Abstract:
A rotary saw blade for cutting fiber cement board materials. In one embodiment, a rotary saw blade is provided having a main body plate and a central opening with respect to an axis of rotation. A plurality of cutting teeth are disposed about the periphery of the plate. Arcuate tooth support portions extend rearwardly from the cutting teeth and have a center of curvature offset from the axis of rotation. Peaked shoulders having a forwardly sloping portion, a peak and a rearwardly sloping portion extend from the tooth support portions. The peaked shoulders partially define hook-shaped gullets between the shoulders and the cutting teeth.

Description:
CLAIM FOR PRIORITY 
     The present patent claims priority to U.S. Provisional Application Serial No. 60/185,941, entitled CIRCULAR SAW BLADE FOR CUTTING FIBER CEMENT MATERIALS, filed on Feb. 29, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     Fiber cement materials are being used more frequently in outdoor applications in new construction. These fiber cement materials, often in the form of flat boards, are ideal for use as roof, wall and floor sheathing and wall siding. The boards may be fiber reinforced and silicone impregnated to provide uniform structural characteristics, while being resistant to fire, rot, water damage, insects and freezing. 
     Because of their heavy and stiff construction, fiber cement boards have the disadvantage of being more difficult to work with than conventional wood materials. In particular, the fiber cement boards are difficult to cut with conventional tools. While hand-held circular power saws are most often used to cut the boards, conventional saw blades and other types of blades have proven less than ideal for the task. 
     When used on fiber cement materials, conventional blades often produce a very rough, chipped cut edge. Furthermore, the stiff nature of the fiber cement boards provides significant resistance to the teeth of a conventional circular blade, thereby straining the motor of the power tool and producing a significant amount of frictional heat at the blade edge. This excess heat can dull the blade edge rapidly and compromise the construction of the braze joint between the blade and tooth tip portions. 
     These conventional blades also produce a tremendous amount of dust and flying debris when cutting fiber cement board, since they typically have a large number of teeth. The dust results in a difficult working environment for the user and the silica contained in the dust is a known health hazard. Furthermore, the dust reduces visibility for the user, which can have a significant effect on the accuracy of the cuts and prove dangerous to the user. 
     There is therefore a need for an improved saw blade design for use with fiber cement materials that alleviates the foregoing disadvantages. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention and in one embodiment thereof, a rotary saw blade is provided having a main body plate and a central opening with respect to an axis of rotation. A plurality of cutting teeth are disposed about the periphery of the plate. Arcuate tooth support portions extend rearwardly from the cutting teeth and have a center of curvature offset from the axis of rotation. Peaked shoulders having a forwardly sloping portion, a peak and a rearwardly sloping portion extend from the tooth support portions. The peaked shoulders partially define hook-shaped gullets between the shoulders and the cutting teeth. 
     In another aspect of the present invention, another embodiment of the invention may be provided in the form of a rotary saw blade for use in cutting fiber cement board material. The blade includes a generally circular main body plate having a central opening with respect to its axis of rotation. Cutting teeth are disposed about the periphery of the plate, and each tooth is preceded by a peaked shoulder. Each shoulder is at least partially defined by a forwardly sloping portion, a peak and a rearwardly sloping portion, wherein the rearwardly sloping portion has a length at least twice the length of the forwardly sloping portion. A hook-shaped gullet is defined at the periphery of the plate between each shoulder and the proximate cutting tooth. Each of the gullets is at least partially defined by the rearwardly sloping portion of an adjacent shoulder and an arcuate portion having a partially circular shape. A plurality of tooth support portions extends between the rear of each tooth to the forwardly sloping portion of the shoulder. 
     The invention may also be embodied in a method of cutting fiber cement board material. The method includes the steps of providing a handheld power tool and attaching a blade to the power tool. The blade includes a main body plate having a central opening with respect to an axis of rotation and between four and ten cutting teeth disposed about the periphery of the plate. A plurality of arcuate tooth support portions extend rearwardly from the cutting teeth and have a center of curvature offset from the axis of rotation, and a plurality of peaked shoulders are distributed about the periphery of the plate rearwardly of the tooth support portions. A plurality of hook-shaped gullets are further distributed about the periphery of the plate between the shoulders and the cutting teeth. A fiber cement board is then provided, and the board is cut using the power tool. 
     The saw blades of the preferred embodiments described herein provide improved means for cutting fiber cement materials such as flat rock wallboards and DUROCK® fiber board products. DUROCK® products are cement board products specially manufactured for use in potentially wet environments, such as for backing ceramic tile. The improved design disclosed herein incorporates fewer teeth than conventional blades and produces significantly less dust than conventional blade designs. The improved design also results in blades having a significantly longer life span than prior art blade designs or conventional carbide blades when used with fiber cement materials. The disclosed blades may be utilized with conventional-drive or worm-drive handheld circular saws or table saw equipment, and can facilitate all aspects of construction where fiber cement materials are used. 
