Abstract:
A screw driving device is provided which can counter-sink a screw at angles off of normal from a workpiece. The device includes a shank held in contact with a screw bit to drive the tip when a plurality of balls are held in contact between a screw bit head and a sleeve surrounding the shank and to disengage the shank from the bit when the screw is at a desired counter-sunk depth. The disengagement of the shank from the screw bit is provided by permitting the plurality of balls to slide out of contact between the rotating shank and bit to thus disengage the shank from the screw bit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/129,008, filed May 29, 2008, which is a continuation-in-part of U.S. application Ser. No. 11/363,951 filed Mar. 1, 2006, now U.S. Pat. No. 7,387,054 issued Jun. 17, 2008 (which is hereby incorporated by reference). 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device for driving screws, and in particular, a device for driving screws having a drive mechanism to countersink screws into a workpiece. 
     BACKGROUND OF THE INVENTION 
     Conventional devices for driving screws using a power tool such as a drill or the like are common in the art. These devices have a screwing head with a screw bit tip end which fits onto the head of a screw and a driveshaft end which is attached to the drive mechanism of the power tool. Recent advancements in screwing heads include devices with drive mechanisms which allow a screw to be counter-sunk at or below the surface of a workpiece. For example, the drive mechanism may include a clutch system in which a driveshaft is disengaged from the drive mechanism of the power tool to thereby stop the bit from turning when a desired counter-sinking depth is achieved. At the counter-sinking depth, the drive mechanism disengages from the screw bit thereby ceasing rotation of the screw bit, and likewise ceasing the turning of the screw. Examples of prior screwing heads include the devices of U.S. Pat. Nos. 4,287,923 and 4,753,142. 
     One disadvantage of prior screwing heads is that the radius of the screwing head proximate the screw driving bit is relatively large. A relatively large screwing head limits the number of degrees off normal the screwing head can be from the workpiece and still completely counter-sink the screw. Specifically, the suitable angle at which the screw can be driven into a workpiece, relative to the surface of the workpiece, is determined by the radius of the screw head, the radius of the screwing device proximate the bit tip, and the counter-sink depth. If the angle is too great, as the screw enters the workpiece at an angle, the drive mechanism of the screwing head will disengage from the screw bit, resulting in part of the head of the screw remaining above the surface of the workpiece, and therefore not counter-sunk into the workpiece. Although it is preferable to direct or drive screws into a workpiece at an angle normal (perpendicular) to the workpiece, often a screw is not perfectly normal and may be at an angle relative to the workpiece. With conventional screw driving heads, which have relatively large radii, e.g. 7.00 to 8.50 mm, the maximum angle at which the screw can be relative to the workpiece is typically less than 6.5 degrees off normal, i.e. 83.5 degrees relative to the workpiece surface. Since, the maximum angle between the screw and the workpiece surface in order to completely counter-sink a screw is determined by the radius of the screw head, the radius of the screwing driving device proximate the tip end and the counter-sink depth, the relatively large screw driving head radii of prior screwing heads limits the angle at which a screw can be driven and countersunk into a workpiece. 
     Accordingly, there is a need in the art for a screwing head which permits a screw to be at an angle greater than 6.5 degrees off of normal and still be able to counter-sink the screw into a workpiece. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a screw driving head which can accommodate driving a screw into a workpiece at angles off of normal and counter-sink the screw into the workpiece. The screw driving head accomplishes this with a device having a relatively smaller radius than conventional driving devices. 
     The present invention, in one form, is a device for driving screws comprising a shank having an end portion defined by a wall of annular cross-section defining a seat. The end portion terminates at an end surface. A plurality of radial bores are formed in the annular wall of the shank. A screw bit has a head end which is received in the seat of the shank and a driver end adapted to drive a screw. A sleeve surrounds at least a part of the end portion of the shank and is axially movable relative to the shank. The sleeve has a surface facing the shank with a recessed portion, which may comprise, for example, plurality of recesses. The sleeve has a bottom surface with an aperture through which the screw bit is disposed. A spring is disposed between the end portion of the shank and the bottom of the sleeve to provide a biasing force between the shank and the sleeve. A plurality of balls are disposed in respective bores in the end portion of the shank. The balls, in a driving configuration, are held in engagement with the screw bit head. The balls in a non-driving configuration are movable in a radial direction away from the screw bit head into the recessed portion, disengaging contact with the screw bit head. 
