Protective mechanism for circular saws

In a hand-held circular power saw, a mechanism whereby a blocking pawl moves into the path of a projection fixed to the rotatable blade guard of the saw, preventing motion of the blade guard and protecting the operator. The blocking pawl is moved into the blocking position during the opening of the blade guard, when the projection fixed to the blade guard tangentially forces a cam-shaped surface to rotate, the cam-shaped surface thereby forcing the blocking pawl into the return path of the blade guard projection. The pawl is kept in this position by means of a spring biased arm which is forced against a toggle such that motion of the lever is prevented.

FIELD OF THE INVENTION 
This invention encompasses protective guards for rotary blades on circular 
saws. The invention may also be used to protect any operation using a hand 
held power tool with an exposed cutting edge. 
BACKGROUND OF THE INVENTION 
Hand held power tools are quite commonly used today, both by workers in 
various fields of industry and by individuals employing such tools for 
home use, as well as for hobbies. Such hand-held tools have inherent, 
although correctable, dangers. For instance, hand-held circular power saws 
have a saw blade which must necessarily be exposed in order to perform a 
cutting operation. These saws are generally activated by the operator 
depressing a finger trigger-type switch within the handle. At times, 
although not making a cut, the exposed blade will still rotate due to the 
operator's continued grip of the trigger on the saw handle. Serious harm 
results with contact between the blade and the operator's body. For this 
reason, saw manufacturers have placed rotatable blade guards on virtually 
all the hand held circular saws in use today. These rotatable guards are 
spring energized, biased to close the guard over the saw blade. When force 
is placed on the guard, for instance through contact with a workpiece, the 
rotary blade is exposed, The guard will then telescope into a preformed 
chamber surrounding the saw blade. 
The rotatable guard has an inherent deficiency as it presently exists. It 
is the object of this invention to eliminate this deficiency without 
destroying the saw's utility. The deficiency lies in the fact that the saw 
blade can be exposed, with risk of injury to the operator, as a 
consequence of an unintended guard reopening. Previous guards were 
designed to open whenever the saw was advanced upon the workpiece. Those 
guards, however, will also open if the saw is unintentionally advanced 
upon any part of the operator's body. This can and does happen when a 
kickback occurs, causing the operator to lose control over the saw, 
allowing the saw to come in contact with the operator's body causing 
reopening of the guard. During such an occurrence the blade continues to 
rotate under power since the operator invariably maintains or increases 
his grip on the saw's handle, with his finger on the switch trigger, as he 
attempts to maintain control over the saw. The present invention controls 
this reopening of the blade guard which, in turn, controls the exposure of 
the saw blade and thereby prevents injury to the operator. 
Two previous references of which the inventor is aware have dealt with the 
problem of the blade guard on a saw. U.S. Pat. Nos. 1,811,577 (Crowe) and 
1,813,231 (Crowe) both contain a blade guard which is spring loaded to 
cover the exposed blade of a circular saw. Yet, both inventions do not 
encompass the rotatable guards present in modern circular saws. Nor do 
these inventions contain a mechanism which ensures that the blade guard 
continues to cover the saw blade once kickback has occurred and the spring 
loaded guard has returned to its protective position. 
SUMMARY OF THE INVENTION 
The present invention contains a latching mechanism connected at any point 
on the stationary part of the saw surrounding the blade and an activating 
means which is attached to the rotating blade guard. The latching 
mechanism typically consists of two pieces. First there is an operating 
lever which has an operator arm and a cam leg. This operating lever has 
two distinct positions. One is a "latched" position and the other is an 
"unlatched" position. The operating lever is physically held at either 
position by any suitable means such as, but not limited to, detents, 
toggles, ball and ramp, magnets etc. The operator arm of this operating 
lever is used by the operator to "unlatch" the mechanism prior to each 
cut. The cam leg of this operating lever is actuated by the blade guard to 
reset the latch mechanism to the "latch" position for the next cut, as the 
blade guard begins to open for the cut about to be made. 
