Patent Publication Number: US-7716840-B2

Title: Tubing cutter

Description:
BACKGROUND 
   This application relates to the art of cutting devices and, more particularly, to improvements in tools for cutting workpieces having a circular cross section such as tubing. Although the preferred embodiment will be described in connection with a manual tubing cutter apparatus for cutting plastic tubes by hand, it is to be appreciated that the invention has application in other areas including devices for cutting, clipping, or otherwise applying a force to associated workpieces. 
   A wide variety of tubing cutters has been provided heretofore for cutting plastic tubing of the character used in commercial and domestic water systems, such as schedule 40 PVC tubing, for example. Such cutters have included scissors-type cutters such as that shown in U.S. Pat. No. 6,513,245 to Aubriot and U.S. Pat. No. 6,658,738 to King wherein a tube to be cut is supported in a cradle portion of the cutter and a blade is displaceable about a fixed pivot axis to cut a tube interposed between the cradle and blade. In the King patent, the pivot axis is adjustable to accommodate the cutting of tubes of different diameter. 
   The scissors-type cutters which require a squeezing action of the handles requires an excessive effort on the part of the user to achieve a cutting operation, especially with larger diameter tubing. Partly in this respect, these tools require the user to rock or rotate the tube and cutter in opposite directions while squeezing the handles to apply a cutting load. Furthermore, with initially cutting through a larger diameter tube, a user who has a small hand span has difficulty in applying the necessary closing force on the handles to achieve initial cutting of the tube and, often, has to grasp the handles with both hands to initiate cutting. 
   Another type of tubing cutter heretofore available includes a cradle for supporting a tube to be cut and a pivotal cutting jaw or blade which is intermittently displaced toward the cradle by means of a ratchet mechanism. While the ratchet mechanism allows a smaller stroke of the cutter handles relative to one another for each intermittent cut, whereby a user can operate the cutter without a large hand span, the cutters are structurally complex and a cutting operation requires a number of sequential displacements of the ratchet handle relative to the cutting head to complete a cutting operation, especially with respect to larger diameter tubes. Accordingly, more work and time is required than is desirable. 
   In addition to such tubing cutters, a number of metal shears and pruning devices have been provided in which manipulation of the handles of the cutters provide for a slicing displacement of a cutter blade relative to an anvil surface or the like against which an object is pressed during the cutting operation. Such shears are shown, for example, in U.S. Pat. No. 2,508,790 to Herr, U.S. Pat. No. 2,528,816 to Boyer, and U.S. Pat. No. 2,564,154 to Compton. These cutting devices are characterized by a pair of handles pivotally interconnected with one another, a cutter blade pivotally attached to one of the handles and a mechanism such as a pin and slot arrangement between the blade and the other handle by which the blade is displaced in a shearing and slicing motion in response to closure of the handles relative to one another. The angular blade travel during cutting with shears of this character is less than the angular displacement required to close the handles relative to one another, whereby the diameter of an object to be cut is limited in order to provide for a user to grasp and close the handles with just one hand. Further, cutting is achieved by a combination of shearing and slicing motions, whereby the force required on the handles to achieve cutting is very uniform throughout the cutting stroke. 
   BRIEF DESCRIPTION 
   In accordance with the present application, an improved tubing cutter is provided, especially for plastic tubing of the type mentioned above, which advantageously enables the single stroke of large diameter tubing, such as 1-⅜ inch tubing for example, with less force than heretofore required with regard to closing the handles of the cutter to achieve the cutting operation. More particularly in this respect, the cutter is characterized by a first handle having a cradle for supporting a tube to be cut, a second handle pivotally attached to the first handle, a cutter blade attached to the second handle for displacement therewith and relative thereto, and a pin and slot interengagement between the cutter blade and the first handle by which the angular displacement of the cutter blade from an open to a closed position relative to the cradle is greater than the angular displacement of the handles to achieve such blade displacement. Accordingly, a longer cutting stroke is achieved with a given handle displacement than heretofore possible, thus enabling the cutting of large diameter tubing with a single stroke, one hand manipulation of the cutters by a user. 
   In accordance with another aspect of the application, an improved tubing cutter is provided, especially for plastic tubing of the type mentioned above, which advantageously provides a mechanical advantage to users of the tubing cutter. In this aspect of the application, the slot configuration provides for displacement of the blade relative to the cradle to initially apply a higher cutting force which is followed by a transition to a lower cutting force and a higher rate of blade displacement. Accordingly, a user can grasp the open handles of the cutters closer to the pivot axis between the handles to promote a better gripping of the handles and then, when the cutting stroke is in progress, the user can grasp the handles closer to the outer ends thereof and apply the same cutting force as was initially applied with the hands close to the pivot axis. In this respect, as the transition takes place to the lesser cutting force the user&#39;s grasping of the handles adjacent the outer ends thereof increases the leverage and thus enables obtaining the initial force in completing the cutting operation. 
   It is accordingly an overarching object of the present application to provide an improved tubing cutter, especially for plastic tubing. 
   Another object is the provision of an improved tubing cutter of the character having a pair of handles pivotally interconnected with one another and a blade pivotally attached to one of the handles and interconnected with the other for displacement of the handles from an open to a closed position to pivotally displace the blade from an open to a closed position relative to a tube being cut. 
   Yet another object is the provision of a tubing cutter of the foregoing character in which the angular displacement of the blade from the open to the closed position is greater than the angular displacement of the handles from the open to the closed position. 
   A further object is the provision of a tubing cutter of the foregoing character which provides for single stroke cutting of tubing to be achieved with less physical effort than heretofore required on the part of a user. 
   Still another object is the provision of a tubing cutter of the foregoing character which provides a high leverage during the initial cutting of a tube followed by lower leverage and a higher cutting rate as the cutting operation is completed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing objects, and others, will in part be obvious and in part pointed out more fully hereinafter in conjunction with the written description of preferred embodiments of the invention shown in the accompanying drawings in which: 
       FIG. 1  is a perspective view of a tubing cutter apparatus in accordance with the preferred embodiment; 
       FIG. 2  is an exploded perspective view of the tubing cutter in accordance with the present application and as shown in  FIG. 1 ; 
       FIG. 3  is a plan view of the cutter blade of the tubing cutter of  FIGS. 1 and 2 ; 
       FIGS. 4   a ,  4   b , and  4   c  are partial cross-sectional views of the subject tool illustrating a relative range of movement between the handle portions and the blade portion thereof; 
       FIG. 5  is a plan view of the subject tool shown in partial cross-section with a free body force diagram overlaid thereon; and, 
       FIG. 6  is a graph showing a mechanical advantage provided by the subject tool over a range of degrees of handle travel. 
   

