Abstract:
A positioning device for a power tool. A tool, such as a drywall screw gun, is equipped with a projector which projects two light rays, which form a “V.” The axis of a screw driven by the gun lies in the plane of the “V,” as by bisecting the “V.” If the two rays are positioned so that they illuminate a framing member, such as a 2×4 stud, then this axis will intersect that stud. In effect, (1) the stud becomes the horizontal base of a triangle, (2) the legs of the “V” become the sides, and (3) the axis becomes the altitude. The altitude (axis) necessarily intersects the base (stud). This intersection occurs whether or not a sheet of material, such as drywall, covers part of the stud, provided extremeties of the stud are exposed for the illumination described above. Thus, the location of the concealed part of the stud can be determined, despite the fact that a sheet of material obscures that part.

Description:
When a drywall screw gun is positioned in the center of a sheet of drywall, that part of a  2 × 4  stud located behind the sheet, and to which the sheet is to be attached, is not visible. The invention locates this invisible part, and informs the operator where to place the screw gun. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 illustrates a sheet  3  of material, such as plywood or gypsum wallboard. Such a sheet  3  is generally installed over framing members  6 , which can take the form of joists, studs, or rafters. One installation method utilizes an electric drill, which drives threaded screws through the sheet, and into the framing members  6 . 
     However, when a screw is to be installed a distance from the edge  9  of the sheet, such as at point  12  along central longitudinal axis CAX, it is difficult to locate the framing member  6 , because that member is not visible at point  12 . One solution to the problem is to visually estimate the position of the framing member  6 , but that approach often results in errors, and produces screws which must be removed because they miss the framing member  6 . 
     Another solution is to snap a chalk line across the sheet  3 , which is aligned with the visible parts of the framing member  6 , as from points P 1  to P 2 . This solution is effective, but time-consuming. 
     OBJECTS OF THE INVENTION 
     An object of the invention is to provide an improved system for driving screws through sheet material into framing members. 
     SUMMARY OF THE INVENTION 
     In one form of the invention, an optical projector projects two rays of light outward from a common location, forming a “V.” The axis of the fastener extends through the vertex of the “V,” and lies in a common plane with the “V.” For example, the axis may bisect the angle formed by the “V.” 
     If these rays are properly positioned near two edges of a sheet of drywall, the axis will intersect a framing member located behind, and concealed by, the sheet, thereby indicating where to drive a screw. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a sheet  3  adjacent framing members  6 , such as a sheet of plywood  3  positioned over floor joists  6 . 
     FIGS. 2 and 3 shows a scanner  30 , which projects a line  36  of light. 
     FIG. 4 shows the scanner  30  attached to a band  40 . 
     FIG. 5 shows the scanner  30  attached to a clip  50 . 
     FIG. 6 illustrates several static light sources  60 . 
     FIG. 7 illustrates the light sources  60  of FIG. 6 projecting spots S onto a sheet  3 . 
     FIG. 8 illustrates the scanner  30  attached to an electric drill  90 . 
     FIG. 9 illustrates one form of the invention. 
     FIG. 9A illustrates another form of the invention. 
     FIG. 10 illustrates a bracket which allows adjustment of projector S 1 . 
     FIG. 11 illustrates geometric elements which explain how the invention functions. 
     FIGS. 12-18 illustrate other forms of the invention. 
     FIG. 19 illustrates a stick  200  positioned on a sheet  3 . 
     FIG. 20 illustrates two eyes E which sight the tip T of the stick  200 , and thereby place it over framing member  6 . 
     FIG. 21 illustrates telescopes  240  which may assist the process described in connection with FIG.  21 . 
     FIG. 22 illustrates how a single eye E can utilize the telescopes, if mirrors  290  are provided. 
     FIGS. 23 and 24 illustrate devices implementing the principles shown in FIGS. 20-22. 
     FIGS. 25-27 illustrate additional forms of the invention. 
     FIGS. 28 and 29 illustrate why the apparatus of FIGS. 25-27 operates successfully. 
     FIG. 30 illustrates another form of the invention. 
     FIG. 31 illustrates a modification of the device of FIG.  30 . 
     FIGS. 32A,  32 B,  32 C, and  32 D illustrate one mode of achieving the modification shown in FIG.  31 . 
     FIGS. 33-35 illustrate another form of the invention. 
     FIGS. 36-38 illustrate operation of the invention of FIGS. 33-35. 
     FIGS. 39 and 40 illustrate another form of the invention. 
     FIG. 41 illustrates operation of the invention of FIGS. 39 and 40. 
     FIG. 42 illustrates another form of the invention. 
     FIGS. 43 and 44 illustrate operation of the invention of FIG.  42 . 
     FIGS. 45-50 illustrate another form of the invention. 
     FIG. 51 illustrates another form of the invention. 
     FIG. 52 illustrates rays R forming a sheet of light. 
     FIG. 53 illustrates rays R 2  replacing rays R of FIG.  52 . 
     FIG. 54 illustrates one form of the invention. 
     FIG. 55 is a simplified view of another form of the invention. 