Although the descriptions contained herein describe the operating lever as 
a one piece item, it does not have to be so constructed. The only 
necessity is that the operating lever be constructed to provide the 
operator with a means to unlatch the mechanism for the purpose of 
permitting the guard to open, and providing a means by which the motion of 
the guard, as it begins to open, can reset the mechanism so that the guard 
will latch as it returns to its closed position. 
Second, a pawl is incorporated within the latch mechanism. The pawl's 
fundamental purpose is to block the blade guard, preventing the blade 
guard's opening when in the latched position; the pawl also allows the 
blade guard to return to its closed position. The pawl is retracted from 
its blocking position when the operating lever is placed, by the operator, 
into the unlatched position. The guard is thereby allowed to open when a 
cut is made. The pawl pivots through a small arc about a pivot point, 
which may be common with the operating lever. The pawl is spring biased to 
the limit of its arc of travel in the direction which is associated with 
blocking. The pawl spring force is insufficient to influence the position 
of the operating lever. Its permissable arc of travel is sufficient to 
allow the guard projection to move past as it forces the pawl out of its 
path, against the effort of the pawl biasing spring. This occurs as the 
guard returns to its closed and blocked position. The position of the 
operating lever positions the pawl in the blocking position, or retracts 
it from that position. The operating lever and blocking means are usually 
rotatably mounted to the stationary section of the saw adjacent to the 
rotatable blade guard. Both the operating lever and the blocking means 
will usually pivot about the same point. 
The activating mechanism consists of a projection, which may be an integral 
part of the rotatable blade guard. This projection is aligned so that when 
the blade guard is rotated, it moves tangentially along the cam leg of the 
operating lever, which causes the operator arm of that mechanism to move 
to its latched position. In addition, this motion causes the pawl of the 
blocking member to move into the path of the projection on the rotatable 
guard. When the blade guard rotates back to its initial position, at the 
end of making a cut or during a kickback, the projection on the rotatable 
guard forces the pawl on the latching mechanism away from the blade guard, 
permitting rotation of the blade guard to the closed position. The spring 
mechanism which biases the pawl, forces the pawl back into the path of the 
projection on the rotatable guard. Thus when the blade guard attempts to 
reopen, for any reason, the projection is blocked by the pawl, and motion 
is thereby prevented. The blade stays covered, and injury is avoided. 
In a second embodiment, the blade guard also has a handle attached to it. 
This handle enables the operator to manually operate the blade guard so 
that during a cut the pawl on the handle comes into contact with the 
unlatched operator lever, and the cam leg causes the operator arm to move 
to its latched position, again preventing reopening. 
In another embodiment, the latching means, that is, the operator arm, the 
cam leg and the blocking pawl, are all contained in one piece and 
rotatable about the same axis on the stationary part of the saw. In this 
mechanism, the guard handle is rotatably mounted instead of rigidly fixed 
as before, and is spring biased to place the path of travel of a pawl 
attached to the handle in line with the blocking means of the operating 
lever in the "latched" position. The rotatable handle and its pawl have a 
very limited arc of travel about the pivot point on the blade guard. When 
the rotatable handle manually opens the guard, it pivots to the limit of 
its arc of travel sufficient to position the pawl attached to the handle 
out of the path of the blocking means of the operating lever. Thus, when 
manual opening of the guard by use of the handle is being performed, it is 
unnecessary to "unlatch" by use of the operating lever. However, when the 
manual handle is not used, it becomes necessary to "unlatch" by means of 
the operating lever permitting the blade guard to open automatically as 
the saw is advanced onto the workpiece. Under either condition the cam leg 
of the operating lever is positioned to be forced back to its "latched" 
position by a stationary projection on the rotatable blade guard, just as 
in the first embodiment.

