Abstract:
A locking mechanism for a rotary power tool that includes an elongated locking member that is retained by, and is at opposite first and second end portions within, at least one of a motor housing and a gearbox end casting and being slideable between unlocked and locked positions, the locking member first end portion being accessible by a user to move the locking member to the locked position. The locking member also includes a locking portion intermediate the first and second end portions that is configured to engage the non-circular configured portion of a rotatable armature shaft and prevent rotation thereof when the locking member is in its locked position. A biasing element is also included and configured to bias the locking member toward said unlocked position.

Description:
The present invention generally relates to power hand tools and more particularly to a shaft locking mechanism for such tools. 
     Many power hand tools have rotating cutting blades, grinding blades and other rotating tool accessories that may be mounted on an armature shaft of an electric motor that drives the rotating blade or the like. To change blades or other tools that are mounted in this manner, prior art systems have been designed and developed which enable the user to hold the blade stationary while a mounting nut or bolt can be removed. One way in which this has been done in the past is to have the armature shaft ground to produce a pair of opposed flats that can be engaged by a wrench or the like for holding the shaft while the nut is loosened and removed. However, a problem with grinding flats on the shaft is that the flats necessarily weaken the shaft, which may require utilization of a larger diameter stock metal shaft to compensate for the loss of strength resulting from the grinding of the flats. 
     Other systems use one or two holes in a gear hub or gear that is attached to the output shaft in which a pin or other protrusion is inserted to hold the shaft while the mounting nut can be removed. Another problem with both of these prior art configurations is that there are only one or two engagements per revolution of the blade which results in some inconvenience in quickly locking the shaft. Still other prior art systems have used a locking element that is a complementary gear that engages an output gear of the tool which can create unnecessary wear to the gear and reduce its useful life, particularly if the user brings the braking gear portion into contact with the output gear while the shaft is still turning. It is a goal of designers to develop a spindle lock mechanism that is inexpensive, effective and convenient to engage and which does not risk damage to the output gears or the like during operation. 
     SUMMARY OF THE INVENTION 
     A preferred embodiment of the spindle lock mechanism of the present invention comprises an elongated, preferably stamped steel locking member that is configured to fit within slotted openings in at least one of the motor housing end casting and the main housing, which comprises the locking member that has a spindle lock configuration that can be moved into engagement with a hex shaped bushing that is preferably press fit on the armature output shaft of the motor, and which is normally biased away from the armature shaft. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective of a circular saw which has a portion of the lock mechanism embodying the present invention illustrated therein; 
         FIG. 2  is a diagrammatic plan view of the shaft locking mechanism assembled in a motor; 
         FIG. 3  is a perspective side view of portions of a motor used in the circular saw shown in  FIG. 1  and which is illustrated together with the gearbox end casting and a major portion of the shaft locking mechanism embodying the present invention; 
         FIG. 4  is a view of the interior of the gearbox end casting in which the shaft locking mechanism substantially resides; 
         FIG. 5  is a perspective view of the end casting with the motor locking member shown with major portions of the motor; 
         FIG. 6  is a perspective view of the locking member; 
         FIG. 7  is a side view of the locking member shown in  FIG. 6 ; 
         FIG. 8  is a top view of the locking member shown in  FIG. 6 ; 
         FIG. 9  is a top view of a hex shaped bushing that is press fit on the armature shaft; and 
         FIG. 10  is a side view of the hex shaped bushing shown in  FIG. 9 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the preferred embodiment of the shaft locking mechanism of the present invention is shown with a circular saw, it should be understood that the mechanism may be adapted for use with other types of tools in which a blade or rotatable output shaft needs to be held in place while a blade bolt or blade nut is loosened so that a blade or other tool can be removed or installed. 
     Turning now to the drawings, and particularly  FIGS. 1 and 2 , a circular saw is shown with a portion of the preferred shaft locking mechanism, indicated generally at  10 , that is shown at an interface between a main motor housing  12  and a gearbox end casting  14  that is shown to have a number of louvers  16  through which air is exited during operation of the motor that has an associated fan blade  18  ( FIG. 3 ). The circular saw has a saw blade housing  20  that surrounds a saw blade (not shown) and an auxiliary handle  22  as well as a foot  24  that has a bevel quadrant structure  26  and a locking mechanism  28 . The saw blade is in turn coupled to a spindle or armature shaft  30  of an electric motor (not shown) that drives the saw blade or the like. 
     Turning now to  FIG. 6 , the preferred shaft locking mechanism  10  includes an elongated locking member  32  having front and rear end portions  34 ,  36  with a spindle lock portion, designated generally at  38 , disposed generally intermediate of the front and rear end portions. The front end portion  34  includes a front longitudinal portion  40  that extends through a slot  42  or other opening that is preferably located at the interface of the gearbox end casting  14  and the motor housing  12 . At an external end of the front longitudinal portion  40  is a transverse end  44 , which the operator can push inwardly to engage the spindle and lock it against rotation so that the saw blade may be removed. 