     FIG. 56 shows the invention of FIG. 55, positioned perpendicularly to a sheet  515  of sheet rock, ready to drive a drywall screw  530 . FIG. 56 shows some typical, approximate dimensions. 
     FIG. 57 is a simplified representation of FIG.  56 . 
     FIGS. 58 and 59 show another form of the invention, wherein lasers  505  and  506  lie aft of the end  560  in FIG. 58 of the drywall screw gun  500 . 
     FIGS. 60,  61 ,  62 , and  63  illustrate several approaches to supporting the lasers  505  and  506 , by using collapsible, or folding, masts M. 
     FIG. 61A illustrates a light source  605 , a transparent slide  601  containing an image of a bull&#39;s eye BE, a focusing system  610 , and a projected image BEIM of the bull&#39;s eye. 
     FIG. 64 shows lasers  505  and  506  projecting fan-like beams, which project elliptical spots EL. 
     FIG. 65 shows a laser  700  having an ideal, concentric axis  705  defined therein. 
     FIG. 66 illustrates two rays R 1  and R 2  deviating from the ideal axis  705 . 
     FIG. 67 illustrates a laser  700  projecting a fan FN, and how the line created by the fan FN on target  710  can deviate in at least two ways, as lines L 1  and L 2 . 
     FIG. 68 is a schematic view of a mounting device for laser  700 . 
     FIGS. 69,  70 ,  71 , and  72  illustrate a sequence of steps utilized in aligning the laser  700 , using the apparatus of FIG.  68 . 
     FIG. 73 illustrates two aligning devices  750  mounted in a drywall screw gun  500 . 
     FIG. 74 illustrates a laser  700  projecting a spot SP, which deviates from ideal axis  705 , and a range  900  indicating the allowable limits of deviation. 
     FIG. 75 illustrates a range  905 , centerline CL of FIG. 74, and an error bar EB. 
     FIG. 76 illustrates four lines D 1 , D 2 , D 3 , and D 4 , which represent line LL in FIG.  60 . Lines D 1 , D 2 , D 3 , and D 4  are co-planar with ideal axes  510  and  511  in FIG. 60, and with the drill axis  50 . FIG. 76 illustrates how, even if spots SP are positioned within the error bars EB, the lines D 1 -D 4  can still deviate as indicated from the ideal position. 
     FIG. 77 is similar to FIG. 76, but showing larger error bars EB, and larger deviation. 
     FIG. 78, left side, illustrates how fans F 1  and F 2  can be mis-aligned, and the right side illustrates alignment of the fans. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 illustrates a scanner  30 , which scans a light beam through successive positions  33 . Such scanners are known in the art, and one type of this scanner is used at point-of-sale terminals, to scan bar codes. 
     The scanning is done rapidly, so that the spot projected by the light beam appears as a line  36  shown in FIG.  3 . The user positions the scanner  30  so that the ends E of line  36  coincide with the framing member  6 . The user then utilizes the central part C of line  36  to position a screw (not shown) to be driven into the framing member  6 . The line  36  acts as a virtual chalk line. 
     The scanner  30  can be fastened to a head band  40  in FIG. 4, and worn about the user&#39;s head, or a smaller band  40  can fasten the scanner to the user&#39;s hand or forearm. Alternately, a clip  50  can be attached to the scanner  30 , as in FIG.  5 . The clip attaches to eyeglasses, or safety glasses, which are worn by the user, or to a tool used by the user. 
     FIG. 6 illustrates an alternate type of scanner. Instead of a single projector producing a continuous line, as in FIGS. 2 and 3, several static light sources  60  can be used, to produce a sequence of spots S, as shown in FIG.  7 . Since the spots are closely spaced, such as at six inches or a foot apart, it is a simple matter to interpolate between them, and locate a screw over the framing member  6 . 
     In another form of the invention, the scanner  30  in FIG. 8 is attached to an electric drill  90 . It projects rays  33 . 
     In one variation of this approach, two light sources S 1  and S 2  in FIG. 9 are attached to the drill  90 . These sources are adjustable in position, as indicated in FIG.  10 . For example, light source S 1  is rotatable about pivot P. A locking means L holds source S 1  in position. 
     The system shown in FIG. 9 obeys the following conditions. One, the light beams B and the axis  50  of the drill bit (not shown) lie in the same plane. Two, the light beams B are positioned so that they project spots S onto the framing member  6 . Under these conditions, if the drill is held perpendicular to the sheet  3 , the drill bit will necessarily lie above the framing member  6 , and a screw (not shown) driven by it will enter that member  6  when the drill chuch  51  rotates. 
     Preferably, the light sources S 1  and S 2  are supported by brackets which are an integral part of the housing of the drill  90 , as shown in FIG.  9 A. They can take the form of laser pointers, or simpler optical projectors. 
     FIG. 11 justifies this operation from a geometric perspective. The beams B 1  and B 2  assume the legs of a “V,” and lie in the same plane (not indicated). They generate spots S. Any line extending between the two spots S will also lie in that plane. 