DETAILED DESCRIPTION 
As seen in FIG. 1, in a circular saw 10 there will generally be a 
stationary section 12 which contains a housing for the motor not shown, 
and the shaft 14 extending from the motor or its driven shaft upon which 
the circular saw blade 16 is mounted. When the shaft rotates, the blade 
does so with it and a cut may be made. In addition, there will generally 
be a rotatable guard 18 covering the saw blade. This guard is spring 
loaded, by a spring not shown, so that when no force is exerted on it, the 
guard covers the exposed saw blade and thereby prevents injury. Force is 
exerted on the blade guard 18 in a direction parallel to the cut being 
made by the guard 18 coming into contact with the workpiece 20. When this 
contact occurs, the guard 18 telescopes into a performed chamber 22 as 
best seen in FIG. 4 in the stationary section 12 of the saw 10 surrounding 
the saw blade 16, and the spring connected to the blade guard 18 is 
tensioned. When the force against the guard ceases, the guard 18 again 
returns to its unforced position. As seen in FIG. 2, on this rotating 
guard 18 is a projection 24, an integral part of the guard 18, or rigidly 
fixed by a pin 25. This projection 24 will generally be a piece of 
machined metal. It is mounted so that the projection 24 remains generally 
tangent to the arc described by the motion of the rotating guard 18. 
As seen in FIG. 3, the latching mechanism 26 is mounted on the stationary 
part 12 of the circular saw 10. This mechanism is generally composed of 
two pieces and their connecting parts. There is an operating lever 27 
consisting of a leg with a cam surface 28 and an operator arm 32 serving 
as a manual operator. As a unit it is rotatably mounted on a pin 30, and 
positioned so that the cam leg 28 can be moved into the path of the 
projection 24 described by the arcuate motion of the rotating guard 18. 
The operator arm 32 of the operating lever 27 and the cam leg 28 are 
secured together. As seen in FIG. 3, the cam leg 28 and the operating arm 
32 are generally formed from one piece 27, constructed as an L-shape. As a 
unit the operator arm 32 is mounted on pin 30 and rotates with the cam leg 
28. The operator arm 32 and cam leg 28, if not part of the same piece of 
material, are nevertheless connected together to act as a unit so that 
rotation of the cam leg 28 away from the path of the blade guard 18 will 
cause rotation of the operator arm 32 to its latched position. The second 
member of the latching mechanism 26 is the blocking means 34. This 
blocking means 34 will generally constitute a spring loaded pawl. At least 
one surface 37 of this piece will be planar, so that is is formidable 
enough to block the motion of the projection 24 mounted on the blade guard 
18. The blocking section 34 is also shown pin-mounted to pin 30 so that it 
rotates about the same axis as the operating lever 27 consisting of the 
operator arm 32 and the cam leg 28, although this concurrence of axes is 
not necessary. It is connected to the operating lever by means of a spring 
36. As seen in FIG. 1, when the cam leg 28 has moved away from the path of 
the projection 24 on the rotating blade guard 18, causing the operator arm 
32 to move in the same direction as the cam leg 28, the planar surface 37 
of the blocking section 34 is caused to move into the path of the 
projection 24 on the blade guard 18 due to the tension of the spring 36 
which biases the blocking section 34 to one limit of its possible arc of 
travel. 
Back to FIG. 3, the piece which completes the latching mechanism is the 
toggle 38 located on the stationary part 12 of the saw 10 toward the end 
of the operator arm 32. It is this toggle 38, generally in the form of a 
detent, which keeps the mechanism in an unlatched (unprotective) or 
latched (protective) position. As seen in FIG. 1, the operator arm 32 has 
been moved into the protecting latched position by being placed on one 
side of the toggle 38. As seen in FIG. 4, the operator arm 32 is now in 
the unlatched, unprotective position, on the opposite side of the toggle 
38. When in this initial unlatched position, the operator arm 32 sits to 
the side of the toggle 38 which causes the blocking section 34 to be out 
of the arcuate path of the projection 24. 
