Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
Fleld of the Invention
This invention relates to table mounted, power circular saws
Iwhich are primarily intended to perform a chopping function.
Description of the Prior Art
Traditlonally chop saws are pivotably mounted on a saw
table, between a raised rest posi-tion and a lowered operational
position. For safety reasons, it is desirable to provide a hood
to cover the saw blade when the saw is in the rest position.
Convenience dictates that any such blade guard should be mounted
in a manner such that it will be swung clear of the saw blade
when the saw is pivoted from its res-t position to its operational
position. Prior art devices, such as German Offenlegungsschrift
28 29 297, have attempted to solve this problem by coupling the
swinging hood to a saw table with a cable in order to pivot the
hood to clear the blade when the saw unit is lowered to its oper-
ational position.
An inherent problem with such prior art devices is that when
the saw unit is in the raised rest position, the blade guard ham-
pers attempts to change the saw blade. Likewise, it is difficult
to change a saw blade in the operational position because the saw
table gets in the way.
When the chop saw is not in use, it is also desirable for
safety reasons to lock the saw-unit in its rest position with the
blade covered. Prior art locking systems, such as the one dis-
closed in German Gebrauchsmuster 74 20 476, keep the raised saw
unit in the rest position by means of a locking element that
engages a stationary locking surface. To be released, the
locking element must displace a spring. In such an arrangement,
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the entire weight of the saw unit rests upon the locking element,
which accordingly must be very rugged in order to prevent damage
when the user inadvertently attempts -to force the saw-unit down
while the locking element remairs engaged to the locking surface.
The instant invention has overcome many of the disadvantages
of prior art devices by providing a linkage system which effec-
tively clears the blade guard from the saw blade when the chop
saw is ]owered to the operational position while being partially
collapsible in order to facilitate changing of the saw blade by
allowing the protective blade guard to be swung out of position
while the saw is maintained in the rest position. Additionally,
the linkage system of the present invention engages a locking
element when the saw unit is in its rest position in a manner
that reduces the forces that must be absorbed by the locking
element.
Additional advantages of the invention are set forth in part
in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the inven-
tion.
SUMMARY OF THE INVENTION
The objects and advantages of the invention may be realized
and attained by means of the instrumentalities and combinations
particularly pointed out in the appended claims.
In a chop saw pivotally mounted on a bearing bracket for
movement between a lowered, operational position and a raised,
rest position, having a motor-driven saw blade rotatably sup-
ported on a shaft, a housing partially encasing the saw blade and
a swinging blade yuard disposed to cover an exposed segment of
the saw blade when the chop saw is in the raised position, the
1.
invention comprising a linkage system for moving the blade guard
in response to movement of the chop saw between the lowered and
raised positions. The linkage system includes a frame member
fixed to and extending upwardly from the bearing bracket, an
actuation lever, a first hinging means for pivotally mounting the
housing near the base of the frame member, a second hinging means
pivotally attaching one end of the actuation lever to the frame
member upwardly from the first hinging means, a third hinging
means pivotally attaching the other end of the actuation lever to
the swinging blade guard, and a fourth hinging means pivotally
connecting the swinging blade guard to the housing. The third
hinging means is eccentrically positioned on the blade guard with
respect to the fourth hinging means and the distance between the
thi d and fourth hinging means being substantially less than the
distance between the first and second hinging means such that the
blade guard immovably covers the exposed segment of the chop saw
in the raised position and is moved to uncover the exposed seg-
ment when the chop saw is moved to the lowered position.
Preferably the linkage system of the invention further
includes means for selectively disengaging the second hinging
means to permit temporary shortening of the effective length of
the actuation lever and moving of the blade guard to uncover the
exposed segment when the chop saw is in the raised position for
facilitating changing the saw blade.
It is also preferred that the linkage system include a
locking means for detachably engaging the actuation lever when
the saw is in the raised position.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, whlch are incorporated in and
constitute a part of the specif:ication, illustrate embodiments of
Ithe invention, and, together with the description, serve to
explain the principals of the invention.
Figure l is a schematic diagram of the linkage system in
both the operational and rest positions.
Figure 2 is a side elevation of the chop saw with a fragmen-
tary sectional view of the locking mechanism and a portion on the
;linkage system.
Figure 3 is a cross-sectional view of the chop saw taXen
along line III-III of Figure 2, emphasizing the rel~tlonship of
the pivot bolt that attaches the frame member to the actuation
lever.
Figure 4 is an elevation view of the actuation lever.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made in detail to the present pre-
ferred embodiments of the invention, examples of which are illus-
trated in the accompanying drawings.
