Patent Publication Number: US-2004050223-A1

Title: Apparatus and method for cutting fiber-reinforced gypsum and/or cement

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to apparatuses and methods for cutting fiber-reinforced gypsum and/or fiber-reinforced cement materials.  
       BACKGROUND  
       [0002] Wallboard is used to form walls and ceilings in the construction of residential and commercial buildings. Plasterboard, plywood and other materials can be used as wallboard. Plasterboard, the most commonly used, is typically made of several plies of paper bonded to a hardened gypsum core. Plasterboard is widely used because it provides a smooth, attractive surface that can be easily painted or wallpapered.  
       [0003] Plasterboard, however, can be dented, broken or punctured relatively easily. Its relatively weak strength makes it less suitable for high-impact applications (e.g., loading docks, prisons, college dorms). Fiber-reinforced plasterboard, however, has been developed specifically for high-impact applications. One such product is Fiberock® manufactured by U.S. Gypsum Company. It is composed of gypsum and recycled paper or cellulose, but it does not have a heavy paper lining bonded to the exterior surface. Fiber-reinforced plasterboard (also known as fiber-reinforced gypsum) provides superior strength and durability relative to standard plasterboard. With its increased strength and stiffness, it is much more likely to resist denting, breaking and puncturing. Accordingly, it is desirable to use fiber-reinforced plasterboard in applications where improved strength is necessary.  
       [0004] One disadvantage of using fiber-reinforced plasterboard is that, unlike standard plasterboard, fiber-reinforced plasterboard is difficult to cut. Standard plasterboard can be scored with a knife and then easily broken or snapped along the score. After it is snapped, the paper lining can be trimmed on the uncut side with a pair of scissors or a sharp knife. Furthermore, irregular angles and circular cuts can be made with a jigsaw. Fiber-reinforced plasterboard, however, generally cannot be cut using the score and snap method because the fibers in the plasterboard prevent a clean, attractive break. The rough, uneven break in fiber-reinforced gypsum precludes, for practical purposes, using the score and snap method. Cutting fiber-reinforced plasterboard with a saw is also not feasible because the saw generates large amounts of fine dust that create a very unpleasant working environment.  
       [0005] Fiber-reinforced plasterboard is even more difficult to cut once it has been nailed, screwed or otherwise fixed to a wall or ceiling. Sometimes, it is desirable to cut out a window, door or vent after the fiber-reinforced plasterboard has been installed. Conventional blades, including blades for cutting fiber-cement materials disclosed in U.S. Pat. Nos. 5,993,303 and 6,250,998 (which are herein incorporated by reference), and other blades for cutting sheet metal are not well suited for cutting fiber-reinforced plasterboard after it has been hung for several reasons. First, conventional blades may not track along the framing to achieve straight, precise cuts when cutting out an area for a window, door, or other opening. Second, conventional blades may fail prematurely or cause premature failure of the drive assembly or motor assembly when cutting fiber-reinforced plasterboard. Third, conventional fiber-cement blades may not be able to cut out a corner of a framed window or door. Fourth, conventional blades may chew-up a cross-member of the adjoining framing when cutting out a window or door. Fifth, conventional fiber-cement blades may rip through fiber-reinforced plasterboard causing the plasterboard to crack along unpredictable paths.  
       SUMMARY  
       [0006] The present invention is directed toward blade assemblies for cutting fiber-reinforced wallboard and other fiber-reinforced materials, cutting tools having such blade assemblies, and methods for cutting fiber-reinforced materials. In one embodiment, a blade assembly has first and second fingers attachable to a cutting tool. The first finger has a first guide surface and a first interior surface, and the second finger has a second guide surface and a second interior surface. The first and second interior surfaces are spaced apart from one another, and the first and second guide surfaces define a guide plane. The guide surfaces, for example, can be flat, planar surfaces that position the cutting tool at a desired angle relative to a workpiece.  
       [0007] The blade assembly also has a reciprocating cutting member between the first and second fingers. The cutting member has a body pivotally coupled to the first and second fingers and a blade projecting from the body. The blade has a first side surface facing the first interior surface of the first finger, a second side surface facing the second interior surface of the second finger, and a top surface between the first and second side surfaces. In one embodiment, the top surface has an arcuate portion with a generally constant radius defining a cutting surface that is at least approximately coterminous with a distal end of the blade. The arcuate portion of the top surface, for example, can have a radius of greater than approximately 2 inches. At least part of the arcuate portion is configured to be a cutting surface. In another embodiment, the top surface has an arcuate portion with a generally constant radius for an arc length of at least approximately 1.8 inches. In another embodiment, the distal end of the blade includes a nose with an rounded portion having a radius of at least approximately 0.3 inch. In another embodiment, the blade can also include a tail projecting away from the top surface. The tail is configured to follow the framing while the blade assembly is cutting.  
