Abstract:
A fixed base router with an adjustable depth of cut comprising a motor unit including a first threads and an output spindle, a router bit operatively connected to the output spindle of the motor unit, an adjustment ring including a second threads for cooperation with the first threads of the motor unit for adjustment of the depth of cut of the router bit, a base for supporting the adjustment ring, and a plurality of clip assemblies for selectably coupling the adjustment ring to the base assembly, and wherein the clip assemblies are simultaneously operable by the fingers of one hand of the person using the router.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of power tools. In particular the present invention relates to a depth of cut adjustment arrangement for a router. More particularly, it relates to a router depth of cut adjustment employing a threaded ring. 
     2. Discussion 
     Various types of power tools comprise a cutting tool or bit that is raised or lowered relative to a base that rests on or against the workpiece. Often the tool or bit is attached to the output shaft of a motor unit that can be vertically or axially moved relative to the base. Movement of the motor unit and attached tool bit relative to the base unit determines the depth of cut into the workpiece. 
     Routers, including some laminate trimmers, are constructed according to this basic design. The router bit is attached to the motor output spindle by means of a tool holder such as a collet or chuck and the bit projects through an opening in the base to contact the workpiece. The motor unit is mounted to the base by means that allow the operator to move the motor and bit axially relative to the base in order to determine the depth of cut of the bit. 
     Router base and depth of cut systems fall into two commonly recognized categories. They are plunge base routers and fixed base routers (including so-called D-handle bases). Generally speaking, plunge routers comprise a generally planer base element, a motor unit, and a plurality of support columns on which the motor unit is vertically movably mounted above the base. Usually, the motor unit is biased upward or away from the base. Means are provided for finely adjusting the depth of cut and for locking the motor unit at the selected depth/height against the biasing force. 
     Fixed base routers usually comprise a generally cylindrical base and a motor unit with a cylindrical housing portion. The cylindrical portion of the motor housing fits snugly but movably within an annulus of the cylindrical portion of the base with the motor spindle and router bit projecting downward beyond the lowest portion of the base. The cylindrical portion of the base often includes a longitudinal or axial cut or gap that permits the base diameter to expand or contract slightly under the force of a clamp mechanism that bridges the gap and that can be used to tighten the base onto the motor housing within. Means for adjusting the depth of cut by adjusting the vertical or axial position of the motor unit and bit within the base are also provided. The base clamp is loosened for adjusting the cutting depth and after the desired depth is set with the depth adjusting means the base clamp is tightened to lock the motor housing at the set position. 
     One known means for adjusting the depth of cut in a fixed base router employs a rack and pinion arrangement. A toothed rack is attached in the axial direction on the exterior of the motor housing while a pinion is attached to the base so as to engage the pinion. Means, such as a knob, are provided for the operator to turn the pinion. Turning of the pinion drives the rack and the attached motor and bit. See for example U.S. Pat. No. 3,466,973 to Rees. 
     Another well known means for adjusting the depth of cut consists essentially of providing threads on the exterior of the motor unit and matching threads on the base assembly. Screwing the motor unit into and out of the base assembly raises and lowers the motor and cutter like a nut in a bolt. See for example U.S. Pat. No. 1,899,833 to Sacrey and U.S. Pat. No. 2,562,143 to Godfrey et al. Among several disadvantages of this means for adjusting the depth of the router is that the rotation of the router power head within the base assembly is problematic due to the presence of the power cord connected to the motor, which tangles or interferes with the rotation of the motor unit. 
     A refinement on the threaded motor unit concept is the replacement of a fully threaded base with a threaded ring or nut rotatably mounted on the base element. In such a mechanism, the ring can be manually rotated to raise and lower the power head relative to the base element without relative rotation between the motor unit and base element. See for example U.S. Pat. No. 2,988,199 to Godfrey et al. In some embodiments according to this concept means are provided to restrain the motor from turning within the base. These restraining means can take the form of an axial groove within the annulus of the base that is slideably engaged by a stud or projection on the exterior surface of the motor housing or vice versa. The engagement of the projection and the groove prevents the motor housing from turning within the base. 
