No. 4,425,830. However, the overlapping guard portion is provided on a preceding side link, the overlying guard portion extended rearwardly of the rear rivet of the side link which precedes the forward rivet of the cutting link. As will be noted from
FIG. 3
thereof, the rearwardly extended guard portion pivots upwardly as the chain traverses the nose of the chain saw. Such upward pivoting inhibits the ability of the cutter to achieve a desired cutting penetration during nose cutting.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a side view of a sequence of links provided for a saw chain of the present invention;
FIG. 2
is a top view of the sequence of links illustrated in
FIG. 1
;
FIG. 3
is an illustration of a sequence of links in accordance with the invention mounted on a nose sprocket as when rounding the nose of a chain saw guide bar; and
FIG. 4
is a side view of the center link only of the saw chain of
FIG. 1
, but showing a cutting link in phantom.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is made to
FIGS. 1 and 2
which illustrates a section of saw chain
10
of a preferred embodiment of the invention. The saw chain
10
includes a left-hand cutting link
12
L and an opposing tie strap or side link
14
pivotally connected at the forward end by a rivet
16
to a rearward end of a guard bearing center link
18
. The front end of the guard or guard bearing center link
18
is pivotally connected to the rear ends of a pair of opposing side links
14
, which in turn are connected at their front ends to the rear end of a conventional center link
20
. The front end of the center link
20
is connected to a right-hand cutting side link
12
R and opposing tie strap or side link
14
. A guard center link
18
precedes the cutting side link
12
R, the cutting side link
12
R having an opposing standard side link
14
, which are then preceded by a standard center link
20
. The sequence is then repeated. All connections are pivotal connections provided by rivets
16
. The reader will however appreciate that the above sequence of links can and is modified and that the invention is not limited by any specific sequence.
The present invention encompasses the guard-bearing center link
18
and its relation to the succeeding cutting link
12
L/
12
R, which is illustrated in
FIGS. 1 and 2
when travelling on a straight reach of the saw bar, and in
FIG. 3
when travelling around the nose end of the bar and supported on a nose sprocket
22
. Before describing the above relationship, the configuration of the guard or guard-bearing center link
18
will be described by way of example with reference to FIG.
4
. As shown in
FIG. 4
, the chassis or body portion
24
encompasses front and rear rivet holes
26
,
28
respectively. Extended below the chassis
24
is a drive tang
30
, which is adapted to slide in a groove formed in a guide bar of a chain saw. It also seats in the gullets of the nose sprocket when traversing the nose of the bar as seen in FIG.
3
and engages the drive sprocket at the opposite end for driving the chain (not shown but well known to those skilled in the art). Projected above the chassis
24
is a front upwardly extended portion
32
and a rear upwardly extended portion
34
. In
FIG. 1
, the guard portions
32
and
34
of the center link
18
preceding cutting link
12
L can be observed to extend above the side links
14
which correspond in height to the chassis or body portion
24
of the center link
18
.
Again by way of example and not intended as a specific limitation of the invention, the front portion
32
provides an inclined upper edge
36
that is slightly curved as it extends rearwardly. An imaginary rearward extension of edge
36
is illustrated by dash line
38
. As shown, an upper edge
40
of the rear portion
34
is also slightly inclined front to rear and is substantially parallel to and below dash line
38
. Intermediate the edges
36
,
40
is a relief
42
that defines a bottom edge
44
that transcends from a concave semicircle to a smooth convex curve
46
that merges with edge
40
. As will be noted from the dash line overlay
48
representing a following cutter link
12
L/
12
R, the rear portion
34
of the center guard link
18
substantially overlays depth gauge
50
of cutting link
12
L/
12
R, both of which are positioned over a common pivot, i.e., a pivot
16
extended through rivet hole
28
as illustrated in FIG.
3
.
The above overlapping relationship of the guard center link
18
and cutting link
12
can be further viewed in
FIGS. 1 and 2
. The side-by-side relation of the overlapping portions (depth gauge
50
and rear portion
34
having upper edge
40
) is illustrated in
FIG. 2
as well as the relationship of these components to the common rivet
16
.
Reference is now made to
FIG. 3
wherein the saw chain components as described above are shown in the position where the components are rounding the nose of the guide bar and supported on nose sprocket
22
. It will be observed that the chain links (
12
L/
12
R,
14
,
18
,
20
) pivot relative to each other (note center lines
54
connecting the centers of rivets
16
). Because the depth gauge
50
and guard portion
34
(identified in
FIG. 3
by the upper edge
40
) are controlled pivotally by the same rivet
16
, the relative pivoting of depth gauge
50
and rear portion
34
is minimal. The three edges
36
,
40
and upper edge of depth gauge
50
cooperatively function to guide the wood into the cutting edge
52
of the cutting tooth
12
L/
12
R and effectively inhibits the likelihood of the cutting tooth taking an excessive bite into the wood being cut. Such is accomplished without undue interference with chip flow (see
FIG. 1
) and thus both safety and cutting performance are achieved.
The above preferred embodiment is but an example of the present invention and is subject to numerous variations and modifications without departing form the true and intended scope of the invention, which is defined by the claims appended hereto.
Claims
- 1. A saw chain for a chain saw comprising:a sequence of pivotally connected links including alternating side link pain and center links each having a chassis portion including a forward and rearward connecting pivot and each forward pivot of the side link pairs and rearward pivot of the center links being a common pivot as is the rearward pivot of the side link pairs and forward pivot of the center links, certain of said side link pairs including a cutting link having a cutting portion extended above the chassis and an opposed tie strap, and certain of said center links preceding said certain of said side link pairs provided with a protective guard feature; said guard feature including a forward guard portion and a rearward guard portion projected above the chassis of said certain of said center links and above the respective forward and rearward pivots of the center link and cooperatively configured to provide a relief spacing between the forward and rearward guard portions; said cutting links provided with a depth gauge portion projected above the chassis at the front pivot of the cutting links and having side-by-side overlapping relation with the rearward guard portion of the center links.
- 2. A saw chain as defined in claim 1 wherein an upper edge of the depth gauge and each of the guard portions are cooperatively sloped to provide cooperative ramping engagement of a wood member during a chain saw cutting operation.
- 3. A saw chain as defined in claim 2 wherein the upper edge of the forward guard portion defines a slope adjacent the relief spacing which projects rearwardly along an imaginary line that is spaced above the upper edge of the rearward guard portion.
US Referenced Citations (15)
Foreign Referenced Citations (3)
Number |
Date |
Country |
721087 |
Nov 1965 |
CA |
1 040 796 |
Oct 1958 |
DE |
2 067 465 |
Jul 1981 |
GB |