Abstract:
A power miter saw having a circumferential louvered blade guard that articulates relative to the saw blade as the miter saw is pivoted downwardly into engagement with the workpiece. The louvers in the guard are specially configured to substantially prevent or impede the ejection of cutting debris through the louvers while also permitting the operator to precisely align the saw blade with a mark on the workpiece while maintaining a stationary vision point from a natural operating position, regardless of the angle of articulation of the guard.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates generally to a guard device for a power saw having a circular blade, and more specifically to a circumferential guard which allows the operator of the saw to view the saw blade in relation to the desired cut to be made in the workpiece. 
     In general, it is desirable to provide for a guard to use in conjunction with a power saw. The guard primarily serves to protect the operator from the blade of the saw, as well as helping to confine saw dust and other particles generated during the sawing process. However, as both professional and home do-it-yourselfers can appreciate, conventional guards have the undesirable side effect of also obscuring the operator&#39;s vision of the position of the saw blade relative to the workpiece, thereby making it difficult to make precise cuts. 
     The most frequently proposed solution to this problem is to provide a blade guard that is composed of a transparent material. However, such devices suffer the disadvantage of providing rapidly deteriorating visibility with use caused by scratching and clouding of the material, as well as particles &#34;sticking&#34; to the surface of the guard. Thus, a transparent guard does not satisfactorily solve the problem. 
     In addition, it has been proposed to provide guards having viewing slats or holes formed along the lateral surfaces of the saw guard. These devices, however, have the disadvantage of not allowing the operator to visually align the saw blade with the mark on the workpiece. Due to parallax, it is difficult for the operator to precisely align the saw blade when viewing it from an angle relative to the plane of the blade. Thus, these devices also fail to adequately solve the above-described problem. 
     It is therefore desirable to provide a saw blade guard that allows the operator to precisely align the saw blade in relation to the workpiece when the operator is in the normal operating position. In addition, it is desirable to provide a guard which enables such viewing without diminishing the effectiveness of the guard as a protective device. It is further desirable to design the saw blade guard in a manner adapted for efficient manufacturing so as to ensure that the saw blade guard can be produced economically. 
     To achieve the foregoing objectives, the present invention provides a circumferential guard for a power saw where the power saw is adaptable to accommodate circular blades of a given range of radii, the guard comprising: a semi-circular channel, the channel having a radius greater than the radius of the saw blade and having a channel width much wider than the thickness of the saw blade. The guard is pivotally attached to the power saw so as to cover the upper radial portion of the saw blade and to substantially center the saw blade between the walls of the channel. The guard further has a plurality of louvers disposed along the width-wise edge of the channel, the louvers enabling the operator to align the saw blade with the workpiece. In one embodiment according to the present invention, the louvers are cut into the width-wise edge of the channel in a manner so as to provide viewing access (from a stationary natural operating stance) by the operator throughout the range of movement of the saw blade and the guard. In an alternative embodiment of the invention, the louvers are configured such that the height of each louver opening is less than the thickness of the guard. 
     Other objects, features, and advantages of the present invention will be readily appreciated and better understood by referring to the following description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a power miter saw incorporating a louvered blade guard according to the present invention, and showing an operator viewing a workpiece through the louvered saw blade guard; 
     FIG. 2 is a side view of the power miter saw showing the saw blade and guard in the articulated position corresponding to the initiation of a cutting operation of a relatively tall workpiece; 
     FIG. 3 is a side view of the power miter saw showing the saw blade and guard in the articulated position corresponding to the initiation of a cutting operation of a relatively short workpiece; 
     FIG. 4 is an enlarged sectional view, taken from FIG. 2 along line 4, depicting the orientation of the louvers in a first preferred embodiment; 
     FIG. 5 is a further enlarged sectional view of the louvers taken from FIG. 3 along line 5; and 
     FIG. 6 is a similar sectional view of an alternative embodiment of the louvered saw blade guard. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown generally in FIGS. 1 and 2, a miter saw 10 having a circumferential guard 20 of the present invention is provided. Specifically, the miter saw has a circular saw blade 30 which is shielded by the guard 20. The guard 20 is pivotally attached to the miter saw 10, and also has a pivot arm assembly 40 linked between the miter saw arm and the guard 20 to help ensure proper articulation of the guard throughout the range of movement of the miter saw 10. As can best be seen in FIG. 1, an operator using the miter saw 10 to cut a workpiece 50 is able to view the workpiece 50 through the louvers 60 in the guard 20. The operator&#39;s line of sight 70 is unobstructed through the louvers 60, allowing the operator to line up the saw blade 30 with the marking on the workpiece 50. 
     As shown in FIGS. 4 and 5, the shape and disposition of the louvers 60 in one of the preferred embodiments is detailed. Specifically, the guard 20 is preferably composed of a rigid transparent plastic material. Because one of the purposes of the guard 20 is to confine particles and debris created by the saw blade during the sawing process, the outer height, H, of the louvers is limited to a maximum of 4 mm. This dimension is established by safety certification agencies such as Underwriters Laboratory (&#34;UL&#34;) in the U.S. and CENELEC in Europe. As can best be seen in FIG. 5, the louvers 60 are wider towards the inner surface of the guard 20 and taper to a narrower dimension toward the outer surface of the guard. As diagrammatically depicted in FIG. 1, the tapered configuration of the louvers 60 enhances the line of sight visibility of the operator to the workpiece along the plane of the saw blade. 
