Abstract:
A power driven portable sheet metal cutter includes a head with two blades that mounts to a hand-held electric or pneumatic rotating power unit. The fixed blade has a primary shearing surface that has a convex or radiused cutting edge, a convex or radiused bevel, and a convex or radiused body feature. 
     There is also a clearance radius and a nose radius so that the cutter can cut a wide variety of shapes and configurations of corrugated building panels. 
     A head with a right hand set of blades predominately cuts curves to the right, and a head with a left hand set predominately cuts curves to the left.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to powered hand held shears for cutting sheet metal and corrugated building panels used in construction. 
       BACKGROUND OF THE INVENTION 
       [0002]    The construction industry uses sheet metal in various ways. For example, sheet metal is used in ductwork, and as the exterior panels and roofing material of commercial buildings. As the speed of building increased, faster tools for quickly cutting the material were needed. There are several ways of cutting metal corrugated panels: with hand snips, power nibblers and power shears. On massive construction sites professionals use stationary industrial machines with blades designed to cut unique profiles. 
         [0003]    Using circular saws is undesirable because they leave a cut edge without any treatments such as paint, zinc coating, or galvanizing. Shears, on the other hand, have a natural “edge sealing” effect, smearing the coating or treatment over the freshly cut edge. Shearing may be done with muscle power, as with tin-snips, or by an electrically or pneumatically powered tool that works similarly, but has greater power and speed. 
         [0004]    Examples of portable powered shears to cut sheet metal are found in U.S. Pat. No. 2,635,335 to James, U.S. Pat. No. 4,173,069 to Sidenstick et al., U.S. Pat. No. 4,682,416 to Stolfa, and U.S. Pat. No. 7,093,365 to Peterson. U.S. Pat. No. 4,173,069 was assigned to Kett Tool Company, the assignee of the current application. 
         [0005]    U.S. Pat. No. 4,173,069 discloses a single moving blade, having two shear surfaces, working in cooperation with a fixed blade on either side, each of which has one shearing surface. U.S. Pat. Nos. 2,635,335, 4,682,416, and 7,093,365, on the other hand, use only one movable blade and one fixed blade. 
         [0006]    Each of these devices can cut materials of various thicknesses with some level of success. Cutting flat sheet metal of low thickness (higher gauge numbers) is the easiest. However, the building industry continues to expand their use of metal corrugated panels. Corrugated panels are now more complex than early versions that had only rolling corrugations similar to the pattern found in common corrugated cardboard. Current corrugations are engineered in a variety of depths, shapes, and patterns. The pitch (spacing) between corrugations may be small or large. When viewed in cross-section, the corrugations may be trapezoidal, with sharp angles and deep valleys. Testing of portable shearing devices on the market reveals that they cannot cut all of the corrugated panels available. Therefore, a need exists for an improved tool, having the geometry and materials necessary to smoothly cut a greater variety of corrugated panels. Such a tool should be easy to use to make curved cuts, and ergonomically comfortable. Preferably the tool would bend the cut metal in a way that does not obstruct the tool, the user&#39;s hands, or the user&#39;s view of the cut. 
       SUMMARY OF THE INVENTION 
       [0007]    To achieve the foregoing objectives, and in accordance with the purposes of the invention as embodied and broadly described, herein, a power driven portable head for a sheet metal cutter has a housing and a movable blade pivotally coupled to a fixed blade. The fixed blade has a leg portion attached to the housing, and on the other end of the leg portion is a foot extending laterally away from the plane of the leg portion. 
         [0008]    A clearance radius on the foot adjacent the leg portion provides clearance for the blade to maneuver through the material. A primary shearing surface is on the foot adjacent to the clearance radius and displaced laterally away from the plane of the leg portion, on the side opposite the movable blade. The foot has a back surface separated from the primary shearing surface by a thickness. On the back surface is a convex body feature that continues to a convex bevel that intersects the primary shearing surface at a convex edge. 
         [0009]    The movable blade is mounted to oscillate about a pivot axis during operation of the head. One end of the movable blade is forked, and arranged to be driven by an eccentric on a portable rotational drive applied to the head. The driving of the fork oscillates the movable blade about the pivot axis. The other end of the movable blade is shaped to pass beneath the foot of the leg portion and to terminate in a secondary shearing surface that co-operates with the primary shearing surface. Both the primary and secondary shearing surfaces are in a plane parallel to the plane of the leg portion, but spaced from it. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings wherein: 
           [0011]      FIG. 1  is an elevational view of a portable power shear of the present invention. 
