Cutter link for a motorized saw chain

A cutter link for a chain saw chain containing a conical raker spaced forward of a round cutter face. The raker protects most of the cutter face from sudden impact and, together with the cutting and rake angles of the cutter face, provides for a filing rather than a chiseling action by the cutter link. Saw chains incorporating the novel cutter link are impact and wear resistant.

FIELD OF THE INVENTION 
This invention relates generally to chain saws, and more particularly to a 
saw chain cutter design which permits cutting a wide variety of materials 
while reducing dulling and breakage. 
BACKGROUND OF THE INVENTION 
Chain saws have been available for several decades. The chains used in 
chain saws commonly include drive links which engage into a power 
sprocket, connecting links and cutter elements. Such saw chains have been 
primarily intended for cutting wood. It has been found, however, that 
chain saws can be used to cut many different substances in addition to 
wood. Materials which can be cut by chain saw means include pumice stone, 
brick, tile, asbestos cement board, stucco, pipe and frame house and roof 
structures, which include shingles of a variety of materials including 
nails, joists, hangers and gravel and stone on top of built-up roofs. 
Firefighters have to use chain saws for cutting house structures on an 
emergency basis. 
An extensive amount of prior art describes various chains developed for 
many cutting purposes. The known prior art traces attempts to develop a 
cutter more resistant to blunting and shock destruction than the 
conventional stamped-out steel cutter commonly used by the wood industry. 
A number of inventions relate to the shape of the cutting element and also 
to the use of hard metal alloy inserts, such as carbide compositions 
attached to steel supports. The prior art generally shows permanent 
attachments, that is, connecting of a hard metal insert to a body element 
by braising or soldering, for example. This type of structure is shown in 
U.S. Pat. Nos. 3,292,675, 2,976,900, 2,862,533, 2,798,517 and 4,606,253. 
U.S. Pat. Nos. 2,746,494 and 2,994,350 describe hard metal cutting inserts 
which are removable from the cutter body. The known prior art is primarily 
concerned with cutters having cutting edges which are rectangular or 
L-shaped, and which, due to the rapid movement of the chain, act as 
chisels, chipping away the material. 
No prior art teaches the concept of effectively protecting the entire scope 
of the cutting edges from the effects of sudden impacts of hard material. 
Only U.S. Pat. Nos. 3,292,675 and 4,606,253 acknowledge or describe an 
attempt to remedy the impact problem. The '253 patent concerns a chain 
using a carbide composition insert supported by a steel element having two 
parallel flanks and made from a single piece of bent steel of relatively 
low hardness, intended to withstand the impact shock without detaching the 
cutting insert. This design, however, does not protect the carbide insert 
from frontal impact. The softness of the steel from which the chain links 
are manufactured causes rapid lengthening of the chain during cutting, 
which in turn may cause the chain to disengage itself from the leading 
groove of the saw bar or the sprocket or both. 
The '675 patent claims a chain adequate for cutting through the mixed 
materials. It concerns an L-shaped cutter element of carbide with the 
cutting edge only partially mating with a notch in an L-shaped body of the 
cutting link. 
SUMMARY OF THE INVENTION 
Broadly speaking, this invention involves a new cutter element for chains 
which move rapidly and unidirectionally for the purpose of cutting through 
various materials. Such chains are predominantly, but not exclusively, 
used as cutting devices in power chain saws and the like. 
A primary objective of this invention is a novel cutter link and cutter 
element to be incorporated with a chain which cuts rapidly through various 
materials of different hardness, is resistant to dulling and, more 
importantly, is able to withstand shock when, in a relatively soft 
material such as wood, a hard substance such as metal or mineral is 
encountered during cutting. This need is especially evident in 
applications such as cutting rapidly through various inhomogenous debris, 
such as encountered in natural catastrophe containment, for example, home 
fire, military use and in cutting through timber containing rock or sand. 
This objective is accomplished by the novel shape and design of the cutter 
element, providing long lasting sharpness and resistance to impact. One 
advantage resulting from this novel structure is that the cutting elements 
in the chain act more as files than as chisels. 
The cutter of this invention can readily be incorporated as a component 
into the construction of existing conventional saw chains. The cutter is 
provided with a cutting edge being the circumference of a round or a 
semilunar plate which can be an integral part of the cutter, or be made 
from a hard metal firmly attached to the support body. The cutting face is 
effectively protected against frontal impact by a conical raker placed in 
front of the face's entire operative circumference. Unlike the prior art 
which generally describes cutter faces with cutting edges of rectangular 
shapes, this invention provides for a round face with its cutting edge 
being approximately the entire operative circumference of the face's 
frontal aspect. 