     If the spots S are positioned as shown in FIG. 9, a line can be drawn between them which lies above the framing member  6 . If, in FIG. 11, the axis  50  of the drill chuck (shown in FIG. 9) lies in that same plane, and lies between the legs of the V in FIG. 11, then that axis  50  will intersect line L. 
     If line L is positioned above the framing member (not shown), by virtue of spots S being positioned on that member, then axis  50  will intersect the framing member. Thus, a screw (not shown) driven by the drill will enter that framing member. 
     FIG. 12 illustrates an accessory for attachment to an existing electric drill. A bracket  200  supports two housings  205  and  206 . Each housing supports a pivot pin PV, each of which defines an axis of rotation A 1  and A 2  for a light source S 1  or S 2 . A clamp, detent, or brake, generally indicated by blocks  250 , locks each light source against movement, once properly positioned. The bracket  200  can be attached to an electric drill (not shown) by adhesive tape, or by a more elaborate clamping means. 
     FIG. 13 illustrates the apparatus installed in a drill  90 . 
     ADDITIONAL EMBODIMENT 
     As background, to illustrate general principles involved in this embodiment, some approaches to positioning the drill will be explained, in three steps. 
     As step  1 , in FIG. 19, an upright stick  200  is placed onto the sheet  3 . The stick  200  represents the screw to be driven. The stick  200  is shown positioned over the framing member  6 , but that is coincidental. 
     As step  2 , in FIG. 20, two associates (not shown) position their eyes E over the framing member  6 , as indicated by lines L 2 . Each eye E sights the far section of the framing member, located beyond the opposite end of the sheet  3 , as indicated by arrows A. 
     The associates look for the top T of the stick, and instruct the stick-holder (not shown) to move the stick until the top T coincides with arrow-lines A. When this coincidence occurs, the stick will be positioned over the framing member  6 . (Of course, given the assumption that an eye E lies above the framing member, only a single eye E is required to position the stick  200  over the framing member  6 . However, in the general case discussed later, this condition is not fulfilled, so the equivalent of two eyes is required, as will be seen.) 
     Continuing this type of approach, in step  3 , the associates can sight through optical systems, which, in principle, can be viewed as short-range telescopic rifle scopes  240  in FIG. 21, which are mounted to the drill by arms  245 . If the optical axes A are coplanar with the axis  270  of the drill chuck  260 , then if the framing member  6  is centered in the cross-hairs (not shown) of each scope  240 , the drill axis  270  will intersect the framing member  6 . 
     The principles just illustrated can be implemented as shown in FIG.  22 . In FIG. 22, two mirrors direct the sight-lines A to a single eye E. Insert I indicates the images seen in the mirrors  290  when the drill is properly positioned. The framing members  6  are centered in the circular viewing aperture of the scopes  240 , and part of the sheet  3  is shown. Cross-hairs of the scopes  240  are not shown. 
     Telescopes are not necessarily required. Hollow tubes  310 , shown in cross-section in FIG. 23, can be used. They, and mirrors  290 , are fastened to the drill by a support which is not shown. In FIG. 24, the assembly is shown positioned within the body of the drill, specifically, within the handle, and fastened to the drill in that position. Cross-hairs can be provided by stretching threads across one, or more, diamaters of the tubes. 
     Additional Embodiment 
     The projector  30  of FIG. 2 can be positioned to the side of the drill  90 , as shown in FIG.  25 . Drill bit  405  and screw  400  are shown. In this case, the drill axis  50  is not coplanar with the light rays  33 . 
     FIG. 26 is a perspective schematic view, showing the line  420  generated by the projector. Preferably, the projector is positioned so that the line  420  crosses the tip of the screw, which is designated TIP. 
     In operation, the line  420  in FIG. 27 is positioned so that its ends E lie above the framing member  6 . With this positioning, the screw  400  will necessarily lie above the framing member  6 , as FIGS. 28 and 29 explain. 
     FIG. 28 shows an imaginary plane PL which contains the axis  50  of the screw  400 . FIG. 29 superimposes upon this a second plane PL 2 , which contains the scanned rays R produced by the projector  30 . The intersection of those planes produces line  420 , because the latter plane PL 2 , by stipulation, contains the point TIP. 
     Of course, multiple, scanned rays R are not required. Two single rays, as shown in FIG. 27, will suffice. 
     The same principles just described can be used in the optical viewing system described earlier. The left side of FIG. 30 illustrates the assembly comprising tubes  310  and mirror  290 , labeled as unit  460 . This unit  460  is shown installed on the drill, on the right side of the Figure. Optical axes B, C, D, and E on the right side of the Figure correspond to those on the left side. 
     These axes B, C, D, and E are arranged to lie in the same plane PL 4 . Further, that plane contains line  420 A, which runs through the point TIP. The user&#39;s eye EE sights rays E and D, and positions the drill as explained in connection with FIG.  22 . 