           [0012]      FIG. 2  is a cross-section as indicated in  FIG. 1 . 
           [0013]      FIG. 3  is a partial top view as indicated in  FIG. 1 . 
           [0014]      FIG. 4  is an exploded view of a portion of the embodiment of  FIG. 1 . 
           [0015]      FIG. 5  is an elevational view of the stationary blade from the side opposite that shown in  FIGS. 1 and 4 . 
           [0016]      FIG. 6  is a perspective view as indicated in  FIG. 5 . 
           [0017]      FIG. 7  is an elevational view of the stationary blade as seen in  FIG. 4 . 
           [0018]      FIGS. 7A , and  7 B are views as indicated in  FIG. 7 . 
           [0019]      FIG. 7C  is a partial view of the fixed blade as seen in  FIG. 3 . 
           [0020]      FIG. 7D  is a rotated partial view of the fixed blade of  FIGS. 7A ,  7 B, and  7 C, and illustrates specifics of one embodiment. 
           [0021]      FIG. 8  is an elevational view of the moving blade of the embodiment of  FIG. 1 . 
           [0022]      FIGS. 8A ,  8 B and  8 C are views as indicated in  FIG. 8 . 
           [0023]      FIG. 8D  is a rotated detail view of a portion of the blade in  FIG. 8 , and illustrates specifics of one embodiment. 
           [0024]      FIGS. 9 ,  10 ,  11 ,  12  and  13  are schematic views of a right-handed tool as in the embodiment of  FIG. 1 , cutting corrugated material. 
       
    
    
     DETAILED DESCRIPTION  
       [0025]    With reference to  FIG. 1 , a portable shear  10  comprises a power unit  12  and a head  14 . The power unit may be electric, pneumatic, or driven by another energy source. The head  14  has a movable blade  16  and a fixed blade  18  assembled in a housing  20  with three fasteners  22   a, b, c.  A pivot axis  24  passes through the movable blade and the fixed blade so that the movable blade can oscillate around the pivot axis relative to the fixed blade. A fixed spacer  26  is on the side of the movable blade  16  opposite from the fixed blade  18 . The power unit, housing, pivot axis and method of driving the movable blade are described in other documents, for example, U.S. Pat. No. 4,173,069 for a power shear head issued to Sidenstick and assigned to the same assignee as the current application. U.S. Pat. No. 4,173,069 is hereby incorporated by reference. 
         [0026]    Referring to  FIGS. 1-4 , the housing has a longitudinal slot  28 . On one side is a first seat  30  ending in a first shoulder  32 , and on the opposite side is a second seat  34  ending in a second shoulder  36 . The housing can accept both right hand and left hand versions of the movable and fixed blades, but the right hand and left hand versions must be installed as a set. The fixed spacer  26  can be used with either the right hand set  38  or the left hand set (not shown, as it would simply be a mirror image of  38 ). 
         [0027]    A housing having a right hand set  38  makes a right hand embodiment, as described and illustrated in  FIGS. 1-13 . The term right-hand refers to a person standing behind and over the portable shear looking down at the view of  FIG. 3  and seeing that the fixed blade and the moving blade are on the right-side of the power shear. For the right-hand embodiment the fixed blade  18  mates against the first shoulder  32  and the first seat  30  and a fixed spacer  26  locates on the second seat  34  against the second shoulder  36  with the moving blade  16  between the two. As illustrated in  FIGS. 9-13 , a right-handed embodiment is convenient for a right-handed person to use while standing to the left of the work material that they need to cut. A right-hand embodiment will easily cut curves to the right as shown in  FIG. 13 . If the left handed blades were installed (not shown), the fixed blade would be installed where the spacer is shown in  FIG. 3 , and the spacer would be installed where the fixed blade is currently shown. The blades would be to the left as viewed from the top and the tool would cut curves to the left. 
         [0028]    First the details of the components used for assembly will be further described. After that, details of the individual blades that are relevant for cutting performance will be described. 