       [0008] An embodiment of a method for cutting wallboard includes contacting a first surface of the wallboard with guide surfaces of two spaced apart fingers of a cutting tool. The method further includes reciprocating a blade between the fingers along a stroke having an open position and a closed position. The blade has a cutting surface that contacts the wallboard at the distal tip of the blade in the closed position. The method further includes moving the wallboard and/or the cutting tool relative to the other along a cutting path. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is an isometric view of a hand-held cutting tool with a blade assembly in accordance with one embodiment of the invention.  
     [0010]FIG. 2 is a side elevational view of the blade assembly of FIG. 1.  
     [0011]FIG. 3 is a top plan view of the blade assembly of FIG. 2.  
     [0012]FIG. 4A is a side view of a portion of the blade assembly of FIG. 2 with the cutting member shown in an open position and a closed position.  
     [0013]FIG. 4B is a side view of a portion of a prior art blade assembly with a cutting member shown in an open position and a closed position.  
     [0014]FIG. 5A is a side view of a portion of a blade assembly with the cutting member shown in an open position and a closed position in accordance with another embodiment of the invention.  
     [0015]FIG. 5B is a side view of a portion of the prior art blade assembly of FIG. 4B.  
     [0016]FIG. 6 is a side view of a portion of a blade assembly with the cutting member shown in an open position and a closed position in accordance with another embodiment of the invention.  
     [0017]FIG. 7A is a side view of a portion of the blade assembly of FIG. 2 with the cutting member shown in an open position and a closed position.  
     [0018]FIG. 7B is a side view of a portion of the prior art blade assembly of FIG. 4B.  
     [0019]FIG. 8 is a top plan view illustrating cuts made by the blade assemblies of FIGS. 7A and 7B.  
     [0020]FIG. 9 is a side elevational view of a cutting member in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
     [0021] The present invention is an apparatus for cutting interior wallboard or exterior siding products. Many specific details of certain embodiments of the invention are set forth in the following description and in FIGS.  1 - 9  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the invention may be practiced without several of the details described in the following description. For example, even though many embodiments are described with reference to cutting fiber-reinforced gypsum, they can also be used to cut fiber-reinforced cement materials and other building products.  
     [0022]FIG. 1 is an isometric view of a hand-held cutting tool  10  with a blade assembly  50  in accordance with one embodiment of the invention. The cutting tool  10  also includes a motor unit  20  and a head  30  attached to the motor unit  20 . The blade assembly  50  is attached to the head  30  and includes a cutting member  70 , a first finger  60   a  on one side of the cutting member  70 , and a second finger  60   b  on the other side of the cutting member  70 . The cutting member  70  reciprocates between the fingers  60   a - b  for cutting a workpiece W.  
     [0023] The motor unit  20  of the illustrated embodiment includes a housing  22 , a motor  24  (shown schematically in phantom) inside the housing  22 , and a switch  26  operatively coupled to the motor  24 . The housing  22  has a handle  27  configured to be gripped by an operator. Suitable electric motor units  20  are the No. 3208-90 electric motor manufactured by Black and Decker Corporation and No. 0201-60 electric motor manufactured by Milwaukee Electric Tool Corporation. Suitable pneumatic motor units  20  are the No. 7802 pneumatic motor manufactured by Ingersoll-Rand Corporation and the No. 1446E-SLH pneumatic motor manufactured by Sioux Tools Incorporated.  
     [0024] In the illustrated embodiment, the output of the motor unit  20  is converted into a reciprocal motion by the head  30  which has a casing  32  and a reciprocating drive assembly  36  (shown schematically in phantom). The casing  32  is attached to the housing  22  of the motor unit  20 . Additionally, the reciprocating drive assembly  36  is coupled to the motor  24  via a gear assembly  38  (shown schematically in phantom) to translate the rotational output from the motor unit  20  into a reciprocating motion. A suitable drive assembly is disclosed in U.S. Pat. No. 4,173,069, entitled “Power Shear Head,” which is herein incorporated by reference.  
