Chain saw nose guard

An assembly is provided which guards a curved portion of the guide bar tip of a chain saw in order to prevent kickback accidents. The guard assembly is attached on one side of the guide bar at a hole through the bar near the nose. It includes a plate which projects beyond the nose parallel with the plane of the guide bar. The plate has an internally threaded shaft projecting from it, allowing it to be bolted to the guide bar through the hole. A spacer between the plate and the guide bar holds the plate away from the cutting edge of the chain.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a guard assembly for the nose of a chain saw. 
2. Description of the Prior Art 
A well known safety problem in the use of a chain saw is the occurrence of 
"kickback". This is a violent movement of the saw which can occur when the 
nose, that is, the forward end of the saw, contacts a solid object. The 
conditions giving rise to kickback are as follows. The chain of the saw 
tends to bite into an object with a force proportional to the speed of the 
chain. At the same time, there is a corresponding reaction force exerted 
on the saw by the object. If the momentum of the chain and other moving 
parts of the saw carries the chain into the object, then the energy of the 
chain is expended in the cutting action and the reaction force on the saw 
is greatly reduced. However, at lower chain speeds, the momentum may not 
be sufficient to sustain the cutting action. In fact, the chain may become 
seized by the object. If the chain is not carried on through a cut, the 
saw is suddenly subjected to the full reactive force. When this force is 
exerted at the middle or on the upper quadrant of the nose of the saw, the 
nose moves suddenly upward in rotation generally about the rear of the 
saw. 
Because of the way that a chain saw is held, the kickback motion is 
extremely difficult for the operator to control; thus there is 
considerable risk that he will be hit by the moving chain. If the saw is 
being held horizontally at the time of the kickback, then its motion will 
be somewhat opposed by the weight of the saw. This opposition decreases 
substantially as the saw is held more nearly vertically. For this reason, 
perhaps the most dangerous kickback situation is when the saw is being 
used to cut an object overhead. There may be additional lack of control in 
this situation if the operator's arms are extended to reach the object 
above. 
One approach to minimizing the injurious effects of kickback is to employ a 
safety brake on the saw which quickly stops it when kickback occurs. A 
number of such brakes have been developed. This is a relatively elaborate 
and expensive partial solution to the problem. It stops the chain, but it 
does not prevent rotation of the saw. There is also the possibility that 
the saw will be damaged. Even under the best of circumstances, kickback 
represents a significant inconvenience. 
SUMMARY OF THE INVENTION 
The present invention provides a guard assembly which shields the cutting 
edge of the chain at the curved part of the guide bar tip of a chain saw 
in order to prevent cutting engagement by that portion of the chain. The 
guard assembly includes a plate and means for attaching the plate to the 
guide bar. Although the plate can be mounted on either side of the bar, it 
is preferably mounted on the flush cutting side of the bar. Means are 
provided for holding the plate away from the guide bar and thus away from 
the edge of the chain. The plate projects beyond the nose of the saw to 
guard it from contact. 
Most of the advantages of the present invention flow from its simplicity. 
It is an extraordinarily inexpensive solution for the widespread safety 
hazard and inconvenience produced by kickback. It is compact and 
convenient to carry in the pocket for use on those occasions when it is 
needed. Attachment and detachment of the guard assembly is simple and does 
not require special tools. Because the plate shields the cutting edge 
around the nose, the saw may be safely used in restricted space situations 
where operation of a conventional bare-nosed saw would be hindered by 
abrasive obstructions. 
Even though the guard assembly is inexpensive, its shape permits it to be 
built quite ruggedly. While the assembly is on the saw, the chain is 
within view and completely accessible. The guard does not accumulate an 
unusual amount of sawdust or debris; nor does it contribute to jamming.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, a guard assembly, indicated generally by the reference numeral 
10, is mounted on a chain saw 12. The chain saw 12 includes a chain 14 
which is shielded and protected by the assembly 10. The protected zone is 
the periphery of a curved portion of the "nose" of the saw which is 
indicated generally by the reference numeral 16. A bolt 18 fastens the 
guard assembly 10 on a guide bar 20 near the center of curvature of nose 
16. The guard assembly 10 includes a circular plate 22 which is concentric 
with the arc of nose 16, but projects beyond the nose. 
