Saw chain having cutter link with central pivot on bottom edge

A saw chain is disclosed which includes cutting links having a central pivot on the bottom or inner edge of such cutting link which contacts the track of a saw bar on which the chain is mounted. A front foot portion and a rear foot portion which extend from the central pivot to the front end and the rear end, respectively, of the cutting link are normally spaced from such track when it is not cutting. The cutting link tilts about the pivot rearwardly and forwardly during cutting to provide a smooth rocking motion which reduces vibration and injury to the operator. One embodiment of the cutting link employs a single pivot located centrally between the front rivet opening and rear rivet opening. Another embodiment of the cutting link employs two pivots which are spaced apart and are both located centrally between the front and rear rivet openings. The saw chain includes side cutting links and side tie strap links connected by rivets to central drive links. Such drive links may also be provided with guard portions which extend outward in front of depth gauge portions of the cutting links to reduce kickback.

BACKGROUND OF INVENTION 
The subject matter of the present invention relates generally to saw chain 
for chain saws and in particular to saw chain having cutter links with a 
central pivot on the bottom edge of such cutter link which contacts the 
saw bar track to tilt the cutter link backward and forward during cutting 
to reduce vibration. 
As saw chain is moved along the track of the saw bar of a chain saw it 
causes considerable vibration when the cutter links of such chain engage 
wood during cutting. This vibration is produced at least in part because 
the cutter links dig into the wood and tend to rear up when they pivot 
about the rear foot portion of the cutter link on the saw bar which raises 
the depth gauge portion and causes the cutter link to reduce its cutting 
edge penetration. When the cutter cuts through the wood to produce a 
severed wood chip it pivots back down so that its front foot portion 
contacts the saw bar track with considerable force. The repeated back and 
forth pivoting of the cutting link results in a hammering action on the 
saw bar thereby producing vibration which is transmitted to the hands of 
the chain saw operator. This vibration can cause injury to the hands of 
the operator of various types including Raynaud's Syndrome, numbness, 
muscle fatigue, tendonitis and the like. Previous attempts to solve this 
saw chain vibration problem have not been entirely successful. 
As shown in U.S. Pat. No. 4,567,803 of Anderson, issued Feb. 4, 1986, it is 
known to provide a so-called anti-kick safety saw chain with guard links 
mounted in front of the cutter links to prevent the depth gauge or other 
portion of the cutter links from digging into the wood and causing 
kickback. In order to reduce the vibration of such a safety chain, it has 
been proposed in U.S. Pat. No. 4,643,065 of MacGavin, issued Feb. 17, 
1987, to provide such guard links with a rear foot portion which is cut 
away to space such rear portion from the saw bar to enable the safety link 
to pivot without impacting such saw bar and reduce vibration. 
An early attempt to reduce vibration of a conventional saw chain without 
guard links is shown in U.S. Pat. No. 4,122,741 of Engman, et al., issued 
Oct. 31, 1978. The Engman patent shows a saw chain having a side cutter 
link with the rear foot portion or heel at the bottom of the cutter link 
cut away to raise up and space such heel from the saw bar. The side link 
tie strap on the opposite side of the chain from such cutter is also 
provided with a raised heel portion spaced from the saw bar. This raised 
heel causes the cutting link to pivot about a front foot portion which 
contacts the saw bar track under the front rivet during cutting so that 
the cutting edge of the cutter link tends to pivot downward, thereby 
lowering the cutting edge rather than raising it to prevent such cutting 
edge from further digging into the wood as occurs when such cutter link 
pivots about a rear foot under the rear rivet. In a second embodiment, 
this patent provides a cutter link in which both the front foot portion 
and rear foot portion of such link are cut away and raised up so they are 
spaced from the saw bar during cutting. This causes the chain to pivot 
about the rear rivet of the preceding side link tie strap thereby even 
more effectively preventing the cutting edge of the cutter link from 
raising during cutting to reduce vibration. 
U.S. Pat. No. 4,573,386 of Lindemann, et al., issued Mar. 4, 1986, shows a 
saw chain in which the rear foot portion of the cutter link is cut away so 
that such rear foot portion contacts the saw bar only at a tilt point 
ahead of the rear rivet opening to cause the cutter link to tilt about the 
tilt point. This reduces the amount of tilt elevation of the cutting edge 
when such cutter link engages wood thereby reducing tilt displacement of 
the cutting edge during cutting and partially reducing vibration. However, 
the front foot portion of the cutting link engages the saw bar at a 
position ahead of the forward rivet opening so that cutting results in 
continued tilting of the cutter link up and down about the tilt edge 
causing the front foot portion of the cutter link to slam repeatedly into 
contact with the saw bar with a hammering action which still transmits 
considerable vibration to the saw bar and the chain saw operator's hands. 