     [0025] In the embodiment shown in FIG. 1, the first finger  60   a  is attached to one side of the head  30 , the second finger  60   b  is attached to the other side of the head  30 , and the cutting member  70  pivots between the first and second fingers  60   a  and  60   b  . The first finger  60   a  is separable from the second finger  60   b  . In alternative embodiments, the first and second fingers  60   a  and  60   b  can be portions (for example, integral portions) of a single alignment member. In the illustrative embodiment, the first finger  60   a  has a guide surface  62   a  and a first interior surface  64   a  generally transverse to the guide surface  62   a  . Similarly, the second finger  60   b  has a second guide surface  62   b  (shown in phantom) and a second interior surface  64   b  generally transverse to the guide surface  62   b  . The first and second fingers  60   a  and  60   b  are attached to the head  30  to leave a space between the first and second interior surfaces  64   a  and  64   b  that defines a gap  66  in which the cutting member  70  may be received. Additionally, the first and second guide surfaces  62   a  and  62   b  are generally flat to rest on an upper surface U of the wallboard workpiece W for aligning the cutting member  70  with the workpiece W. In other embodiments, only a portion of the guide surfaces  62   a - b  are flat.  
     [0026]FIG. 2 is a side view and FIG. 3 is a top plan view of the blade assembly  50  illustrated in FIG. 1. The cutting member  70  has a body portion  71  with a first width approximately equal to a gap distance G (shown in FIG. 3) between the first interior surface  64   a  of the first finger  60   a  and the second interior surface  64   b  of the second finger  60   b  . In alternate embodiments, the body  71  can have a width less than the gap distance G and one or more spacers (not shown) can be placed between the body  71  and the interior surfaces  64   a - b  of the fingers  60   a - b.  The cutting member  70  also has a blade  72  projecting from the body  71  between the first and second fingers  60   a  and  60   b  . The blade  72  has a first side surface  74  facing toward the first interior surface  64   a  , a second side surface  75  (FIG. 3) facing toward the second interior surface  64   b  , a curved top surface  76 , and a front surface  96  (FIG. 2). Referring to FIG. 3, the edge along the top surface  76  and the first side surface  74  defines a first cutting edge  77 , and the edge along the top surface  76  and the second side surface  75  defines a second cutting edge  78 .  
     [0027]FIG. 3 also shows the spacing between the blade  72  and the fingers  60   a - b.  The first side surface  74  is spaced apart from the first interior surface  64   a  by a distance S 1  to define a first side space  82 . Similarly, the second side surface  75  is spaced apart from the second interior surface  64   b  by a distance S 2  to define a second side space  84 . The distances S 1  and S 2  of the first and second side spaces  82  and  84  may be a function of the thickness and the type of fiber-reinforced material of the workpiece W. For example, in one embodiment when the workpiece W is a fiber-reinforced gypsum wallboard with a thickness of approximately 0.625 inch, the distances S 1  and S 2  are between 0.05 and 0.06 inch and the gap width G is approximately 0.25 inch. In other embodiments, the distances S 1  and S 2  can be different for cutting a workpiece with a different thickness or a different fiber-reinforced material. For example, when the workpiece W is a fiber-cement panel or plank with a thickness of 0.25-0.3125 inch, the side distances S 1  and S 2  are between 0.035 and 0.049 inch, and the gap width G is approximately 0.25 inch. The spacing between the first and second side surfaces  74  and  75  and the fingers  60   a - b  can be selected by adjusting the width of the top surface  76  of the blade  72 . In one embodiment with a gap width G of 0.25 inch between the fingers  60   a - b,  the width of top surface  76  of the blade  72  can be approximately 0.14 inch. The thickness of the blade  72  for cutting fiber-reinforced gypsum is generally less than that used for cutting fiber cement materials because fiber-reinforced gypsum tends to rip or crack along unpredictable lines when it is cut with a thicker blade.  
     [0028] Referring back to FIG. 2, the top surface  76  of the cutting member  70  has a generally constant radius of curvature that is concave with respect to the guide surfaces  62   a - b  of the fingers  60   a - b.  Accordingly, the first and second cutting edges  77  and  78  are also concave with respect to the wallboard workpiece W. In one embodiment, the top surface  76  has a radius of approximately 3.3 inches. However, in alternative embodiments, the top surface  76  can have any radius greater than 2 inches. The curvature of the top surface  76  is at least approximately coterminous with the distal surface  96 . The length of the constant curvature on the top surface  76  provides a long cutting region (the portion of the cutting edges  77  and  78  that cut through the workpiece W) that can cut to the distal end  69  of the blade  72  as the blade  72  moves upward between the fingers  60   a - b.    
