Undercut saw height adjustment, handle, blade guard improvements

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 with a fastener assembly is configured to move up and down in a slot on the height adjustment skirt. Turning a lead threaded member raises and lowers the top plate.

TECHNICAL FIELD

The invention relates to power tools and more specifically to power tools for installation of flooring.

BACKGROUND ART

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.

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 inFIG. 1, existing undercut saw100has a fixed blade guard assembly120consisting of a first top plate140and a second height adjustment skirt160. Top plate140is fixedly joined to a rotary power unit180(commonly circular saw or grinder based power units). When movable guard200is retracted, the front of the top plate140preferably covers less than 180 degrees of the circular saw blade220so the saw100can operate in tight areas, such as inside corners. The back of the top plate140has a downwardly protruding back edge240which is typically semi-circular so that it can be precisely machined to a controlled outside diameter. The downwardly protruding back edge240of the top plate140mates with an inner surface260formed in the height adjustment skirt160which is also semi-circular. These two mating semi-circular parts may telescope up and down creating a height adjustment mechanism for existing undercut saw100, while also providing a fixed blade guard assembly120surrounding the back of the blade220. Base450is an integral part of height adjustment skirt160. The bottom surface451of the base450forms the surface upon which the saw is placed while in use on a floor surface.

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 edge240of the top plate140. 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.

In some more recent existing saws, one of which is shown inFIG. 1, the fasteners consisted of two threaded wing screws280which fastened into two tapped holes300in the downwardly protruding back edge240of top plate140. Spring340and washer360were also mounted on wing screw280ahead of guide washer320. Spring340and washer360pressure guide washer320against the curved outer surface305of the height adjustment skirt160within an outer guide washer channel380. Thus, even when a wing screw280is 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.

Existing guide washers have typically been generally trapezoidal cast shapes with a semi-circular inside surface315that precisely mates with the curved outer surface305within guide washer channel380of the height adjustment skirt160. Two or three guide washers along with two or three sets of the aforementioned fasteners have been used on existing saws.

Since the rotary power unit180and rotatable circular saw blade220are fixedly assembled onto top plate140, the height at which top plate140is frictionally held by the fasteners determines the height of cut. The top plate140may be frictionally held at any point in a vertical range of about one inch within the height adjustment skirt160. This enables the height of cut for circular saw blade220to 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.

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.

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.

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.

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' saw as disclosed could not perform such cuts, due to its bulky blade housing.

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' lead screw mechanism, this is shown in FIG. 9 of Williams. Williams describes the mechanism as a “jack screw”160rotatably fastened onto an outer sleeve63on two bosses151. When a knob155is turned, a teeter161having a lead nut160may be raised or lowered. Teeter161has an arm162with a thin end67which may pass through a slot through the case and engage a cavity37in the case30. Spring166biases teeter into cavity37. However, a separate tightening clamp76may close down the diameter of sleeve63to frictionally hold the case.

A lead screw mechanism such as Williams' “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 clamp76provides such a secondary holding mechanism.

Williams' 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.

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).

Some existing undercut saws have been manufactured with a grinder motor as a power unit. As shown inFIG. 2, grinder motor370has a first axis of rotation375(long armature axis) operatively coupled to a perpendicular second axis of rotation385(spindle axis). A first handle380and switch400are typically located towards the back of the saw. A spindle housing420is typically located at the front of the saw. Spindle housing420is typically made out of aluminum, which is suitable for mounting a second, forward, movable handle for controlling the front of the saw.

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.

For this reason, as shown inFIG. 2, existing undercut saws have been made with a narrow, plastic, U-shaped handle such as handle440for their second, forward, movable handle. U-shaped handle440is bolted into tapped holes500on both sides of spindle housing420with bolts480and lock washers460. U-shaped handle440is preferably narrower than the width of top plate140below so that it does not prevent the saw from undercutting in tight areas, such as inside corners.