Other attempts to reduce vibration in saw chain operation include using a 
center drive cutter link as shown in U.S. Pat. No. 4,898,057 of Hille, 
issued Feb. 6, 1990. In this chain the side link tie strap connected to 
the rear rivet of the center cutter link has been shaved away at its front 
foot portion to space such front foot away from the saw bar. Here again, 
this reduces tilt displacement of the cutting edge by causing the center 
cutter link to pivot about its forward rivet rather than its rearward 
rivet which results in the cutting edge moving downward rather than 
raising further into the wood when it engages the wood during cutting. 
However, a center cutter link saw chain is not as desirable in some 
circumstances as saw chain with side cutter links which employs alternate 
cutters on opposite sides of the chain with left-handed and right-handed 
cutter congfiguration for more efficient cutting. 
The saw chain of the present invention employs side cutter links of 
improved design with a central pivot which contacts the saw bar to tilt 
about such pivot for reduced vibration and efficient cutting. 
The cutter link of the present invention has a rear foot portion extending 
from a central pivot to the rear of the cutter link which is normally 
spaced from the track of the saw bar. In addition such cutter link has a 
front foot portion extending from such pivot to the front end of the 
cutter link which is also normally spaced from said track. This allows the 
cutter link to pivot or tilt about the central pivot in both a rearward 
and a forward direction by a significant amount without striking the saw 
bar with either the front or rear foot portion of the cutter thereby 
reducing vibration during cutting. In one embodiment of the present 
invention, the central pivot is provided by a single pivot point located 
centrally of the forward rivet opening and the rearward rivet opening of 
the cutter link. In another embodiment the pivot is provided by a pair of 
central pivot points longitudinally spaced apart and both located between 
the forward rivet opening and the rearward rivet opening of the cutter 
link. In addition, the tie strap side link on opposite side of the saw 
chain from the cutter link is provided with a central pivot located 
between the forward rivet opening and the rearward rivet opening of such 
tie strap which contacts the saw bar for tilting about such pivot in a 
similar manner to the cutter link. The saw chain of the present invention 
not only reduces vibration but also operates with efficient cutting by 
employing side cutter links with right-handed and left-handed cutters 
alternating along the length of such chain. The saw chain may be provided 
with a guard link portion on the top of the center drive link to protect 
the front of the depth gauge of the cutter link thereby reducing kickback. 
Thus, the cutting chain of the present invention operates in a safer 
manner than cutting chains not employing such guard links. 
SUMMARY OF INVENTION 
It is therefore one object of the present invention to provide an improved 
saw chain for cutting wood with less vibration by employing a cutter link 
with a central pivot on the bottom or inner edge thereof to enable the 
cutter link to pivot in a forward and rearward direction on the track of 
the saw bar during cutting. 
Another object of the invention is to provide such a saw chain in which the 
central pivot of the cutter link is located forward of the rear rivet 
opening and rearward of the front rivet opening of such cutter link to 
allow the cutter link to tilt about such pivot without raising the cutting 
edge of such cutter link significantly during cutting. 
A further object of the invention is to provide such a saw chain in which 
the cutting link is a side cutting link and a side tie strap link is 
provided on the opposite side of the chain from such cutting link with 
such tie strap link also being provided with a central pivot between the 
front and rear rivet openings which contacts the track of the saw bar 
while the front foot portion and the rear foot portion of such tie strap 
link are spaced from the saw bar to enable pivoting in a forward and 
rearward direction on the saw bar. 
An additional object of the present invention is to provide such a saw 
chain in which the side cutter links are left-handed and right-handed 
cutter links on opposite sides of the chain which alternate with distance 
along the chain for efficient cutting. 
Another object of the invention is to provide such a saw chain in which the 
center drive link is provided with a guard link portion in front of the 
cutter link which protects the depth gauge portion of the cutter link to 
reduce kickback for greater safety. 
Still another object of the invention is to provide such a saw chain in 
which the cutter link has a central pivot provided by a single pivot point 
which is located centrally between the forward rivet opening and the 
rearward rivet opening and has a front foot portion normally spaced from 
the saw bar when not cutting, extending from the single pivot point to the 
front end of the cutting link and has a rear foot portion normally spaced 
from the saw bar which extends from the single pivot point to the rear end 
of the cutting link to reduce vibration. 
A still further object of the present invention is to provide such a saw 
chain in which the cutter link is provided with a central pivot in the 
form of a pair of pivot points which are located in a central foot portion 
rearward of the front rivet opening and forward of the rear rivet opening 
of the cutter link to further reduce vibration.