     [0029] Referring to FIGS. 2 and 3, the reciprocating cutting member  70  is pivotally coupled to the first and second fingers  60   a  and  60   b  by a bushing  92 . The bushing  92  is generally cylindrical and has two side portions and a center portion with a larger radius. The center portion is received within an aperture  97  in the cutting member  70 . The two side portions are received within an aperture  95  in each finger  60 . The bushing  92  has an aperture  93  to receive a bolt  94  (shown in FIG. 1) to secure the bushing  92 , the fingers  60   a - b  and the cutting member  70  to the head  30  (FIG. 1). The fingers  60   a - b  are also fixed to the head  30  by another bolt (not shown), and accordingly, only the cutting member  70  can pivot. In the illustrated embodiment, the fingers  60  are removable so that they can be changed when worn. Furthermore, the first finger  60   a  is at least similar to the second finger  60   b  so that the fingers  60   a - b  are interchangeable. In other embodiments, each finger  60  can have the same or similar ends so that the fingers  60   a - b  can be turned around when one end is worn.  
     [0030] The reciprocating cutting member  70  in the illustrated embodiment has a driven end  79  configured to engage the reciprocating drive assembly  36  of the head  30 . The driven end  79  has two spaced-apart fingers  73  that are alternately engaged by a rotating cam of the drive assembly  36 . In operation, the motor  24  actuates the drive assembly  36  when an operator depresses the switch  26 . The drive assembly  36  reciprocates the blade  72  of the cutting member  70  along a reciprocating path R between an open position and a closed position. In the open position, the top surface  76  of the blade  72  is below the guide surfaces  62   a - b  of the fingers  60   a - b.  In the closed position, the top surface  76  of the blade  72  is above the guide surfaces  62   a - b  of the fingers  60   a - b.  In one embodiment, the blade  72  reciprocates at approximately 100-3,000 strokes per minute. As the blade  72  moves from the open position to the closed position, the first cutting edge  77  and the first interior surface  64   a  shear the wallboard workpiece W along one line, and the second cutting edge  78  and the second interior surface  64   b  shear the wallboard workpiece W along a parallel line. The top surface  76 , accordingly, lifts and separates a cut section (not shown) of the wallboard workpiece W with each upward stroke of the cutting member  70 . To cut a continuous line through the workpiece W, an operator pushes the cutting tool  10  across the workpiece W as the cutting member  70  reciprocates.  
     [0031] There are several advantages to embodiments of the tool  10  that increase the cutting region and shift the cutting region toward the distal end  69  of the cutting member  70 . For example, increasing the length of the cutting region extends the useful life of the blade assembly  50 . The life of the blade assembly  50  is extended because the cutting edges  77  and  78  of the cutting member  70  can cut more material with each stroke so that fewer strokes are required to cut the material.  
     [0032] Another benefit of several embodiments of the tool  10  is that they can cut out corners of a hole for installing windows and door in pre-hung sheets of wallboard within a framed structure. FIGS. 4A and 4B illustrate that increasing the length of the cutting region and shifting the region to the distal end  69  of the cutting member  70  permits the blade assembly  50  to cut out corners. FIG. 4A is a side view of a portion of the blade assembly  50  of FIG. 2 with the cutting member  70  shown in an open position (solid line) and a closed position (broken line). In the illustrated embodiment, the guide surface  62   a  of the first finger  60   a  contacts the upper surface U of the workpiece W. At this point with the blade  70  in the open position, the workpiece W includes a cut portion  210  and an uncut portion  212 . Having the cutting region extend to the distal end  69  of the blade  72  is advantageous because the blade  72  cuts the workpiece W all the way out to the distal end  69  when the blade  72  is in the closed position. As such, the blade assembly  50  can cut out corners (such as around windows, vents and doors) even when the distal end  69  of the blade  72  rubs against a cross-member  200  of the framing and precludes further forward movement of the tool. By contrast, FIG. 4B is a side view of a portion of a prior art blade assembly  250  with a cutting member  270  in an open position (solid line) and a closed position (broken line). The prior art cutting member  270  cannot cut a section D of the workpiece W because the cutting surface on the prior art cutting member  270  does not extend to a distal end  269  of a blade  272 , and because the cross-member  200  of the framing precludes further forward movement of the cutting member  270 . Furthermore, shifting the cutting region toward the distal end  69  of the blade  72  lengthens the life of the motor  24  (FIG. 1) and the drive assembly  36  (FIG. 1) by decreasing the amount of dust generated during the cutting process that accumulates on a bushing  92  (FIG. 2). Decreasing the dust that accumulates on the bushing  92  reduces the stress and loads on these components.  
