Abstract:
An undercut saw including a motor, a drive shaft rotated by the motor, a blade mount mechanically linked to the drive shaft, the blade mount allowing a saw blade to be mounted and a fixed blade guard circumscribing a portion of the saw blade. The fixed blade guard includes a top plate and a height adjustment skirt in telescoping attachment joined by fasteners. A guide washer including a guide washer slot runner is configured to move up and down in a slot on the height adjustment skirt.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. provisional application No. 61/035,704, filed Mar. 11, 2008. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to power tools and more specifically to power tools for installation of flooring. 
       BACKGROUND ART 
       [0003]    An undercut saw is a specialty circular power saw used by flooring installers for undercutting walls, moldings, door jams, and cabinetry so that new floors may be installed underneath. When the area is undercut using the saw, the new flooring is simply slid underneath the undercut area, which saves time and presents a visually appealing finish. Without an undercut saw, the flooring should be precisely cut to fit around these areas, which is laborious, costly, and often leaves unsightly gaps. 
         [0004]    Most existing undercut saws have been constructed with a fixed blade guard assembly which consists of two telescoping parts that serve both as a blade guard and a height adjustment mechanism for the saw. As shown in  FIG. 1 , existing undercut saw  100  has a fixed blade guard assembly  120  consisting of a first top plate  140  and a second height adjustment skirt  160 . Top plate  140  is fixedly joined to a rotary power unit  180  (commonly circular saw or grinder based power units). When movable guard  200  is retracted, the front of the top plate  140  preferably covers less than 180 degrees of the circular saw blade  220  so the saw  100  can operate in tight areas, such as inside corners. The back of the top plate  140  has a downwardly protruding back edge  240  which is typically semi-circular so that it can be precisely machined to a controlled outside diameter. The downwardly protruding back edge  240  of the top plate  140  mates with an inner surface  260  formed in the height adjustment skirt  160  which is also semi-circular. These two mating semi-circular parts may telescope up and down creating a height adjustment mechanism for existing undercut saw  100 , while also providing a fixed blade guard assembly  120  surrounding the back of the blade  220 . Base  450  is an integral part of height adjustment skirt  160 . The bottom surface  451  of the base  450  forms the surface upon which the saw is placed while in use on a floor surface. 
         [0005]    There are practical considerations of this existing height adjusting mechanism with respect to the fasteners used to hold the telescoping members at a desired height. The following is a history of various fastener combinations that have been used. In existing early model undercut saws, the fasteners used were carriage bolts socketed into square holes in the downwardly protruding back edge  240  of the top plate  140 . The carriage bolts extending from the back of the top plate passed through slots in the height adjustment skirt forming threaded ends for mounting additional fasteners. First mounted on these threaded ends were so-called “guide washers”, which were specialized cast shapes designed to move within channels formed on a back surface of the height adjustment skirt. Last mounted on these threaded ends were wing nuts which were tightened down on the guide washers. The clamping force generated by the wing nuts pressured the guide washer against an outer surface of the height adjustment skirt, while the downwardly protruding back edge of the top plate was drawn against the inner surface of the height adjustment skirt by the pulling action of the carriage bolt. This clamping force frictionally held the top plate at a desired height within the height adjustment skirt. 
         [0006]    In some more recent existing saws, one of which is shown in  FIG. 1 , the fasteners consisted of two threaded wing screws  280  which fastened into two tapped holes  300  in the downwardly protruding back edge  240  of top plate  140 . Spring  340  and washer  360  were also mounted on wing screw  280  ahead of guide washer  320 . Spring  340  and washer  360  pressure guide washer  320  against the curved outer surface  305  of the height adjustment skirt  160  within an outer guide washer channel  380 . Thus, even when a wing screw  280  is loosened, pressure from the spring keeps the guide washer in its channel, providing at least some stability and guidance for the assembly during the adjustment process. 
         [0007]    Existing guide washers have typically been generally trapezoidal cast shapes with a semi-circular inside surface  315  that precisely mates with the curved outer surface  305  within guide washer channel  380  of the height adjustment skirt  160 . Two or three guide washers along with two or three sets of the aforementioned fasteners have been used on existing saws. 
         [0008]    Since the rotary power unit  180  and rotatable circular saw blade  220  are fixedly assembled onto top plate  140 , the height at which top plate  140  is frictionally held by the fasteners determines the height of cut. The top plate  140  may be frictionally held at any point in a vertical range of about one inch within the height adjustment skirt  160 . This enables the height of cut for circular saw blade  220  to be set from floor level (i.e., flush to the floor or no height of cut) to a height of one inch above floor level. 
         [0009]    The characteristics of these guide washer and fastener mechanisms for these existing height adjustment mechanisms are as follows: First, the guide washers sometimes do not frictionally hold the assembly together with sufficient force, and the top plate can shift within the height adjustment skirt as the saw is being used. Particularly as the user lifts and places the saw at various locations around a jobsite, the weight of the saw motor can cause the top plate to slip downward within the height adjustment skirt. As a result, in some places the undercut is not of sufficient height, and the user has to re-adjust and re-cut many areas. 
         [0010]    Another characteristic of the existing fastening mechanisms and guide washers is that they do little to ensure that the top plate (and thereby the blade) is always parallel with the flat floor surface on which the saw rests during use. The blade should be kept parallel to the floor during undercutting so that the blade will not angle up or down in relation to the floor during a cutting operation. Keeping the blade parallel with the floor surface ensures that the height of undercut will be consistent. Otherwise, angling of the blade may cause the blade to wedge upward or downward. This can result in inconsistent height of cut. Angling of the blade can also bog down the motor during a cutting operation, or even cause the saw to kick back. An improved height adjustment mechanism that worked to prevent the top plate from being set at angles that are not parallel to the floor could prevent undesirable inconsistencies in the height of cut, and would promote safer usage by reducing the possibility of saw kickback. 
