Abstract:
A drive system for releasably interconnecting a motor shaft of a rotary hand held power tool and an input shaft of an attachment device. The system includes an elongated flexible drive shaft connected to the input shaft, wherein the flexible drive shaft has an outer end portion with a non-circular cross-section configured to engage a complementarily shaped cavity of an output shaft operatively attached to the power tool motor shaft, where the output shaft has a generally cylindrical outer configuration along its length and a rearward mounting portion for attachment to the motor shaft, an intermediate portion having the complementarily shaped cavity for receiving the flexible drive shaft and a forward portion with an enlarged concentric opening for receiving and guiding the outer end portion of the flexible drive shaft into the cavity during mounting the attachment device on the power tool.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to small handheld power tools, and more particularly to a dust collection attachment system for such tools. 
     Small handheld power tools that perform drilling, sawing and other types of cutting and the like are known in the prior art and have been widely used by hobbyists, artisans, tradesmen and others in a wide variety of applications. Such rotary hand tools generally have a motor with a rotary output shaft that extends from a nose portion that is more recently configured to connect to various accessories or attachment devices. Some of these rotary hand tools are quite powerful for their size and are used by tradesmen in the building trades as spiral saws that use a side cutting rotary bit to penetrate and rapidly cut holes in drywall sheets and other materials for electrical switches, outlets, light fixtures and the like. 
     As is known in the art, such rotary hand tool tasks can be more easily performed by using an attachment device that is attached to the tool. For example, a right angle attachment device may be mounted on the power tool and such devices may be configured to drive a circular saw blade, a grinding wheel, a sanding pad or polishing pad. 
     Such a right angle attachment device has an input shaft that must be interconnected with the output shaft of the tool when the attachment device is mounted on the tool. The interconnection can present problems resulting from the relatively high speed operation, together with misalignment of the two shafts, which can create undesirable vibration. A drive system that minimizes such vibration and facilitates quick and easy mounting and removal of such attachment devices is desirable. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to a drive system for releasably interconnecting a motor shaft of a rotary hand held power tool and an input shaft of an attachment device that is mounted thereon, the system comprising, an elongated flexible drive shaft connected to the input shaft of the attachment device, the flexible drive shaft having an outer end portion with a non-circular cross-section configured to engage a complementarily shaped cavity of an output shaft operatively attached to the power tool motor shaft, an elongated output shaft operatively connected to the motor shaft of the power tool, the output shaft having a generally cylindrical outer configuration along its length and having a rearward mounting portion for attachment to the motor shaft, an intermediate portion having the complementarily shaped cavity for receiving the flexible drive shaft and a forward portion with an enlarged concentric opening for receiving and guiding the outer end portion of the flexible drive shaft into the cavity during mounting the attachment device on the power tool. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view taken from the front left of a rotary handheld power tool that incorporates an embodiment of the present invention; 
         FIG. 2  is an isometric view of a right angle attachment device which also incorporates an embodiment of the present invention, with the attachment device being capable of being mounted to the power tool shown in  FIG. 1 ; 
         FIG. 3  is a cross section taken through the center of the output shaft of the tool shown in  FIG. 1 ; 
         FIG. 4  is an isometric view of a portion of the output shaft shown in  FIG. 3 , having a collet inserted in the outer end thereof; 
         FIG. 5  is a view similar to  FIG. 4  wherein a collet nut is attached to the output shaft; 
         FIG. 6  is a cross-section taken generally through the middle of the output shaft, collet and collet nut shown in  FIG. 5 ; 
         FIG. 7  is a cross-section of a portion of the power tool shown in  FIG. 1 , with the attachment device shown in  FIG. 2 , with both being shown in cross section generally through the center thereof, but illustrating the attachment device in position where it is beginning to be mounted to the power tool; and 
         FIG. 8  is a cross-section similar to  FIG. 7 , but showing the attachment device attached thereto, and more particularly showing the attachment device mounted and secured to the power tool. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to a drive system for releasably interconnecting an output shaft of a rotary handheld power tool or the like and an input shaft of an attachment device that is mounted on the power tool. Such a drive system may be particularly desirable for small handheld power tools having an elongated housing with a rotary output shaft is provided at a nose portion thereof, wherein the nose portion is configured to attach an attachment device thereto. Such an attachment device may be a right angle drive which has its own output shaft that may drive a circular saw blade, grinding wheel, or the like. 
