Abstract:
An anti-rotation reciprocating drive apparatus for a reciprocating saw utilizes a wobble plate assembly that includes a drive shaft and an elongated arm with an interface structure for engaging a spindle. The interface structure has two ball-type interfaces that are concentrically aligned with one another, with the outer one being smaller than the inner one and both engaging a receiver portion of the spindle. The larger ball-type interface causes reciprocating movement of the spindle and the smaller outer interface prevents rotation of the spindle. The contact between the interfaces and the spindle receiver is a single point contact which reduces operating friction, wear of the parts and heat being generated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to hand tools, and more particularly, to power reciprocating hand tools.  
         [0002]     Reciprocating tools that are motor driven, such as saber saws, larger reciprocating saws and the like are usually driven by electric motors that have a rotating output shaft. Therefore, this rotating motion must be translated into reciprocating motion for moving a saw blade or the like in a reciprocating manner. While various types of mechanisms have been known in the art for translating the rotation motion into reciprocating motion, one common type of motion conversation mechanisms are wobble plate drives. A wobble plate drive shaft is typically connected to the motor through a gear arrangement that usually functions to reduce the speed of rotation of the motor output shaft and the wobble plate drive causes a wobble arm to reciprocate in a path that is parallel to the motion of the saw blade or the like which the wobble plate drive is used for. The blade of a reciprocating saw is mounted in a blade clamping mechanism that is located at the end of a spindle, the other end of which is operatively connected to a wobble arm.  
         [0003]     In some prior art wobble plate drives, the spindle has a rectangular or square cross-section that is located in a rectangular or square opening to restrain the spindle from any movement other than reciprocating movement. While these noncircular cross-section spindles operate in a desirable manner, the noncircular cross-section increases the cost relative to a tubular spindle construction which is more desirable. However, a tendency of wobble plate drives for driving a spindle is to exert forces on the spindle which tend to cause it to rotate. Since rotation of the spindle would necessary rotate the reciprocating blade, such rotation must be prevented.  
       SUMMARY OF THE INVENTION  
       [0004]     A preferred embodiment of the present invention is directed to an anti-rotation reciprocating drive apparatus for a reciprocating saw that utilizes a wobble plate assembly that includes a drive shaft and an elongated arm with an interface structure for engaging a spindle. The interface structure has two ball-type interfaces that are concentrically aligned with one another, with the outer one being smaller than the inner one and both engaging a receiver portion of the spindle. The larger ball-type interface causes reciprocating movement of the spindle and the smaller outer interface prevents rotation of the spindle. The contact between the interfaces and the spindle receiver is a single point contact which reduces operating friction, wear of the parts and heat being generated.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a side view of a preferred embodiment of a reciprocating saw of the present invention, shown partially in section and in simplified form;  
         [0006]      FIG. 2  is a side view of the preferred embodiment of the wobble plate assembly and a portion of the spindle and spindle receiver, with the latter shown partially in section;  
         [0007]      FIG. 3  is an end view of a portion of the wobble plate assembly and spindle receiver shown in  FIG. 2 , shown partially in section;  
         [0008]      FIG. 4  is another side view of the wobble plate assembly of the preferred embodiment;  
         [0009]      FIG. 5  is another view of the wobble plate assembly shown in section generally through the middle of the assembly;  
         [0010]      FIG. 6  is an end view of the wobble plate assembly shown in  FIG. 4 ;  
         [0011]      FIG. 7  is a perspective view of the spindle and receiver of the preferred embodiment;  
         [0012]      FIG. 8  is an end view of the spindle and receiver shown in  FIG. 8 ;  
         [0013]      FIG. 9  is a cross-section taken generally along the line  9 - 9  of  FIG. 8 ; and  
         [0014]      FIG. 10  is a cross-section taken generally along the line  10 - 10  of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION  
       [0015]     The preferred embodiment of the present invention is shown in the drawings and is a reciprocating saw, the general size and shape of which is similar to saws that are currently marketed. The present invention is also adapted for other types of tools such as saber saws, for example, or other types of tools that have a reciprocating action and are powered by a motor having a rotating output shaft. As shown in  FIG. 1 , the reciprocating saw, indicated generally at  10 , has an outer housing  12  which includes a nose portion  14  that is flared outwardly so that a user can hold the nose portion with one hand while holding a handle  16  with the other. A trigger switch  18  is provided in the handle portion for turning on a motor  20  that drives the tool. The saw has a shoe  22  at the nose end portion  14  and a saw blade  24  is mounted in a blade clamping mechanism  26  that is mounted at the end of an elongated spindle and receiver, indicated generally at  30 , which is slideable in a hollow cylindrical sleeve  32 . The motor  20  has an output shaft  34  with a pinion gear  36  mounted on the shaft  34 , with the gear  36  engaging a larger gear  38  that is connected to a wobble plate assembly, indicated generally at  40 , which drives the spindle and receiver  30  in a reciprocating manner as the gear  38  drives the wobble shaft assembly.  