DESCRIPTION OF PREFERRED EMBODIMENTS 
As shown in FIGS. 1 and 2, one embodiment of the saw chain apparatus of the 
present invention includes a saw chain having side cutter links 10 which 
are pivotally connected to center drive links 12 by front rivets 14 and 
rear rivets 16. The drive links 12 are interconnected by tie strap side 
links 18 which are connected by front rivets 20 and rear rivets 22 to such 
drive links. The interconnected links form an endless loop of saw chain 
which moves along a saw bar 24. The saw bar 24 has a guide track for 
guiding movement of the saw chain along such saw bar. The guide track 
includes a pair of track rails 26 separated by a track groove. The drive 
links 12 have depending drive tangs 28 which extend into the track groove. 
The bottom or inner edges of the side links including the cutter links 10 
and the tie strap links 18 engage the track rails 26 and slide along such 
track rails as the chain is driven by the motor of the chain saw in a 
conventional manner in the direction shown by arrow 30. 
As shown in FIG. 2, a cutter link 10 in accordance with the present 
invention, includes a central pivot 32 on a central foot portion of the 
bottom or inner edge of such cutter tooth which engages the saw bar track 
rail 26. The central pivot is positioned centrally between a forward pin 
or rivet opening 34 and a rearward pin or rivet opening 36. A front foot 
portion 38 at the bottom or inner edge of the cutting link extends from 
the central pivot 32 to the front end of the cutting link 10 and is 
normally spaced from the saw bar track 26 when not cutting as such cutting 
link moves along a straight portion of the track as shown in FIGS. 1 and 
5. The cutting link 10 also includes a rear foot portion 40 which extends 
from the central pivot 32 to the rear end of the cutting link. Such rear 
foot portion is also normally spaced away from the saw bar track 26 when 
not cutting, as shown in FIGS. 1 and 5. 
The cutting link 10 includes a cutter portion having a cutting edge 42 
provided at the top or outer edge of the cutting link. A depth gauge 
portion 44 extends upward from the front of the cutter link body at a 
position ahead of the cutting edge to limit the depth of penetration of 
the cutting edge into the wood. In the normal position of the cutting link 
10, shown in FIG. 1, the cutting edge 42 extends slightly above the top of 
the depth gauge 44 so that such cutting edge engages the wood article 45 
being cut to produce the saw kerf. 
As shown in FIG. 2, when the cutting edge 42 cuts into the wood it tends to 
pivot the cutting link backwards from the normal position of FIG. 5, to 
the rearward tilted position 10 shown in solid lines in FIG. 2. Since the 
central pivot 32 is the only portion of the bottom or inner edge of the 
cutting link which engages the saw bar track 26 in the normal position of 
such cutting link, the cutting link tilts backward about pivot 32 during 
cutting from the normal position into the tilted position 10 where the 
rear foot portion 40 engages the track 26. This raises the depth gauge 
portion from the normal position shown in FIG. 5 to the raised position 44 
shown in solid lines in FIG. 2 which tends to further limit the depth of 
cut of the cutting edge 42 into the wood. As a result, the cutting edge 
breaks free of the wood and the cutter link 10 tilts forward about the 
pivot 32 into a forward tilted position 10'. The normal tension on the saw 
chain while it is moved by the drive sprocket acts as a spring to urge the 
cutting link 42 into a horizontal position. Thus, as the cutting link is 
moved by external forces on the cutting edge 42 and the depth gauge 44 
from its normal horizontal position the chain tension provides a restoring 
force that together with the recessed foot portions 38 and 40 and central 
pivot 32, reduces the impact of the cutting link on the saw bar while such 
cutting link rocks forward and backward. 
In contrast, a conventional side cutting link 46 is shown in FIG. 4 which 
is similar to the cutting link of the present invention shown in FIG. 2 
but does not have a central pivot 32 or raised foot portions 38 and 40 on 
its bottom or inner edge. Instead, the prior cutting link 46 includes a 
front foot portion 48 which normally contacts the saw bar track 26 at a 
point beneath or forward of the front rivet opening 34. Similarly, such 
cutter link includes a rear foot portion 50 which contacts the track 26 at 
a point beneath or rearward of the center of the rear rivet opening 36. As 
a result, when the prior cutter link 46 engages the wood with its cutting 
edge 42 such cutting link pivots about the rear foot portion 50 causing 
the cutting edge 42, the depth gauge 44 and the front foot 48 to raise 
from the solid line position to the dashed line position thereby resulting 
in reduced penetration of the cutting edge until it breaks free of the 
wood. This causes a violent tilting of the cutter link 46 backward and 
forward from the solid line position to the dashed line position and back 
to the solid line position so that the front foot portion 48 and the rear 
foot portion 50 both slam into the track 26 with a hammer-like impact. The 
result is considerable vibration which is transmitted through the saw bar 
to the hands of the operator causing numbness, thought to contribute to 
Raynaud's Syndrome. This vibration problem is greatly reduced by the 
smooth tilting operation of the cutting links of the present invention. 
