Abstract:
A power tool in one embodiment includes a motor supported by a frame, a foot defining a first plane, a first guide fixedly positioned with respect to the foot and defining a first arc in a second plane, a second guide fixedly positioned with respect to the foot and defining a second arc in a third plane, wherein the second plane and the third plane are orthogonal to the first plane and the first arc and the second arc are offset when projected onto a reference plane parallel to the second plane and the third plane, a first pin fixedly positioned with respect to the motor and guided by the first guide; and a second pin fixedly positioned with respect to the motor and guided by the second guide.

Description:
FIELD 
     The present disclosure relates generally to power tools and particularly to power hand tools. 
     BACKGROUND 
     Power hand tools such as miter saws, circular saws, as well as other hand tools are often provided a support member or “foot” that is placed against a work piece when using the tool. The blade usually extends through the foot structure at a location that is hidden from the view of the user. Accordingly, an indicator is provided on the foot structure that can be used to align the blade with the desired cut location of the work piece. 
     These hand tools are frequently provided with the capability of adjusting the bevel angle of the cut that is made with the tool. Even when performing a bevel cut, however, the foot structure rests upon the work piece while the rest of the tool is at a pivoted location with respect to the foot. Thus, in order to maintain the blade indicator aligned with the blade during a bevel cut, the pivot axis for these power tools is optimally defined by the intersection of the plane defined by the saw blade and the plane defined by the foot of the tool. 
     Placement of a pivot at the intersection of the saw blade and the foot of the tool, however, is not possible. Accordingly, some power tools incorporate a virtual pivot point which is defined by a pin which rides within an arc-shaped guide slot. In order to provide desired stability, one pin and guide slot arrangement is provided at the front portion or quadrant of the power tool while a second pin and guide slot arrangement is provided at the rear quadrant of the power tool. Locking mechanisms are provided for the front and rear guide slot arrangements to lock the pins at the desired locations within the guide slots. 
     While the above described pin and guide slot arrangement is effective in defining a virtual pivot point at the intersection of the saw blade and the foot of the tool, the pin and guide slot arrangement exhibits various shortcomings. One shortcoming of a pin and guide slot arrangement is that the tool becomes unstable once one of the locking mechanisms is unlocked. Specifically, once one pin is unlocked, the weight of the tool causes a torque about the pin that is still locked. Because the unlocked pin is free to move in a direction tangential to the walls of the guide slot within the guide slot, the unlocked pin moves within the guide slot unless the pin is providentially positioned such that the weight borne by the pin is directed directly into a wall of the guide slot. 
     Moreover, once both pins are unlocked and the tool is pivoted, any such providential alignment is necessarily destroyed. Thus, the position of the pins in the associated guide slot can become offset if care is not taken to ensure equal movement of the front and back pins. Furthermore, once a pin is locked in a pivoted position, care must be taken to prevent inadvertent movement of the unlocked pin, which will generally be in an unstable position, prior to locking the second pin. Thus, offsets between the front and rear pin and guide slot arrangements can frequently result when pivoting power tools. 
     Once an offset exists between the two pin and guide slot arrangements, the axis of rotation defined by the pin and guide slot arrangements is no longer aligned with the plane of the blade. If the axis of rotation is not aligned with the plane of the blade, the tool can bind as the blade makes a cut into a work piece. Since the offset described above can be subtle, an operator may not become aware of the misalignment until binding occurs. 
     What is needed therefore is an improved arrangement for providing a virtual pivot point for a power tool. 
     SUMMARY 
     In accordance with one embodiment of the present disclosure, there is provided a power tool which includes a motor supported by a frame, a foot defining a first plane, a first guide fixedly positioned with respect to the foot and defining a first arc in a second plane, a second guide fixedly positioned with respect to the foot and defining a second arc in a third plane, wherein the second plane and the third plane are orthogonal to the first plane and the first arc and the second arc are offset when projected onto a reference plane parallel to the second plane and the third plane, a first pin fixedly positioned with respect to the motor and guided by the first guide; and a second pin fixedly positioned with respect to the motor and guided by the second guide. 