The use of bolts480and lock washers460to bolt a second, forward, movable handle, such as U-shaped handle440, to spindle housing420is preferred for simplicity and low cost. The user can tighten down the bolts480, and the lock washers460tend to hold the handle in place. The handle440can also be rotated backward (i.e., towards the first, back handle380) whenever the saw is used to undercut in a low clearance area, such as underneath the toe-space of a cabinet.

However, if the user pushes excessively hard on U-shaped handle440, it can rotate forward (towards blade220). This is not preferred as this puts the user's hand in closer proximity to blade220. 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.

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 inFIG. 3(a bottom view of an existing undercut saw), fixed blade guard assembly120(comprised of top plate140, and height adjustment skirt160) and movable guard200are 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.

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.

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.

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.

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

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'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'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.

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.

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'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.

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.

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.

DETAILED DESCRIPTION

As shown inFIG. 4, undercut saw2000has a fixed blade guard assembly2120which consists of two parts: a first top plate2140and a second height adjustment skirt2160. A rotary power unit2180is fixedly attached to top plate2140. 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. Blade2220is mounted on the spindle of rotary power unit2180using a blade mount (not shown) which keeps it parallel to a substantially flat top face2130of top plate2140.

Top plate2140has a downwardly protruding back edge2240which forms a semi-circular vertical edge surface. Height adjustment skirt2160has an inside face2260which also forms a corresponding semi circular vertical edge surface. The downwardly protruding back edge2240of top plate2140and inside face2260of height adjustment skirt2160together form precisely mating telescoping surfaces. Base2450is an integral part of height adjustment skirt2160. Base2450has a bottom surface2451which is the surface upon which the saw rests or is moved while in use.

To fix the height of top plate2140in relation to base2450, top plate2140has a tapped hole2300which is centered in the location of a corresponding slot2310in height adjustment skirt2160. Wing screw2280extends through a horizontal hole2325in guide washer2320and is threaded into tapped hole2300in downwardly protruding back edge2240of top plate2140. Guide washer2320has an added guide washer slot runner2330. As shown in greater detail inFIG. 10, guide washer2320includes a guide washer slot runner2330having a width2335slightly narrower than slot2310(FIG. 4) in height adjustment skirt2160(FIG. 4). This is so it can enter this slot with a slight amount of play. Guide washer slot runner2330has a length2337long enough to enter slot2310(FIG. 4). In a preferred embodiment, as shown inFIG. 4, guide washer slot runner2330is long enough that, once wing screw2280is tightened down on the outer surface of the guide washer, guide washer slot runner2330contacts surface2347(on downwardly protruding back edge2240of top plate2140—exposed within slot2310). As shown inFIG. 10, guide washer2320includes radial shaped faces2339,2341designed to rest flush against a corresponding radially-shaped vertical face2343(FIG. 4) of guide washer channel2345(FIG. 4). These large corresponding contact surfaces are used to apply and control frictional holding force between the components. As shown inFIG. 4, spring2340along with washer2360may be mounted on wing screw2280ahead of guide washer2320.

In this embodiment, guide washer slot runner2330runs in a slot2310to guide the motion of height adjustment skirt2160during 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 ofFIG. 4is preferred. Multiple slots weaken height adjustment skirt2160, making it prone to breakage if the undercut saw2000is 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.

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 saw100ofFIG. 3). Afterwards, wing screw2280is loosened, and the height adjustment skirt2160is free to telescope up or down. Guide washer slot runner2330remains in slot2310and is pressed up against downwardly protruding back edge2240due to pressure from spring2340. As height adjustment skirt2160is moved up or down, the outer edges of guide washer slot runner2330guide its motion through contact with the inside edges of slot2310. This guidance ensures that the height adjustment skirt will be guided up or down in a substantially vertical direction. Top plate2140thus tends to stay parallel to base2450. Thus, the blade will be kept parallel to the base during adjustment. When the desired height is set, wing screw2280may be tightened down on guide washer2330, pressing it against the inner surface of guide washer channel2345of height adjustment skirt2160, and in turn drawing the downwardly protruding back edge2240of top plate2140against inside face2260of height adjustment skirt2160. This clamping pressure on the components frictionally holds the desired height of cut.