         [0011]    The use of such existing telescoping height adjustment mechanisms fastened with guide washers and threaded fasteners was preferred for simplicity and low cost. However, various different mechanisms for setting and holding the height of cut for an undercut saw have been designed to address slippage and blade angling during use. Such designs have largely not been adopted because they were impractical for jobsite conditions or too expensive to manufacture. For example, U.S. Pat. No. 5,784,789 to Vargas discloses an undercut saw with a rack-and-pinion mechanism for height adjustment. The undercut saw of this disclosure employs a grinder based power unit. A circular saw blade is mounted onto its spindle. A cylindrical sleeve is mounted to the grinder motor to cover the rotating spindle. The sleeve has a rack formed in its back side. The sleeve is assembled into a base. The base holds the pinion. Thus, as the pinion is turned, the rack on the sleeve causes the power unit and blade to move up or down. The rack and pinion design ensures that blade will move up and down in a precise manner that keeps the blade parallel with the floor at all times. Two screws threaded through the base may contact the sleeve to fix the sleeve at a given height. The rack and pinion mechanism of saw proved too expensive for mass production, and was prone to binding from saw dust. As a result, it was not widely adopted. 
         [0012]    U.S. Pat. No. 6,678,960 to Williams discloses an undercut saw with a housing which rests on a floor surface and itself has a fixed height. A tapped sleeve is mounted on top of the housing. A rotary motor with a central axis and a threaded case may be threaded into the tapped sleeve. The blade when mounted on the central motor armature axis may be moved up and down within the housing as the threaded case is turned within the tapped sleeve. The height is fixed by means of a jam nut also threaded onto the threaded case. This threaded adjustment mechanism ensures that the blade will be kept parallel to the floor at all times. The tapped sleeve and large threads on the motor housing of this design proved too expensive for mass production. This mechanism was also prone to binding from saw dust. Furthermore, the requirement that the blade be mounted on a central armature axis about which the entire assembly turned required that only motors such as routers having a single, central armature axis (without any offset spindle gear) could be employed. Such high RPM low torque motors are not powerful enough for large amounts of undercut sawing. In particular, a great deal of power is used by a saw to undercut an inside corner area. Williams&#39; saw as disclosed could not perform such cuts, due to its bulky blade housing. 
         [0013]    Other mechanisms for fixing the height of cut are disclosed within this application, including rack-and-pinion, frictional, interlocking, and lead screw mechanisms. With regard to Williams&#39; lead screw mechanism, this is shown in  FIG. 9  of Williams. Williams describes the mechanism as a “jack screw”  160  rotatably fastened onto an outer sleeve  63  on two bosses  151 . When a knob  155  is turned, a teeter  161  having a lead nut  160  may be raised or lowered. Teeter  161  has an arm  162  with a thin end  67  which may pass through a slot through the case and engage a cavity  37  in the case  30 . Spring  166  biases teeter into cavity  37 . However, a separate tightening clamp  76  may close down the diameter of sleeve  63  to frictionally hold the case. 
         [0014]    A lead screw mechanism such as Williams&#39; “jack screw” generally requires a secondary holding mechanism besides the lead screw to hold the mechanism in position. Otherwise, an accidental bump on the lead screw knob or even vibration during use can cause the mechanism to shift unexpectedly. For Williams, the separate frictional mechanism of clamp  76  provides such a secondary holding mechanism. 
         [0015]    Williams&#39; jack screw design presents many manufacturing challenges that make it cost prohibitive. Much as with the threaded case of the embodiment previously discussed, Williams jack screw embodiment has a specialized motor housing having a precisely shaped outer “case” capable of sliding within a sleeve. This is not preferred as most commonly available power units come in the shape of a grinder or circular saw, and such power units have no such precisely shaped case. Furthermore, the tightening clamp used to frictionally hold the case within the sleeve is a large, tight tolerance slide fit mechanism which would entail high machining cost to produce. A lead screw mechanism which did not engage the case of the power unit would be preferred as just about any power unit could be employed. 
         [0016]    A lead screw mechanism that worked in conjunction with existing low cost guide washers and fastener assemblies could provide additional support for the existing telescoping top plate and height adjustment skirt at a much lower cost. Such would be preferred as a low cost mechanism to provide the benefits of reduced slippage and angling of the blade. Williams teaches that “peripheral studs” (carriage bolt or wing screw fastener assemblies) or “wing nuts”, are “slow because several fasteners require adjustment” (Background of the Invention, paragraph 3). 
         [0017]    Some existing undercut saws have been manufactured with a grinder motor as a power unit. As shown in  FIG. 2 , grinder motor  370  has a first axis of rotation  375  (long armature axis) operatively coupled to a perpendicular second axis of rotation  385  (spindle axis). A first handle  380  and switch  400  are typically located towards the back of the saw. A spindle housing  420  is typically located at the front of the saw. Spindle housing  420  is typically made out of aluminum, which is suitable for mounting a second, forward, movable handle for controlling the front of the saw. 
         [0018]    Existing grinders typically have a second handle formed in the shape of a threaded post fastenable into tapped holes on either side of the aluminum spindle housing. Such threaded posts extend out quite a distance from either side of the spindle housing, which is preferred during a grinding operation to provide counter leverage for the user. However, such a handle assembly is not suitable for use in undercut saws. The extension of the handle prevents the saw from entering tight areas, such as inside corners. 
