GB2347111A

GB2347111A - Automatic guard arrangement for table saw

Info

Publication number: GB2347111A
Application number: GB9904479A
Authority: GB
Inventors: Marcello Bettacchini; Lucio Ginocchini; Micro Rossetti
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1999-02-27
Filing date: 1999-02-27
Publication date: 2000-08-30
Also published as: GB9904479D0

Abstract

A saw 1 includes a saw assembly comprising an upper saw blade guard 8 and a motor 30 driving saw blade 9 mounted on the assembly. The saw assembly is pivotally mounted on saw table 3 such that the saw assembly can be lowered towards the table to cut a workpiece. A lower guard 10 is pivotally mounted to the upper guard 8 so that the lower guard is moveable to expose the saw blade, and an automatic guard arrangement is provided for retracting the lower guard when the saw assembly is lowered. The automatic guard arrangement comprises a rigid lever 12, pivotally mounted at 14, and having first end 20 with first end surface 15 which bears against first cam surface 13, the first cam surface being located on the saw so that it remains in a fixed position when the saw assembly is lowered. The lever has second end surface 22 which bears against second cam surface 24 on the lower guard. Lowering of the saw assembly moves the pivot point 14 towards the first cam surface 13, causing the first end surface 15 of the lever to move along the cam surface 13 and rotate the lever about pivot 14 so that second end surface 22 of the lever engages the second cam surface 24 to retract the lower guard.

Description

AUTOMATIC GUARD ARRANGEMENT FOR TABLE SAW The present invention relates to saws, such as chop saws, mitre saws and flip over saws, and in particular relates to saws comprising a table and a saw assembly carrying a motor driven saw blade which is pivotally mounted on the table such that the saw assembly can be lowered towards the table to plunge the saw blade into a workpiece, resting on the table.

Such saws generally have a fixed upper saw blade guard for protecting a user of the saw from the upper part of the saw blade and a moveable lower saw blade guard for selectively exposing the saw blade when a cut is to be made in a workpiece and otherwise for protecting the user from the lower part of the saw blade. It is desirable that at any time the part of the saw blade that is exposed by the lower guard is contained within a workpiece to be cut or within a slot in the saw table so that as little of the motor driven saw blade as possible is exposed to a user of the saw. To achieve this, it is preferred that the lower guard moves automatically to expose the saw blade as the saw assembly is lowered towards the saw table, such that gradually more of the lower part of the saw blade is exposed as the saw assembly is moved closer to the saw table. For the benefit of a user of the saw the automatic movement of the lower guard should be smooth and not jerky and should require only a small extra force to be applied by the user to lower the saw assembly towards the saw table.

Such arrangements are disclosed in DE 31 36 591 and DE 196 32 229.

DE 196 32 229 discloses a saw assembly in which a lower moveable guard is retracted into an upper fixed guard using an articulated lever one end of which is pivotally mounted to the lower guard and the other end of which is pivotally mounted to the saw assembly. A closed cam slot is located in the lever towards said other end within which a cam follower located at a first end of a second lever can slideably move.

The second end of the second lever is connected to a portion which does not pivot with the saw unit. As the saw assembly is lowered the movement of the pivot point of the first lever relative to the fixed portion causes the cam follower to move along the slot to move the first articulated lever anti-clockwise to retract the lower guard. This design is relatively complicated requiring numerous parts. In particular it requires numerous articulated joints and a closed cam slot and follower arrangement all of which are exposed to the saw dust and wood chippings that are generated by operation of the saw.

Therefore, after prolonged use the articulations and cam slot and follower arrangement can stick due to contamination by dust etc. which increases the force required to retract the lower guard and reduces the smoothness of the retraction movement of the lower guard.

DE 31 36 591 discloses a similar saw assembly to that described in DE 196 32 229 in which an articulated lever is used to retract two lower guard parts in opposite directions into an upper guard part to expose a saw blade when the saw assembly is lowered towards a saw table. The articulated lever is pivotally attached to the saw assembly and has a cam follower at its lower end which can move slideably within a closed cam slot in a body which does not move with the saw assembly. Again this design is relatively complicated requiring numerous parts and requires numerous articulated joints and a closed cam slot and follower arrangement all of which after prolonged use can stick due to contamination by dust etc. This can increase the force required to retract the lower guard and reduce the smoothness of the retraction movement of the lower guard.