   DETAILED DESCRIPTION 
   Referring now in greater detail to the drawings, wherein the showings are for the purpose of illustrating preferred embodiment of the present invention and not for the purpose of limiting the invention,  FIG. 1  provides a perspective view of the subject tubing cutter apparatus  10  in a partially opened position and  FIG. 2  is an exploded perspective view illustrating the various preferred components thereof and their preferred arrangement in the subject tool. 
   As shown in those Figures, the preferred form of the tubing cutter  10  comprises a first elongate member  12  pivotally attached at a handle axis  14  with a second elongate member  16 , and a cutter blade  20  pivotally attached at a blade axis  22  with the second elongate member  16  as shown. In the preferred embodiment illustrated, the first elongate member  12  is defined by handle halves  12   a  and  12   b , each of which has a first end  24  and an opposite second end  26 . Ends  24  are provided with corresponding arcuate cradle portions  30  which, when the cutter is assembled, provide a cradle area for supporting a tube to be cut. The opposite ends  26  of the first elongate member  12  are provided with first handle portions  28  used for gripping the cutter tool  10  during use thereof. Somewhat centrally located in the first elongate member  12  is provided a first guide portion  32  for guiding movement of the cutter blade  20  relative to the first and second elongate members  12 ,  16  in a manner to be described in greater detail below to provide an increased cutting range, enhanced mechanical advantage, and other benefits. 
   In the preferred embodiment illustrated, the cutter tool  10  includes a second elongate member  16  pivotally mounted to the first elongate member  12  by a pin  40  having opposite ends received in a pin support  42  in each of the handle halves  12   a ,  12   b , only one of which is visible in  FIG. 2 , whereby the second elongate member  16  and the pivot pin  40  are captured between the assembled handle halves  12   a ,  12   b . Overall, the second elongate member  16  includes first and second ends  44 ,  46 , the first end  44  being pivotally attached with the first elongate member  12  at the handle axis  14  and the second free end  46  defines a second handle portion  48  of the tool. The second handle portion is configured to complement the first handle portion  28  the pair and together are useful for gripping and operating the subject cutter tool  10  by hand. 
   The cutter tool  10  further includes a cutter blade  20  pivotally mounted on the second elongate member  16  by means of a blade pivot pin  50  which extends through a blade pin opening  52  in the cutter blade  20 . The blade pivot pin  50  has opposite ends received in a pin support pair  54  formed of the second elongate member  16 , only one of which is visible in  FIG. 2 . In this manner, the cutter blade  20  is movable about the blade pivot pin  50  in a blade axis  22  substantially aligned in parallel with the handle axis  14 . It is to be appreciated by those skilled in the art that the cutter blade  20  is pivotally movable in a plane extending perpendicular with each of the handle and cutter blade axes  14 ,  22 . 
   With particular reference now to  FIG. 3 , showing the cutter blade  20  removed from the first and second elongate members  12 ,  16  , the blade pin opening  52  is formed on a first end  60  of the cutter blade and a cutting edge  62  is formed on a second end  64  of the cutter blade opposite the first end  60  . In addition, a second guide portion  66  is provided on the cutter blade between the first and second ends  60 ,  64  as illustrated. The second guide portion  66  is operative with the first guide portion  32  provided on the first elongate member  12  to effect the desired movement of the cutter blade  20  relative to the first and second members  12 ,  16  during use of the tool. In its preferred form, the second guide portion  66  defines an elongate cam slot  70  receiving a cam follower which in the present embodiment is in the form of a pin  72  and roller  74 . The pin  72  has opposite ends received in pin recesses  76  formed in the handle halves  12   a ,  12   b , only one of which is visible in  FIG. 2 , whereby the follower and thus cutter blade  20  are captured between the assembled handle halves. A torsion spring  78  is mounted between the handle halves  12   a ,  12   b  coaxial with the cam follower and has opposite ends respectively interengaging the first and second handles to bias