Abstract:
A portable, air powered drill has an automated feed system and an adjustable dwell for producing countersunk holes in a workpiece. The feed system uses hydraulic cylinders and pneumatic control logic to control the feed rate, and the dwell time of a countersink drill bit at the end of the drill stroke. A movable mechanical stop permits an operator user to adjust countersink depth. The control logic provides fully automatic feed of the drill bit, and adjustment of the dwell time to consistently produce identical countersunk holes in a variety of workpiece materials.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of a provisional application No. 60/753,574 filed Dec. 22, 2005 under 35 USC Section 119 (e). 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to power operated drills, and deals more particularly with a portable drill having an automated feed and adjustable dwell for producing countersunk holes. 
     BACKGROUND OF THE INVENTION 
     Countersunk holes are commonly used throughout industry where it is necessary or desirable to recess the head of a fastener, such as a screw or rivet. For example, countersunk holes are extensively employed in the aircraft industry, where rivets are used to attach an outer skin to frame members. In this latter mentioned application, it is particularly important that the top of the rivet be flush with the outer surface of the skin, otherwise non-flush rivets disturb the airflow over the skin, creating turbulence which adds to drag on the aircraft. Consequently, it is important that the tapered side walls of the hole countersink have a precise depth calculated so that the top of the rivet is flush with the skin surface. 
     In the past, forming a countersunk hole in aircraft applications was a two step, manual process that involved drilling a hole of the desired diameter in a first operation, and then countersinking the hole with a countersink tool in a second operation. Because two steps were required using two different tools, the process was time consuming. In addition, because the process was performed manually, consistent results depended in large part on the skill of the operator. 
     Accordingly, there is a need in the art for a countersink drill that overcomes the deficiencies of the prior art discussed above. The present invention is directed towards satisfying this need. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a portable drill comprises stationary and movable portions and a feed motor for displacing the movable portion between home and displaced positions. The stationary portion is adapted to be mounted in a fixed position relative to a workpiece in which a hole is to be drilled. The moveable portion is mounted on the stationary portion for linear movement between the home and displaced positions, respectively representing top-of-stroke and bottom-of-stroke drill positions. The moveable portion includes a mount upon which a drill motor is attached. The stationary portion has an adjustable stop for limiting the displacement of the moveable portion and thereby determine the depth of the hole countersink. A dwell control is provided for controlling the length of time the drill remains in its displaced, bottom-of-stroke position. Displacement of the drill is performed automatically by a pneumatic control system. 
     According to another aspect of the invention, a drill is provided for use in a portable drill fixture for simultaneously drilling and countersinking a hole in a workpiece. The drill comprises a support attachable to the drill fixture; a mount carried on the support for linear movement toward and away from the workpiece; a drill motor carried on and moveable with the mount between top-of-stroke and bottom-of-stroke positions; a countersink drill bit driven by the drill motor; and, a drive system for automatically displacing the mount between the top-of-stroke and bottom-of-stroke positions. The drive system automatically feeds the drill bit into the workpiece so that the hole is drilled and countersunk in a single drill stroke. The drive system includes an adjustable dwell control for controlling the length of time the drill bit remains in the bottom-of-stroke position. The drive control also has an adjustable depth control for controlling the depth of the hole countersink. 
     According to still another aspect of the invention, a portable countersink drill is provided for drilling a countersunk hole in a workpiece. The drill comprises a drill motor for driving a countersink drill bit; a power operated drive for automatically moving the drill motor and drill bit through a drill stroke from a top-of-stroke position to a bottom-of-stroke position in which the drill bit drills and countersinks the hole; and, a dwell adjustment for adjusting the length of time that the drill motor dwells at the bottom-of-stroke position. The dwell adjustment includes a switch actuated by the drive when the drill motor reaches its bottom-of-stroke position, and a pneumatic control system responsive to actuation of the switch for delaying the return of the drill motor from its bottom-of-stroke position. The drive further includes an adjustable depth control for controlling the depth of the hole countersink. 
     An important advantage of the invention resides in its ability to form a countersink hole in a single drill stroke, and without the need for changing drill bits. Further, the automatic control of the present drill provides improved hole-to-hole consistency and better control of countersink depth. Automatic control of the drill assures controlled, repeatable feed rate for various types of workpiece materials. A further feature of the invention lies in its ability to control dwell time of the drill bit at the bottom-of-stroke position, thereby assuring that the hole countersink is fully formed. 
     Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detail description and accompanying drawings that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of one side of the countersink drill of the present invention, a cover having been removed to show internal parts of the drill; 
         FIG. 2  is a view of the opposite side of the drill shown in  FIG. 1 ; 
         FIG. 3  is a top view of the drill shown in  FIG. 1 ; 
         FIG. 4  is a perspective view of the drill shown in  FIG. 1 ; 
         FIG. 5  is a cross sectional view taken in a horizontal plane through forward portions of the drill shown in  FIG. 1 ; 
         FIG. 6  is a cross sectional view of the drill portion shown in  FIG. 5  but taken through a vertical plane; 
         FIG. 7  is an exploded, perspective view of certain components shown in  FIGS. 5 &amp; 6 ; 
         FIG. 8  is a side elevational view of a tool used to install and remove the drill bit used in the countersink drill; 
         FIG. 9  is a sectional view taken along the line  9 - 9  in  FIG. 8 ; 
         FIG. 10  is an end view of the tool shown in  FIG. 8 ; 
         FIG. 11  is a sectional view taken along the line  11 - 11  in  FIG. 9 ; and, 
         FIG. 12  is a combined block and schematic diagram of a pneumatic control system for the countersink drill 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to  FIGS. 1-7 , a pneumatically driven countersink drill  10  has a handle  12  connected with a pneumatic drill motor  14  and a pneumatic coupling  16  adapted to be coupled with a source of pressurized air. The drill motor  14  includes a cylindrical body which passes through and is secured to a generally rectangular bulkhead  18 . An outer cover  20  protectively encloses internal parts of the drill  10  and is secured to the bulkhead  18 , as with screws (not shown). A pair of pneumatic cylinders  22  are secured to opposite sides of the bulkhead  18  and have corresponding linear drive shafts  24  secured to a nosepiece  26 . A pair of hydraulic check cylinders  28  are also secured to the bulkhead and have output shafts  30  secured to the nosepiece  26 . The bulkhead  18  is slideably mounted on the nosepiece  26  by means of shafts  24 ,  30 . 
     The outer end of motor  14  is provided with a drill motor gearbox  32  which gears down an output shaft  34  to a desired speed. The output shaft  34  is coupled to an arbor  36  by means of a threaded sleeve  38 . A generally cylindrical aft stop  40  is received within a cylindrical opening within the nosepiece  26  and is secured to a countersink depth adjustment ring  42 . Ring  42  is mounted by threads (not shown) on the gearbox  32 . Rotation of adjustment ring  42  adjusts the longitudinal position of the aft stop  40 , and thus the depth of the countersink. 
     The outer end of arbor  36  is provided with a threaded internal opening  44  which receives the threaded end of a countersink drill bit  46 . Arbor  36  is journalled for rotation within a nose bushing  48  which is secured to the nosepiece  26  by means of a nose lock-on  50 . The outer end of the nose bushing  48  is provided with opposed slots  52  to permit a tool, such as an allen wrench, to be inserted into an allen head set screw that locks the bit  46  on the arbor  36 . A forward stop  49  is secured to the nose bushing  48  by means of a snap ring  54 , and includes an anvil  56  which extends upwardly through a longitudinal slot  58  in the nosepiece  26 . The aft stop  40  includes an upstanding ear  60  in which there is mounted a pneumatic dwell valve  62  having a plunger actuator  64 . Plunger actuator  64  is longitudinally aligned with and engages the anvil  56  when the drill  10  reaches the bottom of its drill stroke. 
     A compression spring  66  sleeved over one end of the nose bushing  48 , is captured between the forward stop  49  and a shoulder  68  formed on the aft stop  40 . Spring  66  biases the aft stop  40 , and thus bulkhead  18 , away from the workpiece toward its top-of-stroke position. The nosepiece  26  includes a cylindrical intermediate body  70  which may be clamped or otherwise removably attached to a drill fixture (not shown) which is used to precisely position the drill  10  over a workpiece (not shown). It may thus be appreciated that the nosepiece  26 , along with lock-on  50 , bushing  18  and the forward stop  49  are held stationary on the drill fixture during a drilling operation. On the other hand, the bulkhead  18  along with adjustment ring  42 , gearbox  32 , aft stop  40 , arbor  36  and the drill motor  14  move linearly relative to the nosepiece  26  from a starting, top-of-stroke position to a bottom-of-stroke position in which the countersunk hole is fully formed. The relative movement between the nosepiece  26  and bulkhead  18  is produced by the pneumatic cylinders  22  which effectively function to feed the drill bit  46  into the workpiece. 