The invention relates to a saw unit particularly suited to
carrying out a chopping type function. The preferred embodiment
of the chop saw includes a power circular saw-unit 90 pivotably
mounted on a saw table 20 for movement between a raised rest po-
sition and a lowered operational position. The saw-unit
preferably includes an electric motor, not shown, which rotatably
drives a saw blade 32 about its supporting shaft 104; a housing
106 which partially encases -the blade 32 and a pivotably mounted
blade guard 108 that immovably encases the exposed portion of the
saw blade 32 when the saw-unit is in the rest position.
The improvement of this invention as embodied and generally
described herein relates to a linkage system which clears the
blade guard 108 when the saw unit 90 is lowered into the opera-
tional position, thereby exposing blade 32 to the workpiece.
In accordance with the present invention, a preferred em-
bodiment of the linkage system, schematically shown in Figure 1,
includes four hinging means, 1, 2, 3 and 4 as well as four effec-
tive levers, 5, 6, 7 and 8. The first hinge is stationary and is
located at the base of lever 5 which is also stationary. A lever
6 is pivotably mounted to the lower end of lever 5 by the first
hinge. Lever 6 corresponds to the saw housing 106 of Figure 2,
and the pivotal motion of the first hinge corresponds to the
movement of the saw-unit between its rest position and its opera-
tional position. Lever 8 is pivotably connected to lever 6 by
hinge 4. Lever 8 corresponds to the swinging blade guard 108 of
Figure 2. Lever 7 is pivotally connected to lever 5 at hinge 2
and to lever 8 at hinge 3.
The lever positions depicted by solid lines in Figure 1
represent the saw in the operational position. The dashed lines
represent the rest position. Since the effective length of lever
8 is substantially less than the effective length of lever 5,
lever 8, which corresponds to the swinging blade guard 108, has a
much greater arc of rotation than does lever 6, which corresponds
to movement of housing 106 between the rest position and the op-
erational position. In order to reach the operational position,
lever 6' is pivoted clockwise about hinge 1. This causes a
counterclockwise rotation of lever 8 about hinge 4. This
corresponds to the movement of the swinging blade guard 108 as
pi
the saw is lowered. Since initially the distance between hinge
3' and hinge 1 must increase, lever 7' is initially re~ulred to
swing upwardly about hinge 2.
An engaging element 10 is mounted on lever 7. When the saw
is in its rest position, engaging element 10' attaches to locking
element 12 to secure the saw in that position. In the rest posi-
tion, as shown by the dashed line in Figure 1, hinge 3' is fur-
;ther from lever 5 connecting the first and second hinges than is
! hinge 4' and the two essentially form a straigh-t line with hinge
2. Thus, when the saw is in the rest position, the alignment of
the levers is such that the majority of the load acting on the
saw unit is transmitted by levers 7' and 8', thereby alleviating
the bulk of the load on locking element 10.
The safety saw shown in Figures 2 and 3 comprises a conven-
tional saw table 20 with a workpiece stop 22 against which the
workpiece may rest. A revolving seat 24 is rotatably supported
on saw table 20 and holds bearing bracket 26 through which passes
horizontal shaft 28. Frame element 105 is attached to revolving
seat 24. When clamping knob 30 is loosened, frame 105 may be ro-
tated about the axis of shaft 28. This makes possible the miter-
setting of the saw-unit.
Shaft 101 is mounted in frame 105 and supports saw housing
106 in a pivotable manner. This pivot-junction corresponds to
hinge 1 of Figure 1, and housing 106 corresponds in function to
the effective lever 6 of the linkage system shown in Figure 1.
Frame 105 extends upwardly from shaft 101 and terminates at
a pivot junction with actuati.on lever 107. The pivot junction is
formed by a pivot bolt 102 which corresponds to hinge 2 of Figure
1. Frame ].05 corresponds to effective lever 5 of Figure 1 and
actuatiOn lever 107 corresponds to effective lever 7 of the
linkage system shown in Figure 1. Actuation lever 107 is
pivotably connected to swinging blade guard 108 by a pivot joint
103. Pivot joint 103 which corresponds to hinge 3 shown in
Figure 1, is eccentrically positioned on blade guard ]08 about
the saw blade support shaft 104. Swinging blade guard 108
corresponds to lever 8 in Figure 1.
The saw blade 32 is rota-tably supported by a saw blade
support shaft 104 in housing 106 and is driven by an electric
motor, not shown, located on the back of the saw as seen in
Figure 2. The saw blade support shaft shares the same axis of
rotation as swinging blade guard 108. Saw blade support shaft
104 corresponds, in location, to the hinge 4 of Figure 1.
When the saw unit is lowered from its rest position, the saw
housing 106 is rotated about the first hinging means, shaft 101.
