Adaptor to convert a screw gun to a rotary cutter
BACKGROUND OF THE INVENTION 
     In completing building construction projects, it is often necessary to install pieces of gypsum wall board or dry wall within the building. When gypsum wall board is installed, holes must frequently be cut in it to accommodate electrical switches and outlets, windows, etc. Consequently, carpenters installing gypsum wall board have had to employ power tools to: (1) drive screws through gypsum wall board and into the frame of the building and (2) cut holes in gypsum wall board for the electrical light switches and outlets, etc. Generally, the tools which have been used for these operations are a power rotary screw gun (e.g., MILWAUKEER® Screw-Shooter Nos. 6750-1 or 6753-1) for driving the screws into the gypsum wall board and a separate power rotary cutter (e.g., a router with a rotary cutting bit). When not in use, these tools clutter the job site, and their power cables may create safety hazards. Moreover, when a carpenter is using one of the power tools and needs the other, he must walk away from where he is working to retrieve the other power tool. The use of two power tools to install gypsum wall board is thus inefficient, and, therefore, it is desirable to install gypsum wall board with a single power tool. 
     Adaptors to convert rotary power tools from one function to another function are well known. However, such adaptors generally must be physically clamped to the power tool by insertion and locking engagement with a chuck or by clamping to a drill bit already in a power tool chuck. Examples of such adaptors are disclosed by U.S. Pat. No. 1,785,065 to Aborn, U.S. Pat. No. 2,346,220 to Kienzle et al., U.S. Pat. No. 3,260,289 to Whitten, Jr., U.S. Pat. No. 3,783,955 to Gill, U.S. Pat. No. 4,052,078 to Benimetzki, U.S. Pat. No. 4,082,475 to Kuder, and U.S. Pat. No. 4,312,610 to Burt. Such devices do not, however, convert screw guns to gypsum wall board cutters. Moreover, these devices are unsatisfactory, because significant time and effort is required to clamp and unclamp these devices to and from a rotary power tool. Thus, the devices disclosed by these patents fail to satisfy the need for an adaptor which can be operatively oriented in rapid fashion with respect to a screw gun or other similar rotary power tool. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the need for an adaptor to convert a screw gun to a gypsum wall board cutter. In addition, the adaptor can be moved into and out of operative engagement with the screw gun without clamping or unclamping the adaptor to the screw gun. As a result, the adaptor can be quickly positioned on the front end of a screw gun to cut a hole in a piece of gypsum wall board and then removed to drive the screws into the gypsum wall board. The small size of the adaptor makes it suitable for placement in a carpenter&#39;s pocket or workbelt when not in use. However, when it is necessary to cut gypsum wall board, the adaptor can be quickly placed on the end of a screw gun without requiring the carpenter to leave the location where he is working. In addition, the adaptor of the present invention eliminates the need for a second rotary power tool which lays around the construction site where workers can trip over it or its accompanying power cable. Consequently, construction safety is greatly enhanced. 
     The adaptor of the present invention includes a casing having one end from which a rotary cutting bit extends and another end from which an open-ended bulb projects to receive the screw gun. When a screw gun is operatively engaged with the adaptor, the screw driving bit of the screw gun is inserted into a screw head, while the end of the bulb abuts against the sleeve of the screw gun. To cut gypsum wall board efficiently, the rotary cutter of the adaptor must turn at a much higher speed than that of a screw gun. This result is achieved by providing a plurality of gears and bearing-mounted shafts within the casing which increase the rotary speed of the screw gun four to ten fold. These gears, shafts, and bearings are accessed by constructing the casing from two pieces which are separable at a location adjacent these transmission components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of the adaptor of the present invention. 
     FIG. 2 is a cross-sectional view of the present invention taken along line 2--2 of FIG. 1. 
     FIG. 3 is a cross-sectional view of the present invention taken along line 3--3 of FIG. 1. 
     FIG. 4 is a perspective view of the present invention in use. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of adaptor 2 of the present invention for converting screw gun 4 to a rotary cutter. Rotary cutting is accomplished by cutting bit 6 which is clamped within cutting bit chuck 8 by screw 10. Tang 12 of chuck 8 is clamped to main shaft 16 by nut 14 which is threadably-mounted on the end of shaft 16. 