     Pursuant to another embodiment of the present disclosure, there is provided a power hand tool including a motor supported by a frame, a first pin fixedly positioned with respect to the motor, a second pin fixedly positioned with respect to the motor, a first guide plate in slidable contact with the first pin and the second pin, the first guide plate pivotably connected to the frame through the first pin and the second pin, and a foot structure rigidly connected to the first guide plate. 
     In yet another embodiment, a power hand tool includes a foot structure defining a planar support surface, a first guide plate extending upwardly from the foot structure, a first arcuate guide slot in the first guide plate, a second arcuate guide slot in the first guide plate, a first guide supported by the first arcuate guide slot, a second guide supported by the second arcuate guide slot, and an upper portion of the tool pivotably supported by the foot structure through the first guide plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a perspective view of a power tool incorporating aspects of the disclosure; 
         FIG. 2  depicts a partial front plan view of the power tool of  FIG. 1  showing two offset guide slots in the shape of arcs in a front guide assembly used to pivotally support the upper portion of the tool of  FIG. 1  above a foot structure; 
         FIG. 3  depicts an exploded view of the rear guide assembly of  FIG. 1 ; 
         FIG. 4  depicts a partial rear plan view of the power tool of  FIG. 1  showing two offset guide slots in the shape of arcs in a rear guide assembly used to pivotally support the upper portion of the tool of  FIG. 1  above a foot structure; 
         FIG. 5  depicts a partial rear plan view of the power tool of  FIG. 1  showing two offset guide slots in the shape of arcs in a rear guide assembly used to pivotally support the upper portion of the tool of  FIG. 1  above a foot structure when the upper portion of the tool has been pivoted; 
         FIG. 6  depicts a simplified plan view of the rear guide assembly of  FIG. 1  showing how the two pins provide stable support throughout pivoting of the upper portion of the tool of  FIG. 1  above a foot structure; 
         FIG. 7  depicts a partial rear plan view of the power tool of  FIG. 1  showing two offset guide slots in the shape of arcs in a rear guide assembly used to pivotally support the upper portion of the tool of  FIG. 1  above a foot structure when foot structure has been pivoted; 
         FIG. 8  depicts a simplified plan view of the rear guide assembly of  FIG. 1  showing how the two pins provide stable support throughout pivoting of the foot structure of the tool of  FIG. 1  below the upper portion of the tool; and 
         FIG. 9  depicts a partial rear plan view of a power tool showing two pins positioned within a single guide slot in the shape of an arc in a rear guide assembly used to pivotally support the upper portion of the tool above a foot structure. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings, and particularly  FIG. 1 , a circular saw  100  includes a motor housing  102 , a handle  104 , an auxiliary handle  106 , a foot structure  108 , and a blade housing  110  in which a saw blade  112  is located. A frame  114  supports a rotating blade guard  116  and a motor (not shown) located within the motor housing  102 . The motor (not shown) is controlled by a power trigger  118  extending from the handle  104 . 
     The foot structure  108  includes a lower surface  120  that is substantially planar (see  FIG. 2 ). The frame  114  is pivotally connected to the foot structure  108  by a front guide assembly  130  and a rear guide assembly  132 . The foot structure  108  is referred to herein as the “lower portion” of the power tool  100  while the remaining components of the power tool  100 , other than the front guide assembly  130  and the rear guide assembly  132 , are generally referred to as the “upper portion” of the power tool  100 . 
     The front guide assembly  130 , shown more clearly in  FIG. 2 , includes a guide plate  134  with two guide slots  136  and  138  formed in the shape of arcs. Pins  140  and  142  extend through the guide slots  136  and  138 , respectively. A locking mechanism  144  is associated with the pin  142 . The front guide assembly  130  and the rear guide assembly  132  are mirror images of each other with the exception of the locking mechanism  144 , which could be included in the rear guide assembly  132  if desired. Accordingly, while primarily the rear guide assembly  132  is described in fuller detail below, such description applies to the front guide assembly  130  which includes like components arranged in like configurations. 