     [0033]FIG. 5A is a side view of a portion of a blade assembly  350  with a cutting member  370  shown in an open position (solid line) and a closed position (broken line) in accordance with another embodiment of the invention. In the illustrated embodiment, the cutting member  370  has a front surface  396  having an arcuate portion with a radius of approximately 0.46 inch. In alternative embodiments, the cutting member  370  can have a front surface  396  with a different radius of curvature, or without a radius of curvature at all. The large radius of curvature allows the front surface  396  to contact the cross-member  200  of the framing without damaging the cross-member  200 . The blade assembly  350  can thus cut an opening in the workpiece W that extends all the way to the cross-member  200  without damaging the cross-member  200 . FIG. 5B is a side view of a portion of the prior art blade assembly  250  of FIG. 4B with the cutting member  270  shown in an open position (solid line) and a intermediate position (broken line). The smaller radius of curvature on a front surface  296  increases the probability that the cutting member  270  will rip up the cross-member  200  as the cutting member  270  repeatedly strikes it. The smaller radius of curvature can thus cause a piece of the cross-member  200  to break off as the cutting member  270  reciprocates between the open and closed positions.  
     [0034]FIG. 6 is a side view of a portion of a blade assembly  450  shown in an open position (solid line) and a closed position (broken line) in accordance with still another embodiment of the invention. In the illustrated embodiment, the blade assembly  450  includes fingers  460  and a cutting member  470  having a tip  459  at a distal end  469 . The tip  459  is formed by extending a top surface  476  in the direction of the distal end  469  at approximately the same radius. A front surface  496  is also concave toward the extension of the top surface  476  to form the tip  459 . The tip  459  can lengthen the cutting region on the top surface  476  and further assist the blade assembly  450  in cutting out corners, as discussed above.  
     [0035]FIG. 7A is a side view of a portion of the blade assembly  50  of FIG. 2. In the illustrated embodiment, the bottom surface  98  of the cutting member  70  has a tail  34  that projects away from the top surface  76 . The sides of the tail  34  are formed by the first side surface  74  and the second side surface  75  (FIG. 3). The tail  34  projects below the workpiece W sufficiently to ride along the side of a framing  300  as the blade assembly  50  reciprocates between the open (solid line) and closed (broken line) positions and moves through the workpiece W. FIG. 8 is a top plan view illustrating a straight and accurate cut  310  that can be made in the workpiece W when the tail  34  (FIG. 7A) rides along the framing  300 . The tail  34  allows the operator to use the framing  300  as a guide to make accurate and straight cuts through the workpiece W. This is useful when cutting an opening, such as for a window or door. In alternative embodiments, the cutting member  70  might not have a tail  34 , or might have a tail  34  with a different configuration. FIG. 7B is a side view of a portion of the prior art blade assembly  250  of FIG. 4B in which the cutting member  270  does not have a tail  34 . The prior art blade assembly  250  cannot use the framing  300  as a guide because in the closed position (broken line) the cutting member  270  is not configured to remain in contact with the framing  300 . Often the result, as demonstrated in FIG. 8, is an inaccurate cut  320 .  
     [0036]FIG. 9 is a side view of a cutting member  170  configured to cut the workpiece W along a reduced radius arcuate path in accordance with another embodiment of the invention. In the illustrated embodiment, the cutting member  170  includes a body portion  171  having a driven end  179  with two fingers  173 , and a blade portion  172  having a top surface  176 , a front surface  196  and a bottom surface  198  with a tail  134 . A distal portion of the front surface  196  and a portion of the bottom surface  198  extend in the same general direction to form a finger  180  at the distal end  169  of the blade  172 . The finger  180  allows the cutting member  170  to turn with a reduced radius because of the decreased surface area of the side surfaces  174  on the blade  172 . In alternative embodiments, the side surfaces  174  can be canted, such that as they extend from the top surface  176  they converge towards each other.  
     [0037] From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited, except as by the appended claims.