the handles toward an open position relative to one another. The cam slot  70  has a predetermined shape and is defined between spaced apart elongate side walls  80 ,  82  extending between spaced apart end walls  84 ,  86 . In its preferred form, the cam slot  70  is generally L-shaped as shown, but can take on any shape including a generally straight slot, a crescent, an arc, multiple connected arcs, or any other regular or irregularly selected shape to realize the benefits of the subject tool as described above. It is to be appreciated that the shape of the slot is based in part on the dimensions of other components of the subject tool. As noted, the cutter blade defines a blade pin opening  52 . The cutter blade  20  has its first end  60  pivotally attached with the second elongate member  16  by the blade pin opening  52  and the blade pivot pin  50  extending therethrough. The second guide portion  66  includes the elongate slot  70  defined in the blade  20 . The slot  70  is disposed between the blade pin opening  52  of the cutter blade  20  and the second blade end  64  of the cutter blade  20 . 
   As shown schematically in  FIGS. 4   a ,  4   b , and  4   c , the cutter blade  20  is pivotable relative to the second elongate member  16  about the blade axis  22  in a manner described above. Essentially, the cutter blade  20  is pushed forward into the cavity  90  forming a work area as the second elongate member  16  is closed toward the first elongate member  12  through interaction of the blade pivot pin  50  urging the cutter blade  20  forward. Simultaneous with pivotal movement of the blade relative to the second elongate member, the first and second guide portions  32 ,  66  mutually cooperate to urge the second end  64  of the cutter blade carrying the cutting edge through arcuate movement in the cavity region  90 . More particularly, the preferred tubing cutting is configured to enable pivotal movement between the first and second elongate members  12 ,  16  about the handle axis  12  through a first angle Φ 1  between an open position as illustrated in  FIG. 4   a  whereat the first and second handle portions  28 ,  48  are in a fully spaced apart position and a fully closed position as illustrated in  FIG. 4   c  whereat the first and second handle portions  28 ,  48  are in close alignment.  FIG. 4   b  illustrates an intermediate handle position between the fully opened position shown in  FIG. 4a  and the fully closed position shown in  FIG. 4   c . In the preferred embodiment of the hand tool illustrated, the first angle Φ 1  is about 85.5 degrees. 
   Together with movement of the handle portions through the first angle as described above, the cutter blade is rotated and moved forward into the cavity area  90  for cutting an associated tube disposed in the cradle portion  30 . Initially, the cutter blade  20  is disposed in a retracted position whereat the cutting edge  62  of the cutter blade  20  is spaced from the cradle portion  30  of the first elongate member  12 . The cutter blade, however, is pivotally movable about the blade axis  22  through a second angle Φ 2 between the retracted position illustrated in  FIG. 4   a  and an extended position illustrated in  FIG. 4   c  whereat the cutting edge  62  is brought through the cradle portion and cavity  90 . In its preferred form, the second angle is about 91.3 degrees. 
   In addition to the above, it is important to note that the subject tool  10  provides an enhanced mechanical advantage in a first portion X of the second angle between the retracted position and the extended position and a area of lower mechanical advantage Y in a substantially extended region of cutter blade movement. A transition between a higher mechanical advantage and a lower mechanical advantage of the cutter blade occurs at approximately mid travel of the cutter blade through the cavity  90 . Essentially, the ratio of blade travel to handle travel is constantly changing throughout the entire handle advancement. The total blade travel is greater than the total handle travel overall as described above. Preferably, for every degree of handle advancement in a closed direction, the blade advancement is different permitting the cutting of a larger size tube with a smaller hand span than would be possible with a standard scissors cutter. In accordance with the preferred embodiment, for every five degrees of incremental handle travel, the blade rotational movement is between about 8.2 degrees and about 4.4 degrees of movement. A chart identifying respective handle and blade movement is provided below. 
   