     This arrangement requires the operator to position the head to the side of the drill  90 , because rays E and D point away from the drill  90 . The approach of FIG. 31 eliminates this requirement. The mirrors  290  are rotated so that rays E and D are parallel with axis  50  of the drill  90 . The reason why proper rotation moves rays E and D into this parallelism will be explained with reference to FIGS. 32A-32D. 
     FIG. 32A shows ray E being reflected by mirror  290 . Plane PL 4  is a reference plane, and is perpendicular to incoming ray Ein. Point P 5  is the reflection point. In FIG. 32B, an axis AX is drawn running through point P 5 . If mirror  290  is rotated about axis AX, in the direction of arrow AR, to the position shown in FIG. 32C, then ray E will follow the path shown. Ray E has been rotated. 
     In general, if ray E coincides with the axis AX in FIG. 32D, as the mirror (not shown) rotates, the reflected ray E will be forced to trace the surface of a CONE. The APEX of the cone corresponds to point P 5  in FIGS. 32A-32C. The BASE of the CONE is indicated. 
     This type of rotation allows rays D and E to be shifted to the position shown in FIG.  31 . 
     Additional Embodiments 
     The preceding discussion considered devices for positioning a drill over a framing member. The present embodiments concern devices for positioning a screw over the framing member, which is then driven by a drill. 
     FIG. 33 illustrates two optical projectors  501  and  502 , such as commercially available laser pointers. They are connected by a bracket  505 , to which is connected a magnet  508 , which contains a V-groove  510 . The optical projectors are aligned along a common optical axis  515 , as shown in FIG.  34 . Further, the V-groove  510  provides a screw-positioning station which positions a screw  520  in FIG. 35, so that the axis  530  of the screw intersects the optical axis  515 . 
     FIG. 36 is a plan view of the device. In use, the device projects two light beams B in FIG.  37 . The device is moved until these beams B lie above the framing member  6  in FIG.  38 . (Alternately, the device can be moved until beams B lie above screw heads  400  positioned near the edge of the sheet.) Then, a drill (not shown) drills the screw  400  part way. Next, the device is withdrawn from the screw  400 , and the screw is driven fully into the framing member  6 . 
     In the embodiment just described, it was presumed that the light beams grazed the sheet  3 , to thereby produce a visible line of light on the sheet. In another embodiment, the projectors are carried by raised brackets  550  in FIG.  39 . The raised brackets  550  allow the projectors to generate spots  560  shown in FIG.  40 . The operator (not shown) positions the device until it is located as shown in FIG. 41, so that the spots  560  lie atop the framing member  6  (not shown), which assures that the screw axis  530  intersects the framing member  6 . 
     In another embodiment, a tube  580  in FIG. 42 is constructed, whose axis  590  intersects with optical axis  515 . A screw (not shown) is placed into the tube, and the operator (not shown) moves the device until it is positioned as shown in FIGS. 38 or  41 . The screw is driven part way, the device is removed, and the screw is then driven fully. 
     To allow removal, in FIG. 43, a split SP is constructed near the tube  580 . The material surrounding the tube is made flexible, thus allowing the deformation indicated in the Figure. 
     In another form of the invention, weights W are added, as in FIG.  42 . When a screw (not shown) is placed in tube  580  in FIG. 44, the device can pivot about the screw. The weights W cause the beams B to assume a vertical position. The operator (not shown) moves the device left and right until the beams B coincide with a framing member, or markers indicating the presence of the framing member. Then the operator drives the screw, as described above. 
     FIG. 14 illustrates another embodiment. Holes H accept a user&#39;s fingers, and allow the user to hold the device. For example, the user may place the little finger and the ring finger through the holes. Then, with the thumb and index finger, the user manipulates the screw (not shown) into the tube  580 . 
     In FIGS. 15 and 16, a component  700  is slide-mounted to drill  90 , by a spring-loaded slide  701 , thereby allowing it to remain in contact with sheet  3  as the drill travels toward the sheet. That component  700  can take the form of an ultrasonic stud sensor, many types of which are commercially available. The spring-loading of the component  700  maintains it in contact with the sheet  3 , as the drill  90  withdraws. 
     Alternately, that component  700 , shown in FIGS. 17 and 18, can carry two optical projectors S 1  and S 2 , which project light rays R 1  and R 2  which are used as described above. The advantage of the apparatus of FIG. 17 is that, initially, the drill does not obstruct the light beams in region  710 . When the drill does obstruct that region  710 , as in FIG. 18, the light rays are not needed, because the screw has been positioned already. 
     In FIG. 45, a projector PR, which projects light ray R, is fastened to a clothespin-like clamp CL, containing a spring S. FIG. 46 shows the clamp CL clamped to a sheet  3  of plywood. The ray R grazes the surface of the sheet  3 , forming a visible line. The projector is adjustable, to allow ray R to be positioned to assume the grazing position, by the apparatus shown in FIG.  47 . 
     A bracket BR is fastened to the clamp CL. Two threaded PINs, attached to the projector PR, mate with slots SL in the bracket BR, allowing the projector PR to slide upward and downward. Threaded nuts (not shown) lock the projector in position. 