     The bulk of screw gun adaptor 2 is a casing formed from upper housing 18 and lower housing 28 which are separably joined by screws 30. Extending through upper housing 18 is main shaft 16 which is rotatably mounted on bearings 20 and 22. Upper housing 18 and lower housing 28 define an interior transmission chamber 26 containing gears 32, 34, 36, and 42. Gear 32 is coaxially mounted to the end of main shaft 16 and has teeth operatively engaged with the teeth of gear 34. Gear 34 and gear 36 are coaxially mounted on shaft 38 which is rotatably supported by bearings 24 and 40. Gear 36 has teeth which are operatively engaged with those of gear 42. Gear 42 is coupled to drive head 46 which is rotatably supported by bearing 44. The interengagement of the teeth of gear 36 with those of gear 42 and the similar engagement of the teeth of gear 32 with the teeth of gear 34 is shown in FIG. 2. 
     Extending from the end of adaptor 2 opposite to cutting bit 6 is a flexible rubber bulb 48 which is connected to lower housing 28 by interengagement between housing lock member 50 and bulb lock member 52. The distal end of bulb 48 ends at terminating ring 54. 
     When screw gun 4 is operatively engaged with adaptor 2, locator 58, chuck 60, and screw driving bit 62 are inserted within the hollow interior of bulb 48 with a Phillips head screw driving bit 62 operatively received by Phillips drive element head 46. A cross-sectional view of the engagement between adaptor 2 and screw gun 4 along line 3--3 of FIG. 1 is shown in FIG. 3. Terminating ring 54 abuts against sleeve 56 of screw gun 4. Bulb 48 is capable of operatively engaging screw guns having a locator 58 and a chuck 60 of varying lengths. For screw guns with a short locator and/or chuck, bulb 48 is longitudinally compressed (i.e., terminating ring 48 moves closer to lock member 52) so that screw driving bit 62 fits into drive element head 46. For screw guns with longer locators and/or chucks, bulb 48 will be subjected to less compression when utilizing the adaptor. 
     FIG. 4 is a perspective view of the adaptor of the present invention in use. When it is desired to operatively engage adaptor 2 with screw gun 4, the casing formed by upper housing 18 and lower housing 28 is grasped between thumb T and fingers F of hand H and moved toward screw gun 4 in the direction of arrow A. After ring 54 of bulb 48 abuts sleeve 56, as shown in FIG. 1, movement of the adaptor in the direction of arrow A compresses bulb 48 longitudinally until screw driving bit 62 is fitted within drive head 46. When adaptor 2 is in this position, operation of screw gun 4 turns rotary cutting bit 6. During such periods of operation, adaptor 2 is maintained in operative engagement with screw gun 4 by using hand H to hold adaptor 2 in engagement with screw gun 4. When cutting is completed and it is desired to use screw gun 4 for its conventional purpose of driving screws, adaptor 2 can be moved out of operative engagement with screw gun 4 by grasping the casing formed by upper housing 18 and lower housing 28 between thumb T and fingers F of hand H and moving it in a direction opposite arrow A. After adaptor 2 is moved off the end of screw gun 4, the adaptor can be placed in a carpenter&#39;s pocket or tool belt for subsequent use. 
     Internally, when adaptor 2 is operatively engaged with screw gun 4, screw driving bit 62 is fitted into Phillips head drive element 46 such that rotation of screw driving bit 62 turns drive element 46 and, therefore, gear 42. The turning of gear 42 causes gear 36 to rotate by virtue of their interengaging teeth. The rotation of gear 36 imparts rotation to gear 34, because both are commonly and coaxially mounted on shaft 38. The teeth of gears 34 and 32 are in interengagement so that rotation of gear 34 causes gear 32 to turn. The turning of gear 32 ultimately rotates cutting bit 6 by virtue of their being mounted on a common shaft 16. Rotation of these parts is facilitated by mounting drive head 46 on bearing 44, shaft 38 on bearings 40 and 24, and shaft 16 on bearings 20 and 22. By virtue of their difference in diameter, gears 36 and 32 rotate two to five times, preferably three times, faster than gears 42 and 34, respectively. Since gears 32, 34, 36, and 42 operate in a serial fashion, the net effect of this rotational speed variation causes rotary cutting bit 6 to turn four to ten times, preferably six times, faster than screw driving head 62. Adaptor 2 enables screw gun 4 to cut holes in gypsum wall board even though the screw gun&#39;s rotational speed is insufficient to effect such cutting. 
     Although the invention has been described in detail for the purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention which is defined by the following claims.