     In some of these ring designs the ring merely rests atop the base element. This presents a problem, however, if the router is inverted. When inverted, the ring and the motor unit will tend to fall out of the base element unless the base clamp, if provided, has been sufficiently tightened to hold the motor by compression. When a router is mounted upside down in a router table, it is necessary to loosen the base clamp to adjust the depth of cut, then, unless additional connecting structure is provided, the problem remains of the motor and ring falling out of the router base. 
     In a further refinement, the ring can be rotatably connected with the base element so that it can retain and raise or lower the power head even when inverted. See U.S. Pat. No. 2,842,173 to Turner and U.S. Pat. No. 5,613,813 to Winchester et al. A disadvantage of a ring that is permanently axially connected to the base is that it prevents quick removal of the motor unit. Instead the motor must be unscrewed from the ring and base assembly—usually requiring numerous turns of the ring to fully raise and free the motor housing. Quick and easy removal of the motor unit is desirable for convenient access to the motor spindle and collet/chuck when changing router bits. The inability of a fixed ring to quickly release the motor forces design choices between steep thread pitches of approximately 2 inches per revolution or greater, which can lower and raise and free the motor quickly, and fine thread pitches of approximately ½ inch per revolution or less, which provide greater depth control, but require numerous turns to raise and free the motor. 
     In another variation, the Porter-Cable Model 310 laminate trimmer employs a ring that is held axially atop the cylindrical base by means of a pair of steel leaf spring clips. See FIG.  13 . Th clips  140  are mounted to the exterior of the base  120  and engage a v-shaped circumferential groove  136  around the outer side of the depth adjustment ring  130 . So constructed, the ring  130  is axially secured to the base  120 , but the motor using  114  and ring can be quickly detached and removed from the base. 
     Due to their small size, sharp edges, orientation and stiffness, the thin steel leaf spring clips  140  of the Porter-Cable Model 310 are extremely difficult to manipulate and do not appear to have been designed with the intention that the tool user actually operate them with his fingers. In practice, the Model 310 motor  114  is removed from the base  120  by a pull on the motor sufficient to overcome the compression force of the clips  140  engaged in the ring groove  136 . Thus, the leaf spring clips  140  act rather as a mere detent mechanism that the motor  114  and ring  130  can be pushed in and pulled out of with only modest force. After adjustment of the depth a cut the base is tightened on the motor with a base clamp, as described above. 
     Laminate trimmers are essentially, however, very small routers. The motors of laminate trimmers are of less than one horsepower and usually draw less than 5 amps. Such small motors usually weigh less than five pounds. Furthermore, laminate trimmers are not usually used inverted and are not intended for mounting upside down in router tables. For such small lightweight routers that are infrequently inverted, the Model 310 clips provide satisfactory retention of the ring and motor with convenience of removal. 
     Regular, fixed based, wood working routers, however, have motors of approximately 1 to 3 or more horsepower, draw 5 to 10 or more amps, and weigh 5 or more pounds. Construction professionals and woodworking hobbyists frequently use such routers upside down and want to be able to mount them inverted under a router table for prolonged periods. The Model 310 ring system, however, does not scale up well to retain and operate these larger and heavier motors. The leaf spring clips do not exert sufficient compressive force to hold the ring and heavy motors against the force of gravity and the occasional shock. Moreover, as mentioned above, the size, sharp edges, orientation and stiffness of the Model 310 leaf springs clips make them difficult to manipulate, so that in practice the motor and ring are pulled out of the base with the clips serving as a detent. Furthermore, the structure of the Model 310 clips do not permit the user to loosen the clips with one hand while grasping the motor or base with his or her other hand. 
     SUMMARY OF THE INVENTION 
     It is, therefore, one object of the invention to provide a tool with an axial depth of cut adjustment arrangement that both securely retains the motor unit in the base when inverted, but also provides for quick and convenient release of the motor from the base. 