       FIG. 3  depicts an exploded view of the rear guide assembly  132 . The rear guide assembly  132  includes a guide plate  150  with two guide slots  152  and  154  formed in the shape of arcs. The guide plate  150  is depicted in  FIG. 3  as separate from the foot structure  108 . When assembled, however, the guide plate  150  is fixedly connected to the foot structure  108  and may be integrally formed with the foot structure  108  if desired. 
     Two pins  156  and  158  extend through the guide slots  152  and  154 , respectively. The pins  156  and  158  are threadingly engaged with threaded bores  160  and  162  in a bracket  164 . If desired, a locking mechanism such as the locking mechanism  144  may be associated with one of the pins  156  and  158 . The bracket  164  is fixedly attached to the frame  114  using a bolt (not shown) which extends through a bolt hole  166 . 
     The guide slot  152  includes an upper wall  170  and a lower wall  172  which extend from the rear surface of the guide plate  150  to the front surface of the guide plate  150 . The upper wall  170  and the lower wall  172  are spaced apart by a distance that is substantially equal to the diameter of a shaft  174  of the pin  156 . The guide slot  154  includes an upper wall  178  and a lower wall  180 . The upper wall  178  and the lower wall  180  are spaced apart by a distance that is substantially equal to the diameter of a shaft  182  of the pin  158 . 
     As shown in  FIG. 4 , the guide slot  154  is formed along an arc having a radius  184  with an origin  186  that is located at the intersection of the plane defined by the bottom surface  120  of the foot structure  108  and the plane defined by the blade  112 . The guide slot  152  is formed along an arc having a radius  188  with an origin  190  that is collocated with the origin  186 . The guide slots  152  and  154  thus define a pivot axis  192  shown in  FIG. 1  that is located at the intersection of the plane defined by the bottom surface  120  of the foot structure  108  and the plane defined by the blade  112 . Accordingly, when the pins  156  and  158  ( 140  and  142 ) are received within the guide slots  152  and  154  ( 136  and  138 ), respectively, the upper portion of the power tool  100  can pivot about the pivot axis  192  with respect to the foot structure  108  as discussed more fully below. 
     Pivoting of the upper portion of the power tool  100  with respect to the foot structure  108  is accomplished by moving the locking mechanism  144  from the locked position to an unlocked position with the foot structure  108  positioned in a surface. In the embodiment of  FIG. 1 , this entails rotating the locking mechanism  144  in a counter clockwise direction from the horizontal position shown in  FIG. 1  to a vertical position. When the locking mechanism  144  is unlocked, the upper portion of the power tool  100  is supported by the foot structure  108  through the pins  140 , 142 ,  156  and  158  as explained with reference to  FIGS. 3 and 4 . 
     With reference to the rear guide assembly  132 , the weight of the upper portion of the power tool  100  is transferred by the bracket  164  to the pins  156  and  158 . In the configuration of  FIG. 4 , the pin  156  is nested against the left end of the guide slot  152  while the pin  158  is nested against the left end of the guide slot  154 . Accordingly, the downward force generated by the weight of the upper portion of the power tool  100  is passed to the lower wall  172  of the guide slot  152  and to the left end of the guide slot  154 . Similarly, the pins  140  and  142  and guide slots  136  and  138  provide support at the front of the power tool  100 . Thus, the upper portion of the power tool  100  is supported stably by the foot structure  108  through the front guide assembly  130  and the rear guide assembly  132  even though the locking mechanism  144  is unlocked. 
     The user then pivots the upper portion of the power tool  100  in a clockwise direction (as viewed in  FIG. 4 ) while maintaining the foot structure  108  supported on a surface until the desired angle is obtained between the plane defined by the bottom surface  120  of the foot structure  108  and the blade  112 , such as the angle depicted in  FIG. 5 . 
