Window assembly and lower saw guard for circular saw

Abstract: A window assembly (25) is provided for use on a hand-held circular saw (10). The window assembly (25) has a transparent member (26) that is attached to an upper guard of the saw. The transparent member (26) has a forward edge and a rearward edge and slopes downwardly to form a rearwardly facing acute angle with respect a planar base (21) of the saw. The acute angle has a minimum value (α) to prevent light from overhead sources from reflecting into the user's eyes and has a maximum value (β) to prevent light from forward light sources from reflecting into the user's eyes. The forward edge of the transparent member is located rearwardly of the point at which a predetermined line (30) intersects the guard. Additionally, a lower blade guard (20) is provided for use on a circular saw having a clear viewing window on the upper blade guard. The lower blade guard has a truncated portion that allows a line of sight between the workpiece being sawed and the clear viewing window even when the lower guard is in a fully retracted position.

Description: This invention relates to a circular saw having a viewing window on the upper guard. One of the problems associated with the use of a hand-held circular saw is properly aligning the saw so that the desired cut is achieved. Typically, a user will draw a line on the material to be cut. This line represents the location of the desired cut. The problem arises when the user of the hand-held circular saw attempts to align the blade with the line on the material. The problem continues as the user attempts to keep the blade tracking on the desired cut line. To assist in the alignment, circular saws are typically provided with a guide slot. The guide slot is usually located on the planar cutting base of the saw, and is positioned in front of, and in line with, the circular saw blade. The user then positions the saw so that the line on the material appears in the guide slot. While the provision of such a guide slot does aid the user in proper saw alignment, problems still exist. First, because the guide slot is located in front of the blade, if the saw blade is not perpendicular relative to the workpiece, the guide slot can be positioned on the cut line while the blade is not. If the user begins to cut the material with the saw in this orientation, it is often difficult to correct the alignment problem. Second, because the blade is covered by a saw guard, the user cannot see the blade as it exits the material, and therefore cannot directly monitor the travel of the blade. Attempts have been made to allow the user of the saw to view the blade as it exits the material, thereby allowing the user to properly guide the blade along the desired cut line. A device that allows a user to view the blade is disclosed in U.S. Patent No. 4,450,627. This patent discloses a circular saw with a viewing window on the upper saw guard. The window is intended to allow users of the saw properly to align the saw to the workpiece by allowing them to view the blade. While this viewing window solves the above problems to some degree, its positioning remains a problem. If the viewing window is not properly positioned, the user will be unable to see the blade exiting the material due to the reflection of light by the transparent section of the viewing window. To compensate, the user may attempt to reposition the light source, such as a flashlight, or may reposition himself relative to the saw. This repositioning can affect efficiency as well as the quality of the work being performed. If the user repositions himself relative to the saw, the resulting position may be an uncomfortable one from which to operate the saw. Further, the trial and error necessary to find the proper position of saw, user and light source wastes the user's time. The position of the viewing window must also account for the sawdust generated as the saw cuts through the workpiece. If the window is positioned too far forwardly, the sawdust can accumulate on the transparent section of the window and impair the user's view of the blade as it exits the workpiece. The viewing window must therefore be positioned so as to minimise or eliminate the accumulation of sawdust on the viewing window. Further, circular saws having a viewing window have heretofore not adequately addressed the problem caused by the lower saw guard in relation to the provision of a viewing window. The lower saw guard surrounds the lower 5 portion of the blade when the saw is not in use. When the saw is being used, the front portion of the lower saw guard engages the workpiece and is rotated upwardly to expose the lower portion of the blade. When the lower guard is rotated fully upwardly, the rear portion of the lower saw guard can 0 impair the user's view of the blade through the transparent section of the viewing window. This impairment does not affect the user's view as the cut is initiated, but rather impairs the view when the saw is sufficiently engaged with the workpiece so as to rotate the lower guard to a fully retracted position. Therefore, a window assembly is needed that is properly positioned in the upper saw guard of a circular saw so that the user can view, from a normal operating position, the blade exiting the workpiece. A window assembly is needed