Accordingly the present invention aims to provide a simplified automatic guard arrangement which minimises exposure of a motor driven blade of a saw to a user, which operates smoothly even after prolonged use and requires only a relatively small force to retract the guard and which is simple and requires few parts.

According to the present invention there is provided a saw comprising; a saw assembly comprising an upper saw blade guard and a motor which can rotatingly drive a saw blade mounted on the assembly, which saw assembly is pivotably mounted on a saw table such that the saw assembly can be lowered towards the table to cut a workpiece resting on the table, a lower moveable guard which is pivotably mounted to the upper guard so that the lower guard is moveable to expose a saw blade mounted on the assembly, and an automatic guard arrangement for automatically retracting the lower guard when the saw assembly is lowered, characterised in that the retraction arrangement comprises; a rigid lever having a first end with a first end surface which bears against a first cam surface, which first cam surface is located on the saw so that it remains in a fixed position when the saw assembly is lowered, said lever having a second end with a second end surface which bears against a second cam surface located on the lower guard and said lever is pivotally mounted to the saw assembly at a portion of the lever between said first and second ends, such that lowering of the saw assembly moves the pivot point between the lever and the saw assembly towards the first cam surface to cause the first end surface of the lever to move along the first cam surface to rotate the lever about the pivot point so that the second end surface of the lever engages the second cam surface on the lower guard to retract the lower guard.

In the present invention the articulated levers known in the prior art are replaced with a single rigid lever which much simplifies the guard arrangement according to the present invention over known arrangements. In addition a cam arrangement is used to engage the lever and the lower guard to retract the lower guard thus removing a further articulation. Using a cam arrangement between the lever and the lower guard and between the lever and a part of the saw that is not moved when the saw assembly is lowered, enables a rigid lever to be used and reduces the vulnerability of the retraction arrangement to infiltration by dust and the like.

In a preferred embodiment the retraction arrangement additionally comprises a spring arrangement which acts to urge the lower guard into its closed position in which it covers a saw blade mounted on the saw assembly, such that lifting of the saw assembly causes the spring arrangement to move the lower guard and automatic guard arrangement back into its original position. By biasing the lower guard into the closed position, at any position of the retraction arrangement the spring arrangement ensures that the lower guard covers as much of the saw blade as is possible. Thus, any slack in the retraction arrangement that could result in the lower guard exposing more of the blade than is desirable is automatically removed. Furthermore, the use of the spring arrangement aids the smooth operation of the retraction arrangement to move the lower guard over the saw blade when the saw assembly is lifted after a cut has been made in a workpiece. Preferably, the spring arrangement comprises a tension spring which acts between the lower guard and a portion of the rigid lever between said first and second ends of the lever.

Preferably, at least one of the end surfaces of the lever is an open surface which cooperates with an associated open cam surface. By using an open end surface of the rigid lever to co-operate with an open cam surfaces as opposed to the closed cam surfaces or cam slots and cam followers that are used in the prior art discussed above, the retraction arrangement is less vulnerable to infiltration by dust. This is because dust is much less likely to be caught on an open cam surface than it is to be caught in a closed cam slot.

Also, the repeated bearing of the open end surfaces of the lever against the open cam surfaces will act to remove dust etc. To reduce the collection of dust on the end surfaces of the lever and on the first and second cam surfaces, it is preferred that at least one of the said surfaces and preferably all of them are substantially flat or convex.

Preferably, the lever is bent and is pivotally mounted to the saw assembly at said bend. This enables the translation of a force on the lever in a first direction due to the bearing of the first end surface of the lever against the first cam surface to be translated into a force in an appropriate different direction exerted by the second end surface of the lever onto the second cam surface located on the lower guard, depending on the angle of the bend in the lever. It is also preferred that the first end surface is closer to the bend than the second end surface, so that a small relative movement of the first end surface as it bears against the first cam surface can be amplified into a larger movement of the second end surface in order to retract the lower guard by the desired amount.

Preferably the second end surface is located laterally of the lever to enable it to exert a pulling force on the lower guard and more preferably, this second end surface engages a rib extending from an inner surface of the lower guard to exert a pulling force on said lower guard as the lever pivots about its pivot point.