The cutting element may be an integral portion of the body of the cutter 
chain link. Alternatively, the cutting element may be an insert secured to 
the body by appropriate means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference now to the drawing, and more particularly to FIGS. 1 and 2, 
there is shown a segment of saw chain of the prior art. This cutting chain 
is intended to be used for cutting hard type materials such as brick, 
tile, and asbestos cement board, and mixed material items such as frame 
house structures and roof structures, without requiring the cutting 
elements to be touched up or sharpened on a very frequent basis. It is 
intended to withstand severe impacts without separating the cutting 
element from the body or cutting link. 
The chain of FIG. 1 is comprised of three different elements, a 
multiplicity of which are connected together to form the continuous chain. 
Each of these elements is connected together by specific types of rivets, 
sometimes referred to as pintles, which allow one element to pivot with 
respect to the element to which it is coupled. Connecting side links 11 
interconnect sprocket drive lugs 12 by means of pintles 13. Normally two 
connecting links are required for each connection of two drive lugs, one 
on each side. Alternating positions of the connecting links on the chain 
include cutter links 14 and 15 replacing one of connecting links 11. These 
cutter links are positioned on alternating sides of the chain as shown in 
FIG. 1. For example, cutter link 14 is shown on the upward side of the 
chain in the plane of the paper and cutter link 15 is shown on the lower 
side of the chain. This alternating arrangement is normal in saw chains, 
much like a typical saw of any type which has alternating teeth set in 
opposite directions with respect to the center line of the movement 
direction of the teeth. Pintles 13 are also used for connecting cutter 
links 14 and 15 to drive lugs 12 in conjunction with one of the connecting 
links. 
Cutter link 15 is shown in FIG. 2 having cutting element or tip 16 having 
face 17 offset from a perpendicular to the line of travel 18 by an angle 
indicated by reference normal 21. This results in a sharp leading point 
22. Preceding the cutting element as it passes through the material being 
cut is depth gauge 23 spaced forwardly of the cutting edge. The purpose of 
the depth gage is to limit the depth of bite for the cutting tips as they 
engage the material being cut. Note that the cutting tip of the prior art 
acts as a chisel, removing chunks of material as it passes through the 
kerf which the saw creates. 
One embodiment of the cutting tip of the invention is shown in FIGS. 3-6. 
Base 36 of cutter link 31 is formed substantially the same as the 
equivalent prior art devices. Lobes 32 and 33 are made to accommodate 
openings 34 and 35 through which the pintles pass to connect the cutter 
link to the drive lugs of the chain, in conjunction with connecting links. 
The cutter link is provided with a hard steel body comprised of base 36 on 
top of which is cutting element 37 having cutting face 41 of circular or 
semilunar shape. On the forward top part of the cutter link, aligned with 
the longitudinal axis of cutting element 37, is conical raker 42 having a 
crest 43 at its superior aspect and a circular profile 44 at its posterior 
aspect. 
Cutting face 41 has a cutting angle .theta. (FIG. 4) typically ranging 
between 3.degree. and 20.degree., and a rake angle .alpha. (FIG. 5), 
typically ranging between 10.degree. and 45.degree.. For cutting hard 
materials such as would be expected on a gravel covered asphalt roof, and 
when expecting sudden impact in the cut material such as nails, the 
cutting angle will preferably be in the range of 8.degree. to 15.degree. 
and the rake angle will be in the range of 15.degree. to 25.degree.. When 
cutting predominantly homogenous and softer materials, such as wood, the 
preferred cutting angle will be in the range of 10.degree. to 20.degree. 
and the rake angle would preferably be about 30.degree. to 4520 . The 
cutting angle .theta. is the angle between face 41 and the vertical plane 
(FIG. 4). The rake angle .alpha. is the angle between face angle 41 and 
the transverse plane (FIG. 5). 
None of the prior art devices provides for effective protection of the 
entire cutting face and cutting edge against impact. This is 
understandable, since the previously described cutting elements generally 
are either L-shaped, rectangular, or nearly rectangular. The prior art 
only describes "depth gauges", that is, teeth-shaped promontories 
protruding upwardly from the frontal part of the cutter base, generally 
having the same thickness as the base, and mating with the cutting face, 
although minimally (see FIG. 2). 