     
       
         
             
             
             
             
           
             
                 
             
             
               Incremental 
               Cumulative 
               Incremental 
               Cumulative 
             
             
               Handle Travel 
               Handle Travel 
               Blade Travel 
               Blade Travel 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
          
             
                 
               Open Position 
                 
               Retracted 
             
             
                 
                 
                 
               Position 
             
             
               5 
               5 
               5.6 
               5.6 
             
             
               5 
               10 
               5.1 
               10.7 
             
             
               5 
               15 
               4.8 
               15.5 
             
             
               5 
               20 
               4.7 
               20.2 
             
             
               5 
               25 
               4.6 
               24.8 
             
             
               5 
               30 
               4.5 
               29.3 
             
             
               5 
               35 
               4.4 
               33.7 
             
             
               5 
               40 
               3.5 
               38.3 
             
             
               5 
               45 
               4.7 
               43.0 
             
             
               5 
               50 
               4.9 
               47.9 
             
             
               5 
               55 
               5.1 
               53.0 
             
             
               5 
               60 
               5.4 
               58.3 
             
             
               5 
               65 
               5.7 
               64.0 
             
             
               5 
               70 
               6.0 
               70.0 
             
             
               5 
               75 
               6.4 
               76.3 
             
             
               5 
               80 
               6.8 
               83.1 
             
             
               5.5 
               85.5 
               8.2 
               91.3 
             
             
                 
               Closed 
                 
               Extended 
             
             
                 
               Position 
                 
               Position 
             
             
                 
             
          
         
       
     
   