     It is another object of the invention to provide a retaining mechanism with exposed and graspable elements that will permit the tool user to release the motor from the base by operation of those elements with one hand. 
     It is still another object of the invention to provide a fixed base router with a threaded depth adjustment ring that can be selectably detachable from the router base. 
     This and other objects of the invention are attained by a fixed base router, with a height adjustment ring that is in turn removably attached to the base by a manually operable clip. The clip is large enough and resilient enough to retain the motor unit of a large router when inverted and can be manually released. 
     Because of the provision of a convenient mechanism for release of the motor from the base, another object of the invention is the identification of thread pitch for the motor housing and depth adjustment ring that provides an optimal compromise between fine and accurate depth control and quick and convenient gross adjustment depth adjustment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiments that make reference to the drawings of which: 
     FIG. 1 is an exterior perspective view of a power tool selectably detachable depth adjustment ring according to the present invention. 
     FIG. 2 is an exterior perspective view of the motor unit of the power tool of FIG.  1 . 
     FIG. 3 is an exterior side view of the base assembly of the power tool of FIG.  1 . 
     FIG. 4 is an axial cross-section view of a portion of the base and depth adjustment ring of the power tool of FIG.  1 . 
     FIG. 5 is an axial cross-section view of the depth adjustment ring of the power tool of FIG.  1 . 
     FIG. 6 is an exterior side view of the depth adjustment ring of the power tool of FIG.  1 . 
     FIG. 7 is an axial cross section view of the base, depth adjustment ring, and clip assembly portions of the power tool of FIG.  1 . 
     FIG. 8 is an exterior side view of the base, depth adjustment ring, and clip assembly portions of the power tool of FIG.  1 . 
     FIG. 9 is an expanded cross section view of the base, depth adjustment ring, and clip assembly portions of the power tool of FIG.  7 . 
     FIG. 10 is a further expanded cross section view of the base, depth adjustment ring, and clip assembly portions of the power tool of FIG.  7 . 
     FIG. 11 is an exterior side view of the clip lever of the power tool of FIG.  1 . 
     FIG. 12 is a top view of an alternative embodiment of the base and clip assembly in accordance with the present invention. 
     FIG. 13 is an axial cross-section view of the depth adjustment and retention portions of a prior art power tool. 
    
    
     DETAILED DESCRIPTION 
     The present invention provides a depth adjustment mechanism for a power tool. More particularly it provides a depth adjustment mechanism for a power tool wherein a motor unit is axially movable within a base element. While shown through the drawings in various embodiments of a fixed base router, those skilled in the art will appreciate that the invention is not so limited in scope. In this regard, the teachings of the present invention will be understood to be readily adaptable for use in any tool incorporating a motor housing axially movable in a base assembly by means of rotatable ring element threadably engaged with the motor housing. 
     Turning generally to the drawings in which identical or equivalent elements have been denoted with like reference numerals, and particularly to FIGS. 1,  2 , and  3  a power tool is illustrated and designated with the reference numeral  1 . The particular power tool shown is, for example, a fixed base router  1  including a motor unit  10 , a base assembly  20 , and a depth of cut adjustment ring  30 . 
     The motor unit  10  contains an electric motor (not shown) in a housing comprising a head portion  13  and a cylindrical portion  14 . The motor is powered through a cord  11  and controlled by a switch  12 . Projecting from the bottom of the motor unit  10  is the motor spindle  18  on the end of which is located a collet  4  of the well known kinds. Motor housing cylindrical portion  14  has exterior threads  16  that engage the depth of cut adjustment ring  30 . Motor cylindrical portion  14  also includes an exterior and axially oriented longitudinal slot  17  that serves to prevent rotation between the motor unit  10  and the base  20  by engaging with a stud (not shown) in the interior of the base. 