     The present invention in another form thereof concerns a method for counter-sinking a screw into workpiece. The method includes inserting the head of screw onto a screw bit end of a counter-sinking screw driving device having a drive mechanism to permit the screw to be counter-sunk into a workpiece at/or below a surface thereof before disengaging a driveshaft from the screw bit. The threaded end of the screw is pressed into a workpiece with a shaft of the screw forming an angle with the workpiece surface between 90 degrees and at least less than 83.7 degrees. The counter-sinking device is activated to cause the bit end to rotate, and thereby drive the screw into the workpiece and counter-sink the screw so that the top surface of the head of the screw surface is at or at least slightly below the surface of the workpiece before the driveshaft disengages from the screw bit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded view of a screw driving device in accordance with the present invention; 
         FIG. 2  is an elevational view of the screw driving device of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the device of  FIG. 1  taken along line  3 - 3  of  FIG. 2  with the device shown in a screw driving engagement configuration; 
         FIG. 4  is a cross-sectional view of the device similar to  FIG. 3  but showing a disengaged, non-driving configuration; 
         FIG. 5  is a plan view of the device of  FIG. 2 , viewed from below; 
         FIG. 6 a    is a schematic view of a prior screw driving device shown driving a screw into a wall surface workpiece and  FIG. 6 b    is a schematic view of the prior screw driving device shown driving a different screw into a wall surface; and 
         FIG. 7 a    is a schematic view showing a screw driving device in accordance with the present invention driving a screw into a wall surface and  FIG. 7 b    is a schematic view of the present driving device shown driving a different screw into a wall surface. 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to the Figures in which like elements are numbered the same throughout the views, screw driving device  10  comprises a drive mechanism in the form of a shank  11  which has an end portion  12  with an annular wall  13 , an end surface  14  and a top surface  15 . A plurality of bores  16  are formed through annular wall  13 . A respective one or a plurality of balls  17  are disposed in the bores  16 . 
     Screw bit  20  has a head end  21  received in a seat portion  24  of the shank  11  defined by the annular wall  13 . A screw bit tip  22  which is opposite the head end  21 , is adapted to fit onto the head of a screw  40  to be driven. 
     Sleeve  30  surrounds the annular wall  13  of the shank  11  and a substantial portion of the screw bit  20  including head end  21 , with the bit tip  22  extending through sleeve aperture  31 . Recessed portion  32  is formed on the inner surface  33  of sleeve  30  so that the plurality of the balls  17 , in the non-driving configuration when the balls move away from contact with screw bit head  21 . A pin  18  is disposed through sleeve slots  39  and shank apertures  19  to lock the shank  11  with the sleeve  30 . 
     Advantageously, radius  52  of the sleeve  30  proximate the bit tip  22  is less than 8 mm. This relatively small radius allows a screw to be completely countersunk into a workpiece even when directed into a workpiece at an angle off normal. Conversely, the larger radii of prior screwing devices prevents the complete countersinking of screws directed into a workpiece when the angle off normal is too great. 
     For example, referring to  FIG. 6 , and in particular,  FIG. 6 a   , the relatively larger radius of prior device  60 , with a diameter of 20 mm/radius of 10 mm, can countersink screw  41  with a screw head diameter of 8 mm into wall  62  from 90 degrees up to 83.9 degrees (6.1° off normal) relative to the wall surface before the exterior edge  63  contacts the wall. Referring to  FIG. 6 b   , the prior device  60  can countersink screw  42  with screw head diameter of 7 mm into wall  62  from 90 degrees up to 83.7 degrees (6.3° off normal) relative to the wall surface before the exterior edge  63  contacts the wall. When driving screw  41  with a 8 mm head diameter, at angles greater than 83.9 degrees, the exterior edge  63  will contact wall  62  prior to fully countersinking the screw  41  at or below the surface of wall  62 , resulting in a portion of the screw  41  being above the surface of the wall. Similarly, when driving screw  42  with a 7 mm head diameter, at angles greater than 83.7 degrees, the exterior edge  63  will contact wall  62  prior to fully countersinking the screw  42  at or below the surface of wall  62 . 
     However, as shown in  FIG. 7 , the narrower screw driving device  10 , with 14 mm diameter/7 mm radius, can countersink screws directed in a workpiece, such as wall  62 , at angles from 90 degrees up to 82.2 degrees (7.8° off normal) when driving screw  41  with a 8 mm screw head and from 90 degrees up to 81.2 degrees (8.8° off normal) when driving screw  42  with a 7 mm screw head diameter. As a result, the screw driving device  10  can countersink screw  41  directed at a workpiece at an angle up to 82.2 and screw  42  directed at an angle up to 81.2 degrees since edge  64  will not contact wall  62  before the head of the respective screw  41 ,  42  has been countersunk. Conversely, the prior device  60  with 20 mm diameter/10 mm radius, shown in  FIGS. 7 a  and 7 b    as a broken line, cannot countersink screw  41  when directed at an angle over 83.9° as its exterior edge  63  will contact the wall  62  before the head of screw  41  is countersunk. Likewise, prior device  60  cannot countersink screw  42  directed at an angle over 83.7 degrees as edge  63  will contact wall  62  before countersinking screw  42 . 