   As noted above, it is to be appreciated that the subject cutter tool provides an optimized mechanical advantage to users of the tool in cutting plastic pipe. More particularly, a mechanical advantage M A  is provided relative to an applied force F A  applied equally and oppositely against the handle portions  28 ,  48  of the first and second elongate members  12 ,  16  in turn effecting a compressive force F C  by the cutting edge  62  of the cutter blade  20  on an associated circular workpiece such as a plastic pipe.  FIG. 5  shows a free body diagram layered upon a cross-sectional view of the mechanical linkages forming the subject cutter tool  10 . As illustrated, an applied force F A  is applied at a distance E from the handle axis  14 . With the first elongate member  12  held fixed, the applied force F A  moves the second elongate member  16  from the opened position shown in  FIG. 4   a  to a closed position shown in  FIG. 4   c  to effect a cutting of the associated circular workpiece  100 . 
   As noted above, pivotal movement of the handle portion  28  of the second elongate member  16  about the handle axis  14  urges the cutter blade  20  forward through the first and second guide portions  32 ,  66  formed in the first elongate member  12  and in the cutter blade  20 , respectively. Also, pivotal movement of the cutter blade is effected during movement of the second elongate member  16 . As shown in  FIG. 5 , the roller  74  carried on the pin.  72  in the first guide portion  32  creates a counteractive loading force F L  against the first side wall  80  of the cam slot  70  in reaction to the cutting force F C  applied to the workpiece  100 . As those of ordinary skill in the art would understand, both the loading force F L  as well as the cutting force F C  are generated in directions normal to their respective load surfaces. In the case of the loading force F L , the force is applied against the first side wall  80  in a direction normal to a surface thereof. Similarly, the cutting force F C  is applied to the associated workpiece  100  in a direction normal to a surface thereof. 
   Overall, a mechanical advantage M A  is provided in the subject cutter tool  10  during the initial portions of a cutting stroke through a workpiece illustrated at X in  FIG. 4   a . For purposes of illustrating an advantage of a preferred embodiment of the subject cutter tool,  FIG. 6  shows a mechanical advantage graph realized by the subject tool while cutting an associated workpiece in the form of a standard plastic pipe having a one inch (1″) nominal outer diameter (actual O.D. is 1.315 inches). As illustrated there, the mechanical advantage is at its greatest when the handles of the cutter tool are in an opened position to enable the user to grip the tool and more easily squeeze and cut the workpiece with an opened hand. This occurs with the handles being operated between about 90° and about 70°. Typically of course, users have more hand strength as the hand is more fully closed rather than in an opened position. The subject tool compensates for the decreased mechanical advantage in the hand in an opened position by providing additional mechanical advantage during that phase of the operation. As the user&#39;s hand is closed, however, the mechanical advantage realized in the first portion of tool operation is diminished slightly but is easily overcome by the user&#39;s strength. This occurs with the handles being operated about 70° and about 35°. 
   With reference once again to  FIG. 5 , the mechanical advantage provided by the tool is based upon dimensions and the geometry of the tool and the shape of the slot  70  formed by the cutter blade  20 . In  FIG. 5 , the blade axis  22  is spaced from the cutting force F C  in a direction perpendicular to the cutting force F C  by a first distance A. Also as shown there, the handle axis  14  is spaced from the cutting force F C  in a direction perpendicular to the cutting force F C  by a second distance B. In addition, the handle axis  14  is spaced from the loading force F L  in a direction perpendicular to the loading force F L  by a third distance C. Also, as noted above, the applied force F A  is applied at a distance E from the handle axis  14 . Lastly, the blade axis  22  is spaced from the loading force F L  in a direction perpendicular to the loading force F L  by a fourth distance D to provide a mechanical advantage M A  according to: 
   
     
       
         
           
             M 
             A 
           
           = 
           
             
               
                 F 
                 C 
               
               
                 F 
                 A 
               
             
             = 
             
               
                 
                   ( 
                   
                     E 
                     · 
                     D 
                   
                   ) 
                 
                 
                   
                     ( 
                     
                       B 
                       · 
                       D 
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       C 
                       · 
                       A 
                     
                     ) 
                   
                 
               
               . 
             
           
         
       
     
   
   The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.