Abstract:
A pistol grip drill ( 1 ) has two control triggers ( 3  and  9 ) on its hand grip ( 4 ). One trigger ( 3 ) controls power to a motor in a casing ( 2 ) of the drill and the other trigger ( 9 ) initiates a sequence which interchanges the positions of two chucks ( 20, 21 ). The chucks ( 20, 21 ) are mounted on a forward extension ( 8 ) of the casing ( 2 ). The extension ( 8 ) has two degrees of freedom. It is firstly capable of rotating through ninety degrees about the axis of a pivot ( 14 ) to bring the unused chuck to the driving position in front of the casing ( 2 ). The second degree of freedom allows the extension to be then rotated about the driving axis of a drill drive shaft ( 5 ) so that the displaced chuck is moved from an upwardly-pointing position to a downwardly position directly in front of the pistol grip. The interchanging of the chucks ( 20, 21 ) can be controlled by the hand of the user holding the hand grip ( 4 ).

Description:
FIELD OF THE INVENTION 
   The present invention relates to a pistol-grip tool having two chucks that are interchangeable in position, and is more specifically concerned with such a tool capable of being controlled by one hand of a user so that his/her other hand is freed for some other purpose. 
   BACKGROUND OF THE INVENTION 
   The use of a tool such as an electric drill, at an overhead position presents special problems. When drilling a hole it is often necessary to first form a pilot hole and then enlarge it with a second drill of larger diameter. If the user is standing on a ladder to form the pilot hole, it is necessary for him to descend the ladder if using a single chuck drill, and then replace the drill bit with one of larger size. The user must then ascend the ladder once again to find the pilot hole to be enlarged. If the pilot hole is not sufficiently deep for the larger drill, the whole process must be repeated. 
   The need for a tool having two chucks that are interchangeable in position has long been recognized and is the subject of a number of patented proposals. However these proposals have either resulted in a tool that is impracticable to use or which does not allow the user to interchange the positions of the chucks without using both hands. Thus the advantage of having one hand free for some other purpose, such as to hold a ladder the user may be standing on, is lost. 
   It is therefore an object of the present invention is to provide an improved two-chuck drill. 
   SUMMARY OF THE INVENTION 
   According to the present invention there is provided there is provided a pistol-grip tool having first and second chucks one of which may be replaced by the other at a common driving position; a releasable device operable to disconnect a rotary drive shaft from the chuck at the driving position when the chucks are to be interchanged; a chuck-changing unit operable with drive obtained from a drill motor, after the releasable device has been released, to re-position and then to turn it about the drive shaft axis to occupy a position in front of the pistol-grip bringing the second chuck from a position in front of the pistol-grip to the common driving position; and a mechanism operable by the same hand of the tool user as is holding the pistol-grip, to initiate operation of the chuck-changing unit and the disengagement and re-engagement of the releasable device so that the drive from the drive shaft is only imparted to the chuck at the driving position when the other chuck is occupying a position in front of the pistol-grip of the tool. 
   ADVANTAGE OF THE INVENTION 
   An advantage of the tool of the present invention is that the chuck not in use always occupies a position in front of the pistol-grip where it is stationary and allows normal operation of the tool. When it is required to interchange the positions of the chucks this may be carried out, for example, by the user depressing a second trigger on the pistol grip while the tool is not working. This can be arranged to initiate a control sequence that interchanges the positions of the chucks, and then restores the driving connection between the drive shaft and the chuck at the common driving position. Preferably, the tool cannot transmit power from the drive shaft to either of the chucks until the chuck-interchange sequence has been completed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example, with reference to the accompanying largely diagrammatic drawings; in which: 
       FIG. 1  is a cross-sectional side view of the front end of a pistol-grip drill made in accordance with a preferred embodiment of the present invention, the drill shown having a first chuck stationed at a position of use in front of the drill; 
       FIG. 2  is a similar view to that of  FIG. 1 , this time showing a first stage of a preferred automated process for interchanging the positions of the first and a second chuck of the drill; 
       FIGS. 3 ,  4 ,  5 ,  6 , and  7 . are similar views to that of  FIGS. 1 &amp; 2 , each showing a further stage of the preferred automated process of interchanging the positions of the first and second chucks of the drill; 
       FIG. 8  is a cross-sectional front perspective view of the drill of  FIGS. 1 to 7 , this time showing the second chuck stationed at the position of use in front of the drill after the position of the first and second chucks has been interchanged; 
       FIGS. 9 &amp; 10  are cross-sectional side views of the drill of  FIGS. 1 to 8 , again showing the second chuck stationed at the position of use in front of the drill, but this time illustrating the final stages of the preferred automated chuck change process; and, 
       FIGS. 11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 , and  18 . are cross-sectional side views of the drill shown in  FIGS. 1 to 10 , this time showing a preferred automated process for returning the first chuck to the position of use in front of the drill, each figure showing a different stage of the preferred return automated chuck change process. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the figures, corresponding parts of the drill have the same reference numbers. 