         [0019]    For this reason, as shown in  FIG. 2 , existing undercut saws have been made with a narrow, plastic, U-shaped handle such as handle  440  for their second, forward, movable handle. U-shaped handle  440  is bolted into tapped holes  500  on both sides of spindle housing  420  with bolts  480  and lock washers  460 . U-shaped handle  440  is preferably narrower than the width of top plate  140  below so that it does not prevent the saw from undercutting in tight areas, such as inside corners. 
         [0020]    The use of bolts  480  and lock washers  460  to bolt a second, forward, movable handle, such as U-shaped handle  440 , to spindle housing  420  is preferred for simplicity and low cost. The user can tighten down the bolts  480 , and the lock washers  460  tend to hold the handle in place. The handle  440  can also be rotated backward (i.e., towards the first, back handle  380 ) whenever the saw is used to undercut in a low clearance area, such as underneath the toe-space of a cabinet. 
         [0021]    However, if the user pushes excessively hard on U-shaped handle  440 , it can rotate forward (towards blade  220 ). This is not preferred as this puts the user&#39;s hand in closer proximity to blade  220 . Forward rotation is also not preferred, because whenever the handle is oriented at such an angle, the saw is less able to operate in tight areas, such as inside corners. Some added mechanism to prevent the forward handle of the saw from rotating forward from the normally preferred 90 degree angle would be a usability and safety improvement. A more solid handle and better mounts on the spindle housing could provide such an improvement. However, as previously explained, this handle should also be able to rotate backward for undercutting beneath a toe-space. 
         [0022]    An undercut saw is primarily used to undercut walls, door jams, and cabinet areas so that new flooring materials may be fit underneath. Some flooring materials are very thin, such as sheet vinyl or linoleum. To provide the proper undercut for thin sheet vinyl, the undercut saw should cut flush to the floor. For this reason, in most existing saws, as shown in  FIG. 3  (a bottom view of an existing undercut saw), fixed blade guard assembly  120  (comprised of top plate  140 , and height adjustment skirt  160 ) and movable guard  200  are both open on the bottom. This allows the blade height to be adjusted as close to the floor as possible. However, the undercut saw is not always used to undercut flush to the floor. In many cases, such as for ceramic tile or hardwood plank flooring, the undercut is made higher, because the flooring material to be installed is thicker. In such cases, additional guarding structures may be added to increase safety. Such structures may be removably mounted onto the components comprising the fixed blade guard, or the movable blade guard, to cover more of the blade when the saw is not being used for undercutting to fit thin materials, such as sheet vinyl. 
         [0023]    It is an object to provide an undercut saw with an improved mechanism for guiding the telescoping motion of the top plate and the height adjustment skirt so that during height adjustment the top plate tends to stay parallel with the base of the saw, thereby keeping the blade parallel to the floor surface upon which it is placed during use. 
         [0024]    It is an object to provide an undercut saw with an improved mechanism for holding a top plate at a fixed elevation within a height adjustment skirt which is economical enough for mass production. 
         [0025]    It is an object to provide an undercut saw with an improved handle fastening mechanism which may be more rigidly fixed to the spindle housing of a grinder motor, which may be adjusted to various angles, but stopped from certain angles that are not preferred. 
         [0026]    It is an object to provide an undercut saw with additional safety mechanisms which may be removably mounted to the fixed and movable guards. 
       SUMMARY 
       [0027]    The device has several embodiments including an undercut saw with a fixed guard assembly comprising a telescoping top plate and height adjustment skirt, with some embodiments including improved guide washers including an added guide washer slot runner. Certain other embodiments include a lead screw mechanism threaded vertically through the guide washer to assist in setting and holding a height of cut. In certain other embodiments having a right angle grinder motor for their power unit, the saw includes a handle with a pattern of teeth encircling a hole in the handle for mounting the handle to the saw&#39;s spindle housing. In addition, a similar pattern of interlocking teeth is formed at a handle mount location on at least one side of the saw&#39;s spindle housing. The teeth on the handle and the spindle housing may thus interlock to allow the handle to be fixedly joined at a range of preferred angles. The handle and the spindle housing may additionally include certain bosses acting as stops to prevent the handle from being rotated forward to certain angles which are not preferred. Certain other embodiments include removable cover plates covering the blade to increase safety which may be removed to enable the saw to cut flush to a floor surface. 
         [0028]    The improved guide washer may incorporate any one of several added features. The first feature, which will be described herein as a “guide washer slot runner”, is a boss or projection extending from the inner surface of the guide washer. This projection is sufficiently long and has a precise width to extend (with a small degree of play) into its corresponding slot in the height adjustment skirt. In existing saws, the slots in the height adjustment skirt served only to allow passage of the bolts extending through the guide washers to fasten into the downwardly protruding back edge of the top plate. The added guide washer slot runner extends into and may contact the edges of the slots in the height adjustment skirt to guide the telescoping motion of the top plate and the height adjustment skirt during adjustment. This helps keep the base of the height adjustment skirt parallel to the top plate. This helps ensure that the top plate will be adjusted in a manner that keeps the blade parallel to the floor surface. 