that minimises any light reflected into the eyes of the user from both above and in front of the viewing window. Further, a window assembly is needed that is properly positioned in the upper saw guard of a circular saw so that the accumulation of sawdust on the viewing window is reduced or eliminated. Finally, a lower saw guard is needed which will allow a user to view the saw blade exiting the workpiece, through a transparent member of the window assembly in the upper saw guard, even when the lower guard is in a fully retracted position. It is an object of the present invention to provide a window assembly in the upper guard of a circular saw positioned so as to minimise any light reflected into the eyes of the person using the saw. It is another object of the present invention to provide a window assembly located rearwardly of a predetermined point to minimise accumulation of sawdust on the window assembly. A further object of this invention is to provide a window assembly having a transparent member oriented at an angle greater than a minimum angle of inclination of the viewing window relative to the workpiece. A still further object of this invention is to provide a window assembly having a transparent member oriented at an angle less than a maximum angle of inclination of the viewing window relative to the workpiece. Yet another object of the invention is to provide a lower saw guard, to be used on a circular saw with a viewing window, that will not obstruct the view through the transparent member of the window even in a fully retracted position. According to a first aspect of the present invention, there is provided a window assembly according to the features of claim 1. According to another aspect of the present invention, there is provided a hand-held circular saw having a substantially planar base for supporting the saw on a workpiece,a window assembly as defined by the first aspect of the invention above, and a lower saw guar comprising: a forward section for engaging the workpiece, wherein when the forward section engages the workpiece, the lower guard rotates upwardly towards the upper guard to expose a lower portion of the blade; an arcuate perimeter wall surrounding a portion of a perimeter of the blade, the wall disposed between an inner side and an outer side; and a rear section, characterised in that the rear section has a truncated portion allowing a line of sight between the viewing window and the point at which the blade exits the workpiece, wherein the line of sight is maintained even when the lower guard has been rotated upwardly to a fully retracted position. To establish the minimum angle of inclination for the transparent member of the window assembly, a first line is constructed from the point at which the blade exits the workpiece to the rear edge of the transparent member of the window assembly. A second line is then constructed extending horizontally outward from the rear edge of the top surface of the transparent member. A third line is constructed bisecting the angle formed by the previous two lines. This third line establishes the minimum angle of inclination for the top surface of the transparent member. An embodiment of a window assembly will now be described with reference to the accompanying drawings, in which like reference numerals are used to indicate like parts in the various views, and in which: Figure 1 is a front perspective view showing a properly located window assembly of the present invention attached to the upper guard of a circular saw; Figure 2 is a side elevation view of the saw of Figure 1 showing the lower guard in a fully retracted position; Figure 3 is an enlarged partial top plan view taken along line 3-3 of Figure 2, with part of the transparent member being broken away to show particular details of construction; Figure 4 is an enlarged partial perspective view taken along line 4-4 of Figure 3 showing the lower guard in a fully retracted position; Figure 5 is a schematic view of the saw of Figure 1, illustrating the method of calculating the minimum angle of inclination for the transparent member of the window assembly; and Figure 6 is a schematic view similar to Figure 5, illustrating the method of calculating the maximum angle of inclination for the transparent member of the window assembly. Referring to the drawings in greater detail, and initially to Figure 1, a power circular saw designated generally by numeral 10 is shown. Saw 10 has a motor 12 which is operably attached to a circular saw blade 14. A power cord (not shown) supplies electrical power to motor 12. The upper portion of blade 14 is surrounded by an upper saw guard 18. Upper guard 18 is fixedly secured to motor 12. The lower portion of blade 14 is surrounded by a lower saw guard 20. Saw 10 further has a planar base 21 with an alignment notch 23. Lower guard 20 exposes the lower portion of blade 14 in a manner that is well-known in the art. More specifically, the front edge 22 of lower guard 20 engages the leading edge of a workpiece 24. As the saw passes further into workpiece 24, lower guard 20 is rotated generally upwardly to expose the lower portion of the blade. Guard 20 is spring loaded so that when saw 10 is disengaged from workpiece 24, lower guard 20 returns to its lower, blade covering position. Upper guard 18 is provided with