     The clamp CL of FIG. 47 contains a STOP and a LIP. These function as in FIG.  48 . The LIP assures that plate PL lies flat on the sheet  3 , by applying a clamping force along a line about which the entire assembly can pivot, thereby allowing plate PL to pivot into flatness. The STOP acts as a positioning surface, to align the ray R perpendicular with the edge of the sheet to which the clamp CL is clamped. 
     It may be desired that ray R in FIG. 46 does not graze the sheet  3 . Thus, no line will be formed on the sheet  3 , although dust in the air will probably render the ray R visible. But when fastener  200  is moved into intersection with the ray, the ray illuminates it, thereby indicating that the fastener is in-line with the ray R. 
     In FIG. 49, the projector PR is offset to the side of clamp CL. The reason is to allow clamp CL in FIG. 50 to clamp the sheet  3 , while allowing the projector PR to lie above the framing member  6 . There is no space at the interface of framing member  6  and sheet  3  into which the jaws of clamp  3  can fit. 
     An exception to this statement is possible. The sheet  3 , at point P 9  in FIG. 50, may not be fastened to the framing member at the location where the clamp CL is installed. The sheet is deflected away from the framing member, and one jaw of the clamp CL is inserted between the sheet  3  and the framing member  6 . After an appropriate number of screws have been positioned, the clamp CL is removed, and the sheet  3  is screwed down at that location. 
     ADDITIONAL CONSIDERATIONS 
     1. The discussion above was framed in terms of drywall screws. However, other types of fasteners, such as deck screws and power-driven nails, can be used, and other fastener drivers can be used, such as nail guns, gunpowder-charged power hammers, and so on. 
     2. In one form of the invention, the projectors are made an integral part of a fastener driver, such as a drill or a nail gun, as indicated in FIG.  9 A. In another form of the invention, an apparatus is provided for retro-fitting to an existing fastener driver, such as the apparatus in FIG.  12 . 
     3. In one form of the invention, the sheet  3  is four feet wide, by a standardized length, such as 8, 10, 12 feet, and so on. Thus, if the invention is positioned as shown in FIG. 9, each beam B will be about two or three feet in length. The sheet comprises two pairs of opposing edges. For example, in a 4×8 sheet, the two four-foot edges form one pair of opposing edges, and the two eight-foot edges form another pair. 
     4. The beams B in FIG. 9, if extended, will intersect, forming a V. Each adjustment about the pivot P in FIG. 10 will change that angle. That is, both projectors S 1  and S 2  need not be adjusted, in order for that angle to change, although they can be. 
     5. FIG. 51 illustrates another form of the invention. A commercially available ultrasonic stud locator SL, commonly called a “Stud Sensor” or “Stud Finder,” is shown. Attached to it, is a clip CLIP for holding a nail or SCREW. The clip is positioned so that, when the stud locator is held in its normal position over a stud, the nail held by the clip will also lie over the stud. 
     6. FIG. 52 illustrates rays R, projected by projector  30 , and which form a fan-shaped sheet of light. If the rays R are fixedly positioned with respect to the drill  90 , then they can be replaced by a pair of rays R 2 , shown in FIG.  53 . The invention is used as explained in connection with FIG.  9 . 
     7. FIG. 54 illustrates an electric drill  90 , fitted with an extension EXT, which represents a self-feeding mechanism which feeds screws to the drill, for driving the screws into flooring material, while the human operator (not shown) remains in a standing position. The invention can be used with this apparatus, as indicated by projectors S 1  and S 2 . 
     ADDITIONAL EMBODIMENT 
     FIG. 55 is a simplified perspective view of one form of the invention. A drywall screw gun  500  supports two lasers  505  and  506 , which project light beams along optical axes  510  and  511 . A support for the lasers is not shown in this Figure. 
     FIG. 56 is an elevational view of a similar system, shown adjacent a sheet of drywall  515 , which is supported by a framing member  520 , such as a  2 × 4  piece of lumber. 
     Representative dimensions are shown in FIG.  56 . The drywall screw gun  500 , plus screw  530 , is approximately one foot long, as indicated, measured from the tip T of the {fraction (15/8)} inch drywall screw  530  to the end E of the gun  500 . Axes  510  and  511  intersect at a vertex V, which is about 0.5 foot above the end E, as indicated. 
     The drywall sheet  515  is four feet wide, as indicated. Axis  510  intersects the framing member  520  within dashed box  540 , and generates a spot SP, shown as a top view. Axis  511  generates a similar spot (not shown). 
     FIG. 57 is a simplification of FIG. 56, and will be used to compute numerical values of certain angles. If dimension D, the displacement of the spot SP from the edge ED of the drywall sheet  515 , is two inches, then angle AN is about 55 degrees. That is, 55 degrees is the inverse tangent of the quantity (26/18), 26 being the distance in inches between spot SP and axis  50 , and 18 being the distance from vertex V to the sheet  515 . 