     A hand tool  72 , shown in  FIGS. 8-11 , is used to install and remove the drill bit  46  from the drill  10 , and obviates the need to remove the entire nosepiece  26  in order to switch out the bit. The tool  72  includes a cylindrical body  74 , preferably formed of metal, having a hollow end defined by an axial opening  78  adapted to receive a portion of the drill bit  46  therein. A pair of diametrically opposed legs  80  extend longitudinally from the side walls of the body, adjacent the opening  78 . As best seen in  FIG. 11 , each of the legs  80  includes an outer surface  82  possessing a curvature matching that of the inside wall of the nose bushing  48 . A pair of handles  76  extend oppositely from the other end of the body  74 , forming a T-grip that may be grasped by an operator and used to turn the tool  72  during installation/removal of the drill bit  46 . 
     In use, the operator inserts the hollow end of the tool  72  into the nose busing  48  so that the drill bit is received within the axial opening  78 . The operator then rotates the tool  72  until the legs  80  engage lateral protrusions on the drill bit  46 . These protrusions may comprise allen head screws or pins secured to the drill bit  46 . Rotation of the tool  72  screws the drill bit  46  either into or out of the threaded opening  44  in the arbor  36 . 
     The operation of the drill  10  is controlled by a pneumatic control system, the details of which are shown in  FIG. 12 . A pair of push button actuated, two way pneumatic valves,  84 ,  86  are mounted on the rear end of the drill, passing through the cover  20  so as to be accessible by the operator. Valves  84 ,  86  may comprise, for example, MAV-2, two way, normally closed valves available from Clippard Instrument Laboratory. When actuated, valve  84  connects an air supply  88  with the air cylinders  22  to commence a drill feed cycle. Valve  86  controls the flow of air from the supply  76  through a check valve  90  to an accumulator tank  92  and pneumatic logic control  94 . The check valve  90  may comprise an MCV-2 check valve available from Clippard Laboratories. Valve  86  when actuated, functions as an emergency stop which terminates the drill feed. 
     The pneumatic logic control  94  will be configured to meet the requirements of each particular application, however in the illustrated embodiment, the logic control  94  may comprise a controller available from Dynamco configured as a DA20D0A00. The pneumatic control  94  controls the flow of air between the various components of the control system. 
     The dwell valve  62  is connected through a restrictor valve  96  and dump valve  98  to accumulator tank  92 , as well as to the pneumatic control  94 . When the dwell valve plunger actuator  64  engages anvil  56 , pressure is slowly reduced on dump valve  98  at a rate dependent upon the setting of the restrictor valve  96 . When the pressure on dump valve  98  falls below a preset level, the air pressure within accumulator tank  92  is reduced, which in turn reduces the air pressure applied to cylinders  22 . When the return force of spring  66  exceeds the force supplied by cylinders  22 , the bulkhead  18  returns to its top-of-stroke position. The length of time (dwell) that the bulkhead  18 , and thus the drill bit  46 , remain at their bottom-of-stroke position depends on the setting of restrictor valve  96  which functions as a dwell adjustment. Normally, the dwell time is set so that the countersunk hole is fully formed before the drill bit  46  returns to its top-of-stroke position. The provision of an adjustable dwell accommodates variations in workpiece materials and the cutting efficiency of differing drill bits. 
     In operation, the drill  10  is clamped into a suitable drilling fixture (not shown) which is positioned on a workpiece with the drill bit  46  aligned with a point on the workpiece in which the countersunk hole is to be formed. The operator adjusts the countersink adjustment ring  42  to a desired countersink depth. This depth setting may be achieved through calibrations applied to the ring  42 , or manually using a depth gauge fixture to set the maximum drill bit depth. The operator then actuates the push button feed valve  84 , causing the pneumatic control  94  to initiate an automatic drill cycle. The operator also actuates a trigger actuator  100  which starts the drill motor  14 . Pneumatic cylinders  22  move the bulkhead  18  toward the nosepiece  26 , feeding the drill bit  46  into the workpiece at a controlled rate. Hydraulic cylinders  28  act to dampen and regulate movement of the bulkhead  18  during the feed process to assure a steady, regulated feed rate. 
     When the bulkhead  18  (and thus the drill bit  46 ) reach the bottom-of-stroke position, the dwell valve plunger  64  is displaced by anvil  56 , initiating a dwell cycle. After the dwell cycle is complete, the spring  66  returns the bulkhead  18  to its home or top-of-stroke position, completing the drilling process. 
     From the above, it is apparent that the countersink drill of the present invention provides a fully automated drill process that is not dependent on operator skill or intervention. Moreover, a completely formed, countersunk hole is produced in a single drilling operation without the need for changing drill bits. 
     Although this invention has been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.