a viewing window assembly 25. Window assembly 25 has a transparent member 26 which is held in place on guard 18 by a window frame 27. Transparent member 26 allows the user of saw 10 to view blade 14 as it exits workpiece 24, thereby allowing the user to properly align, and maintain alignment, of saw 10. Transparent member 26 must be properly positioned on guard 18 to allow the user of saw 10 to properly align and monitor the travel of blade 14. First, the forward-most position of transparent member 26 on guard 18 must be determined. Locating transparent member 26 beyond the proper forward-most position can result in the sawdust generated by blade 14 accumulating on transparent member 26. If sawdust accumulates on transparent member 26, either transparent member 26 must be cleaned or the user's view through transparent member 26 will be obstructed by sawdust. Further, the proper angle of inclination of transparent member 26 must be determined and used. Generally, there is a range between a minimum angle of inclination and a maximum angle of inclination that may be used. If transparent member 26 has an angle of inclination different from the angles calculated in the manner described below, the user's view through transparent member 26 will be impaired by light reflecting from the top surface of transparent member 26. In order to determine the forward-most position of transparent member 26 on guard 18, the point at which blade 14 exits workpiece 24 is first located. This point is designated in the drawings by reference numeral 28. The cutting depth for blade 14 can be adjusted by repositioning planar base 21 so that thinner or thicker workpieces may be sawed. Manufacturers typically ship saw 10 with blade 14 at its maximum cutting depth. In determining exit point 28, blade 14 should be set at maximum depth which is the most common depth utilised by saw users. As shown in Figure 2, from point 28, a line is constructed extending tangentially away from blade 14 and upwardly towards guard 18. This tangential line is designated in the drawings by the reference numeral 30. The point at which line 30 intersects guard 18 defines the maximum forward-most point at which the forward edge of transparent member 26 should be positioned. This intersection point is defined in the drawings by reference numeral 32. Locating transparent member 26 at or behind intersection point 32 ensures that transparent member 26 is located behind the main path of the dust particles generated by blade 14 when saw 10 engages workpiece 24. Such a location will decrease the need and frequency at which transparent member 26 must be cleaned. Therefore, locating transparent member 26 rearwardly of intersection point 32 increases the ability of the user of saw 10 to view blade exit point 28 without having the view obstructed or impaired by sawdust particles. Having properly located the forward-most point for transparent member 26, the proper angles of inclination of transparent member 26 must also be determined. Referring to Figure 5, to determine the minimum angle of inclination, a line is constructed between blade exit point 28 and the rear edge of transparent member 26. Again, this line is constructed with blade 14 at its maximum cutting depth. The rear edge of transparent member 26 is located on guard 18 to allow a line of sight between the user in a normal saw operating position and blade exit point 28. The line between blade exit point 28 and the rear edge of transparent member 26 is shown in the drawings by reference numeral 34. The point at which line 34 intersects guard 18 and the rear edge of the top surface of transparent member 26 is shown in the drawings by reference numeral 36. A second line 38 is constructed extending from point 36 outwardly from guard 18. Line 38 is constructed to be horizontal so that it will be substantially parallel to workpiece 24 and planar base 21. A third line 40 is constructed and extends from point 36 downwardly between lines 34 and 38. Line 40 is constructed so as to bisect the angle formed by first line 34 and line 38. Line 40 establishes the minimum angle of inclination, indicated by in the drawings, for transparent member 26. Therefore, the angle formed by the plane of the top surface of transparent member 26 relative to workpiece 24 should be no less than the acute angle established between line 40 and workpiece 24. When transparent member 26 has an angle of inclination equal to or greater than this minimum angle, only light originating from below line 38 is capable of reflecting into the eyes of the user. Any light originating from above line 38, such as from a ceiling light, will reflect away from the user's eyes. Having determined the minimum angle of inclination, the maximum angle of inclination for transparent member 26 can be determined as outlined below, with reference to Figure 6, to establish the range of angles that may be used for transparent member 26. In determining the maximum angle of inclination, first line 34 is constructed in the same manner as for determining the minimum angle of inclination. Therefore, point 36 is determined in the same fashion with blade 14 at its maximum depth. Next, a forward point 42 is located 15 centimetres (six inches) directly in front of blade exit point 28, in a line extending from, and in line with, blade 