One form of a chop saw guard arrangement according to the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a partial cross-section of a chop saw guard arrangement according to the present invention; Figure 2 shows a side view of the guard arrangement of Figure 1.

The saw (1) has a base table (3) on which is located a pivot block (2). A saw housing (5) is mounted pivotally on the pivot block (2) about a pivot axis (7). The saw housing (5) comprises a motor (30) for driving a circular saw blade (9) about an axis (11), a motor casing (18) within which the motor (30) is mounted and a fixed upper saw blade guard (8) which covers the upper part of the saw blade (9). The housing (5) is actuated by a handle (32) (shown fully in Figure 2) to pivot the housing (5) about pivot axis (7) and plunge the blade (9) into a slot (not shown) in the table (3), through a workpiece (not shown) resting on the table (3).

Attached to the pivot block (2) is a bearing which takes the form of a roller (13) mounted on an axle (4). The axle (4) is formed by a bolt which passes through receiving holes formed in two parallel arms (6) which extend from a part of the pivot block (2) which is fixed to the saw table (3) and so does not pivot about the axis (7) when the saw housing (5) is lowered. The roller (13) is mounted for rotation on the part of the bolt (4) which extends between the two arms (6).

A retractable lower guard (10) is pivotally mounted to the fixed upper guard (8) about axis (11) so that the lower guard (10) can be retracted into the upper guard (8) to expose the saw blade (9). A single rigid lever (12) is used to cause the lower guard (10) to retract into the upper guard (8) to expose the saw blade (9) when the saw housing (5) is pivoted about axis (7) towards the saw table (3). The lever (12) is substantially Ushaped. At a first bend in its lower part the lever (12) is pivotally mounted at hinge pint (14) to an extension (16) of the saw housing (5). A first lower end (20) of the lever (12) adjacent to the first bend has an end surface (15) which bears against the bearing (13).

The surface of the bearing (13) forms an open cam surface against which the end surface (15) of the lever bears. At the opposite second end of the lever (12) is located a plastic ledge (22) which extends to one side of the lever (12) and forms an end surface of the lever which is engageable with a substantially radial rib (24). The ledge (22) forms an open end surface of the lever (12) which engages the radial rib (24) which forms an open cam surface on the lower guard (10). The rib (24) extends from the inner surface of the lower blade guard (10).

A tension spring (17) connects a middle part (25) of the lever (12) to a part (26) of the edge of the lower guard (10). The spring (17) biases the lower guard (10) towards a position in which it covers the saw blade (9).

In use when the saw housing (5) is lowered towards the saw table (3), the hinge point (14) which pivots with the saw housing (5) about axis (7) moves towards the roller bearing (13). As indicated above the roller bearing (13) is attached to a part of the pivot block (2) which does not pivot about axis (7). The engagement of the end surface (15) of the lever (12) with the roller bearing (13) causes the lever (12) to pivot in an anticlockwise direction about hinge point (14) as the saw housing (5) is lowered. This anticlockwise pivoting of the lever (12) causes the second end of the lever to move relative to the upper guard (8) in the direction of arrow (A). The ledge (22) on the lever (12) engages the rib (24) and slides radially outwardly along the rib (24) and pulls the lower guard (10) causing it to pivot in an anti-clockwise direction about axis (11). In this way the lower guard (10) is retracted into the upper guard (8) to expose the saw blade (9) when the saw housing (5) is lowered towards the saw table (3). The ledge (22) is made of plastic to reduce the friction between the ledge (22) and the rib (24) as the ledge slides along the rib.

After the saw blade has completed a cut into a workpiece, the saw housing (5) is moved away from the saw table (3) and the action of the tension spring (17) between points (25) and (26) causes the lower guard (10) to pivot in a clockwise manner about axis (11). The spring (17) and the relative movement of the hinge point (14) and the roller bearing (13) away from each other causes the lever (12) to pivot in a clockwise direction about hinge point (14) and the ledge (22) on the lever (12) to slide radially inwardly along the rib (24). These actions together cause the lower guard to cover the blade (9) as it is retracted from a workpiece.