     The attachment device has an input shaft that must be interconnected with the output shaft of the power tool and it has been known that the interconnection of these two components can produce undesirable levels of vibration at relatively high operating speeds if there is misalignment of the shafts. Such vibration can be reduced by having the input shaft of the attachment device be made of a flexible material, which can be a multiplicity of parallel steel wires that are compressed under high pressure to form a shaft having a non-circular end, and preferably a square end, for engagement with the output shaft of a power tool, but which is sufficiently flexible that it can compensate for slight misalignment and significantly reduce vibration that would otherwise occur. Such flexible shafts are known in the prior art. 
     Embodiments of the drive system of the present invention greatly facilitate easy and fast mounting of an attachment device to such a power tool without interfering with a common use of the power tool where a collet and collet nut can be installed to attach standard tool bits to the output shaft, such as spiral saw bits and the like. 
     Turning now to the drawings and particularly  FIG. 1 , an elongated power tool, indicated generally at  10 , is shown and has an elongated housing, indicated generally at  12 , and a nose portion, indicated generally at  14 . The housing has a top surface  18 , side surfaces  20  and a bottom surface  22  and a motor is contained within the housing. The size of the housing  12  is such that most users can grip the tool with one hand with their fingers curling around under the bottom portion  22 . When a person is holding the tool  10  as described, their thumb is in position to operate a switch  32  which turns on the motor for operating the tool. The switch  32  is preferably designed so that can be slidingly moved between its ON and OFF positions. The tool  10  shown in  FIG. 1  has a power cord  34  that can be plugged into a source of AC power. It should be understood that power tools similar to that shown in  FIG. 1  may incorporate battery packs and in such event, they may be slightly larger. The present invention is suited for use with power tools that use such power packs. 
     The nose portion  14  has an attachment interface that is described in a co-pending patent application entitled “AN ATTACHMENT INTERFACE FOR ROTARY HAND TOOLS”, Ser. No. 12/700,003 (U.S. Patent Application Publication No. 2011/0188957), that is filed concurrently with this application and is incorporated by reference herein. The nose portion, which may be made of aluminum, has a cylindrical wall, indicated generally at  40 , which has outer threads  42 , as well as an inner surface that has a number of keys  44  that are configured to engage complementary shaped keys on an attachment device that may be mounted on the nose portion  14 . 
     The tool  10  has an output shaft, indicated generally at  50 , which is best shown in  FIGS. 1 and 3  which is configured to be able to accept a collet and collet nut for mounting a cylindrical tool bit, such as spiral bit, for example, and is also configured to accept an input shaft of an attachment device that can be mounted on the nose portion  14  of the tool  10 . 
     The output shaft  50 , which may be made of steel, is best shown in  FIG. 3  and has a rearward (i.e., the left end) mounting portion, indicated generally at  52 , for attachment to a drive shaft of the motor of the power tool  10 , which is an armature shaft of the motor, an intermediate portion, indicated generally at  54 , that is configured to receive an input shaft (which may also be made of steel) of the attachment device and a forward portion, indicated generally at  56 , that is configured to initially guide the input shaft of an attachment device into the intermediate portion  54  as well as interact with a collet and collet nut for mounting a tool bit to the output shaft  50 . It is noted that the three portions, i.e., the mounting portion, intermediate portion and forward portion are approximately equal in length, although the proportions of each relative to the other may be varied as desired. 
     With regard to the mounting portion  52 , it has a central bore  60  that has a chamfered end surface  62  to facilitate entrance by the armature shaft  64  (see  FIGS. 7 ,  8 ) of the tool motor. The bore  60  preferably is only slightly larger than the outer diameter of the armature shaft  64 , so that it is securely fastened therein after the mounting portion is compressed or crimped onto the shaft  64 . The mounting portion  52  also has radial openings  66 , each with a chamfered outer surface  68  which is sized to receive a pin of a locking mechanism for locking the output shaft from rotation so that a tool bit can be firmly secured in a collet by tightening a collet nut. 