         [0016]     More particularly, the wobble shaft assembly  40  has a drive shaft indicated generally at  42 , to which the gear  38  is attached. The shaft has an end portion  43  that is supported in a ball bearing  44  or the like and the shaft  42  has its opposite end supported in a ball bearing  45  that is mounted in the housing  12 . It should be understood that the manner in which the motor  20 , gears  36  and  38  as well as the shaft  42  are mounted in the structure is not in and of itself part of the present invention and the manner in which the housing is constructed and the rotating parts are supported is well known to those of ordinary skill in the art.  
         [0017]     With regard to the wobble plate assembly  40  and referring to  FIGS. 4 and 5 , the shaft  42  has different diameter portions  43 ,  46  and  48  with the smallest diameter end portion  43  being supported in the ball bearing  44 , and the section  46  having the gear  38  mounted on it. The opposite end  50  is supported in ball bearings  45 . An enlarged center portion  54  of the shaft  42  has a cylindrical shaped center portion  56  that is oriented at an acute angle relative to the axis of the shaft  42  as shown in  FIG. 5  and ball bearings  58  are positioned to permit an elongated arm  60  to rotate relative to the cylindrical portion  56 . As the shaft  42  is rotated, the angular orientation of the cylinder  56  changes so that the outer end of the arm  60  is moved in a reciprocating manner, i.e., to the left and right as shown in  FIG. 2 . As is shown in  FIGS. 4-6 , the arm  60  has generally flat sides  62  that extend from the bottom upwardly toward the outer end of the arm  60  and then merge into a curved portion that has a oval shape cross-section near the bottom at location  64  and which reduces in size and becomes circular shaped in cross-section near the outer end at location  66  where it merges with a first ball-type interface  68  that in turn merges into a generally cylindrical portion  70  that merges into a second ball-type interface  72 . The interfaces  68  and  72  have a generally spherical form albeit truncated, where each merges with adjacent structure  66  and/or  70 . It should be understood that these ball-type interface portions do not need to be strictly spherical but are desirably generally near-spherically curved so that point contact is made between these interfaces and the spindle and receiver  30 .  
         [0018]     Referring to  FIGS. 1, 2  and  8 - 10 , the spindle and receiver  30  has a tubular spindle  80  that merges into a right end solid generally circular section  82  that has a vertical slot  84  in which the shank end of the blade  24  may be inserted. The end  82  also has an aperture  86  in which a pin of the blade clamping mechanism  26  may be attached. At the opposite end of the spindle  80  is a receiver  88  that has a cylindrical extension  90  that is sized to closely fit within the interior of the tube portion  80  and which is also preferably braised to securely hold the two components together inasmuch as extreme forces are incurred by the spindle structure during operation.  
         [0019]     The receiver has a main body portion  92  that has a circular opening  94  that merges into an elongated slot  96  the length of which is oriented in the same direction as the axis tubular portion  80  as shown in  FIGS. 7 and 10 . The ends of the slot  96  are flared outwardly as shown at  98  to accommodate the reciprocating motion that is caused by the elongated arm  40  and particularly the ball-type interfaces  68  and  72  that are positioned in the opening  94  and slot  96 , respectively. As shown in  FIGS. 2 and 3 , the first ball-type interface  68  is positioned in the opening  94  with the outside of the interface being generally in a point contact with the sidewall of the opening  94 . The second ball-type interface  72  also rides in the slot  96  and as is best shown in  FIG. 3 , the diameter of the interface  72  is only slightly smaller than the width of the slot and thereby effectively prevents the spindle from rotating.  
         [0020]     Because of the preferably spherical-shaped configuration of the interfaces  68  and  72  which are positioned in the opening  68  and slot  96  have straight side wall straight surfaces in the vertical direction, there is only point contact between the interfaces and the sidewalls during the entire movement of the elongated wobble arm. This point contact results in the advantages of reduced wear between the interfaces and the receiver  88  and less heat generated during operation. Also, because of the curvature of the ball interface portions with the straight sidewalls, there is only point contact at all times, regardless of the tolerances and clearances between the parts. It is also preferred that grease be applied to the receiver to further reduce friction between the ball-type interfaces and the receiver.  
         [0021]     An added advantage is achieved in that the point contact of the placement of the first ball interface  68  in the receiver  88  is at a vertical elevation relative to the tube portion  80  that is inside of the tube portion. This contact location applies reciprocating force to move the spindle close to the center of the tubular portion  80  as is desired.  
         [0022]     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.  
         [0023]     Various features of the invention are set forth in the following claims.