         [0029]    The guide washer may include an additional tapped hole through a vertical cross section, for receiving an added threaded member. This threaded member may be rotatably fastened on the base of the saw&#39;s height adjustment skirt using a collar or other nut type fastener. This threaded member thus forms a lead screw mechanism capable of lifting or lowering the guide washer (and thereby the top plate and blade). Such a lead screw mechanism may be included on one or more guide washers in the assembly, though it is preferred they be used on all such guide washers. This is so the height of cut can be adjusted incrementally on all sides through equal turns of all threaded members. The threaded members provide added support to hold the desired height of cut and prevent slippage. The guide washers may still include the existing fasteners such as wing screws threading into the downwardly protruding back edge of the top plate to provide a second frictional mechanism to hold the height of cut. 
         [0030]    In embodiments including a grinder motor for a power unit, the second, forward, movable handle may be affixed to the spindle housing with corresponding circular patterns of interlocking teeth on one or more sides of the handle and the spindle housing. In one embodiment, a two piece handle assembly is provided, made in two halves joined by a pivot pin. The pivoting action of the halves allow the assembly to be closed or opened to enable interlocking or disengagement of the circular tooth patterns on the handle and the spindle housing. When these circular tooth patterns are interlocked, a secure joint is produced between the components preventing unexpected rotation during use. The handle may be pivoted open for adjustment backward to a number of angles to enable the saw to be used in low clearance areas, such as under toe spaces. Added stops on the handle and the spindle housing prevent the handle from rotating to forward angles (acute angles less than 90 degrees) in relation to the long armature axis of the saw. 
         [0031]    For improved guarding, removable cover plates may be added to the bottom of the downwardly protruding back edge of the top plate, the bottom surface of the height adjustment skirt, or the movable guard. These cover plates may be removed to enable flush cutting when installing thin flooring materials, such as sheet vinyl. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a side perspective view of an existing undercut saw showing existing guide washers and guide washer mounting hardware such as wing screws. 
           [0033]      FIG. 2  is perspective view of an existing undercut saw using a grinder motor as a power unit and an existing U-shaped handle mounted to the spindle housing using bolts and lock washers. 
           [0034]      FIG. 3  is a bottom perspective view of an existing undercut saw showing how the fixed guard assembly and movable guards are open at bottom to enable flush cutting. 
           [0035]      FIG. 4  is a side view of an undercut saw including an improved guide washer having an added guide washer slot runner. 
           [0036]      FIG. 5  is a perspective view of an improved, two-part pivoting handle for an undercut saw with a circular pattern of teeth which can be interlocked with a corresponding pattern of teeth on the spindle housing. 
           [0037]      FIG. 6  is a bottom view of an undercut saw showing a removable cover plate mounted on the base of the height adjustment skirt, and a removable cover plate on the movable blade guard. 
           [0038]      FIG. 7  shows a removable cover plate mounted on the bottom of the downwardly protruding back edge of the top plate. 
           [0039]      FIG. 8  is a side perspective view of an undercut saw including an improved guide washer with guide washer slot runner and additionally including a threaded member threading through a vertically tapped hole in the guide washer forming a lead screw mechanism. 
           [0040]      FIG. 9  is a top view of the undercut saw showing the preferred locations where the two guide washer assemblies may be fastened through the height adjustment skirt and into tapped holes in the downwardly protruding back edge of the top plate. 
           [0041]      FIG. 10  is a perspective view of a guide washer including the added guide washer slot runner. 
           [0042]      FIG. 11  is a side view of an assembled undercut saw having a grinder motor for its power unit showing two preferred angles in the orientation of the forward handle. 
           [0043]      FIG. 12  is a top view of an undercut saw showing preferred locations of two lead screw mechanisms. 
           [0044]      FIG. 13  is a perspective view of a shoulder pan head screw. 
           [0045]      FIG. 14  shows a section view of an undercut saw showing how a shoulder pan head screw may be rotatably mounted to the base using a hex nut. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    As shown in  FIG. 4 , undercut saw  2000  has a fixed blade guard assembly  2120  which consists of two parts: a first top plate  2140  and a second height adjustment skirt  2160 . A rotary power unit  2180  is fixedly attached to top plate  2140 . In the illustrated embodiment, the power unit is a grinder motor. However, other embodiments may include other types of power units attached to the top plate, including circular saw or router type power units. Blade  2220  is mounted on the spindle of rotary power unit  2180  using a blade mount (not shown) which keeps it parallel to a substantially flat top face  2130  of top plate  2140 . 
         [0047]    Top plate  2140  has a downwardly protruding back edge  2240  which forms a semi-circular vertical edge surface. Height adjustment skirt  2160  has an inside face  2260  which also forms a corresponding semi circular vertical edge surface. The downwardly protruding back edge  2240  of top plate  2140  and inside face  2260  of height adjustment skirt  2160  together form precisely mating telescoping surfaces. Base  2450  is an integral part of height adjustment skirt  2160 . Base  2450  has a bottom surface  2451  which is the surface upon which the saw rests or is moved while in use. 
