GB2452085A

GB2452085A - Guard apparatus for a saw blade

Info

Publication number: GB2452085A
Application number: GB0716563A
Authority: GB
Inventors: John Douglas Woodward
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-08-24
Filing date: 2007-08-24
Publication date: 2009-02-25
Anticipated expiration: 2027-08-24
Also published as: GB0716563D0; GB2452085B

Abstract

A guard apparatus for a saw blade 10, of the kind comprising a saw bench 11, comprises a guard element 17 movable transversely of a saw bench surface, and a plurality of actuators normally projecting into the path of a workpiece 12 sliding along the workbench surface towards the blade. The actuators are spaced in the direction of travel of the the workpiece, and are deflectable by a workpiece, such that the guard element moves out of the way of a workpiece approaching the blade only when more than one of the actuators have been deflected by the workpiece. Preferably, the saw blade is a circular saw blade 10, and a further guard 18 is also provided. The actuators may be in the form of micro-switches 19, 20, 21.

Description

"GUARD APPARATUS FOR MECHANICAL SAW BLADE" This invention relates to guard apparatus for a mechanical saw blade and is provided to prevent injwy to a person using the saw. By a mechanical saw is meant a circular saw, or a fretsaw or scroll saw, the blade of which rotates or reciprocates relative to a saw bench over the top surface of which a workpiece of wood, metal or a plastics material is advanced to the blade.

In the use of such saws there is considerable danger of injury to fmgers pushing the workpiece to the blade, especially in the last stages of the cut. Push sticks are used to keep the fingers at a distance from the blade but these can be awkward to use or may slip, tempting the operator to use his or her fingers to move the workpiece.

Safety devices used in the past have concentrated on stopping the saw blade in the event of is danger. These solutions are far from perfect because an emergency can arise in an instant whereas it takes time to arrest a rotating or reciprocating saw blade. The solution of the present invention is to prevent human access to the saw blade rather than to stop it.

In accordance with the present invention there is provided guard apparatus for a mechanical saw blade, the mechanical saw being of the kind comprising a saw bench along the surface of which a workpiece can slide into contact with a rotating or reciprocating saw blade, the guard apparatus comprising a guard element moveable lransversely of the saw bench surface on the upstream side of the saw blade between positions obstructing or not obstructing a workpiece sliding toward the blade and a plurality of actuators normally projecting into the path of a workpiece sliding along the workbench surface toward the blade, the actuators being spaced in the direction of movement of a workpiece toward the blade, the actuators being deflectable by a workpiece out of its path of movement toward the blade, the arrangement being such that the guard element will move out of the way of a workpiece approaching the blade only when more than one of the actuators have been deflected by the workpiece.

Preferably a hood and side plates are provided which prevent access to the saw blade from above or from either side.

The guard element may be a plunger or -like guard which is vertically moveable through a slot in the saw bench between a raised position in which it obstructs movement toward the blade and a lowered position permitting movement of a workpiece toward the blade.

Preferably a second guard element is provided which moves vertically relative to the saw tO bench on the upstream side of and separated from the first-mentioned guard element between a lowered position obstructing movement of a workpiece toward the saw blade and a raised position not obstructing movement of the workpiece toward the saw blade, the arrangement being such that the second guard element will not rise until more than one of said actuators is depressed and such that the first-mentioned guard element will not be lowered until after the second guard element has risen.

The arrangement is preferably such that after a workpiece has passed under the second guard element and before the first-mentioned guard element is lowered the second guard element is dropped onto the top surface of the workpiece to slide along the same as the workpiece travels toward the blade, dropping further to the saw bench behind the workpiece as the workpiece moves beyond the second guard element.

Preferably the actuators are at least three in number, spaced along the path of a workpiece sliding along the saw bench toward the saw blade, the arrangement being such that deflection of a single one of said three actuators has no effect upon either of the guard elements, simultaneous deflection of the first and second actuators causes the second guard element to rise while the first-mentioned guard element remains in its raised position and simultaneous deflection of all three actuators causes the second guard element to drop to the workpiece and the first-mentioned guard element to be lowered.

The first-mentioned guard element may be biassed by a counterweight to adopt the raised position in the event of failure of the power source by which it is lowered..

The actuators may be microswitches embedded in the saw bench, the microswitches controlling the circuit of a solenoid or a pneumatic or hydraulic ram arranged to move the or each guard element.

A preferred embodiment of the invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which I0 Figures 1,2 and 3 are similar side elevations of a circular saw and its saw bench showing guard elements in accordance with the invention in their different positions, and Figure 4 is a plan view of the apparatus of Figures 1-3.

The blade 10 of a circular saw rotates about a fixed axis just below the surface of a saw bench 11. A workpiece 12, for example a block of wood to be split, is slid along the saw bench 11 into contact with the saw blade 10. Behind the blade 10 is a stationery riving knife 13 a forward extension 14 of which constitutes a hood over the saw blade 10. On either side of this hood 14 drop plates 15 and 16 prevent access to the blade 10 from either side, while the hood 14 prevents access from above.