14. Forward point 42 represents the distant edge of a typical workpiece 24, the importance of which is more fully discussed below. A fourth line 44 is constructed connecting forward point 42 with intersection point 36. Thereafter, a fifth line 46 is constructed bisecting the angle formed by first line 34 and fourth line 44. Fifth line 46 establishes the maximum angle of inclination of transparent member 26, indicated by in the drawings. Therefore, the angle formed by the plane of transparent member 26 relative to workpiece 24 should be no greater than the acute angle established between line 46 and workpiece 24. Workpiece 24 is often light in colour and thus can reflect a considerable amount of light. When transparent member 26 has an angle of inclination equal to or less than this maximum angle, the operator will only be able to see a reflection of the top surface of workpiece 24 from about point 42 and beyond. Therefore, because the typical workpiece is approximately 15 centimetres (six inches) wide, orienting transparent member 26 with an angle of inclination equal to or less than the acute angle prevents the majority of light reflected from workpiece 24 from reaching the user's eyes. Thus, the user will be better able to view the blade exit point as the cut is made. By locating transparent member 26 rearwardly of point 32 and between the minimum angle of inclination and the maximum angle of inclination as determined above, transparent member 26 will be located in a position which minimises any obstruction caused by sawdust, and which allows the user to view exit point 28 through transparent member 26 without his or her vision being obstructed by unwanted reflections from the top surface of transparent member 26. In an alternative embodiment, transparent member 26 is oriented with an angle of inclination equal to or greater than the acute angle. In this embodiment an opaque vertical rib 47, shown in dashed lines in Figure 6, is attached to upper guard 18 adjacent the forward edge of transparent member 26. Again, orienting transparent member 26 at an angle greater than acute angle prevents light from overhead sources from reflecting into the user's eyes. Rib 47 extends outwardly from upper guard 18 and thus prevents light from any forward light sources from reflecting into the user's eyes. Rib 47 could also extend along the sides of transparent member 26 if it is desired to block light sources from the sides. Thus, the orientation of transparent member 26, at an angle greater than the minimum angle of inclination, and rib 47 operate to block unwanted reflections so that the user can view exit point 28 through transparent member 26. As outlined above, a properly positioned window assembly having a transparent member allows the user of saw 10 to view workpiece 24 free of unwanted reflections and sawdust obstructions. However, even with a properly positioned window assembly, the user's view of the point at which the blade exits the workpiece can be obstructed by the lower guard. Such an obstruction can result when the lower guard is in a fully rotated position. Therefore, lower guard 20 of the present invention has a truncated portion 48 on a rear section of lower guard 20, as best seen in Figures 3 and 4. Truncated portion 48 allows the user of saw 10 to view blade 14 as it exits the workpiece, even when lower guard 20 is in a fully retracted position, as shown in Figures 2 and 3. A line of sight is maintained through transparent member 26 to blade exit point 28, as illustrated by reference line 51 in Figure 2. Lower guard 20 has a perimeter wall 52 that extends between an inner side 54 and an outer side 56. Truncated portion 48 is formed as a "cut-out" from perimeter wall 52 and inner side 54, as best seen in Figures 3 and 4. Truncated portion 48 has an inner edge 58 extending perpendicularly from inner side 54 of lower guard 20. Inner edge 58 terminates at an outer edge 60. Outer edge 60 extends from inner edge 58 to a rear edge 62 of perimeter wall 52. Outer edge 60 is tapered towards outer side 56 as best seen in Figure 3. Inner edge 58 and outer edge 60 define the area through which a line of sight is provided, thus allowing the user to view blade exit point 28 even when lower guard 20 is in a fully retracted position. It should be noted that inner edge 58 could extend to outer side 56, thus eliminating outer edge 60. Such a structure would still provide a line of sight to workpiece 24 through transparent member 26, but would offer less coverage of blade 14 when lower guard 20 is in a normal, blade covering position. In use, the user of saw 10 places planar base 21 on workpiece 24 and positions saw 10 so that the desired cut line is within alignment notch 23. The user then aligns saw 10 so that the front edge of blade 14 is also on the desired cut line. The user can view blade 14 for this purpose through transparent member 26. As the user begins to saw workpiece 24, lower guard 20 is rotated upwardly. The user can continually monitor the point at which blade 14 exits the workpiece by viewing this point through transparent member 26. As the user saws into workpiece 24, lower guard 20 will eventually be in a fully retracted position. The user can monitor blade exit point 28 even when lower guard 20 is in this fully retracted position due to truncated portion 48.