Actuation lever 107 is similarly rotated in a clockwise manner
about pivot bolt 102. As is apparent from the schematic diagram
of Figure 1, this combination of motion causes a relatively large
rotation of the swinging blade guard 108 about the saw blade sup-
port shaft 104 corresponding to a relatively small rotation of
the saw housing 106 about shaft 101. This combination of motions
allows the swinging blade guard 108 to rotate clear of the saw-
blade 32 when the saw unit is lowered to its operational posi-
tion.
In a preferred embodiment, actuation lever 107 is L-shaped.
Such a s-ructure assures that the actuation lever will always be
outside the range of displacernent of saw blade support shaft 104.
This permits the entire linkage system to be mounted essentially
in a single plane. L-shaped actuation lever 107 has a pivot
:;
point aperture 40 at the outer end of its longer leg, as can be
seen by reference to Figure 4. Adjoining the pivot point aper-
ture 40 is a slot 41 which runs longitudinally along the center
of the longer leg of the L-shaped actuation lever 107. The width
of slot 41 is less than the diameter of pivot point aperture 40.
As shown in Figure 3, it is preferred that pivot bolt 102
has a threaded end section of lesser diameter than its shank.
When the saw unit is operational, pivot bolt 102 is threadably
secured to frame member 105. The pivot point aperture 40 of
actuation lever 107 receives the shaft of pivot bolt 102. It is
preferred that the width of slot 41 be less than the diameter of
the shaft of pivot bolt 102, but greater than the diameter of the
threaded portion of -the pivot bolt.
It is further preferred that an opening 45 be cut into hous-
ing 106 in a location such that it will be aligned with pivot
bolt 102 when the saw unit is in its rest position. The opening
45 preferably consists of a bore 47 expanded by an inner cavity
49 internal to the housing 106.
To accommodate changing saw blade 32, the saw unit is placed
in the rest position. A screw driver, inserted through the open-
ing 45 in saw housing 106 can be used to partially withdraw pivot
bolt 102 from frame member 105. It is preferred that the face of
inner cavity 49 be located in a manner such that while it pre-
vents pivot bolt 102 from being totally withdrawn from frame
member 105, it allows sufficient space for the shank of pivot
bolt 102 to be cleared from the L-shaped actuation lever 107.
This allows the actuation lever to slide freely along the
threaded portions of pivot bolt 102. The swinging blade guard
108 can then be raised without moving the saw unit from its rest
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position. Saw blade 32 may then be freely changed without any
obstruction from blade guard 10~. The head of pivot bolt 102
which is within inner cavity 49 prevents the saw-unit from being
lowered to it's operational pos:ition until the actuation lever
107 has been returned to its normal position and pivot bolt 102
is turned back into place.
In a preferred embodiment, a locking element 50 engages the
actuation lever 107 when the chop saw is in its rest posi-tion.
Locking element 50, which is pivotably mounted about pivot axis
52, is connected to a lock release button 54 by a release lever
55. The release lever itself is mounted pivotably about a pivot
axis 56.
In order to lower the saw blade so it may engage a work-
piece, the locking element 50 must be disengaged. To accomplish
this, lock release button 54 is depressed. As a result, release
lever 55, which is attached at one end to lock release button 54,
is rotated about pivot axis 56. This rotation causes an upward
displacement of pin 60 which is mounted at the opposite end of
release lever 55. Locking element 50 is provided with a curved
slit 62 that has an enlarged clearance 64 at the lower end there-
of. When pin 60 is forced upwards by the actuation of lock
release button 54, it forces locking element 50 to rotate in a
clockwise direction as seen in Figure 2. This rotation of
locking element 50 causes actuation lever 107 to rotate about
pivot bolt 102 in a counterclockwise direction. Simultaneously,
the third hinging means 103, which corresponds to hinge 3 in the
schematic shown in Figure 1, is raised above the line connecting
hinges 2 and 4 (which correspond to pivot bolt 102 and sawblade
support shaft 104 respectively), thereby eliminating the dead
position. Thereupon, locking element 50 is disengaged and -the
saw unit can be easily lowered.
Tension springs 70 and 71 are mounted to the frame at one
end and to the housing at their other end, in a manner such that
they exert an upward force on the pivotably mounted housing 106.
Springs 70 and 71 automatically pivot the saw into the rest posi-
tion shown in Figure 2 when the user releases housing 106.
threaded borehole 80 is present in frame 105 between the
points acted upon by the springs 70 and 71 on one side and -the
pivot bolt 102 on the other. The borehole 80 is configured to
receive a locking screw 83 that is mounted on the housing unit
106 in a manner such that when the saw unit is lowered into its
operational position, the Iocking screw 83 and the borehole 80
are aligned. It is therefore possible to lock the saw unit in
its lowered position, which is desirable, for example, when the
saw unit is being transported.
It will be apparent to those skilled in the art that various
modifications and variations could be made to the chop saw link-
age of the invention without departing from the scope or spirit
of the invention.
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