     In particular, as best illustrated by way of example in FIG. 2, when a tall workpiece 50, such as a 4×4, is to be cut, the guard 20 is in the articulated position shown when the saw blade 30 is lowered into contact with the workpiece 50. In this position, the operator&#39;s natural line of sight to a mark on the top surface of the workpiece 50 is through the louvers 60 generally toward the upper area of the guard 20, with the exact line of sight depending upon factors such as the position and height of the operator, or the position and elevation of the saw, for example. It will be appreciated that the tapered boundary surfaces of the louvers 60 provide the operator with a direct line of sight along substantially the entire upper surface of the workpiece. 
     In FIG. 3, an additional view of the miter saw in a different articulated position is shown by way of example. In this view the workpiece 50&#39; to be cut is relatively short, such as a 1×6. As can be seen from this figure, when the saw blade 30 is lowered into contact with the workpiece 50&#39;, the operator&#39;s natural line of sight to the top surface of the workpiece 50&#39; is now through the louvers 60 toward the lower area of the guard 20, when the same operator is standing in the same position as that illustrated in FIG. 2. In this position as well, it will be appreciated that the configuration of the louvers provides the operator with a direct line of sight along substantially the entire upper surface of the workpiece 50&#39;, without significantly changing his or her position from that illustrated in FIG. 2. 
     Consequently, it will be appreciated that in both extreme positions illustrated in FIGS. 2 and 3, as well as the range of articulated positions in-between, the louvers 60 in the guard 20 enable the operator to work from a natural operating position in order to sight along the plane of the saw blade 30 to accurately align the saw blade with a mark on the workpiece. 
     In the preferred embodiment of the invention illustrated in FIGS. 4 and 5, the specific geometry of the louvers 60 is determined in the following manner. With particular reference to FIG. 5, the slat 70 defining the lower boundary 75 of the third louver 80 and the upper boundary 85 of the fourth louver 90 (from the top) comprise the reference boundary surfaces. As shown in FIG. 5, both the lower reference boundary surface 75 and the upper reference boundary surface 85 are formed at an 11° radial angle relative to the radial line 95 through the center of the slat 70. Consequently, the two reference boundary surfaces 75 and 85 define an included angle of 22°. All of the remaining lower boundary surfaces of the louvers 60 are formed parallel to the reference lower boundary surface 75 and all of the remaining upper boundary surfaces of the louvers 60 are formed parallel to the reference upper boundary surface 85. Consequently, as best shown in FIG. 4, it will be appreciated that, as one progresses downwardly from the reference slat 70, the lower boundary surfaces of the louvers 60 are formed at progressively greater radial angles. Significantly, as depicted in FIG. 1, this configuration enables the operator to maintain a stationary vision point of the workpiece from a natural operation position regardless of the angle of articulation of the guard. 
     In addition, as will also be appreciated by those skilled in the art, the present preferred configuration of the louvers 60 enhances the manufacturability of the guard 20 by facilitating convenient release of the formed plastic part from the mold. 
     Turning now to FIG 6, an alternative embodiment of a guard 20 according to the present invention is shown. In this embodiment, the upper and lower boundary surfaces 110 and 120 of all the louvers 100 in the guard 20 are substantially parallel. However, it will be noted that the height dimension (&#34;H&#34;) of each of the louvers 100 is less than the thickness (&#34;T&#34;) of the guard material as measured along the respective louver&#39;s boundary surfaces. This alternative louver configuration significantly minimizes the discharge of cutting debris through the louvers 100 in the guard 20, or at least serves to remove a sufficiently large percentage of the kinetic energy of the particles that are ejected so as to virtually eliminate the potential hazard or nuisance of ejected particles to the operator. As cutting debris is ejected tangentially from the tips of the saw blade, it will be appreciated that this function is accomplished in the embodiment illustrated in FIG. 6, by impeding the path through the guard 20 for such ejected particles. Consequently, any particles (diagrammatically illustrated by reference numeral 106) propelled by the cutting blade will either contact a boundary surface and upon deflection remain inside the guard 20 (as illustrated in the lower portion of FIG. 6), or lose a sufficient amount of its kinetic energy due to deflection in the louver spaces such that the resulting exit velocity from the guard is small and therefore not a hazard (as illustrated in the upper portion of FIG. 6). At the same time it will be appreciated that the alternative configuration of the guard 20 shown in FIG. 6 satisfies the above-described primary advantage of the present invention of providing the operator with a stationary direct line of sight along the saw blade to the workpiece from a natural operating position. Moreover, this line of visibility is provided in this embodiment, as well as in the previous embodiment, regardless of the articulated position of the guard from the lowest cut (e.g., small workpiece) to the highest cut (e.g., large workpiece) position of the miter saw blade. 
     The preceding discussion of the preferred and alternative embodiments has been provided for the purposes of illustration. It is recognized that, through exercise of ordinary skill in the art, the inventive concepts disclosed herein could be adapted to suit a variety of embodiments without departing from the scope or spirit of the invention.