         [0048]    To fix the height of top plate  2140  in relation to base  2450 , top plate  2140  has a tapped hole  2300  which is centered in the location of a corresponding slot  2310  in height adjustment skirt  2160 . Wing screw  2280  extends through a horizontal hole  2325  in guide washer  2320  and is threaded into tapped hole  2300  in downwardly protruding back edge  2240  of top plate  2140 . Guide washer  2320  has an added guide washer slot runner  2330 . As shown in greater detail in  FIG. 10 , guide washer  2320  includes a guide washer slot runner  2330  having a width  2335  slightly narrower than slot  2310  ( FIG. 4 ) in height adjustment skirt  2160  ( FIG. 4 ). This is so it can enter this slot with a slight amount of play. Guide washer slot runner  2330  has a length  2337  long enough to enter slot  2310  ( FIG. 4 ). In a preferred embodiment, as shown in  FIG. 4 , guide washer slot runner  2330  is long enough that, once wing screw  2280  is tightened down on the outer surface of the guide washer, guide washer slot runner  2330  contacts surface  2347  (on downwardly protruding back edge  2240  of top plate  2140 —exposed within slot  2310 ). As shown in  FIG. 10 , guide washer  2320  includes radial shaped faces  2339 ,  2341  designed to rest flush against a corresponding radially-shaped vertical face  2343  ( FIG. 4 ) of guide washer channel  2345  ( FIG. 4 ). These large corresponding contact surfaces are used to apply and control frictional holding force between the components. As shown in  FIG. 4 , spring  2340  along with washer  2360  may be mounted on wing screw  2280  ahead of guide washer  2320 . 
         [0049]    In this embodiment, guide washer slot runner  2330  runs in a slot  2310  to guide the motion of height adjustment skirt  2160  during height adjustment. Others skilled in the art might imagine similar combinations of slots through the height adjustment skirt and bosses (guide washer slot runners) on an inner face of the guide washer which could run in the slots to perform the same function. Such may include multiple slots in the outer face of the height adjustment skirt, for multiple guide washer slot runners on an inner face of the guide washer. One such slot may be the slot provided for passage of a fastener used to fasten the top plate within the height adjustment skirt. Alternatively, the slot may have no other function than for receiving the boss forming a guide washer slot runner. The slot itself may be a slot or a groove of only partial depth in the outer surface of the height adjustment skirt performing the same function of receiving a slot runner. However, the embodiment of  FIG. 4  is preferred. Multiple slots weaken height adjustment skirt  2160 , making it prone to breakage if the undercut saw  2000  is dropped. A single, central guide washer slot runner running within a single slot centers and controls the assembly on a single vertical axis. Multiple axes would require tight tolerances on a larger number of surfaces, adding unnecessary expense. 
         [0050]    In this embodiment, when height adjustment is performed, normally the saw is turned upside down and rested on the second, forward, movable handle (as shown as undercut saw  100  of  FIG. 3 ). Afterwards, wing screw  2280  is loosened, and the height adjustment skirt  2160  is free to telescope up or down. Guide washer slot runner  2330  remains in slot  2310  and is pressed up against downwardly protruding back edge  2240  due to pressure from spring  2340 . As height adjustment skirt  2160  is moved up or down, the outer edges of guide washer slot runner  2330  guide its motion through contact with the inside edges of slot  2310 . This guidance ensures that the height adjustment skirt will be guided up or down in a substantially vertical direction. Top plate  2140  thus tends to stay parallel to base  2450 . Thus, the blade will be kept parallel to the base during adjustment. When the desired height is set, wing screw  2280  may be tightened down on guide washer  2330 , pressing it against the inner surface of guide washer channel  2345  of height adjustment skirt  2160 , and in turn drawing the downwardly protruding back edge  2240  of top plate  2140  against inside face  2260  of height adjustment skirt  2160 . This clamping pressure on the components frictionally holds the desired height of cut. 
         [0051]    As used herein, and as shown in  FIG. 4 , the term “guide washer fastener assembly” includes at least one threaded fastener (such as wing screw  2280 ). The guide washer fastener assembly is used in conjunction with a guide washer, but the guide washer itself is considered a separate element. In one embodiment, the guide washer fastener assembly includes only wing screw  2280 . In a preferred embodiment, the guide washer fastener assembly additionally includes a washer  2360  installed first on the wing screw  2280 , followed by a spring  2340 . In some embodiments, one or more guide washer fastener assemblies may be included, used in conjunction with one or more guide washers. However, in one embodiment, such as shown in  FIG. 9 , only two such guide washer fastener assemblies  6000 ,  6200  are included, (comprising wing screw  2280 , washer  2360 , and spring  2340 ). Guide washer fastener assemblies  6000 ,  6200  are used in conjunction with two guide washers  2320 ,  2321 . The use of only two such fastener assemblies with two guide washers provides ample clamping force on both sides of fixed blade guard assembly, yet leaves room for other saw features, such as dust port  6300 . Persons skilled in the art may envision the use of other fastener combinations which may be used to form a guide washer fastener assembly. For example, another embodiment of a guide washer fastener assembly may include carriage bolts and wing nuts used in conjunction with guide washers, as has been described in existing references. 
         [0052]    As shown in  FIG. 4 , wing screw  2280  along with tapped hole  2300  work to generate clamping force to frictionally hold the downwardly protruding back edge  2240  of the top plate  2140  against the inner surface  2260  of height adjustment skirt  2160 . This holds the height of the top plate  2140  relative to the bottom surface  2451  of base  2450  of height adjustment skirt  2160 . Since the rotary power unit  2180  and rotatable circular saw blade  2220  are fixedly assembled onto top plate  2140  when the saw is assembled, the height of the top plate  2140  determines the height of cut. The top plate  2140  may be adjusted and frictionally held in a vertical range of about one inch within the height adjustment skirt  2160 . This enables the height of cut for circular saw blade  2220  to be set from floor level (i.e., flush to the floor or no height of cut) to a height of one inch above floor level. In this embodiment, the added guide washer slot runner guides the motion of the height adjustment skirt to help ensure that the blade will be kept parallel to a floor surface. This prevents angling of the blade. However, the frictional holding mechanism of this embodiment may not be sufficient to hold a desired height of cut. Additional support mechanisms may be added to hold a desired height of cut. 