The cutting element of this invention is distinctly different from the 
prior art. It is especially designed to be a round face. The face's 
cutting edge can be either a full circle or a substantial part of a 
circle. The diameter of the cutter face is generally in the range of 0.12 
to 0.38 inch. Nearly the entire face 41 is solidly protected by the 
anteriorly placed raker. The shape of raker face 44 roughly matches cutter 
face 41 except the average diameter of face 44 is somewhat smaller to 
allow for exposure of cutting edge 45 as shown in FIG. 6. Typically, the 
difference in the average diameter will vary from 0.0005 to 0.050 inch and 
will most typically be about 0.015 inch for cutting hard material and for 
use in situations when sudden impact is expected. The diametrical 
difference will typically be about 0.040 inch when homogenous, soft 
materials such as wood is being cut. Different cutter link configurations 
are provided for the expected use of the saw chain. When viewed in the 
lateral plane, the raker has a bullet-shape with crest 43 allowing for the 
pre-scoring of the cut material. The gradual increase of the raker in its 
anterior/posterior aspect serves to deflect any suddenly encountered 
inhomogenous substances. The difference in diameter with respect to the 
cutter face enables the saw chain to function as a file rather than as a 
group of chisels. 
The embodiment of FIGS. 3-6 is a hard steel body 37 which has an integral 
cutting face 41, which is protected by solid, bullet-shaped raker 42. An 
alternative embodiment is shown in FIGS. 7-14 9, having an identical raker 
51 on an identical base 52 but with a two-piece cutter portion, body 53 
and cutter element 54. The cutter element is secured by welding or brazing 
or other suitable means to body 53. Notch 55 in the body receives tab 56 
on the cutter element for proper mating alignment. Cutter element 54 is 
preferably made of a carbide composition which holds a cutting edge very 
well. Otherwise this embodiment has the same shape and functions in the 
same way as the embodiment of FIGS. 3-6. 
Another embodiment of the cutter link is shown in FIGS. 10-12. Body 61 is 
formed from a stamped plate formed through a series of dies into a 
cylinder. This cylinder receives cutter element 62 on the forward end. The 
cutter element is preferably formed with a rearward projection 63 which 
provides mating alignment. That projection may be cylindrical or have any 
desired shape with at least three side points which engage or lie closely 
adjacent the inside surface of cylindrical body 61. These components may 
be secured together by soldering, brazing, welding, or by other suitable 
means. 
Raker 64 is similarly formed into a cone from a flat stamped plate by a 
series of dies. Both the body or the raker, or both, are spot welded, 
laser welded, or otherwise suitably secured to base 65. Note that the body 
and raker of this embodiment may not be completely rounded but may be 
formed with a gap the width of base 65 with the elongated edges welded to 
the base. 
The body and raker of the other embodiments could be made integral with 
their respective bases, or they could be separate elements welded to the 
base. 
Actual testing has been conducted to determine how the cutter of this 
invention performs compared with other cutters in identical chains. The 
other cutters advertise the ability to effectively cut through the various 
materials discussed above. 
This cutter was incorporated into a 3/8" chain base and tested in a double 
blind experiment against commercially available carbide-tip chains sold 
under the names Repco 404 and Stihl Duro, all mounted on identically 
performing motor saws of the same type and origin. The test consisted of 
four consequential cuts to a total of a 60 linear feet, through a prop 
simulating a wood/tar/felt paper with gravel and/or corrugated metal roof 
construction of the type prevalent in the United States. This was 
immediately followed by perpendicular cuts through standard construction 
nails ("16 penny") of about 3 millimeters diameter and inserted 
longitudinally in wooden beams. The results are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Elements of Damage 
Elements of Damage 
Saw Speed 
Cutter Average 
Duration of 
After 60 Feet and 4 Nails 
After Additional 14 Nails 
RPM Max % 
Temperature .degree.C. 
60 Feet Cut 
Cut- 
Dull- 
Carbide Cut- Carbide 
Chain Start 
Decrease 
After 60 Feet Cut 
(min/sec) 
ter 
ing Chip Loss 
ter 
Dulling 
Chip Loss 
__________________________________________________________________________ 
STIHL DURO 
12,500 
39.02 
153 1.54 / yes / / 11 yes 7 19* 
REPCO 404 
12,500 
40.08 
162.5 1.50 5 no / 17 not applicable due to 
previous 
damage 
INVENTION 
12,500 
41.06 
167.5 1.52 / no / / 1 yes 1 4 
__________________________________________________________________________ 
*Could not be tested further due to the extensive damage 
In conclusion, while there were no significant differences in the saw 
speed, cutter temperature or speed of cutting, only the chain with cutters 
made in accordance with this invention remained operational at the 
conclusion of the test. 
In view of the above description, it is likely that modifications and 
improvements will occur to those skilled in the art which are within the 
scope of the accompanying claims.