As used herein, and as shown inFIG. 4, the term “guide washer fastener assembly” includes at least one threaded fastener (such as wing screw2280). 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 screw2280. In a preferred embodiment, the guide washer fastener assembly additionally includes a washer2360installed first on the wing screw2280, followed by a spring2340. 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 inFIG. 9, only two such guide washer fastener assemblies6000,6200are included, (comprising wing screw2280, washer2360, and spring2340). Guide washer fastener assemblies6000,6200are used in conjunction with two guide washers2320,2321. 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 port6300. 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.

As shown inFIG. 4, wing screw2280along with tapped hole2300work to generate clamping force to frictionally hold the downwardly protruding back edge2240of the top plate2140against the inner surface2260of height adjustment skirt2160. This holds the height of the top plate2140relative to the bottom surface2451of base2450of height adjustment skirt2160. Since the rotary power unit2180and rotatable circular saw blade2220are fixedly assembled onto top plate2140when the saw is assembled, the height of the top plate2140determines the height of cut. The top plate2140may be adjusted and frictionally held in a vertical range of about one inch within the height adjustment skirt2160. This enables the height of cut for circular saw blade2220to 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.

As shown inFIG. 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 saw8000includes a guide washer8020including a tapped hole8040. A threaded member such as pan head screw8060is inserted through a hole8080in the base8100of height adjustment skirt8120. Hole8080may be countersunk on its bottom side (not shown) such that the pan head8061of pan head screw8060sockets flush within the countersink. Thus, base8100will be a uniform flat surface on its bottom side8101, which will not catch on floor surface irregularities.

Once inserted in hole8080, pan head screw8060extends vertically up from base8100and may be threaded into tapped hole8040in guide washer8020. Next, collar8210is fastened onto pan head screw8060at an elevation forming a slight gap between the bottom of collar8210and a top surface8260of base8100. This gap enables pan head screw8060to rotate within hole8080. (More secure, lower cost alternatives exist for pan head screw8060and collar8210will be described later.) Finally, for ease of turning, a knob such as three arm knob8140may be fastened on top of pan head screw8060.

The lead screw mechanism formed by a threaded member such as pan head screw8060and tapped hole8040may be included in one or more of the guide washers included in the fixed guard assembly for the saw. As shown inFIG. 12, in this embodiment, two lead screw mechanisms12020,12040are used. A single lead screw mechanism would not evenly lift both sides of the top plate12060. With two such mechanisms12020,12040, 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 mechanisms12020,12040provide adequate support for top plate12060during use of the saw. With three or more such mechanisms, each knob would have to be turned separately, which is cumbersome.

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 inFIG. 8, as previously described, such a frictional mechanism may include a guide washer fastener assembly (such as wing screw8160, washer8180, and spring8200threading into tapped hole8220of the downwardly protruding back edge8280of top plate8240). This guide washer fastener assembly works in conjunction with guide washer8020to 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.

In this embodiment as shown inFIG. 8, the process of height adjustment is somewhat different. First, the user loosens wing screw8160, reducing the frictional hold. However, since pan head screw8060is threaded through tapped hole8040in guide washer8020, top plate8240is held at that elevation until three arm knob8140is turned. If three arm knob8140is turned clockwise, pan head screw8060will be turned clockwise, thereby raising guide washer8020and top plate8240to a higher elevation above base plate8100. If three arm knob8140is turned counter-clockwise, guide washer8020and top plate8240will be lowered. When the desired height is set, wing screw8160may again be tightened, and top plate8240and height adjustment skirt8100will additionally become frictionally held at the desired elevation.