The protective mechanism operates as follows. As in FIG. 1, initially the 
guard 18 is closed, surrounding the saw blade. The operator arm 32 must be 
moved to the unlatched position as in FIG. 4, causing the blocking pawl 34 
to be out of the path of the projection 24 on the rotatable guard 18. The 
cam leg 28 is, however, caused to be in path of the projection 24. When 
the saw is advanced to make a cut, the guard 18 rotates and telescopes 
into the circular chamber 22 created in the stationary piece 12 of the saw 
10. This causes the projection 24 on the guard 18 to begin its rotation 
tangential to the arc described by the rotation of the guard 18. As seen 
in FIG. 5, during this rotation, as the guard begins to open the 
projection 24 comes into tangential contact with the cam leg 28 of the 
latching mechanism 26. The projection 24 causes the cam leg 28 to move out 
of its path, the cam leg 28 rotating about the pin joint 30 to which it is 
connected. With the rotation of the cam leg 28, the operator arm 32 is 
also rotated. This force on the operator arm 32 is sufficient to overcome 
the force exerted on the operator arm 32 at the toggle 38. This force 
causes the latching mechanism to return to its latched position. The 
rotation of the cam leg 28 causes the spring-biased blocking pawl 34 to 
move into the path of the rotatable guard 18 with its projection 24. This 
position is best seen in FIG. 1. It should be recognized that the 
projection 24 moves past the cam leg 28 as the guard 18 is in the process 
of opening. 
When the cut is finished, or when kickback occurs, the spring force on the 
guard 18 causes it to begin to rotate back to a position covering the saw 
blade. As seen in FIG. 5, as the rotatable blade guard closes, the 
projection 24 on the blade guard 18 comes into contact with the blocking 
pawl 34. However, because the blocking pawl 34 is rotatable about its 
pivot 30 and spring-mounted by the spring 36 to the operating lever 27 of 
the latching mechanism 26, the projection 24 causes the blocking pawl 34 
to move out of its path, against the force of its biasing spring, 
permitting guard 18 to pass by. The spring 36 connecting the blocking 
mechanism 34 and the cam leg 28 is further compressed, but does not create 
a force sufficient to push the operator arm 32 across the toggle 38 into 
the unlatched position. 
Once the projection 24 on blade guard 18 passes the blocking pawl 34, the 
biasing force of the pawl spring forces the blocking pawl 34 to snap back 
into the path of the projection 24 on the blade guard 18, while the 
operator arm 32 of the latching mechanism 26 remains in the latched 
position as best seen in FIG. 1. 
Therefore, should the blade guard 18 rebound or should it attempt to move 
from its fully closed position and begin to rotate into the chamber 22 of 
the stationary part 12 of the saw 10, the projection 24 on the blade guard 
18 comes into generally perpendicular contact with surface 37 of the 
blocking pawl 34 on the latching mechanism 26. Further motion of the blade 
guard 18 is prevented, and injury is avoided. An additional cut is 
possible only by moving the operator arm 32 past the toggle 38 and into 
the unlatched position as in FIG. 4. 
Two other embodiments of this invention are described in FIG. 7 and FIG. 8. 
In FIG. 7, the projection mounted onto the blade guard 18 has been 
supplemented with a handle 40. This handle 40 is also rigidly mounted to 
the blade guard 18, and operates similarly to the projection 24 in FIGS. 
1-6. 
In FIG. 8, the latching piece 42 has replaced the latching mechanism 26 of 
FIGS. 1-7. This latching piece 42 is a one-piece combination composed of a 
cam leg 44, operator arm 46 and blocking means 48. This latching piece 42 
is also rotatably mounted to the pin 30. Yet, because it is one piece, 
motion by one member of piece 42 causes motion of the remaining two 
members. Thus, if cam leg 44 has been moved out of the path of the pawl 41 
of handle 40, the blocking means 48 will move into the path of the same 
pawl of handle 40, and the operator arm 46 will move across the toggle 38 
from its unlatched position to its latched position. The handle 40 is 
pivotably mounted on a pin 50 and biased by a circular spring 52. This 
spring 52 forces the handle 40 to pivot into a position where the pawl 41 
will come into generally perpendicular contact with the blocking means 48. 
On the other hand, the permissible arc of travel about pin 50 allows the 
pivoting of the handle 40 to cause the pawl 41 to move out of the path of 
the blocking means 48 during motion by the blade guard 18 to a position 
where it covers the saw blade 16. The spring 52 forces the handle 40 with 
its pawl 41 to its original position once it has passed the blocking means 
48.