     Stated in other words, the angle AN between the optical axis  510  and the axis  50  of the drill bit, or drill chuck  260 , is about 55 degrees. 
     of course, the angle AN can be different, if the equipment is designed differently. For example, for a larger screw gun  500 , vertex V may be positioned 26 inches above the drywall sheet. In that case, angle AN would be 45 degrees. For a smaller gun  500 , vertex V may be located at one foot from the sheet  515 . In that case, angle AN would be about 65 degrees. Therefore, it is contemplated that, in several embodiments, angle AN lies between 45 and 65 degrees. 
     The system is symmetrical, so that a corresponding angle AN 1  also exists, preferably having the same value as AN. 
     FIG. 59 illustrates another embodiment, wherein lasers  505  and  506  are positioned behind gun  500 . FIG. 58 is a top view of the system, and shows angle AN, together with laser  505 , optical axis  510 , and drill axis  50 . A bracket  550  is shown. A significant features is that the lasers  505  and  506  are positioned aft of all mechanical components of the gun  500 . That is, boundary  560  in FIG. 58 indicates the aft limit of the mechanical components of the gun  500 . 
     FIG. 60 shows the lasers  505  and  506  supported within a housing H, attached to the gun  500 . Housing H may be integral with the housing of the gun  500 . In FIG. 61, the housing H is supported by a mast M. This mast M will allow the increased height of the vertex V, discussed in connection with FIG.  57 . As stated above, the vertex may lie 26 inches from the sheet  515 . 
     For storage and transport, mast M may be made collapsible. For example, in FIG. 62, mast M can telescope into the gun  500 , between the phantom position M 1  and solid position M. The telescoping can involve a single-piece mast sliding into a pocket (not shown), or a multiple-piece telescoping mast. 
     In FIG. 63, the mast M may pivot about axis AX, as indicated by arrow A 5 . In another embodiment (not shown), the pivot axis may be vertical, so that the mast swings in a plane parallel to axis  50 . 
     FIG. 64 illustrates another embodiment. Drywall screw gun  500  supports lasers  505  and  506 . The lasers project fan-shaped laser beams FAN 1  and FAN 2 . Beam FAN 1  produces an elliptical spot EL. When the laser  506  is positioned wuch that distance D is about 2.5 feet, corresponding roughly to the positioning shown in FIG. 57, the length L of the elliptical spot EL is preferably in the range from 5 inches to 18 inches. The height HT of the spot EL lies in the range of ⅛ inch to about ½ inch. 
     Lasers producing fan-shaped spots are commercially available. 
     Significantly, substantially all optical energy is confined to the elliptical spot EL, and that spot EL can be located completely upon the edge of lumber of nominal 2-inch thickness, namely, lumber which is 1.5 inches thick. 
     Another significant feature is that the length/height ratio of the spot EL is at least ten. For example, if the height HT is ½ inch, and the length L is 5 inches, the ratio is 10. If the height HT is ¼ inch, and the length L is 12 inches, the ratio is 48. All ratios from 10 to 50 are contemplated, as well as ratios higher than 50. 
     The fans FAN 1  and FAN 2  are substantially flat, having the ratios just described. 
     ADDITIONAL CONSIDERATIONS 
     If angle AN in FIG. 57 is 55 degrees, then angle COMP is the geometric complement, and will equal 90 minus AN, or 35 degrees. If angle AN equals 45 degrees, then angle COMP will equal 45 degrees. If angle AN equals 65 degrees, then angle COMP will equal 25 degrees. 
     The invention covers any angle AN in FIG. 57 between 45 and 55 degrees. In one form of the invention, the lasers  505  and  506  are adjustable, and can pivot about vertex V, or other points, to adjust angles AN and AN 1 . 
     A significant feature of the conventional drywall screw gun is that it resembles a modified electric drill. In FIG. 56, a clutch CL is provided in the drive train. When the resisting force applied to the chuck  260  becomes sufficiently large, the chuck slips. The chuck is adjustable, so that the amount of resisting force required to induce the slip can be varied. 
     A significant feature of the lasers  505  and  506  is that they produce a light beam having minimal divergence. That is, the spot size of spot SP in FIG. 56, at the distances shown, is preferably {fraction (1/8, 1/4, 3/8, 1/2, 5/8)}, or ¾ inch in diameter. In one form of the invention, lasers only are used, and no non-coherent light source is used, such as incandescent light. 
     A significant feature of the use of lasers is that the size of the spot SP in FIG. 56 is sufficiently small that it can fit completely on the edge of the framing member  520 . The edge of “two-by” framing members is 1.5 inches in thickness. In contrast, if an ordinary flashlight were to replace laser  505 , the spot of light projected by the flashlight onto the framing member  520  would not fully be contained within the 1.5 inch wide edge. 
     As a result, using ordinary flashlights instead of the lasers  505  and  506  would cause great difficulty in centering the drill chuck  260  over the framing member  520 , unless special care were taken to provide a particular focusing arrangement. 
     An exemplary focusing arrangement is shown in FIG. 61A. A slide  601 , similar to a 35 mm slide, contains an image of a bull&#39;s eye BE. A light source  605  and a focusing system  610  generate a projected image BEIM of the bull&#39;s eye BE. The projected image BEIM is used in place of spot EL in FIG. 60, and a system of FIG. 61A replaces each of the laser  505  and  506  in FIG.  56 . 
