Adjustable screw driver
SUMMARY OF THE INVENTION 
     An improved screw driver which is capable of adjusting its length according to various working reguirements by using a shank which has engaging teeth consecutively disposed on one of us sides and is inserted into a shank receiving tunnel inside a handle and held firmly in place by a control plate when one side of the square engaging hole is wedged in one of the teeth. 
     The shanks of commonly available screw drivers can be either fixed as one to the handle or removably attached thereto, the former can deal with only one type of screw each time with fixed tip, the latter is more available owing to its flexibilty of attaching different shank for different type of screw, and the subject matter having its shank equipped with two different tips and its length adjustable further increases the practicality of common screw driver. 
     It is obvious a problem which confronted by most people when using a screw driver to reach a spot just out of the reach of the shank, and in view of this, the inventor intends to provide a means for adjusting the length of shank according to working conditions. 
     The first object of the present invention is to provide an adjustable screw driver which takes advantage of a control plate having a rectangular engaging hole through which a shank having a plurality of engaging teeth is disposed, and the length of the shank can be freely adjusted when the side of the rectangular engaging hole is wedged between different engaging teeth. 
     The second object of the present invention is to provide an adjustable screw driver which takes advantage of a wire spring exerting resilient force on the control plate so to make the side of the engaging hole firmly and strongly engaged with the engaging teeth and prevent it from shaking or loosening in operation. 
     The further object of the present invention is to provide an adjustable screw driver which has a restraining board on the periphery of which a cut is disposed in view of easy operation of the control plate. 
    
    
     The feature, structure and operation of the present invention become clear with the description of the accompanying drawing as below: 
     DESCRIPTION OF DRAWINGS 
     Drawing: 
     FIG. 1 is a view of the assembly of the subject matter. 
     FIG. 2 is a view of the exploded components of the subject matter. 
     FIG. 3 is a sectional view of the assembled screw driver. 
     FIG. 4 is the sectional view of the subject matter with the engaging plate being pushed up to release the toothed shank. 
    
    
     Name of component: 
     1--handle 
     12--shank receiving tunnel 
     14--head 
     16--spring-fixing screw 
     18--screw hole 
     21--tip 
     3--restraining plate 
     32--screw mounting hole 
     34--cut 
     41--engaging hole 
     11--flute 
     13--control plate receiving groove 
     15--bottom 
     17--wire spring 
     2--shank 
     22--tooth 
     31--screw 
     33--square opening 
     4--control plate 
     42--aperture 
     DETAILED DESCRIPTION 
     Referring to FIG. 1 and FIG. 2, the present invention comprises a handle 1, a shank 2, a restraining board 3, a control plate 4, and the handle 1 is symmetrically grooved from head 14 to bottom 15 all around for easy grasp; a flute 11 which begins from the edge of the bottom and ends in the middle of the handle 14 with a screw hole is disposed for housing a wire spring 17 fixed therein by a screw 16 and extending into a rectangular control plate receiving groove 13 and engaging with said control plate 4 by setting its other end in an aperture 42 thereof; right at the center of said handle 1, a shank-receiving tunnel 12 is disposed for accession of said shank 2 with two different tips, and on said bottom 15 there are two symmetric screw holes 18 set about said tunnel for attaching said restraining board 3 thereto; said control plate 4 movable along said groove 13 having an said aperture 42 for accession of one end of said wire spring 17 so to enable said control plate to retractably move from right to left owing to the resilience of said wire spring 17, and at the center of said control plate there is a rectangular engaging hole 41 which is just as wide as the shank 2 for tight engagement, and for easy operation of said control plate, the other end opposing the end with an apperture is slightly upward bended; the said restraining board 3 is a circular one with a central square opening 33 which corresponds to the size of said shank 2 as well as the mouth of said tunnel 12, and two screw mounting holes 32 with screw head sinking bore are disposed for attaching said restraining board 3 thereto; and a cut 34 on the periphery of restraining board 3 is specially set in consideration of easy operation of said control plate 4; and a plurality of engaging teeth 22 in cooperation with said control plate 4 to rigidly joint the shank to said handle. 
     To assemble the said screw driver is very simple, by first fixing said wire spring 17 in said flute 11 on said handle 1 by screws 16, and secondly putting the protruding end of the wire spring 17 into said aperture 42 of said control plate 4 locating in the groove 13, and finally screwing said restraining board down to said bottom 15 of said handle 1 by screws 31 locating in screw holes 18 so that the control plate is confinedly disposed therebetween. 
     Referring continuously to FIGS. 3 and 4, the centers of said engaging hole 41 of the control plate 14 and of said central square opening 33 of the restraining board 3 are not collinearly disposed after assembling together so that said shank 2 with square cross section can&#39;t get through the above said openings until the slightly bended end of said control plate is pushed upward as shown in FIG. 4 to make the engaging hole 41 and the square opening 33 as well as the tunnel 12 collinearly located with their centers, and the one side toothed shank 2 is smoothly located in the tunnel 12 and firmly attached to said handle 1 by wedging said engaging hole 41 in between one pair of the teeth 22 when the control plate is released assumming its original position due to the resilient force of said wire spring 17. The length of the screw driver is adjustable with ease according to different requirements of working conditions. 
     The merits of the subject matter is briefly summarized in the following: 
     1. The length of the screw driver can be adjusted to facilitate its use in different working conditions. 
     2. The manufacturing and assembly of the screw driver is simple and economic in cost. 
     3. The shank can be firmly attached to said handle without loosening or shaking in operation.