In accordance with this embodiment of the invention two guard elements 17 and 18 in the form of plungers are vertically moveable one through an aperture in the hood 14 and the other through an aperture in the saw bench 11. The operation of these guard elements 17 and 18 is controlled by three micro-switches embedded in the saw bench, each in turn actuated by depression of a respective button 19,20 and 21. The buttons are normally proud of the top surface of the saw bench 11 but can be deflected downward by a workpiece 12 sliding over them. Preferably the buttons are of a hard material which will resist movement by a relatively soft human finger.

By means of suitable circuitty (not shown) the buttons 19,20 and 21 control solenoids or pneumatic or hydraulic rams for displacing the guard elements 17 and 18. In the event of a power failure the guard 11 will drop under gravity to the saw bench 11. To ensure that in the event of a power failure the other guard 18 will rise to the position of Figure 3 it may be under the influence of a counterweight or spring (not shown) against the action of which the respective solenoid or the like must work.

Instead of plungers 17 and 18 the guard elements may be plates passing through respective slots in the hood and the saw bench.

The circuitiy controlled by the buttons 19,20 and 21 is arranged such that the accidental depression of a single button has no effect upon the guard elements 17 and 18. Only when the buttons 19 and 20 are simultaneously depressed by a workpiece 12 moving over them will the guard element 17 rise to the position of Figure 1, the guard 18 remaining in its raised position. When the third button 21 is also depressed (simultaneously with the other two) the guard 17 will drop onto the top surface of the workpiece and the guard 18 will descend out of the path of the workpiece (Figure 2). When the workpiece 12 moves beyond it the guard 17 will drop to the surface of the saw bench 11. Finally when all three of the buttons 19,20 and 21 are released by the workpiece 12 moving beyond them the guard 18 will rise to the position of Figure 3. This sequence is repeated each time a worlcpiece 12 is moved toward the saw blade 10.

l'his arrangement provides that the opening between the hood 14, the side plates 15 and 16 and the surface of the saw bench 11 through which a workpiece 12 moves toward the blade 10 is at all times obstructed by one or both of the guard elements 17 and 18, cooperating with the workpiece 12, to prevent human fingers reaching the blade 10.

Claims

CLAIMS: I. Guard apparatus for a mechanical saw blade, the mechanical saw being of the kind comprising a saw bench along the surface of which a workpiece can slide into contact with a rotating or reciprocating saw blade, the guard apparatus comprising a guard element moveable transversely of the saw bench surface on the upstream side of the saw blade between positions obstructing or not obstructing a workpiece sliding toward the blade and a plurality of actuators normally projecting into the path of a workpiece sliding along the workbench surface toward the blade, the actuators being spaced in the direction of to movement of a workpiece toward the blade, the actuators being deflectable by a workpiece out of its path of movement toward the blade, the arrangement being such that the guard element will move out of the way of a workpiece approaching the blade only when more than one of the actuators have been deflected by the workpiece.

I 5
2. Guard apparatus as claimed in claim 1, wherein a hood and side plates are provided which prevent access to the saw blade from above or from either side.
3. Guard apparatus as claimed in either preceding claim, wherein the guard element is a plunger or plate-like guard which is vertically moveable through an aperture in the saw bench between a raised position in which it obstructs movement toward the blade and a lowered position permitting movement of a workpiece toward the blade.
4. Guard apparatus as claimed in claim 3, wherein a second guard element is provided which moves vertically relative to the saw bench on the upstream side of and separated from the first-mentioned guard element between a lowered position obstructing movement of a workpiece toward the saw blade and a raised position not obstructing movement of the workpiece toward the saw blade, the arrangement being such that the second guard element will not rise until more than one of said actuators is depressed and such that the first-mentioned guard element will not be lowered until after the second guard element has risen.
5. Guard apparatus as claimed in claim 4, wherein the arrangement is such that after a workpiece has passed under the second guard element and before the first-mentioned guard element is lowered the second guard element is dropped onto the top surface of the workpiece to slide along the same as the workpiece travels toward the blade, dropping further to the saw bench behind the workpiece as the workpiece moves beyond the second guard element.
6. Guard apparatus as claimed in claim 4 or claim 5, wherein the actuators are at least three in number, spaced along the path of a workpiece sliding along the saw bench toward to the saw blade, the arrangement being such that deflection of a single one of said three actuators has no effect upon either of the guard elements, simultaneous deflection of the first and second actuators causes the second guard element to rise while the first-mentioned guard element remains in its raised position and simultaneous deflection of all three actuators causes the second guard element to drop to the workpiece and the first-mentioned guard element to be lowered.
7. Guard apparatus as claimed in claim 4, claim 5 or claim 6, wherein the first-mentioned guard element is biassed by a counterweight to adopt the raised position in the event of failure of the power source by which it is lowered..
8. Guard apparatus as claimed in any one of the preceding claims wherein the actuators are microswitches embedded in the saw bench, the microswitches controlling the circuit of a solenoid or a pneumatic or hydraulic ram arranged to move the or each guard element.
9. Guard apparatus for a mechanical saw blade, the mechanical saw being of the kind comprising a saw bench along the surface of which a workpiece can slide into contact with a rotating or reciprocating saw blade, the guard apparatus being substantially as hereinbefore described and as shown in the accompanying drawings.