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 screw8160), the guide washer preferably includes a guide washer slot runner such as guide washer slot runner8025. In such an embodiment, guide washer slot runner8025performs a different function in that it prevents guide washer8020from rotating when lifting force is applied by pan head screw8060. The reason such rotation is generated and is not preferred is as follows: Tapped hole8040for pan head screw8060is offset at least some distance from through hole8300for passage of wing screw8160through guide washer8020. Otherwise, these components would interfere with each other and not perform their desired function. With this offset, in the absence of guide washer slot runner8025, pan head screw8060would lift guide washer8020on one side, causing it to rotate on wing screw8160. An added feature on guide washer8020resists such rotation. An added guide washer slot runner8025can bear against the inner edges of slot8290during adjustment, thus preventing such undesirable rotation. Therefore, in such an embodiment, guide washer slot runner8025performs an important, though somewhat different function.

As previously explained, pan head screw8060is rotatably affixed to base8100of height adjustment skirt8120by collar8210. Collar8210is affixed to pan head screw8060at a slight elevation above a surface8260on a top face of base8100forming a slight gap that permits such rotation. However, when the saw is lifted off the floor, collar8210performs the additional function of stopping pan head screw from sliding through countersunk hole8080through base8100. Collar8210is affixed to pan head screw8060by means of a set screw8211which may be tightened down on the threads of pan head screw8060at the desired height. However, collar8210is an expensive custom component with a set screw8211which may come loose and cause the assembly to fail.

As shown inFIG. 13, an alternative pan head screw such as shoulder pan head screw13000may be used that includes a shoulder13020. Shoulder13020spaces a standard hex nut such as hex nut13040at a desired height allowing shoulder pan head screw13000to rotate within its hole.FIG. 14shows a partial section A-A of the area of base14100near the countersunk hole for a shoulder pan head screw14020. As shown in section A-A, shoulder14040of shoulder pan head screw14020supports a common hex nut14060at a height above a top surface14080of base14100. Thus, hex nut14060can be tightened down firmly on shoulder14040with reduced concern for coming loose compared with collar8210(FIG. 8). Hex nut14060is also less expensive than collar8210(FIG. 8). Thus, for two reasons, shoulder pan head screw14020and hex nut14060are preferred. However, as shown inFIG. 14, the insertion of either type of pan head screw within a countersunk hole (such as countersunk hole14160) results in a flush surface such as14140on 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 socket14180allows shoulder pan head screw14020to be turned with a hex wrench from the bottom if desired.

During height adjustment, as shown inFIG. 14, graduations14200may be etched on an outer surface on either side of height adjustment skirt14120. These graduations indicate the height of the circular saw blade14220by its relation to a flush bottom edge14240of the downwardly protruding back edge14260of the top plate14280. This is because the flush bottom edge14240is in the same flush plane with circular saw blade14220(covered in this view by movable guard14210). Before performing an undercutting operation, the user may check on both front sides of the height adjustment skirt14120that the flush bottom edge14240of top plate14280is 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.

As defined herein, for the embodiments ofFIG. 8or14, or any embodiments including a lead screw mechanism to support a top plate, the lead screw component (such as pan head screw8060ofFIG. 8, or shoulder pan head screw13000ofFIG. 13, or shoulder pan head screw14020ofFIG. 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 collar8210ofFIG. 8, hex nut13040ofFIG. 13, or hex nut14060ofFIG. 14) will be defined as a lead threaded member holding fastener. A guide washer including a threaded hole (such as tapped hole8040) in guide washer8020ofFIG. 8will be referred to as a lead guide washer.

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 inFIG. 5, undercut saw3100is made with a grinder motor3180having a first long horizontal armature axis3170and a second spindle axis3190. On one end of the long armature axis, a first rearward handle3390with a switch3400forms the back end of the saw. On the other end, an aluminum spindle housing3420forms 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 blade3220is mounted on the spindle on a blade mount (not shown). Spindle housing3420is fixedly joined to top plate3140. Top plate3140and height adjustment skirt3160form a fixed guard assembly3120for the undercut saw. A spring-loaded movable guard3200covers circular saw blade3220and is retractable in the counter-clockwise direction to start a cutting operation.

