Abstract:
A power tool having a depth adjustment mechanism includes a motor housing, a support base for supporting the motor housing, and a depth adjustment member coupled to the support base and movable between two positions. The depth adjustment member in a first position contacts a surface portion of the motor housing and in a second position is distanced from the surface portion of the motor housing such that the movement of the depth adjustment member from the first position to the second position is in a direction parallel to a plane that is substantially tangent to the surface portion of the motor housing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a power tool with means for adjusting the position of a tool bit relative to a support base. In particular it relates to convenient and inexpensive mechanism for switching between a fine and coarse depth adjustment mode in rotary tools such as routers, laminate trimmers, or drywall cutting tools. 
       BACKGROUND OF THE INVENTION 
       [0002]    A router, for example, typically has a base that contacts a work piece. A rotating tool bit is positioned relative to the base and cuts into the work piece. So as to increase the possible range of cuts that may be accommodated with a given tool bit as well as to permit the use of tool bits of different shapes and sizes, a router is conventionally provided with a depth adjustment mechanism. Fine depth adjustment is desirable for precision work, while coarse adjustment is desirable for changing bits or for doing deep cutting work. 
         [0003]    U.S. Pat. No. 7,275,900 discloses a router which incorporates an elevating mechanism comprising a worm drive that in one position cooperates with a rack assembly mounted to the motor housing to enable fine adjustment of the position of the motor housing relative to its support base. Rotation of an eccentric lever urges the worm drive out of contact with the rack assembly in order to enable coarse adjustment of the motor housing. 
       SUMMARY OF THE INVENTION 
       [0004]    A power tool having a depth adjustment mechanism is described comprising a motor having a motor housing, a support base for supporting the motor housing, and a depth adjustment member coupled to the support base and movable between two positions, wherein the depth adjustment member in a first position contacts a surface portion of the motor housing and in a second position is distanced from the surface portion of the motor housing. Movement of the depth adjustment member from the first position to the second position is in a direction parallel to a plane that is substantially tangent to the surface portion of the motor housing. This manner of moving the depth adjustment member away from the motor housing may be preferable to a mechanism that involves swinging or rotation, in so far as a user can actuate such a movement with a single finger or thumb while at the same time grasping the support base. Movement in a straight line requires little force and is a natural movement. 
         [0005]    The depth adjustment member may be a worm gear and the surface portion of the motor housing may comprise a plurality of teeth which are compatible with the worm gear. Such a worm and rack arrangement provides a convenient mechanism for fine adjustment and has the advantage that coarse adjustment is possible by moving the worm gear away from the plurality of teeth. 
         [0006]    A biasing means may be provided for biasing the depth adjustment member into the first position. As opposed to a mechanism that involves moving the depth adjustment member into a second, stable position, the biasing means requires active force to retain the depth adjustment member in the second position. When the force is released from the depth adjustment member, the biasing means returns it automatically to the first, engaged position. 
         [0007]    A conic spring may be provided for biasing the depth adjustment member into the first position. Such a biasing means has the advantage that it centers the carrier within the channel. Alternatively, such biasing may be accomplished via a pair of magnets that repel one another. Magnets have the advantage that they provide a long-lasting, non-mechanical biasing force that will not be damaged over the lifetime of the tool. 
         [0008]    The depth adjustment member may be rotatable with respect to a carrier that is configured for moving the depth adjustment member from the first to the second position. This has the advantage that a single piece (i.e., the carrier) can position and support as well as urge the depth adjustment member by translating the bias from the biasing means. 
         [0009]    The carrier may be positioned within a channel in the support base, wherein the channel has a plurality of channel walls. Such a channel has the advantage that it can provide a place for the carrier to remain associated with the support base, can provide features that properly position the carrier, and provide stability and guidance when the carrier is moved from the first to the second position. 
         [0010]    A first channel wall is may be moveable with respect to the channel and movement of said first channel wall may control a clamping mechanism for clamping the support base to the motor housing. The first channel wall may be pivoted to reveal the inner workings of the depth adjustment mechanism. This advantageously aids in assembly and simplifies reassembly should parts need to be replaced. The same feature beneficially has the dual function of also mediating the clamping mechanism. 