IN FIG. 2, the circular plate 22 is seen to have formed on it a shaft 24 
which is inserted in a hole 26 through guide bar 20. Shaft 24 is 
internally threaded, and plate 22 is fastened to the guide bar 20 by the 
bolt 18 and a washer 30. An annular spacer 32 holds plate 22 away from 
guide bar 20 at a distance sufficient to clear chain 14. 
Operation of the guard assembly 10 is based on the fact that plate 22 
projects beyond nose 16 in parallel with the plane of the guide bar 20. 
The guard assembly thereby prevents the chain 14 from making the kind of 
solid contact with an object which causes kickback. 
Variations are possible in the construction of guard assembly 10. Plate 22 
may be made of any durable material such as metal or plastic. Although it 
is not necessary that plate 22 be circular, there are advantages in its 
being so. When the plate 22 is circular, its position of rotation about 
bolt 18 may shift during use, without affecting the operation of the guard 
assembly 10. Therefore in this embodiment only the single fastener, bolt 
18, is required rather than some arrangement to absolutely fix the 
rotational position of the plate 22. This simplifies the process of 
mounting assembly 10 and allows its immediate use on those saws which are 
made with a single hold near the tip of the guide bar. Since a single 
fastener is used, the circular shape of plate 22 is additionally 
beneficial in minimizing the rotational forces on guard assembly 10, as it 
bumps into obstacles during use. Excessive rotation might tend to loosen 
bolt 18. 
It has been determined that contacting or engaging the cutting edge of the 
chain 14 in the upper quadrant of the curved nose 16, the upper quadrant 
being indicated generally by the dashed line 34, causes the most dangerous 
kickbacks. Therefore it is essential that the critical area, quadrant 34, 
be shielded. Although the circular plate 22 completely shields the 
critical area, it also shields portions of the cutting edge outside of the 
critical area and thereby diminishes the effective cutting length of the 
saw. Thus it may be desirable to shield quadrant 34 with a plate 36 having 
the form of a sector which spans at least 90.degree., as illustrated in 
FIGS. 3 and 4. In this configuration, the plate 36 has a single axis of 
symmetry; therefore, its position relative to the critical area 34 must be 
fixed. Proper orientation and locking are provided by a locking tab or key 
38 which is integrally formed as an offset portion of the shaft 24. The 
locking tab 38 fits into a hole 40 to provide the proper orientation of 
the sector plate 36 with respect to the critical quadrant 34. The 
registration of the tab 36 within the hole 40 prevents rotation of the 
plate with respect to the nose. Other shafts having a rectangular or 
triangular geometrical cross section as illustrated in FIGS. 6 and 7 do 
not require a tab for locking and orientation purposes and may be used to 
good advantage. For added safety, the span of plate 36 may include a few 
degrees on either side of the quadrant 34 as shown in FIGS. 6 and 7. 
Various elements of the guard assembly 10 may be combined, in order to 
reduce the number of parts and thereby simplify mounting. For example, the 
separate spacer 32 could be replaced with a similary shaped spacing means 
formed on plate 22. Bolt 18 and washer 30 could be combined into a special 
bolt with a head the size of washer 30. 
The shaft 24 acts as a fastener. In addition, its length and diameter are 
chosen so that the guard assembly 10 is made to satisfactorily fit the 
hole 26. Shaft 24 could be used without threads, if bolt 18 were made long 
enough to extend beyond plate 22, where the bolt could be fastened with a 
nut. In such an arrangement, shaft 24 would serve to protect the threads 
of bolt 18 from contact with the edges of hole 26 and assure a proper fit 
of the assembly 10 in hole 26. Alternatively, shaft 24, with threads, 
would be joined with washer 30, rather than plate 22. In this 
configuration, bolt 18 would be inserted from the side of the saw opposite 
that illustrated in FIG. 2, through a hole in plate 22. 
Although preferred embodiments of the invention have been described in 
detail, it is to be understood that changes, substitutions, and 
alterations can be made therein without departing from the spirit and 
scope of the invention as defined by the appended claims.