   The drill front end shown generally at  1  includes the forward portion of a drill casing  2  containing an electric motor (not shown) controlled by a trigger switch  3  mounted on a pistol-grip  4  that is gripped by one hand of a user when the drill is in use. 
   The motor rotates a drill drive shaft  5  that can be reciprocated between two axially displaced positions, shown respectively in  FIGS. 1 and 2 , by a solenoid mechanism in a cylindrical box  6  surrounding the shaft  5 . An arrow  7  shows the direction of rotation of the shaft  5 . 
   The casing  2  has a forward extension  8  that can be rotated about the axis of the shaft  5  and also turned through ninety degrees in the same plane as the axis of the shaft. The shaft  5  carries a cylindrical gear  10  that reciprocates with the shaft and is rotated by it. The gear  10  has a ring of parallel teeth having tapered ends to assist their meshing with the teeth of a circular toothed track  12  extending around one side of a disc  13 . In practice only one quarter of the length of track  12  is used. The track teeth also have tapered ends to assist their meshing with the gear  10 . The disc  13  is pivotally mounted on a spindle  14  extending between the extension  8  and a collar  15  through which the shaft  5  is a close sliding fit. Opposite ends of the used section of the track  12  are respectively provided with stops  16  and  17  that limit the angle to which the gear  10  can travel around the track  12  when the shaft  5  is rotated. 
   As explained above, the connection between the casing  2  and the extension  8  allows the extension  8  two freedoms of movement. One freedom of movement includes a rotational movement of the extension  8  through 180.degree. about the axis of the shaft  5  as shown in successive  FIGS. 4 to 8 , and the second freedom of movement allows the extension  8  to rotate through ninety degrees about the axis of pivot  14  as shown in successive  FIGS. 2 to 4 . 
   The casing  8  carries two rotatable drill drive chucks  20  and  21  that project at right angles to one another, as shown in  FIG. 1 . The chuck  20  is shown in the driving position of the drill  1  and is illustrated supporting a conventional removable drill bit  23 . The other chuck  21  is illustrated supporting a counter-sinking bit  24  at a position at which it extends downwardly forwardly of the pistol-grip  4  of the drill  1 . 
   In the position of the drive shaft  5  illustrated in  FIG. 1 , the gear  10  is positioned forwardly of the track  12  so that the gear  10  and track  12  are not in mesh. However, if the mechanism in the box  6  is operated, the shaft  5  is retracted to the right of  FIG. 1  bringing the teeth of the gear  10  into mesh with the teeth of the track  12 . To establish a driving connection to the chuck  20 , 21  in use, the forward end of the shaft  5  is of hexagonal cross-section and fits within a socket of complementary cross-section of whichever of the chucks  20 ,  21  is in the driving position at the left-hand end of the drive shaft  5 . 
   The operation of the chuck-changing mechanism shown in the drawings will now be described. 
   With the parts of the drill  1  in the positions shown in  FIG. 1 , the trigger  3  can be squeezed so that the drive from the drill motor (not shown) is transmitted through the shaft  5  to rotate the drill bit  23  in order to make a drill hole. When a drill hole of the appropriate depth has been formed, its mouth can be countersunk by bringing the chuck  21  and the countersinking bit  24  to the drive position in place of the drill bit  23 . This is achieved by squeezing a second trigger  9  positioned above the trigger  3 . It should be noted that a user of the drill  1  can squeeze the second trigger  9  with the same hand as is holding the pistol-grip  4  and operating the first trigger  3 . 
   The action of pressing the trigger  9  is to energise a sequencing circuit that carries out the following steps: The drill drive motor is first temporarily de-energised and the mechanism in the box  6  is operated against the resilient bias of a spring (not shown) to withdraw the forward end-portion of the shaft  5  from the socket in the chuck  20 . Simultaneously the gear  10  is brought into mesh with the teeth of the used section of the track  12 . This is shown in  FIG. 2 . The user maintains the trigger  9  depressed and the sequencing circuit then re-energises the driving motor (not shown) so that the gear  10  is rotated to drive the disc  13  in its own plane in a clockwise direction by way of the meshing gear  10  and track  12 . This displaces the two chucks  20 , 21  angularly so that the chuck  21  moves towards the driving position formerly occupied by chuck  20  and the chuck  20  moves towards a vertically upward position. Successive stages in this movement are shown in  FIGS. 3 and 4 . When the chuck  20  reaches the position shown in  FIG. 4 , the gear  10  abuts the stop  16  so that further rotation of the disc  13  about the axis of the spindle  14  is prevented. One freedom of movement of the extension  8  has then been completed. 