     The mounting portion  52  has the largest diameter of any of the portions  52 ,  54  or  56  and the interface between the mounting portion  52  and the intermediate portion  54  defines an annular shoulder  72 . The intermediate portion  54  has an outer surface  74  that has a diameter slightly larger than the outer surface  76  of the forward portion  56  so that a front bearing ( 104 ,  FIGS. 7 and 8 ) can be easily slipped on the forward end  56  without interference with the inside surface of the inner race of such a bearing and be mounted on the outer surface  74  of the intermediate portion  54 . The outer surface  74  also has an annular groove  78  for receiving a retaining ring ( 112 ,  FIGS. 7 and 8 ) that holds the front bearing in place. 
     The interface between the intermediate portion  54  and the forward portion  56  defines another shoulder  80  and the smallest outside diameter of the entire output shaft  50  is surface  82 . The surface  76  is slightly larger in diameter and it contains threads which are not shown but are well known to those of ordinary skill in the art for screwing or threading a collet nut onto the forward portion of the output shaft  50 . 
     The bore  60  of the mounting portion  52  is in communication with a cavity  84  that has a preferably square cross section. In this regard, the cross sectional configuration of the cavity  84  can be any non-circular shape that is complementary to the shaft that is inserted into it. This cavity  84  has a length sufficient to hold a complementary shaped shaft ( 98 ,  FIGS. 7 and 8 ) that may be inserted into the forward end portion  56 . It should be understood that any noncircular type of cross section that will enable rotation of the output shaft  50  to positively rotate a shaft that is located within it may be used. Thus, a five sided or hexagonal or other noncircular cross-sectional shape may be used. However a square cross-section is preferred because it does not require close tolerances between the size of the cavity  84  and the size of an input shaft that may be inserted in it. 
     The forward end portion  56  has an initial cylindrical bore portion  86  as well as a smaller step down portion  88  that in turn merges with an inclined conical portion  89  as well as a smaller diameter portion  91  that communicates with the cavity  84 . The progressively smaller inside diameters from the outer end extending inwardly facilitate easy initial insertion of an input shaft from an attachment device and effectively guides the same so that it can be inserted into the cavity  84 . 
     An attachment device is indicated generally at  90  in  FIG. 2  and comprises a right angle saw attachment device which can be mounted on the tool. The device will not be described in detail inasmuch as the present invention deals with only the interconnection of it with the tool on which it is mounted. In this regard, the device  90  has a main housing  92  and a rotatable collar  94  with internal threads  96  that are sized and configured to thread the collar  94  onto the threads  42  of the nose portion  14  of the powertool  10 . 
     The device  90  has an input shaft  98  which has a square outer end  100  that is sized and configured to fit within the cavity  84 . The input shaft  98  is preferably permanently secured such as being crimped in a gear shaft in the attachment device  90  so that it will not be lost when the attachment device is separated from the power tool  10 . The length of the shaft  98  is sufficiently long so that the outer square cross-section end portion  100  will penetrate the output shaft  50  so that it substantially fills the cavity  84  when the device is secured to the tool  10 . 
     In this regard, the view of  FIG. 7  shows the device with the end portion  100  penetrating into the forward portion  56  of the output shaft  50  before the collar  94  is threaded or screwed onto threads  42  of the nose portion  14  as shown in  FIG. 7 . When it is tightened as shown in  FIG. 8 , the square end portion  100  is fully inserted into the cavity  84 . 
     Parenthetically,  FIGS. 7 and 8  diagrammatically show a front bearing  104  with inner and outer races  106  and  108  with ball bearings  110  therebetween and a retaining clip  112  is located in the annular groove  78 . It is also noted that the mounting portion  52  is not completely shown in these drawings. 
     As previously mentioned, the forward portion  56  is configured to receive a collet and to this end, and referring to  FIGS. 4 ,  5  and  6 , a collet  120  is shown to fit within the bore  86 . The collet  120  is only partially inserted in the bore  86  in  FIG. 4 . A collet nut  122  is configured to be threaded onto the threaded surface  76 . As is typical, the collet nut has an inclined inner surface  124  that interacts with an inclined outer surface  126  on the collet and another inclined surface  128  engages the surface  89  ( FIG. 3 ) of the forward portion  56  as is known to those of ordinary skill in the art. When the collet nut  122  is tightened, the internal diameter of the central opening is reduced to provide a holding force on a tool bit inserted in the collet  120 . 
     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims. 
     Various features of the invention are set forth in the following claims.