         [0011]    A portion of the carrier may extend through a second channel wall for allowing a user to move the carrier within the channel. Such an extension may be configured as a user-operable push button, which allows a user to conveniently manipulate the carrier even though it is positioned within the channel. 
         [0012]    A longitudinal slot may be provided on a third channel wall such that the longitudinal slot is used as means for guiding the movement of the carrier within the channel. This has the advantage of restricting movement of the carrier while at the same time allowing the worm gear to turn freely. Such positioning can be advantageously used to ensure that the worm gear will not contact the walls of the channel in a way that would impair its function. 
         [0013]    Adjustment means may extend through the longitudinal slot in the third channel wall for manipulating the depth adjustment member within the channel. Even though the depth adjustment member in the form of a worm gear is sealed within the cavity, convenient means for manipulating the worm gear may be provided outside of the channel in a place that provides convenient access to the user. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a front elevational view of a router in a fine adjustment position according to a first embodiment the present invention. 
           [0015]      FIG. 2  is a front elevational view of the router in a coarse adjustment position. 
           [0016]      FIG. 3  is a perspective view of a carrier which is a component of the depth adjustment mechanism. 
           [0017]      FIG. 4  is a bottom front perspective view of the router base in isolation. 
           [0018]      FIG. 5  is a front elevational view of a router base according to a second embodiment of the invention. 
           [0019]      FIG. 6  is a front elevational view of a router base according to a third embodiment of the invention. 
           [0020]      FIG. 7  is a perspective view of a carrier according to a third embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    A router  10  having a fixed support base  12  fixing the position of a motor unit  14  is shown in  FIG. 1 . So that the position of motor unit  14  relative to support base  12  can be manipulated, a depth adjustment mechanism  16  is provided. Motor unit  14  includes a motor housing  18  for enclosing a motor (not shown) and preferably a gear transmission (not shown) for respectively generating and modulating high speed rotation of an output shaft  20 . A tool bit (not shown) may be attached to output shaft  20  via various tool fixing means, such as collet nut  22 . Power to the motor is provided either with an electrical cord for drawing AC power or via an intrinsic or removable rechargeable DC battery. 
         [0022]    Support base  12  is further provided with handles  24  for guiding a substantially flat bottom surface  26  along a work piece. Alternatively, the router may inverted and secured to the underside of a conventional router table. In this case the router position is fixed and the user guides a workpiece across bottom surface  26 . The adjustment mechanism that will be subsequently described works irrespective of whether the router is upright or inverted or whether it is stationary or fixed in position. 
         [0023]    As will be described in detail, depth adjustment mechanism  16  may take on two configurations, one which facilitates fine adjustment (see  FIG. 1 ) and the other facilitating coarse adjustment (see  FIG. 2 ). A third configuration wherein neither fine nor coarse adjustment is possible is not illustrated, but will be described later. Fine adjustment is mediated by rotation of an adjustment knob  28  which is connected via worm shaft  30  to worm gear  32  associated with support base  12 . Worm gear  32  serves as a depth adjustment member that in its default position engages with a compatible toothed rack  34  which comprises a surface portion of motor housing  18 . Such adjustment is considered “fine” or “precision” adjustment, since one full rotation of adjustment knob  28  will move motor unit  14  only about 1/16″ (1.6 mm) up and down with respect to support base  12 . 
         [0024]    Toothed rack  34  is generally flat-shaped with numerous protruding teeth  36  (see  FIG. 2 ). 
         [0025]    Toothed rack  34  is preferably constructed separately from the remainder of the generally cylindrical motor housing  18  and fixed to it, either by being partially recessed into the motor housing  18  or not recessed so that it slightly protrudes from motor housing  18 . While it is generally flat-shaped, it may also be slightly arc-shaped so as to conform with the overall cylindrical shape of motor housing  18 . Toothed rack  34  may alternatively be an intrinsic part of motor housing  18 , with teeth  36  that are formed into motor housing  18 , for example during manufacture of the housing via a molding process. Whether it is flat or arc-shaped along its width, toothed rack  34  is substantially planar and defines a first generally planar surface from which teeth  36  protrude. Since the teeth are uniform in shape, the outermost portions of teeth  36  may be thought to lay on a second generally planar surface parallel to the first generally planar surface. 