The open camming engagement between the end surface (15) of the first end of the lever (12) with the surface of the roller (13) is less vulnerable to blocking by dust because it comprises two open surfaces which repeatedly bear against each other. Similarly, the open camming engagement between the end surface (22) of the second end of the first lever (12) with the rib (24) is less vulnerable to blocking by dust because it comprises two open surfaces which repeatedly bear against each other.

A guard lock lever (31) (shown in Figure 2) is pivotally mounted using a bolt (35) about point (34) on the handle (32) which extends from the saw housing (5). The lever (31) is biased into an off-position (position X) shown in full black lines in Figure 2 by means of a spring (not shown). The lever (31) can be moved by a user of the saw grasping a hand grip (37) provided at the end of the handle (32) into an on-position (position Y) shown in dotted lines in Figure 2. In the on-position a projection (40) at the free end of the lever (31) engages an actuator of an on-off power switch (42) to activate the motor (30) of the saw.

The guard lock lever (31) has a locking extension (36) which in the off-position extends through a gap in the upper guard (8) to engage with an edge (38) of a slot (39) in the lower guard part (10). The engagement of the locking extension (36) with the edge (38) of the slot (39) prevents the lower guard (10) from being retracted into the upper guard part (8) to expose the saw blade (9). When the lever (31) is moved into its on-position (see Y'shown in dotted lines) the locking extension (36) is moved out of the slot (39) and the lower guard (10) can be retracted as described above. Thus, the lever (31) has the dual function of switching the motor on and off and unlocking and locking the lower guard (10).

When the motor is switched off, the lower guard (10) is locked against retraction into the upper guard (8) and so the saw housing (5) cannot be lowered far towards the saw table (3) because the lower guard (10) blocks such movement. When the motor is switched on, the lower guard is simultaneously unlocked and so the saw housing (5) can be lowered towards the saw table (3) and the lower guard (10) is retracted, as described above, into the upper guard (8) to expose the saw blade (9) so that it can make a cut into a workpiece positioned on the saw table (3).

Claims

CLAIMS: 1. A saw comprising; a saw assembly comprising an upper saw blade guard and a motor which can rotatingly drive a saw blade mounted on the assembly, which saw assembly is pivotably mounted on a saw table such that the saw assembly can be lowered towards the table to cut a workpiece resting on the table, a lower moveable guard which is pivotably mounted to the upper guard so that the lower guard is moveable to expose a saw blade mounted on the assembly, and an automatic guard arrangement for automatically retracting the lower guard when the saw assembly is lowered, characterised in that the automatic guard arrangement comprises; a rigid lever having a first end with a first end surface which bears against a first cam surface, which first cam surface is located on the saw so that it remains in a fixed position when the saw assembly is lowered, said lever having a second end with a second end surface which bears against a second cam surface located on the lower guard and said lever is pivotally mounted to the saw assembly at a portion of the lever between said first and second ends, such that lowering of the saw assembly moves the pivot point between the lever and the saw assembly towards the first cam surface to cause the first end surface of the lever to move along the first cam surface to rotate the lever about the pivot point so that the second end surface of the lever engages the second cam surface on the lower guard to retract the lower guard.
2. A saw according to claim 1 characterised in that the automatic guard arrangement additionally comprises a spring arrangement which acts to urge the lower guard into its closed position in which it covers a saw blade mounted on the saw assembly, such that lifting of the saw assembly causes the spring arrangement to move the lower guard and automatic guard retraction arrangement back into its original position.
3. A saw according to claim 2 characterised in that the spring arrangement comprises a tension spring which acts between the lower guard and a portion of the rigid lever between said first and second ends.
4. A saw according to any one of claims I to 3 characterised in that at least one of the end surfaces of the lever is an open surface which co-operates with an associated open cam surface.

5. A saw according to claim 4 characterised in that said end surface and associated cam surface are substantially flat or convex.
5. A saw according to any one of claims 1 to 4 characterised in that the lever is bent and is pivotally mounted to the saw assembly at said bend.
6. A saw according to claim 5 characterised in that the first end surface is closer to the bend than the second end surface.
7. A saw according to any one of the preceding claims characterised in that said second end surface is located laterally of the lever.
8. A saw according to claim 7 characterised in that said second end surface engages a rib extending from an inner surface of the lower guard to exert a pulling force on said lower guard as the lever pivots about its pivot point.
9. A saw substantially hereinbefore described with reference to any one of the accompanying Figures.