     It is not necessary that the image BEIM be enlarged to the extent that a 35 mm projector enlarges a 35 mm slide. In one embodiment, no significant enlargement occurs at all. 
     The slide  601  may not be necessary. The imaging system  610  may, for example, use a tungsten filament (not shown) within the light source  605  as a point source, or line source, of light, and project that point, or line, as the image which replaces the bull&#39;s eye image BEIM. 
     In FIG. 56, the optical axes  510 ,  511 , and the drill axis  50  lie in the same plane. 
     In FIG. 57, the angle between the two optical axes  510  and  511  is the sum of angles AN and AN 1 . Thus, if angle AN equals 45 degrees, and angle AN 1  equals 45 degrees, the sum is ninety degrees. Axes  510  and  511  would then intersect at 90 degrees. 
     A significant feature is that a handle HH in FIG. 55 of the gun  500  has an axis generally indicated as HAX. Rays  510  and  511  define a plane, which includes axis  50 . Axis HAX is approximately perpendicular to that plane. In one embodiment, handle axis HAX makes an angle A 7  of greater than 90 degrees, and less than 120 degrees, with respect to the plane. Angle A 7  runs between axis HAX and axis  50 . 
     Another way to describe the handle is based on the distance DD in FIG. 55 between its bottom edge BE and axis  50 . That distance DD can be any of 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, or any distance from 2 to 7 inches, or longer. 
     A forward direction FWD is defined in FIG. 64 as the direction in which the chuck  260  points, that is, the direction to which the gun  500  will be moved, in order to drive a screw. The forward direction FWD is also defined by the direction in which an ordinary screw advances when driven by the gun  500 . Directions left L and right R are also defined. 
     A significant feature of the conventional drywall screw gun is that, in operation, the user presses against the back side BS of the handle HH in FIG. 64, in order to maintain the drill bit (not shown) in engagement with the drywall screw (not shown). The user applies the pressure with the palm, or heel, of the user&#39;s hand. Thus, the user applies pressure in the forward direction, but to a surface BS which is transverse, or perpendicular, to that direction. 
     In contrast, many so-called “electric screwdrivers” comprise cylindrical housings containing a motor, and a rotating screwdriver which is coaxial, and concentric with the cylindrical housing. The user applies forward pressure through friction: the user grasps the housing, and friction allows the user to push the housing forward. 
     ALIGNMENT 
     It is possible that the light source used, be it laser or focused incandescent, will not be aligned properly. That is, as shown in FIG. 65, an ideal laser  700  is shown, with its idealized optical axis  705  shown. The ideal axis  705  is concentric with cylinder  700 . A reference target  710  is shown. 
     In the general case, the laser beam will not necessarily coincide with the ideal axis  705 , but may deviate, as indicated by rays R 1  and R 2  in FIG.  66 . Also, if a fan-style beam is used, the plane of the fan may further deviate, as shown in FIG.  67 . The plane of the fan may strike the target  710  and generate line L 1 , or line L 2 , or lines at other angles. 
     FIG. 68 illustrates one type of mounting apparatus which can eliminate, or reduce, the deviations from ideality just described. The laser  700  is clamped into a housing  750 , which can be split at seam  755 , to allow the clamping function. The laser  700  can rotate as indicated by arrows  760 , that is, the laser  700  can “roll,” as that term is used in aeronautics, about a roll-axis  763 . When the laser  700  is rolled into the proper position, bolts (not shown) clamp the housing  750  tight onto the laser, preventing further roll. 
     The housing  750  bears a first pair of pins  770  and  775 . These mate with appropriate yokes (now shown), and allow rotation as indicated by arrows  780 , in the “pitch” direction, or attitude, about a pitch axis  783 . A second pair of pins  790  and  795  mate with appropriate yokes (not shown), and allow rotation as indicated by arrows  800 , in the “yaw” direction, about yaw axis  803 . Both yokes are capable of clamping the housing  750 , once adjusted, to prevent further pitch or yaw. 
     An exemplary adjustment procedure will be described. A fan-style laser beam will be assumed. FIG. 69 illustrates the line LINE which the beam produces on the target  710 . The laser is rotated in the direction of arrow AAI, about the roll axis  763  in FIG. 69, to align the laser LINE parallel with reference line  730 , as indicated in FIG.  70 . 
     Next, the laser  700  is rotated in the direction of arrow AA 2 , about the pitch axis  783  in FIG. 70, to move the LINE to coincide with the reference line  730 , as indicated in FIG.  71 . Finally, in FIG. 72, the laser  700  is rotated in the direction of arrow AA 3  in FIG. 72, about the yaw axis  803 , to center the LINE on the target  710 . 
     FIG. 73 is a partially exploded view of the shell of a drywall screw gun  500 , showing two housings  750  of the type shown in FIG. 68 positioned therein. The lasers  700  are adjusted about the axes just described so that they project their beams as shown in FIGS. 57 or  64 , as appropriate. If incandescent sources are used, they may require adjustment also. 