         [0026]    A bracket  38  serves as a carrier for worm gear  32  (see  FIG. 3 ). Bracket  38  includes two mounting apertures  40  for supporting and allowing worm shaft  30  and therefore worm gear  32  to rotate. Bracket  38  can be moved from the default position (see  FIG. 1 ) wherein worm gear  32  engages toothed rack  34  to a displaced position (see  FIG. 2 ) wherein worm gear  32  is distanced from toothed rack  34 . In this displaced position, coarse depth adjustment is possible, since a user is able to slide motor unit  14  with respect to support base  12 . This is referred to as “coarse”, “rough” or “fast” adjustment since motor unit  14  can be rapidly moved several inches (for example, around 5 cm) relative to support base  12 . 
         [0027]    Biasing means, such as coil spring  42 , urges bracket  38  into the default position. Bracket  36  is confined to a channel  44  formed within a portion of support base  12 . Channel  44  is largely defined by end channel walls  46  and  48  as well as top channel wall  50  and bottom channel wall  52 . Coil spring  42  is preferably a conic spring and it is retained in position by having the larger part of the cone shape retained snugly within channel  44  via rear channel wall  54  and retaining protrusion  56  which extends from channel wall  46 . The smaller aspect of the cone shape of coil spring  42  mates with a protrusion  58  on bracket  38  and is oriented so as to urge bracket  38  away from channel wall  46 . Due to the conic shape of the spring, the bracket is centered within cavity  44 . A push button  60  extends through channel wall  48  at the opposite end of channel  44  (see  FIG. 1 ). This permits a user to manually urge bracket  36  in a direction opposite the biasing force of coil spring  42  (see  FIG. 2 ). 
         [0028]    In order to further support and limit the travel of bracket  38  within channel  44 , top channel wall  50  is provided with a guide slot  62  and bottom channel wall  52  is provided with guide slot  63  through which worm shaft  30  extends. An end portion of worm shaft  30  that extends through guide slot is attached to an adjustment knob  28  (see  FIG. 4 ) which slides generally along the top surface of top channel wall  50 . 
         [0029]    Access to channel  44  is provided by a front channel wall  64  that is configured like a swinging door. Front channel wall  64  acts also as a cam lever with respect to a pin clamp  66  that is configured to either separate or bring together flanges  68  and  70  of support base. This comprises a depth locking mechanism. When channel wall  64  is in the open configuration (see  FIG. 4 ), flanges  68  and  70  are separated, thereby allowing either fine or coarse depth adjustment. When channel wall  64  is in the closed configuration (not shown) pin clamp  66  acts to bring flanges  68  and  70  close together so that support base  12  clamps motor housing  18  of motor unit  14  into a fixed position wherein no depth adjustment is possible. 
         [0030]    In  FIG. 5 , an alternative, but entirely analogous embodiment for the support base is shown. As such, the same numbering scheme is used, but with the addition of an “a” after the number to indicate the feature is from the alternative embodiment of  FIG. 5 . Notably, the orientation of bracket  38   a  within channel  44   a  has been reversed. Further differences in details are illustrated in  FIG. 5  but not described in detail here. 
         [0031]    A further alternative embodiment which is more substantially different from the initial embodiment is shown in  FIGS. 6 and 7 . Once again, the same numbering scheme is used for common elements, but in this cased followed by a “b”. In this embodiment, the biasing force on bracket  38   b  is provided by magnetic repulsion. Permanent magnet  72  is mounted onto bracket  38   b  in cavity  74  and a second permanent magnet  76  is fixed in position within channel  44   b.  The magnet pair is chosen so that the two magnets  72  and  76  repel one another, thereby urging bracket  38   b  into the default position as with the first embodiment. In order to retain permanent magnet  72  in cavity  74 , a flexible snap-fit arm  78  is provided on bracket  38   b.  Other features of bracket  38   b,  such as push button  60   b  and apertures  40   b  are comparable to those in the initial embodiment. 
         [0032]    It is foreseen that an alternative configuration using magnets that attract one another could also be used to retain bracket  38   b  in the default position, but this is less desirable since the user would either need to pull at the bracket rather than push, or a push button would need to be devised that was configured to not interfere with the magnet pair and still permit a pushing motion.