     Throughout the pivoting procedure, the upper portion of the power tool  100  is supported stably by the front guide assembly  130  and the rear guide assembly  132 . Specifically, the weight of the upper portion of the power tool  100  on the pins  140  and  158  will have a tendency to force the pins  140  and  158  toward the lower end of the guide slots  136  and  154 , respectively. Thus, if a user did not carefully balance movement of the front portion of the saw and the back portion of the saw during pivoting, one of the pins  140  or  158  would tend to lag behind the other of the pins  140  or  158  skewing the upper portion of the power tool  100  with respect to the foot structure  108 . 
     Any such skewing, however, is directly opposed by the pins  142  and  158 . The opposition to skewing is described with reference to  FIG. 6  which is a simplified view of the rear guide assembly  132 . In  FIG. 6 , the direction of a force from the upper portion of the tool  100  on the pin  158  tending to move the pin  158  within the guide slot  154  is depicted by the arrow  200 . Because the pin  158  and the pin  156  are both rigidly attached to the bracket  164 , the force applied to the pin  158  would also be applied to the pin  156  in the same direction as the arrow  200  as indicated by the arrow  202 . 
     Thus, while the pin  158  is free to move within the guide slot  154  in the direction of the arrow  200 , the lower wall  180  of the guide slot  154  precludes movement of the pin  156  in the direction of the arrow  202 . The same effect is realized at the front guide assembly  130 . Moreover, at angles between the angle depicted in  FIG. 4  and the angle depicted in  FIG. 5 , the pins  156  and  158  and guide slots  152  and  154  are configured such that lateral movement of either pin  156  or  158  within the respective guide slot  152  or  154  is directly opposed by the contact of the other of the pins  156  or  158  against the respective lower wall  172  or  180  of the respective guide slot  152  or  154 . Thus, regardless of the angle formed between the bottom  120  of the foot structure  108  and the blade  112 , the upper portion of the tool  100  is stably supported by the front guide assembly  130  and the rear guide assembly  132 . 
     The foregoing example describes pivoting of the upper portion of the tool  100  with respect to the foot structure  108 . In some circumstances, however, a user may hold the power tool  100  by the handle  104  and pivot the foot structure  108 . In such circumstances, the upper portion of the power tool  100  is used to support the foot structure  108  through the front guide assembly  130  and the rear guide assembly  132 . In this situation, the front guide assembly  130  and the rear guide assembly  132  also stably support the foot structure  108  as described below. 
     Pivoting of the foot structure  108  with respect to the upper portion of the power tool  100  is accomplished by moving the locking mechanism  144  from the locked position to an unlocked position as described above. Once the locking mechanism  144  is unlocked, the foot structure  108  is supported by the upper portion of the power tool  100  through the pins  140 , 142 ,  156  and  158  as explained with reference to  FIGS. 3 and 4 . 
     Specifically, the weight of the foot structure  108  is transferred by the pins  156  and  158  to the bracket  164 . In the configuration of  FIG. 4 , the pin  156  is nested against the left end of the guide slot  152  while the pin  158  is nested against the left end of the guide slot  154 . Accordingly, the downward force generated by the weight of the foot structure  108  will have a tendency to move the foot structure  108  downwardly away from the pins  156  and  158 . The guide slot  154  provides minimal resistance to such movement in the configuration of  FIG. 4 . The upper wall  170  of the guide slot  152 , however, is directly above the shaft  174  of the pin  156 . The same effect is realized at the front guide assembly with the pin  142  within the slot  138 . Accordingly, the foot structure  108  is stably supported at both the front portion and the rear portion. 
     The user then pivots the foot structure  108  in a counter-clockwise direction (as viewed in  FIG. 4 ) until the desired angle is obtained between the plane defined by the bottom surface  120  of the foot structure  108  and the blade  112 , such as the angle depicted in  FIG. 7 . Throughout the pivoting procedure, the foot structure  108  is supported stably by the front guide assembly  130  and the rear guide assembly  132 . Stable support of the foot structure  108  is described with reference to  FIG. 8 . 