     Referring back to  FIGS. 1-5 , a spring such as coil spring  34  is located between the shank bottom  14  and a sleeve bottom inner surface  35 , with the screw bit  20  being disposed through the center of a coil formed by the spring  34 . The spring  34  provides a biasing force between the shank  11  and the sleeve  30 . A magnet  36  is located at the bottom of  31  near the tip  22  to magnetize the tip  22  so that a screw  40  comprised of a suitable magnetic metal will be attracted to and remain magnetically affixed to the tip  22  when placed thereon. A retainer clip  37  is disposed in tip notches  25  and shank groove  38  to retain the screw bit  20  in the seat  24 . 
     The present screw driver device  10  is designed to fit on the end of a drill or other power tool which provides rotational motion to shank  11 . In use, a user inserts the head of a screw  40  onto tip  22 , magnetized by magnet  36 . Spring  34  biases the shank  11  relative to the tip  20  so that balls  17  are in tight contact between the bit head  21  and the inner surface  33  of sleeve  30 , thus defining the driving engagement configuration of device  10  ( FIG. 3 ). Since, the plurality of balls  17  are held in contact with both the bit head  21  and the inner sleeve surface  33 , rotational force applied to shank  11  will turn tip  22  and thus turn screw  40 . 
     A user then presses the threaded tip end of screw  40  attached to the device into the surface of a workpiece in the direction of arrow  50 . Subsequently, the drill or power tool is activated to cause shank  11  to rotate and thus screw the screw  40  into the workpiece. Once the device has reached a desired depth defined by the length  44  and the distance  51  defined by the distance between balls  17  and the recessed portion  32  when the device  10  is at rest, force applied to shank  11  acts against the biasing force of spring  34  to urge the shank  11  in the direction  50 , eventually resulting in the plurality of balls  17  being moved into the recessed portion  32  and thus away from screw bit head  21 . As a result, screw bit  20  disengages from the drive mechanism of shank  11 , and the device is transformed into a disengaged configuration ( FIG. 4 ). When the device  10  is withdrawn from the workpiece in a direction  51 , the spring  34  forces the shank  11  away from the sleeve  30  which results in the plurality of balls  17  moving away from recesses  32  and again in contact with head  21  and inner sleeve surface  33 , re-establishing connectivity or driving engagement between shank  11  and screw bit  20 . As a result, the device is transformed back into the engagement or driving configuration. 
     As noted, the depth a screw will be countersunk into a workpiece is defined by the length  44  of the portion of tip  22 , i.e. the distance between the bottom of the sleeve  30  and the top of the top surface of the head of the screw to be driven, and distance  51 , defined by the distance the balls  17  traverse when the device  10  is transformed from the driving configuration to the disengaged configuration. Therefore, the countersunk depth can be varied by replacing the screw bit  20  with a screw bit which is longer, resulting in a deeper countersinking depth or a screw bit which is shorter, resulting in a more shallow countersinking depth. Screw bits are interchangeable with device  10  by withdrawing the existing screw bit  20  which is held in place by retainer clip  37 , and inserting a new screw bit through sleeve aperture  31 , until the new screw bit is engaged with retainer clip  37 . 
     Alternatively, the depth a screw will be countersunk into a workpiece can be varied by replacing the sleeve  30  with one which is longer or shorter, or contains a longer or shorter screw bit. Sleeve  30  is replaceable by removing pin  18 , withdrawing the sleeve  30 , inserting a second sleeve, and replacing the pin  18 . 
     It will now be clear to one of ordinary skill in the art that the present device has advantages not found in previous counter-sinking screw driver devices. The relatively small radius allows a screw to be completely countersunk into a workpiece even when directed into a workpiece at an angle off normal. The relatively narrow radius allows the driver to be at an angle relative to a workpiece of between 90 degrees and at least 82.2 degrees and more preferably at least 81.2 degrees, while completely countersinking the screw at or below the surface of the workpiece. Specifically, the more narrow radius means that the bottom of the sleeve  30 , proximate the bit tip  22  will not impede the counter-sinking of a screw by disengaging the shaft  11  from screw bit  20  when a device is at an angle off normal to a workpiece up to at least 81.2 degrees. Since, the maximum angle at which the device can be off normal relative to a workpiece is defined by the radius  52  of the device and by the radius of the screw head, a screw having a more narrow screw head radius will allow the present device to counter-sink the screw at increasing angles off of normal from a workpiece. 
     Further, the smaller radius  52  is accomplished, in part, by arranging the spring  34  below the shank bottom  12  and around the screw bit  20 , thus allowing for a reduction in the radius of the device relative to prior devices such as the one of the U.S. Pat. No. 4,753,142. 
     Although the invention has been described above in relation to preferred embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected in these preferred embodiments without departing from the scope and spirit of the invention.