         [0053]    As shown in  FIG. 8 , additional support mechanisms may be added by including an added vertical tapped hole in the body of the guide washer, which in conjunction with an added threaded member may form a lead screw mechanism capable of raising or lowering the guide washers (and thereby the top plate and blade). Undercut saw  8000  includes a guide washer  8020  including a tapped hole  8040 . A threaded member such as pan head screw  8060  is inserted through a hole  8080  in the base  8100  of height adjustment skirt  8120 . Hole  8080  may be countersunk on its bottom side (not shown) such that the pan head  8061  of pan head screw  8060  sockets flush within the countersink. Thus, base  8100  will be a uniform flat surface on its bottom side  8101 , which will not catch on floor surface irregularities. 
         [0054]    Once inserted in hole  8080 , pan head screw  8060  extends vertically up from base  8100  and may be threaded into tapped hole  8040  in guide washer  8020 . Next, collar  8210  is fastened onto pan head screw  8060  at an elevation forming a slight gap between the bottom of collar  8210  and a top surface  8260  of base  8100 . This gap enables pan head screw  8060  to rotate within hole  8080 . (More secure, lower cost alternatives exist for pan head screw  8060  and collar  8210  will be described later.) Finally, for ease of turning, a knob such as three arm knob  8140  may be fastened on top of pan head screw  8060 . 
         [0055]    The lead screw mechanism formed by a threaded member such as pan head screw  8060  and tapped hole  8040  may be included in one or more of the guide washers included in the fixed guard assembly for the saw. As shown in  FIG. 12 , in this embodiment, two lead screw mechanisms  12020 ,  12040  are used. A single lead screw mechanism would not evenly lift both sides of the top plate  12060 . With two such mechanisms  12020 ,  12040 , the user may use both hands to turn the two knobs each by equal amounts of turn, resulting in uniform level height adjustment. Furthermore, two such mechanisms  12020 ,  12040  provide adequate support for top plate  12060  during use of the saw. With three or more such mechanisms, each knob would have to be turned separately, which is cumbersome. 
         [0056]    In addition to the added lead screw mechanism supporting the height of the guide washer, the guide washer may also include additional frictional mechanisms to further assist in holding the desired height of cut. As shown in  FIG. 8 , as previously described, such a frictional mechanism may include a guide washer fastener assembly (such as wing screw  8160 , washer  8180 , and spring  8200  threading into tapped hole  8220  of the downwardly protruding back edge  8280  of top plate  8240 ). This guide washer fastener assembly works in conjunction with guide washer  8020  to frictionally hold a desired height of cut. The addition of this frictional mechanism is preferred because the lead screw mechanism alone may slip due to vibration or accidental bumping of one of the knobs. 
         [0057]    In this embodiment as shown in  FIG. 8 , the process of height adjustment is somewhat different. First, the user loosens wing screw  8160 , reducing the frictional hold. However, since pan head screw  8060  is threaded through tapped hole  8040  in guide washer  8020 , top plate  8240  is held at that elevation until three arm knob  8140  is turned. If three arm knob  8140  is turned clockwise, pan head screw  8060  will be turned clockwise, thereby raising guide washer  8020  and top plate  8240  to a higher elevation above base plate  8100 . If three arm knob  8140  is turned counter-clockwise, guide washer  8020  and top plate  8240  will be lowered. When the desired height is set, wing screw  8160  may again be tightened, and top plate  8240  and height adjustment skirt  8100  will additionally become frictionally held at the desired elevation. 
         [0058]    In embodiments including both this type of lead screw mechanism as well as a guide washer fastener assembly for frictional holding force (such as wing screw  8160 ), the guide washer preferably includes a guide washer slot runner such as guide washer slot runner  8025 . In such an embodiment, guide washer slot runner  8025  performs a different function in that it prevents guide washer  8020  from rotating when lifting force is applied by pan head screw  8060 . The reason such rotation is generated and is not preferred is as follows: Tapped hole  8040  for pan head screw  8060  is offset at least some distance from through hole  8300  for passage of wing screw  8160  through guide washer  8020 . Otherwise, these components would interfere with each other and not perform their desired function. With this offset, in the absence of guide washer slot runner  8025 , pan head screw  8060  would lift guide washer  8020  on one side, causing it to rotate on wing screw  8160 . An added feature on guide washer  8020  resists such rotation. An added guide washer slot runner  8025  can bear against the inner edges of slot  8290  during adjustment, thus preventing such undesirable rotation. Therefore, in such an embodiment, guide washer slot runner  8025  performs an important, though somewhat different function. 
         [0059]    As previously explained, pan head screw  8060  is rotatably affixed to base  8100  of height adjustment skirt  8120  by collar  8210 . Collar  8210  is affixed to pan head screw  8060  at a slight elevation above a surface  8260  on a top face of base  8100  forming a slight gap that permits such rotation. However, when the saw is lifted off the floor, collar  8210  performs the additional function of stopping pan head screw from sliding through countersunk hole  8080  through base  8100 . Collar  8210  is affixed to pan head screw  8060  by means of a set screw  8211  which may be tightened down on the threads of pan head screw  8060  at the desired height. However, collar  8210  is an expensive custom component with a set screw  8211  which may come loose and cause the assembly to fail. 