       FIG. 8  is a simplified view of the rear guide assembly  132 . In  FIG. 8 , the direction of a force from the weight of the foot structure  108  is depicted by the arrow  204 . The weight of the foot structure  108  thus tends to pull the foot structure  108  downwardly from the pin  158  since the upper wall  178  of the guide slot  154  is not fully supported by the upper part of the shaft  182  of the pin  158 . The upper portion of the shaft  174  of the pin  156 , however, is in contact with the upper wall  170  of the guide slot  152 . Thus, while the pin  158  does not support the foot structure  108 , the pin  156 , along with the pin  142  of the front guide assembly  130 , provides support for the foot structure  108 . Moreover, at angles between the angle depicted in  FIG. 4  and the angle depicted in  FIG. 7 , the pins  156  and  158  and guide slots  152  and  154  are configured such that lateral movement of either pin  156  or  158  within the respective guide slot  152  or  154  is directly opposed by the contact of the other of the pins  156  or  158  against the respective upper wall  170  or  178  of the respective guide slot  152  or  154 . Thus, the foot structure  108  is supported stably by upper portion of the power tool  100  through the front guide assembly  130  and the rear guide assembly  132 . 
     The front guide assembly  130  and the rear guide assembly  132  thus provide stable support for the upper portion of the tool  100  as well as the foot structure  108  throughout the range of pivoting allowed by the span of the guide slots  136 ,  138 ,  152 , and  154 . Since the upper walls and lower walls provide support, depending upon the particular manner in which the upper portion of the power tool  100  and the foot structure  108  are pivoted, the width of the guide slots  136 ,  138 ,  152 , and  154  may be closely matched with the diameter of the shafts of the pins  140 ,  142 ,  156 , and  158 . In one embodiment, the shafts of the pins  140 ,  142 ,  156 , and  158  are in simultaneous sliding contact with both the upper and lower walls of the associated guide slots  136 ,  138 ,  152 , and  154  throughout the pivoting movement. Moreover, while the pins  140 ,  142 ,  156 , and  158  are depicted as including cylindrically shaped shafts, guides with other shapes may be used, so long as the guides can move along the associated guide slots  136 ,  138 ,  152 , and  154 . 
     In the embodiment of  FIG. 1 , the guide slots  136 ,  138 ,  152 , and  154  are offset with the radius  184  of the guide slots  136  and  154  longer than the radius  188  of the guide slots  138  and  152 . The increased radius on the side of the front guide assembly  130  and the rear guide assembly  132  closer to the motor provides a mechanical advantage since the center of mass for the upper portion of the tool  100  will generally be on the side of the front guide assembly  130  and the rear guide assembly  132  closer to the motor. If desired, however, the radius of the guide slots could be reversed. 
     Alternatively, more than one pin may be located in a guide slot. By way of example,  FIG. 9  depicts a tool  204  with a blade  206 , a foot structure  208 , and a guide assembly  210 . The guide assembly  210  includes a guide plate  212  with a single guide slot  214  and two pins  216  and  218 . The guide slot  214  is configured such that when the pin  216  is nested at the left end portion of the guide slot  214 , the foot support  208  is at a ninety degree angle with the blade  206 . The guide slot  214  is further configured such that when the pin  218  is nested at the right end portion of the guide slot  214 , the foot support  208  is at a maximum allowed angle with the blade  206 . 
     Even though the pins  216  and  218  are in a single guide slot  214 , the pins  216  and  218  are spaced apart along the guide slot  214  such that stable support is provided by the guide assembly  210  throughout pivoting. Additionally, the pin  218  is located on a plane defined by the blade  206  in the embodiment of  FIG. 9  with about ninety degrees of separation between the pins  216  and  218  along the arc of the guide slot  214 . In other embodiments, more than ninety degrees of separation may be provided between the pins  216  and  218 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.