The improved handle for the saw is formed from a first, left half3460, a second, right half3480, and an upper pivot pin3500. Left half3460is overlapped at relief3520with relief3540in right half3480. Pivot pin3500is press fit into upper hole3580in right half3480and through upper hole3560in left half3460to 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 half3460and right half3480with pivot pin3500may be referred to as handle assembly3510.

Left half3460and right half3480have circular tooth patterns3600and3620(respectively) formed on their inside surfaces which may engage corresponding circular tooth patterns3640,3660on the left and right hand sides of spindle housing3420(respectively). Threaded four arm screws3680,3700may be inserted through left mounting hole3720in left half3460and right mounting hole3740in right half3480(respectively). Threaded four arm screws3680,3700may further thread into a tapped left mounting hole3760and tapped right mounting hole3780to join handle assembly3510to spindle housing3420.

The circular tooth patterns3600,3620of left half3460and right half3480are designed to interlock with corresponding circular tooth patterns3640,3660in the left and right sides of spindle housing3420and will provide a fixed and solid joint when they are pressed together by threaded four arm screws3680,3700. Because these teeth patterns are circular, handle assembly3510may interlock and become fixedly joined to spindle housing3420at a number of angles. As more clearly illustrated inFIG. 11, for general undercutting, it is preferred that handle assembly11000be oriented at a right angle A perpendicular to the long armature axis11020of grinder motor11040. 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 assembly11000be 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 axis11020of the saw. Any such acute angle places the hand unnecessarily close to blade11060, and could also cause the handle to extend beyond the front edge of top plate11080. Such is not preferred, as that would prevent the saw from operating in tight areas, such as inside corners.

As shown inFIG. 5, others skilled in the art will envision alternative fasteners to fasten a second, forward, movable handle, such as handle assembly3510, to an undercut saw spindle housing, such as spindle housing3420. For example, rather than four arm screws3680, threaded rods may be threaded into tapped left mounting hole3760and tapped right mounting hole3780. 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.

As shown inFIG. 5, to prevent handle assembly3510from moving or being set at any such acute angle in relation to a forward projection of the long armature axis of the saw, left half3460and right half3480include bosses3800,3820. When handle assembly3510is joined to spindle housing3420at a right angle to long armature axis3170, bosses3800,3820come in close proximity to left and right flats3840,3860of spindle housing3420. In this embodiment, if handle assembly3510is rotated forward to an acute angle in relation to the long armature axis3170, bosses3800,3820will contact left and right flats3840,3860. This interference causes handle assembly3510to 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, bosses3800,3820may contact left and right flats3840,3860to stop the handle from being rotated forward to any such acute angle.

Left half3460and right half3480may 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 assembly3510.

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 inFIG. 6, undercut saw6100has a height adjustment skirt4160having a base4450. An additional flush mounted removable cover plate4820may be screwed to base4450using screws4800. Cover plate4820covers blade4810past the depth of the teeth. In addition, movable guard4840may cover the blade4810past the depth of the teeth with its own removable plate4860fastened to movable guard4840as by screws4880.

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 plate4820mounted on base4450covers blade4810to a radius alpha (in relation to the center of the circular saw blade4810). Radius alpha is a shorter radius than radius delta to the outer circumference of the circular saw blade4810. Similarly, cover plate4860mounted on movable guard4840covers blade4810to a radius beta (in relation to the center of the circular saw blade4810). Radius beta is a shorter radius than radius delta.

In an another embodiment, as shown inFIG. 7, a cover plate5120may be removably mounted on a bottom edge of the downwardly protruding back edge5240of the top plate5140using screws5800, rather than on the base5450of height adjustment skirt5160. Cover plate5120covers, blade5820past the depth of the teeth. Cover plate5120covers blade5820to a radius epsilon. Radius epsilon is a shorter radius than radius delta (the outer circumference of the circular saw blade5820).

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. AlthoughFIG. 4illustrates 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. InFIGS. 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.