         [0060]    As shown in  FIG. 13 , an alternative pan head screw such as shoulder pan head screw  13000  may be used that includes a shoulder  13020 . Shoulder  13020  spaces a standard hex nut such as hex nut  13040  at a desired height allowing shoulder pan head screw  13000  to rotate within its hole.  FIG. 14  shows a partial section A-A of the area of base  14100  near the countersunk hole for a shoulder pan head screw  14020 . As shown in section A-A, shoulder  14040  of shoulder pan head screw  14020  supports a common hex nut  14060  at a height above a top surface  14080  of base  14100 . Thus, hex nut  14060  can be tightened down firmly on shoulder  14040  with reduced concern for coming loose compared with collar  8210  ( FIG. 8 ). Hex nut  14060  is also less expensive than collar  8210  ( FIG. 8 ). Thus, for two reasons, shoulder pan head screw  14020  and hex nut  14060  are preferred. However, as shown in  FIG. 14 , the insertion of either type of pan head screw within a countersunk hole (such as countersunk hole  14160 ) results in a flush surface such as  14140  on the bottom side of the base of the height adjustment skirt. A flush surface is preferred so that the bottom side of the base will not hang up on floor surface irregularities. Hex socket  14180  allows shoulder pan head screw  14020  to be turned with a hex wrench from the bottom if desired. 
         [0061]    During height adjustment, as shown in  FIG. 14 , graduations  14200  may be etched on an outer surface on either side of height adjustment skirt  14120 . These graduations indicate the height of the circular saw blade  14220  by its relation to a flush bottom edge  14240  of the downwardly protruding back edge  14260  of the top plate  14280 . This is because the flush bottom edge  14240  is in the same flush plane with circular saw blade  14220  (covered in this view by movable guard  14210 ). Before performing an undercutting operation, the user may check on both front sides of the height adjustment skirt  14120  that the flush bottom edge  14240  of top plate  14280  is at the same graduation. This ensures that the blade is not angled in relation to a flat floor surface upon which the saw is to be placed. 
         [0062]    As defined herein, for the embodiments of  FIG. 8  or  14 , or any embodiments including a lead screw mechanism to support a top plate, the lead screw component (such as pan head screw  8060  of  FIG. 8 , or shoulder pan head screw  13000  of  FIG. 13 , or shoulder pan head screw  14020  of  FIG. 14 ) will be referred to as a lead threaded member. Furthermore, the fastener used to fasten the threaded member to the base of the height adjustment skirt (such as collar  8210  of  FIG. 8 , hex nut  13040  of  FIG. 13 , or hex nut  14060  of  FIG. 14 ) will be defined as a lead threaded member holding fastener. A guide washer including a threaded hole (such as tapped hole  8040 ) in guide washer  8020  of  FIG. 8  will be referred to as a lead guide washer. 
         [0063]    To provide an improved handle for grinder-activated undercut saws, the second, forward, movable handle may be formed from two parts joined by a pivot pin. A toothed surface may be formed on at least one inside surface of a handle which may interlock with a corresponding toothed surface formed on an outer surface of the grinder motor spindle housing. As with existing saws of this kind, and as shown in  FIG. 5 , undercut saw  3100  is made with a grinder motor  3180  having a first long horizontal armature axis  3170  and a second spindle axis  3190 . On one end of the long armature axis, a first rearward handle  3390  with a switch  3400  forms the back end of the saw. On the other end, an aluminum spindle housing  3420  forms the front end and houses the spindle. The spindle (not shown) is operatively coupled to the armature (not shown) at a substantially right angle. A circular saw blade  3220  is mounted on the spindle on a blade mount (not shown). Spindle housing  3420  is fixedly joined to top plate  3140 . Top plate  3140  and height adjustment skirt  3160  form a fixed guard assembly  3120  for the undercut saw. A spring-loaded movable guard  3200  covers circular saw blade  3220  and is retractable in the counter-clockwise direction to start a cutting operation. 
         [0064]    The improved handle for the saw is formed from a first, left half  3460 , a second, right half  3480 , and an upper pivot pin  3500 . Left half  3460  is overlapped at relief  3520  with relief  3540  in right half  3480 . Pivot pin  3500  is press fit into upper hole  3580  in right half  3480  and through upper hole  3560  in left half  3460  to join the two halves. Thus, the two halves may be pivoted closed to enable interlocking of the circular tooth patterns on the handle and the spindle housing, or pivoted open to permit disengagement or disassembly. This assembly of the left half  3460  and right half  3480  with pivot pin  3500  may be referred to as handle assembly  3510 . 
         [0065]    Left half  3460  and right half  3480  have circular tooth patterns  3600  and  3620  (respectively) formed on their inside surfaces which may engage corresponding circular tooth patterns  3640 ,  3660  on the left and right hand sides of spindle housing  3420  (respectively). Threaded four arm screws  3680 ,  3700  may be inserted through left mounting hole  3720  in left half  3460  and right mounting hole  3740  in right half  3480  (respectively). Threaded four arm screws  3680 ,  3700  may further thread into a tapped left mounting hole  3760  and tapped right mounting hole  3780  to join handle assembly  3510  to spindle housing  3420 . 