    
    
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. The invention, together with further objects and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     These and other advantages of the present invention will become more fully apparent as the following description is read in conjunction with the drawings, wherein: 
     FIG. 1 is a side view of a circular blade of the preferred embodiment of the invention showing a four-tooth design; 
     FIG. 2 is a side view of a segment of the circular blade of FIG. 1; 
     FIG. 3 is a cut-away view of the preferred embodiment of FIG. 1 taken along the line  3 — 3 ; 
     FIG. 4 is a side view of a second embodiment of the saw blade of the present invention, showing a six-tooth design; and 
     FIG. 5 is a side view of a segment of the blade of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the figures, FIG. 1 shows a side view of the circular saw blade  20  in a preferred embodiment having four teeth. The preferred blade  20  preferably includes a plate  22  having a hole  24  defined in the center thereof for mounting the saw blade  22  onto an arbor. Preferably, the metal plate  22  is generally circular in shape and is machined from flat-surface tool steel, and the thickness of the blade is approximately 0.063 inches, although 0.047 inches in thickness has been shown to be sufficient as well. The arbor hole  24  is preferably ⅝ inches diameter for use on standard arbors for hand-held circular saws. 
     In this four-tooth embodiment, four teeth  26  are distributed at equal distances about the periphery of the plate  22 . The teeth  26  preferably include tooth tips  28  made from carbide, diamond particles or other suitable hard material. The tooth tips  28  are preferably brazed to the saw plate  22  at points of contact on the edge portion of a tooth support  30  located above the periphery of the plate  22 . 
     Each arcuate tooth support  30  extends rearwardly from each tooth tip  28  of the tooth  26  and traces an arc that decreases in radial distance from the center  25  as a distance increases from the tooth  26 . In the preferred embodiment, the tooth support portion  30  may also trace an arc that is offset from the center  25 , as shown in FIG.  1 . Radius R 3  thus includes a center  40  that is offset a distance from the center  25 . In the preferred embodiment, the radius is approximately 3.937 inches from the offset center  40 . Preferably, the offset center  40  may be positioned relative to a centerline  41  of the plate  22  extending through the center  25  between oppositely located tooth tips  28 . In particular, the offset center  40  is located on radius R 3  angled at angle G (63 degrees) clockwise from centerline  41  and through the center  25 . Along the radius R 3 , the center  40  is positioned approximately 0.63 inches beyond the centerline  41 , denoted in FIG. 1 as distance H. The receding configuration of the tooth support  30  provided by this arc allows only a minimal amount of the blade plate  22  to contact the cut portion of the fiber material after the cut is made by each tooth tip  28 . 
     The tooth support portion  30  terminates in a peaked shoulder  50 . The shoulder  50  includes a forwardly sloping portion  52  and a rearwardly sloping portion  54 , wherein the portions  52  and  54  meet in a peak  56 . As shown in more detail in FIG. 2, the forwardly sloping portion  52  and the rearwardly sloping portion  54  generally comprise substantially straight edge portions of the saw plate  22 . The two portions  52 ,  54  preferably meet at angle β, which preferably ranges between 90 and 110 degrees. In the preferred embodiment, the angle β is 105 degrees. The peak  56  may be either a edge or a slightly rounded portion having a radius of approximately 0.08 inches. In the preferred embodiment, the forwardly sloping portion  52  has a length  11  and the rearwardly sloping portion  54  has a length  12 . Preferably, the length  12 , which is approximately 0.96 inches in the preferred embodiment, is more than twice the length of  11 , which is preferably 0.44 inches in the preferred embodiment. Although other lengths and angles may be utilized, it has been found that these angles produce the most desirable results. 
     Angle α, as shown in FIG. 2, is the angle between the forwardly sloping portion  52  and the rearwardly sloping portion  54  of the tooth support  30 . Angle α is preferably 153.4 degrees. A small radius  60  is preferably introduced at the juncture between support  30  and the portion  56 . In the preferred embodiment, the radius is approximately 0.12 inches. 
     The outer edge  32  of each tooth tip  28  is located at a cutting arc  63  radius R 1  distanced from the center rotational axis  25  of the blade  20 . The radius R 1  is the cutting radius wherein each tooth  26  first makes contact with and cuts the fiber board material during a cutting operation. In the preferred embodiment, the cutting radius R 1  is 3.625 inches. 