         [0029]    The exploded view  FIG. 4  shows details of the assembly. The fixed blade  18  has an outer face  40  ( FIG. 5 ), an inner face  42 , a first hole  44 , and a second hole  46 . The first hole is larger than the second hole. The fixed spacer  26  also has an outer face  48 , an inner face  50  ( FIG. 3 ), a first hole  52 , and a second hole  53 . The first hole is again larger than the second hole. The movable blade  16  has a blade face  56  ( FIG. 8C ), a spacer face  58 , and a pivot hole  60  that is larger in diameter than the first holes  44 ,  52 . A bearing sleeve  54  has a major diameter  55 , a minor diameter  57   a,    57   b,  an inner diameter  59 , and a length  62  from an end  66  to an end  68 . The diameters  55 ,  57   a,    57   b  have a sliding fit with the first holes and the pivot hole so that the moving blade may operate precisely with the fixed blade but be free to oscillate around the pivot axis  24 . The bolt  22   a  passes through the housing  20 , fixed spacer  26 , bearing sleeve  54 , movable blade  16 , and fixed blade  18  and screws into a threaded insert (not shown) in the opposite side of the housing. The bolt  22   b  passes through the housing  20 , fixed spacer  26 , a spacer bushing  70 , and the fixed blade  18 , and screws into a threaded insert (not shown) in the opposite side of the housing  20 . The spacer bushing  70  has an outside diameter  72  greater than the inside diameter of the second holes  46 ,  53 , so the spacer bushing  70  does not enter the second holes  46 ,  53 . The bolt  22   c  ( FIG. 1 ) passes the through the housing  20  and screws into a threaded insert (not shown) in the opposite side of the housing  20 . The bolt  22   c  does not pass through the blades  16 ,  18  or fixed spacer  26 . The length  62  of the bearing sleeve  54  is less than the combined thicknesses of the blades  16 ,  18 , and the fixed spacer  26 . The length of the major diameter  55  is greater than the thickness of the movable blade  16  therefore the bearing sleeve  54  is squeezed by the inner face  42  and the inner face  50 . This squeezing prevents the bearing sleeve  54  from rotating when the movable blade  16  oscillates. 
         [0030]    The features of the blades  16  and  18  that make the cutting process convenient and durable will now be described and are best viewed in  FIGS. 3-8C  with occasional reference to other figures. Note that one of ordinary skill in the art may often use the term “radiused” as synonymous with “convex”, as in a “radiused cutting edge” or “convexed cutting edge”. However, that is not quite correct. Convex edges or surfaces may be more complex than a single radius, or be of a shape other than a radius. In this description and the claims that follow, the term “convex” is used for the broad scope of the invention. When being more specific for certain embodiments, the term “radius” will be used. 
         [0031]    The fixed blade  18  has a leg  74  and a foot  76  at an angle α to the leg  74 . The movable blade  16  has a leg  78  and a foot  80  at an angle β to the leg  78 . The angles α and β are the same, and it has been found by experimentation that 45 (range 40-50) degrees is a preferred value. It is this angle α, β that places the feet of the blades  16  and  18  to the right of the legs  74 ,  78 , when viewed from the top as in  FIG. 3 . The fixed blade  18  and movable blade  16  contact along a straight (when viewed from the top) contact plane  82  that is parallel to a center plane  84  of the portable shear  10 , but offset from it. The contact plane  82  is offset from inner face  42  and blade face  56  by an offset  86 . The offset  86  allows the movable leg  78  to move up and down relative to the fixed blade  18 , without having to bend the cut metal  88  ( FIG. 9 ) as much as it would if the contact plane  82  was not offset. 
         [0032]    The fixed blade  18  has a primary shearing surface  90  with a nose radius  92  at one end, a clearance radius  94  at the other end, and a convex cutting edge  96  at the contact plane  82 . On the other side of the convex cutting edge  96  is a convex bevel  98  having a 3 (2.5-3.5 range) inch radius at an angle  99  to the primary shearing surface  90 . We have found that an angle  99  of 82 (80-85 range) degrees works well. The convex cutting edge  96  continues into an un-ground (as-cast or fabricated) convex body feature  100  on a back surface  102  of the foot. The convex cutting edge  96  and the convex body feature  100  are particularly visible in  FIGS. 5 and 6  respectively. It is the convex body feature  100 , provided in the casting  104  of the fixed blade  18  that makes the current invention so durable and able to cut thicker metals. Without this bulge of material, the convex bevel  98  would not have a uniform width and surface area to distribute the cutting forces from the convex cutting edge  96  into the foot  76  of the fixed blade  18 . In one embodiment ( FIG. 7D ) the convex body feature  100  is in the form of a cast material radius  100 ′ at an angle  152  ( FIG. 7B ) located at a point  150  at a distance  154  and  156  from a reference point  158  ( FIGS. 7B &amp; 7D ). Experimentation has shown that  100 ′ of approximate 3 inches radius at an angle  152  of approximately 42 degrees, at distance  154  approximately equal to 2.76 inches and distance  156  approximately equal to 1.75 inches strengthens the convex cutting edge  96 , thus allowing metals of greater thickness (lower gauge number) to be cut. 