     More specifically, turning to  FIG. 2 , the armature shaft  30  may selectively be prevented from rotation by lockingly engaging the spindle lock portion  38  of the elongated locking member  32  to the armature shaft. Thus, the spindle lock portion  38  may be reciprocated between a locked and an unlocked position. To this end, the elongated locking member  32  is spring biased outwardly in an unlocked position so that the spindle lock portion  38  of the locking member will not engage the armature shaft  30  unless the operator selectively applies sufficient force to move it inwardly toward the armature shaft, which is the locked position. 
     As illustrated in  FIG. 4 , to retain the locking member  32 , the gearbox end casting  14  preferably includes front and rear recesses  46 ,  48  that generally diametrically oppose one another. The front end portion  34  of the locking member  32  engages the front recess  46 , which is preferably disposed in one of the louvers  16 , while a distal end of the rear end portion  36  is preferably retained within the rear recess  48 , which located on the opposite rear wall of the end casting  14 . The louvers  16  extend from a side wall  49  such that distal surfaces thereof extend a predetermined distance from the side wall. While the distal surfaces some of the louvers  16  are planar, the front recess  46  is preferably formed by two louvers that each include at least two surfaces that are elevationally displaced from one another. 
     More specifically, as illustrated in  FIG. 4 , the two louvers  16  that are intermediate top and bottom louvers each include two elevationally displaced surfaces. A first louver  16  includes a first surface  16   a  and a second surface  16   b , where the first surface extends at a greater distance from the side wall  49  than does the second surface. Third and fourth surfaces  16   c ,  16   d  are provided on the other louver  16 , wherein the third surface  16   c  extends at a greater distance from the side wall  49  than does the fourth surface  16   d . However, the second surface  16   b  and the third surface  16   c  are generally coplanar. Thus, the distal surfaces of the two louvers  16  that are intermediate the top and bottom louvers provide for a reduced profile, creating the front recess  46 . 
     Support for the locking member  32  is accordingly provided by the recesses and motor housing  12  in which the member may slide inwardly and outwardly, i.e., to the right and left, respectively, as shown in  FIG. 2 . To provide further support, as shown in  FIGS. 2 ,  6  and  8 , the longitudinal portion  40  that extends outside of the housing preferably includes an enlarged width at location  50  defining shoulders  52  that engage the inside wall of the motor housing  12  and prevent it from moving to the left as shown in  FIG. 2 . 
     The spindle lock portion  38  is configured to lockingly engage a bushing  54  that is press fit on the armature shaft  30 . While the spindle lock portion  38  and bushing  54  may assume any one of a plurality of corresponding configurations, the preferred embodiment includes a hex bushing. Accordingly, the spindle lock portion  38  of the preferred embodiment is configured to be generally one half of a hex head configuration  56  for engaging the hex-shaped bushing  54 . An extension  58  of the spindle lock portion  38  partially surrounds the hex bushing  54  and then extends generally radially toward the rear recess  48  of the gearbox end casting  14 . The rear end portion  36  extends from the extension  58  to preferably engage, and be retained within, the rear recess  48 . Thus, the locking member  32  extends from a position external to the motor housing  12  and gearbox end casting  14 , through the front recess  46 , across an internal diameter of the gearbox end casting  14 , with the rear end portion  38  preferably engaging the rear recess  48 . 
     As is best shown in  FIGS. 2 and 3 , a biasing member, preferably a compression spring  60 , is provided to bias the locking member  32  in the unlocked position. More specifically, the locking member  32  preferably includes a narrow, elongated protrusion  62  disposed within a portion of the front end portion  34  ( FIG. 6 ), on which protrusion the compression spring  60  is preferably mounted. The protrusion  62  preferably includes a first base diameter around and a second shaft diameter, wherein the base diameter is at least slightly greater than the shaft diameter. As is best illustrated in  FIGS. 2 and 4 , one end of the compression spring  60  is coiled most tightly around the base diameter, and abuts a surface at the base diameter of the protrusion  62 , while an opposite end of the compression spring  62  engages a housing pocket  64 . Thus, the spring  60  biases the locking member  32  to the left as shown in  FIG. 2  so that the spindle lock portion  38  does not engage the hex shaped bushing  54 . However, when the operator exerts sufficient force on the transverse end  44  of the front end portion  34 , the spring  60  compresses to permit displacement of the locking member  32 , specifically the spindle lock portion  38 , to engage the bushing  54  and prevent rotation of the armature shaft  30 . Upon release of the transverse end  44 , the spring  60  will decompress to bias the locking member  32  back to the left, as illustrated in  FIG. 2 . 
     While it is contemplated that the bushing  54  may be configured in one of a plurality of shapes, the hex head bushing is particularly advantageous in that it does not require any cutting of the armature shaft  30  and is inexpensive and effective, requiring only the press-fitting of the bushing to the armature shaft. The use of a hex head configuration for the spindle lock portion  38  and for the bushing  54  is preferred, although other configurations such as square, octagon, slots or notches could be used. An additional advantage of the hex head is that there is engagement with the bushing  54  every 60° of rotation of the saw blade. 
     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. 
     Various features of the invention are set forth in the following claims.