Another embodiment of the cutting link of the present invention shown in 
FIGS. 3 and 6 is a double central pivot cutting link 52 which is similar 
to the embodiment shown in FIGS. 2 and 5 except that it employs a pair of 
central pivots 32a, 32b which in the normal position of the cutter link 
when not cutting, both of such pivots contract the saw bar track 26 as 
shown in FIG. 6. The two central pivot points 32a, 32b are spaced apart by 
a U-shaped notch 54 in the bottom of the cutter tooth. However, both 
central pivots 32a, 32b are positioned in a central foot portion located 
between the front rivet opening 34 and the rear rivet opening 36 of the 
cutting link. In addition, the front foot portion 38 and the rear foot 
portion 40 which, respectively, extend from the front pivot point 32b to 
the front end of the link and from the rear pivot point 32a to the rear 
end of the link are normally spaced from the saw bar track 26, as shown in 
FIG. 6. However, since both of the central pivots 32a, 32b are located 
behind the forward rivet opening 34 and ahead of the rear rivet opening 36 
of the cutter link, this distinguishes cutting link 52 of FIG. 6 from the 
prior cutter link 46 of FIG. 4. 
When the cutting link 52 engages wood during cutting it tilts backward 
about a first central pivot point 32a until the raised rear foot portion 
40 of such link contacts the track 26 as shown in solid lines in FIG. 3. 
When this happens, there is very little vertical displacement of the 
cutting edge 42 because the central pivot 32a is close to a vertical line 
through such cutting edge. Thus, in the prior cutter link 46 of FIG. 4 the 
rear pivot 50 is much further displaced horizontally from a vertical line 
through the cutting edge 42' than the central pivot 32a of the second 
embodiment is displaced from the cutting edge of the cutting link 52 of 
the present invention. The same is true of the second central pivot point 
32b about which the cutting link pivots in a forward direction into 
forward tilted position 52' in FIG. 3 until the raised front foot portion 
38 engages the track 26. Thus, the second central pivot 32b is much closer 
to a vertical line through the cutting edge than is the front pivot 48 on 
the front foot of the conventional cutter link 46 of FIG. 4. Also, the 
normal chain tension urges the cutting links 52 into a horizontal position 
which provides a restoring force that tends to prevent the front and rear 
foot portions from impacting the saw bar or reduces such impact. As a 
result, the cutter link of FIG. 6 has a smooth tilting action about the 
pivots 32a, 32b which greatly reduces vibration and the hammering action 
of the front and rear feet when the front and rear feet engage the track. 
When the improved cutting link -0 of FIG. 2 with a single central pivot 32 
is employed in the saw chain a special drive sprocket 56 must be employed 
for driving the saw chain due to the fact that there is no notch in the 
bottom edge of such saw chain which can be engaged by sprocket teeth. The 
drive sprocket 56 is provided with a sprocket rim consisting of a 
plurality of curved rim segments 58 which each have a shape to conform to 
the bottom of the cutting link 10 and to the bottom of the tie straps 18. 
Such a special drive sprocket is not necessary with the embodiment of the 
cutting link 52 shown in FIG. 6 because it is provided with a notch 54 on 
the bottom edge thereof between the two pivot points 32a, 32b which can be 
engaged by the tips of sprocket teeth 57 of a spur tooth sprocket 59 which 
does not have side plates or rims for the side links to ride on, as shown 
in FIG. 8. A similar notch would also be provided on the tie strap side 
links 18 used with such cutter link so that a conventional spur sprocket 
could be employed. It should be known that the drive tang portions 28 of 
the drive links 12 are received by the drive sprocket 56 between the 
sprocket teeth 60 as shown in FIG. 7 for driving the chain. 
Also, it should be noted that the center drive links 12 are provided with a 
ramp-shaped guard portion 62 extending outward in front of the depth gauge 
44 of the cutting links 10 or 52 in order to reduce kickback. In this 
regard, see U.S. Pat. No. 4,567,803 of Anderson referred to above. 
It will be obvious to one having ordinary skill in the art that many 
changes may be made in the abovedescribed preferred embodiments of the 
invention. Therefore, the scope of the present invention should be 
determined by the following claims.