Claims: A window assembly (25) for a hand-held circular saw (10), the saw having a circular blade (14) surrounded adjacent its upper periphery by an upper guard (18) and having a substantially planar base (21) for supporting the saw on a workpiece, the assembly comprising: said circular blade surrounded adjacent its upper periphery by said upper guard, a transparent planar member (26) adapted to be attached to the upper guard adjacent a forward half of the blade, the member (26) having a top surface, a forward edge, and a rearward edge; and wherein the top surface of the member (26) slopes downwardly from the rearward edge to the forward edge to form a rearwardly facing acute angle with respect to the planar base (21), the angle having a minimum value (α) which reduces glare from overhead light sources, that is the value of a bisecting angle of an angle formed by a first line (34) extending from a first point (28) where the periphery of the blade exits the top of the workpiece to the rear edge of the top surface of the member (26) and a second line (38) extending forwardly from the rear edge and parallel to the planar base (21), wherein the rearwardly facing acute angle has a maximum value (β) which reduces glare from forward light sources that is the value of a bisecting angle of an angle formed by the first line (34) and a third line (44) that extends from a second point (42) 15 centimetres directly in front of the first point (28) to the rear edge of the top surface of the member (26). A window assembly according to claim 1 characterised in that the first point is determined when the blade is at its maximum cutting depth. A window assembly according to claim 1 or 2 characterised in that the transparent member (26) is generally planar. A window assembly according to any one of the preceding claims, characterised in that the forward edge of the member (26) is placed at a horizontal location on the upper guard that is rearward of a point (32) where a predetermined line (30) intersects the guard, the line being the tangent line of the point (28) where the blade exits the periphery of the workpiece. A window assembly according to claim 4 characterised in that the exit point of the blade is determined when the blade is at its maximum cutting depth. A window assembly according to claim 5 characterised in that the transparent member is generally planar. A hand-held circular saw (10) having a substantially planar base (21) for supporting the saw on a workpiece, a window assembly according to any one of the preceding claims, and a lower saw guard (26) comprising: a forward section (22) for engaging the workpiece, wherein when the forward section engages the workpiece, the lower guard rotates upwardly towards the upper guard to expose a lower portion of the blade; an arcuate perimeter wall (52) surrounding a portion of a perimeter of the blade, the wall disposed between an inner side (54) and an outer side (56); and a rear section, characterised in that the rear section has a truncated portion (48) allowing a line of sight between the viewing window and the point at which the blade exits the workpiece, wherein the line of sight is maintained even when the lower guard has been rotated upwardly to a fully retracted position. A saw according to claim 7 characterised in that the truncated portion of the rear section extends from the inner side into the perimeter wall and terminates prior to the outer wall.

Inventors: CAMPBELL DAVID C, HESLOP GALE A, CAMPBELL, DAVID C., HESLOP, GALE A.
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1997
Main classification: B27G19
IPC codes: B23D59, B27G19