     The base assembly  20  includes handles  2 , and an upper portion  21 . Upper portion  21  is generally cylindrical in shape and is split by an axial gap  7  that permits expansion or contraction of the upper portion under the influence of clamp  6 , which is constructed and operates in a well known manner. Upper portion  21  defines a generally cylindrical annulus which is sized to accommodate the cylindrical portion  14  of the motor housing such that when the clamp  6  is released the motor  10  may slide easily within the base  20 , and when the clamp  6  is closed/engaged the cylindrical portion  14  is firmly and nonslidably gripped within the upper portion  21  of the base. 
     A depth adjustment ring  30  is connected to the top portion  21  of base  20  by means that will be described in detail below. With reference to the attached FIGS. 4,  5  and  6  the lower portion  34  of height adjustment ring  30  rests on a shelf  24  inside the upper lip  22  of the base  20 . The outer face of ring  30  also defines a circumferential groove  36  including a first surface  36 A substantially perpendicular to the axis of the ring. An upper portion  35  of ring  30  includes ribs  37  to provide an improved gripping surface for turning the ring. The inner face of ring  30  includes a thread  32 . Due to the selectably detachable feature of the depth adjustment ring according to the present invention, the need for a steep screw pitch that can quickly raise and lower the motor for ease of installation/removal is eliminated. Therefore, a pitch more optimally compromised between course and fine depth adjustment can be selected. Preferably, a screw pitch is employed that will raise or lower the motor unit  10  approximately 1 inch per rotation of the depth adjustment ring  30 . 
     Referring now to FIGS. 7,  8 , and  9 , mounted on the base  20  are at least two clip assemblies  40 . The clip assemblies include a lever  44  that is pivotably mounted to the base  20 . A lip  42 , including a second surface  42 A, on each of the levers  44  selectably and slidably engages the ring groove  36  at first surface  36 A and axially retains the ring  30  on the shelf  24  and inside the upper lip  22  of the base  20 . Alternatively, the clips assemblies could be mounted on the ring and slidably engage a groove on the base. 
     With additional reference to FIGS. 10 and 11, the clip assemblies  40  also include a pin  46  and a spring  48 . As depicted the levers  44  are pivotably mounted to the base  20  in cutouts  26  in the upper portion  21  of the base  20 , including the lip  22 . Pin  46  passes through a hole or ears  47  in lever  44  and engages holes  28  in the base  20 . Lever  44  pivots around or with pin  46 . Alternatively, lever  44  could be pivotably connected to the base  20  by means of studs rotatingly captured in holes in the base. 
     Spring  48  is depicted as a leaf spring, but could also include a coil spring around pin  46 , a suitably located compression spring, or other known spring types and configurations. Spring  48  biases pivoting lever  44  into a clamped position, wherein lip  42  engages with the ring groove  36 . Spring  48  acts between the base  20  and the inside of the lever  44  to force the lower portion of the lever outward and the upper portion inward against the ring  30 . The lower portion of the lever  44  constitutes a tab  45  that can be pressed with the operator&#39;s fingers in order to move the lever  44  to a released position. In the released position the lip  42  of the lever  44  is retracted from the groove  36 , so that the ring  30  and motor unit  10  may be removed from the base  20 . 
     Preferably router  1  includes two clip assemblies  40  located at positions around the upper circumference of base  20  such as to adequately grip and retain the ring  30  and also to be simultaneously operable by the fingers of one hand, for example the thumb and forefinger. In order to retain the ring  30  to the base  20  it is not necessary that the clips  40  be directly opposite each other, that is they need not be 180° apart around the circumference of the base. As shown in FIG. 12, the clips  40  can be spaced apart by less than 180°, for example by approximately 145°, in one direction and still adequately secure the ring  30  to the base  20 . The option to shorten the angular separation between the two clips  40  can allow one hand to span the distance between the clips even on larger diameter routers. It also provides design flexibility to relocate a clip or clips if required by the presence of other structural elements. 
     While the above description constitutes a preferred embodiment of the invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the accompanying claims.