     One reason why the adjustment may be significant is explained with reference to FIG.  74 . The narrow edge EDG of a  2 × 4  piece of lumber is shown. The narrow edge is 1.5 inches in height, as indicated. If the spot SP projected by the laser  700  is to remain within the ½ inch tall boundary  900 , and if the laser is positioned 18 inches away, as indicated, then angle A cannot exceed 0.8 degrees. Angle A is defined as the angle between the ideal optical axis of the laser  700  and the actual ray produced by the paser. The idealized optical axis intersects the centerline CL of the  2 × 4 . 
     The limit on angle A is computed by realizing that the center of the spot SP cannot rise above, nor fall below the centerline CL by more than ¼ inch, if the spot SP itself is to stay within boundary  900 . The inverse tangent of (¼)/18 is 0.8 degrees.) 
     Another way to view the limits on the deviation of the laser beam from its ideal axis is shown in FIGS. 75-77. FIG. 75 illustrates a range  905 , and the centerline CL of the  2 × 4 . If the ideal axis of the laser intersects the centerline CL, then the spot produced must lie within the boundary  905 . Conversely, if the spot is placed on the centerline CL, then the ideal axis of the laser must lie within the range  905 . If the range  905  os too large, then placing the spot on the centerline will not cause the screw to enter the  2 × 4 , as will now be explained. 
     FIG. 76 illustrates two error bars EB, located on the edge EDG of a  2 × 4 . The error bars EB are 50 inches apart, as indicated. If the spots SP produced by the lasers are positioned as shown, the actual axes of the lasers can lie anywhere within the error bars EB, as just explained. Consequently, the line defined by the two spots and the centerline of the chuch (not shown) can assume any of dotted lines D 1 , D 2 , D 3 , or D 4 , ot any therebetween. 
     Clearly, if the error bars EB, that is the height of the range  905  in FIG. 75, become sufficiently tall, then the drywall screw may miss the  2 × 4 . FIG. 77 illustrates this possibility. 
     As the error bars EB increase in height, line D 3  approaches the boundary of the  2 × 4 . As a specific example, if the error bars EB were 1.5 inches in height, then, as a matter of probability, line D 3  may coincide with the bottom edge of the  2 × 4 . Thus, any screw driven will meet that edge, and will not be properly driven into the  2 × 4 . 
     Preferably, the error bars EB are less than one inch tall, meaning that the maximum angle of deviation A in FIG. 74 cannot exceed 1.6 degrees. 
     Various situations can be envisioned, with wider framing members, and screw guns of different sizes. Consequently, the following maximum deviations in angle A are specifically covered: every tenth degree, ranging from 0.10 to 5.0 degrees. That is, the series 0.1, 0.2, 0.3 . . . 4.8, 4.9. 5.0 degrees is covered as the maximum allowable deviation in the laser beam from ideality. 
     FIG. 78 illustrates the generalized situation which will occur during manufacture, or re-adjustment, of the lasers  505  and  506 . In the general case, the fan-beams F 1  and F 2  will assume the positions shown on the left side of the Figure. They are neither co-planar with each other, nor with axis  50 . 
     After adjustment, as by using an apparatus similar to that in FIG. 68, they will assume the positions shown on the right side of FIG.  78 . The fans F 1  and F 2  are co-planar with each other, and with the axis  50 , subject to the error represented by the angle A in FIG.  74 . Preferably, angle A is zero, but manufacturing tolerances may not allow attainment of zero. 
     Applicant points out that, if a simple, non-fanned laser beam is used, the three-axis adjustment of FIG. 68 may not be required. That is, if the LINE of FIG. 69 is replaced by a dot (not shown), the dot can probably be centered on the target  710  by rotation of the laser  700  about two axes, such as yaw and pitch, and not three axes. 
     During manufacture of the invention, the lasers are oriented so that they produce the aligned fans shown on the right side of FIG.  78 . However, it should be observed that the orientation steps need not occur when the lasers are installed in the screw gun  500 . That is, for example, the lasers may be aligned at the time of their manufacture, in their own housings, so that they are aligned with their own coordinate system. 
     Then, they are installed into the gun  500 , and their coordinate systems are aligned with that of the gun  500 . 
     It is observed that the alignment process can be reversed, or repeated. For example, if a user drops the drywall screw gun  500 , the lasers  700  may be knocked into misalignment. The alignment procedure may be repeated in this case. Further, the aligned lasers can be moved out of their proper orientation, if desired. 
     It is also observed that the plane of the laser beams, such as that of FIG. 60, need not be perpendicular to the handle of the screw gun. Further, in one embodiment, the important feature is that the two laser beams  510  and  511 , together with the drill axis  50 , be co-planar. This can be accomplished by (1) aligning one of the laser beams so that it lies in the same plane with the drill axis  50 , at the appropriate angle AN in FIG. 57, and (2) aligning the other laser beam into that plane, at the appropriate angle AN 1 . 
     Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.