         [0066]    The circular tooth patterns  3600 ,  3620  of left half  3460  and right half  3480  are designed to interlock with corresponding circular tooth patterns  3640 ,  3660  in the left and right sides of spindle housing  3420  and will provide a fixed and solid joint when they are pressed together by threaded four arm screws  3680 ,  3700 . Because these teeth patterns are circular, handle assembly  3510  may interlock and become fixedly joined to spindle housing  3420  at a number of angles. As more clearly illustrated in  FIG. 11 , for general undercutting, it is preferred that handle assembly  11000  be oriented at a right angle A perpendicular to the long armature axis  11020  of grinder motor  11040 . This provides comfortable knuckle clearance and firm grip. However, when undercutting in low clearance areas, such as underneath toe spaces, it is preferred that the handle be angled back or at an angle greater than a right angle in relation to a forward projection of the long armature axis of the saw, such as angle B. However, it is further preferred that handle assembly  11000  be restricted from being set or moving unexpectedly to any angle which is less than a right angle in relation to a forward projection of the long armature axis  11020  of the saw. Any such acute angle places the hand unnecessarily close to blade  11060 , and could also cause the handle to extend beyond the front edge of top plate  11080 . Such is not preferred, as that would prevent the saw from operating in tight areas, such as inside corners. 
         [0067]    As shown in  FIG. 5 , others skilled in the art will envision alternative fasteners to fasten a second, forward, movable handle, such as handle assembly  3510 , to an undercut saw spindle housing, such as spindle housing  3420 . For example, rather than four arm screws  3680 , threaded rods may be threaded into tapped left mounting hole  3760  and tapped right mounting hole  3780 . Threaded nuts having tapped holes may be threaded onto the ends of the threaded rods. The use of such threaded rods would make it more difficult for the user to remove the handle and use the saw without a handle. Any such fasteners used to fasten a handle or handle assembly to a spindle housing will be referred to herein as handle fastening fasteners. Handle fastening fasteners may include a single fastener or a combination of fasteners combining for this purpose. 
         [0068]    As shown in  FIG. 5 , to prevent handle assembly  3510  from moving or being set at any such acute angle in relation to a forward projection of the long armature axis of the saw, left half  3460  and right half  3480  include bosses  3800 ,  3820 . When handle assembly  3510  is joined to spindle housing  3420  at a right angle to long armature axis  3170 , bosses  3800 ,  3820  come in close proximity to left and right flats  3840 ,  3860  of spindle housing  3420 . In this embodiment, if handle assembly  3510  is rotated forward to an acute angle in relation to the long armature axis  3170 , bosses  3800 ,  3820  will contact left and right flats  3840 ,  3860 . This interference causes handle assembly  3510  to tip forward, displacing the teeth and preventing them from interlocking. Hence, the handle cannot be mounted on the spindle housing at such an angle. In other embodiments with a freely pivoting handle assembly, bosses  3800 ,  3820  may contact left and right flats  3840 ,  3860  to stop the handle from being rotated forward to any such acute angle. 
         [0069]    Left half  3460  and right half  3480  may be economically produced as aluminum castings and will easily handle much greater pushing force than existing U-shaped undercut saw handles fastened by lock washers and bolts. A flexible rubber coating such as plastisol may be added to form a softer, slip-resistant gripping surface on the outer surface of handle assembly  3510 . 
         [0070]    To add removable guarding structures to the bottom portion of the fixed guard of the undercut saw, removable cover plates may be added to any of the height adjustment skirt, movable guard, or top plate. Such removable cover plates may be positioned so as to cover at least a portion of the circumference of the blade past the depth of the teeth. As shown in  FIG. 6 , undercut saw  6100  has a height adjustment skirt  4160  having a base  4450 . An additional flush mounted removable cover plate  4820  may be screwed to base  4450  using screws  4800 . Cover plate  4820  covers blade  4810  past the depth of the teeth. In addition, movable guard  4840  may cover the blade  4810  past the depth of the teeth with its own removable plate  4860  fastened to movable guard  4840  as by screws  4880 . 
         [0071]    As defined herein, in relation to cover plates which may cover the blade, the phrase “past the depth of the teeth” shall describe a cover forming a radius as measured from the center of the circular saw blade which is shorter than a radial distance to the outermost circumference of the circular saw blade. For example, cover plate  4820  mounted on base  4450  covers blade  4810  to a radius alpha (in relation to the center of the circular saw blade  4810 ). Radius alpha is a shorter radius than radius delta to the outer circumference of the circular saw blade  4810 . Similarly, cover plate  4860  mounted on movable guard  4840  covers blade  4810  to a radius beta (in relation to the center of the circular saw blade  4810 ). Radius beta is a shorter radius than radius delta. 
         [0072]    In an another embodiment, as shown in  FIG. 7 , a cover plate  5120  may be removably mounted on a bottom edge of the downwardly protruding back edge  5240  of the top plate  5140  using screws  5800 , rather than on the base  5450  of height adjustment skirt  5160 . Cover plate  5120  covers blade  5820  past the depth of the teeth. Cover plate  5120  covers blade  5820  to a radius epsilon. Radius epsilon is a shorter radius than radius delta (the outer circumference of the circular saw blade  5820 ). 
         [0073]    It will be apparent that various alternatives may be implemented. The Detailed Description discloses a number of additional features, any one of which may be added alone or in any combination to an undercut saw to improve saw design. The handle features and the blade height features may be used separately or together. Although  FIG. 4  illustrates a grinder type saw, the embodiments and features may easily be adapted to other undercut saw configurations, including a circular saw type configuration. The materials, dimensions and positioning are purely exemplary, and numerous alternatives exist. In  FIGS. 1-3 , existing saws are shown, including one having a dust port. The present embodiments and features may be adapted to such saws, to undercut saws having stabilizing features. The handle may be adapted to a number of different tools, some of which are not undercut saws. The improvements to the telescoping height adjustment skirt could be implemented on any tool having a telescoping height adjustment skirts. These are some exemplary alternatives; this is not an exhaustive list of the alternatives that are possible with the present invention.