   As the gear  10  cannot rotate further along the track  12 , further rotation of the drive shaft  5  causes the extension  8  and disc  13  to rotate bodily around the axis of the drive shaft  5 . This moves the chuck  20  from the position shown in  FIG. 4  through the successive positions shown in  FIGS. 5 ,  6  and  7  to the position shown in  FIG. 8  at which the chuck  20  is positioned directly in front of the pistol-grip  4 . During this rotation of the chuck  20  the second chuck  21  remains in the driving position of the drill  1  as shown. Once the chuck  20  has reached the position shown in  FIGS. 8 and 9 , a mechanical switch (not shown) is operated by the extension  8  to stop operation of the mechanism in the box  6  and de-energise the drill drive motor (not shown). The spring (not shown) associated with the mechanism in the box  6  then advances the front-end of the drive shaft towards the front of the drill  1 . This forward movement of the drive shaft  5  disengages the gear from the track  12  (as shown in  FIG. 10 ), and the forward end of the drive shaft  5  then enters the socket in the back of the chuck  21  to establish a driving engagement between the drive shaft  5  and the chuck  21 . On completion of this movement of the shaft  5 , the forward movement of the drive shaft  5  operates a switch (not shown) to allow the operation of the trigger  3  to energise the drive motor (not shown) once again and enable the countersinking bit  24  in the chuck  21  to be used. 
   If it is again required to interchange the positions of the chucks  20  and  21 , the above procedure is repeated as shown in the sequence of  FIGS. 11 to 18 . The mechanism in the box  6  is operated to withdraw the drill shaft  5  from the chuck  21  against the force of the resilient spring bias (not shown), and to temporarily de-energise the electrical circuit to prevent operation of the drill motor (not shown) from the trigger  3 . As shown in  FIG. 11  the withdrawal movement of the shaft  5  brings the gear  10  into mesh once again with the teeth of the arcuate track  12  as shown in  FIG. 11 . When the trigger  9  is now squeezed, the electrical circuit to the motor (not shown) is again energised by the sequencing circuit but in a way which reverses its direction of rotation. The shaft  5  is now rotated in the direction indicated by the arrow in  FIG. 12 , to rotate the disc  13  in a counterclockwise direction, as shown in  FIG. 12 , about the axis of the spindle  14 . 
   The counterclockwise movement of the disc  13  moves the chuck  21  upwardly and brings the chuck  20  into alignment with the drive shaft  5 , as shown in  FIG. 13 . This movement is completed when the track  12  has turned through ninety degrees and the gear  10  abuts the stop  17  at the end of the track  12 . When this occurs, further rotation of the track  12  is prevented and the turning movement of the shaft  5  is imparted to turn the disc  13  and extension  8  bodily about the axis of the shaft  5 . This brings the chuck  21  from a vertically upwards position shown in  FIG. 13 , through the stages shown in  FIGS. 14 ,  15  and  16 , to the vertically downwards position shown in  FIG. 17  when it is located a short distance in front of the pistol-grip  4 . This movement is terminated by the actuation of a switch (not shown) responsive to movement of the extension  8 . The mechanism in the box  6  is de-energised by the switch to allow the resilient spring bias (not shown) on the shaft  5  to move the shaft  5  axially in a forward direction to bring its free end-portion into engagement with the socket at the back of the chuck  20 . Simultaneously the gear  10  is disengaged from the track  12  and the parts of the drill  1  assume the positions shown in  FIG. 18 . The trigger  9 , which initiated the interchange of the two chucks  20  and  21 , is then released automatically by the forward movement of the shaft  5  to allow the drill  1  to be again operated by squeezing the trigger  3 . 
   In a modification (not shown) of the above-described arrangement, the extension  8  carries two opposed spaced parallel tracks  12  which share a common axis of rotation and respectively mesh with the teeth of the gear  10  on its opposite sides. The gear  10  is thus trapped between the two tracks so that a dynamically strong arrangement results in which the risk of the teeth of the gear  10  being forced out of engagement with the teeth of the tracks  12  when under load, is greatly reduced. The additional track  12  used in this modification turns freely about the axis of the spindle  14  and thus is simply an idler and does not participate in the transmission of drive between the shaft  5  and the chuck  20 / 21  at the driving position in front of the extension  8 .