         [0033]    Besides having the strength to cut thicker metals than portable shearing equipment currently sold, the current invention also has the necessary clearance radius  94  to allow the remnant material to be pushed down by the moving blade  16 , while the portable shear  10  is maneuvered as needed to follow corrugations or to make curved cuts. Experimentation has found that a clearance radius  94  of 0.250 inches (0.188-0.250 range) ground at an angle  95  equal to 56.5 (45-60 range) degrees, works, and does not create an excessively weakened condition, when used in combination with radius edges  105 ,  106  ( FIG. 7A ). The radius edges  105 ,  106  maintain enough thickness to distribute the stresses transmitted from the foot  76  to the leg  74 . It has been found that a 0.025 (0.016-0.032 range) inch radius holds up well without significantly impacting the clearance provided by the clearance radius  94 . 
         [0034]    The nose radius  92  contributes to cutting a greater range of corrugations, and to cutting curves more easily through those corrugations. A 9/64 th  (⅛- 3/16 range) inch nose radius  92  allows the blades  16 ,  18  to travel inside the radii and pitches of corrugate material with precision, without becoming trapped at the changes of the slope of material. For the fixed blade  18 , this takes place underneath the material (hidden lines,  FIG. 9 ) and not in view of the operator. 
         [0035]    The movable blade  16  has a secondary shearing surface  108  with a nose radius  110  at one end and an extended heel  112  at the other. The secondary shearing surface ends at a convex cutting edge  114  having a  3  inch radius at the contact plane  82 . On the other side of the convex cutting edge  114  is a ground convex bevel  116  at an angle  117  to the secondary shearing surface  108 . In one embodiment ( FIG. 8D ) the ground convex bevel  116  is a radius  116 ′ located at a point  160  that is a distance  164  and  166  from a reference point  168  ( FIGS. 8A &amp; 8D ). Experimentation has shown that using radius  116 ′ approximately equal to 3 inches at an angle  117  approximately equal to 82 (80-85 range) degrees works well at distance  154  approximately equaling 2.48 inches and  156  approximately equaling 0.54 inches. The approximate values given for the size of  100 ′ and  116 ′ and the distances  154 ,  156 ,  164 ,  166  and the angles  117  and  152  work in cooperation in one embodiment of right hand set  38 . 
         [0036]    The nose radius  110  is 9/64 th  (⅛- 3/16 range) inch and works in the same way as the nose radius  92  does, but it is visible to the operator. The extended heel  112  provides an extension of the secondary shearing surface  108  for easy assembly and for blade-to-blade contact during operation to prevent the movable blade  16  from trying to run on the wrong side of contact plane  82 . One of ordinary skill in the art may consider it normal practice for a cutting tool to maintain contact of the primary shearing surface  90  with the secondary shearing surface  108 , however the improved clearance radius  94  on the fixed blade  18  causes engagement to be lost at the end of the movable blade stroke. The solution to this problem is the extended heel  112  that maintains contact but does not interfere with the clearance radius  94 . 
         [0037]    In keeping with the emphasis of this invention, which is to successfully cut a range of tough corrugated metal panels, the length has been made sufficient to cut up to 4 inch deep corrugated materials. This length is understood as a distance  118  ( FIG. 1 ) from the pivot axis  24  to the intersection of the convex cutting edge  96  with the convex cutting edge  114 . Related to this, specifically on the movable blade  16 , is the length from the pivot axis  24  to the 45 degree angle that demarcates the feet  76 ,  80 . Also related, on the fixed blade, is the length from the pivot axis  24  to the center of the clearance radius  94 . It was important to make distance  118  long enough to keep the cut-zone visibly in front of the housing  20  so the cut zone can be seen by the operator, and also long enough so that when the blade  18  is being buried in the valleys of the corrugations, there is still enough reach to keep the shearing surfaces  90 ,  108  in un-cut metal. 
         [0038]    While the foregoing description has set forth preferred embodiments of the present invention in particular detail, it must be understood that numerous modifications, substitutions and changes can be undertaken without departing from the true spirit and scope of the present invention as defined by the ensuing claims. The invention is therefore not limited to specific embodiments as described but is only limited as defined by the following claims.