     The outermost portion of the peak  56  on the shoulder  50  traces an arc  62 , preferably at radius R 2  from the center  25  of the blade  20 . In the preferred embodiment, the radius R 2  is approximately 0.1 inch less than radius R 1  of the cutting edge of tooth  26 . This allows the shoulder portion  50  to provide a guide ahead of each tooth  26  during the cutting process in direction D and prevents the tooth  28  from cutting substantially more than a 0.1 inch portion of the fiber board on each tooth pass. This prevents the blade from “kicking back” dangerously or otherwise becoming damaged if too large a portion of material is placed before the cutting edge of the blade. 
     Moving clockwise around the edge of the remaining portion of the blade  20 , the lowermost portion of the rearwardly sloping portion  54  of the peaked shoulder  50  is formed with an arcuate section  70  to form a deep, hook-shaped gullet  72 . The lowest point of each gullet  72  lies on a gullet arc  73  having a radius R 4 . Preferably, the radius R 4  is 2.969 inches. The gullet  72  immediately proceeds each tooth  26  and provides a deep area from which to eject chips and debris from the cutting process of the tooth  26 . The arcuate portion  70  of the gullet  72  preferably is formed having a radius R 5  from the center  74  of the arc  70 . In the preferred embodiment, the radius R 5  is approximately 0.52 inches and extends upwardly towards the bottom of the tooth tip  28  and contacts gullet arc  73 . The shape of the gullet arcuate section  70 , in combination with the forward portion  52  of the peaked shoulder  50 , assists in removing debris from the material to be cut and reducing the amount of dust generated by the cutting process. 
     Preferably, the tooth tips  28  in the preferred embodiment are formed from a tungsten carbide material with a layer of poly crystalline diamond (“PCD”) bonded thereon. The hook angle of the cutting tip is approximately 15 degrees. The angle F of the top edge  28   a  of tooth tip  28  is preferably about 12 degrees, and the width of the tooth is approximately 0.079 inches. It is been found that the tungsten and PCD materials are preferable for use in the present cutting configuration of the blade. Other tip materials, such as tungsten carbide or other hardened metals may also be utilized. FIG. 3 shows a cutaway view of the blade  20  taken along line  3 — 3  of FIG. 1 As shown in the drawing, tooth tip  28  has a tooth edge  29  extending horizontally perpendicular to the plane of the plate. 
     In this four-tooth embodiment, the use of these tooth tips is appropriate for cutting stacked and single sheets of fiber cement material. Preferably, the maximum speed of the blade is 8300 RPM. The recommended speed of the blade  20  is approximately 4000 RPM for cutting conventional fiber cement materials. 
     FIG. 4 shows a second, six-tooth embodiment of the present invention. FIG. 4 contains reference numerals corresponding to the reference numerals of the embodiment shown in FIG.  1 . The blade  120  of FIG. 4 includes generally identical features to the four-tooth blade of FIG. 1, such as a plate  122  having a hole  124  defined in the center thereof for mounting the saw blade  122  into an arbor, and teeth  126  including tooth tips  128  distributed at equal distances about the periphery of the plate  122  with some differences in scale to accommodate the equally-spaced six total teeth and the use of carbide tooth tips. In particular, the radius R 1  in this embodiment is preferably 3.625 inches and the radius R 2  at the peak  156  of the peaked shoulder  150  is approximately 3.53 inches. The radius R 3  of the offset arc of the receding tooth support portion  130  is angled at 56.62 degrees clockwise from the centerline  141  and the offset center  140  is offset by a distance H of approximately 0.57 inches from the center  125  along the radius R 3 . 
     The length  11  of the forwardly sloping portion of the shoulder  150  is preferably 0.36 inches and the length  12  of the rearwardly sloping portion  154  is approximately 0.74 inches. The radius R 4  of the gullet arc  173  is preferably 3.129 inches. The radius R 5  of the portion  170  of the gullet  172  is approximately 0.24 inches. The angle between the tooth support portion  130  and the forwardly sloping portion  152  (angle α) is approximately 120 degrees, and the angle β between the sloped portions  152  and  154  of the peaked shoulder  150  ranges between 90 and 110 degrees. The hook angle of each tooth tip  132  is preferably 15 degrees, and the width of each tooth tip  132  is 0.67 inches. 
     Like the previous embodiment, this second embodiment of the blade  120  provides for more efficient, cooler and cleaner cutting of the fiber cement materials. The blade  120  has less of a tendency to kick back or cause damage to the power tool and the object being cut. Furthermore, the comparatively lower number of cutting teeth on the blade  120  produces significantly less dust when cutting fiber cement materials than a conventional blade. 
     Of course, it should be understood that a wide range of changes and modifications could be made to the preferred embodiment described above. In particular, some of the specific measurements noted herein may be changed without departing from the invention. Thus, it is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it be understood that it is the following claims, including all equivalents, which are intended to define the scope of this invention.