Patent Publication Number: US-2010111626-A1

Title: Cushion mechanism for a positive peck feed drill

Description:
TECHNICAL FIELD 
     The invention relates generally to the operation of a positive feed drill and, more particularly, to the addition of a mechanism that creates a more efficient and cleaner pecking operation. 
     BACKGROUND 
     A positive feed drill uses a screw thread to advance a spindle to supply the feed required for drilling, reaming, and other machining operations. During the operation, chips of a material being drilled are created from the cutting action from the removal of the material. The addition of “pecking” allows chips of the material created in the machining process to be broken up into smaller pieces to be evacuated and, thus, improves the quality of the hole in the material. This pecking is conventionally performed by the quick retraction and reinsertion of the positive feed drill cutter (e.g., a drill bit) out of and back into the hole. Typically, a motor drives a spindle in rotation through a gear train. Another gear drives rotation, but also allows the spindle to feed linearly either under positive feed through several gears or through an air feed via a piston in a cylinder. The air feed is used to rapidly retract the spindle, allowing the chips to be evacuated. The spindle is then fast advanced back into the hole in the material. 
     When fast advancing the cutter back to the material, it is important that the cutter does not contact the machining surface at a fast rate under the air feed. If fast contact occurs, the force caused by the contact can damage the cutter. Conventional technologies attempt to set back the relative position of the cutter by stopping the spin of the gear on the spindle, which in turn reduces the capabilities and efficiency of the drilling process. Accordingly, there exists a need in the art for an improved means for rapidly inserting the rapid drill feed without causing damaging contact against the cutter, while also remaining at a constant drilling pressure. 
     SUMMARY 
     The present invention can add a “cushion” to the end of the fast feed, thus giving a controlled feed of the cutter before the positive feed mechanism takes over for machining the material. This cushion can be achieved through the use, for example, of a spring washer, compression spring, or a pneumatic or hydraulic damper. 
     These and other aspects, features, and embodiments of the invention will become apparent to a person of ordinary skill in the art upon consideration of the following detailed description of exemplary embodiments showing the best mode for carrying out the invention as presently perceived. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description, in conjunction with the accompanying figures briefly described as follows. 
         FIG. 1  is a side view of a conventional positive peck feed drill. 
         FIG. 2  illustrates a graphical representation of the lateral position change of a conventional positive peck feed cutter during a machining cycle. 
         FIG. 3  illustrates a graphical representation of a lateral position change of a positive peck feed cutter employing a cushion mechanism according to an exemplary embodiment of the invention. 
         FIGS. 4   a  and  4   b  are a side and a partially exploded view, respectively, of a positive peck feed drill fitted with a cushion mechanism according to an exemplary embodiment of the invention. 
         FIGS. 5   a  and  5   b  are a side and a partially exploded view, respectively, of a positive peck feed drill fitted with an alternative cushion mechanism according to an exemplary embodiment of the invention. 
         FIG. 6  is a side view of a peck positive feed drill fitted with another alternative cushion mechanism according to an exemplary embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     A cushion mechanism for a positive peck feed drill may include one of several different configurations to allow a positive feed drill to be rapidly retracted and advanced without damaging the cutter by forceful contact with a machining surface.  FIG. 1  illustrates a conventional positive peck feed drill. In this illustration, the drill bit support mechanism and tool mounting are omitted. 
     As illustrated in  FIG. 1 , a motor  105  drives a spindle  110  in rotation through a gear train  117 ,  119 , and  115 . The gear  115  drives rotation, but also allows the spindle  110  to feed linearly either under positive feed through gears  120 ,  122  and  125  or through air feed via piston  130  in cylinder  135 . The air feed is used to rapid retract the spindle allowing chips (not illustrated) of a material  145  accumulated at a machining surface  150  to be evacuated. After the rapid retract and evacuation operation is complete, spindle  110  is then fast advanced back towards the machining surface  150  and gear  125  engages on the face with gear  122  providing the positive feed. Piston  130  is mechanically locked in position to ensure that the cutter  140  is fed into the material  145 . 
     When fast advancing back to the material  145 , it is important that the cutter  140  doing the machining does not contact the machining surface  150  in material  145  at a fast rate under the air feed. If fast contact with the machining surface  150  occurs, the force caused by the contact can damage the cutter  140 . Conventional technologies attempt to set back the position of the spindle by stopping the spin of the gear  125  on the spindle  110 , which in turn, reduces the capabilities and efficiency of the drilling process. However, the cushion mechanism of the present invention provides an impedance to the forward advance of the cutter  140  just prior to the cutter  140  re-contacting the machining surface  150 . 
       FIGS. 2 and 3  illustrate the benefits of the cushion mechanism of the present invention. In  FIG. 2 , the y axis represents distance, and the x axis represents time. In a conventional positive feed drill, a cutter  140  is rapidly retracted and advanced without regard for the force exerted between the cutter  140  and the machining surface  150 . This situation is illustrated in  FIG. 2 . Because of the forceful contact, conventional positive feed drills frequently damages the cutter  140 . 
     In  FIG. 3 , a graphical illustration is presented showing a positive feed drill fitted with the cushion mechanism of the present invention. As illustrated, the rapid advance is slowed as represented by reference number  305  just before the cutter  140  reaches the machine surface  150  with the feed controlled through the cushioning mechanism. Specifically, as the cutter  140  gets closer to the machining surface  150  at  305 , the cushion mechanism of the present invention slows the insertion of the cutter  140  so that it does not forcefully contact the machining surface  150 . In this manner, the cushion mechanism described herein prevents the cutter  140  from being damaged by the machining surface  150 . Accordingly, the cushion mechanism allows for smoother contact by the cutter  140  with the machining surface  150 , and does so without lengthening the positive feed drilling time, as occurs with conventional positive peck feed drill systems. 
       FIGS. 4   a  and  4   b  illustrate a positive peck feed drill  400  equipped with a cushion mechanism according to an exemplary embodiment of the present invention. As illustrated in  FIG. 4   b , one or more spring washers  405  are inserted in the piston  130  to create the cushion mechanism. An exemplary embodiment of a spring washer  405  may comprise one or more Belleville washers. When the front surface  415  of the piston  130  is retracted, the spring washer  405 , which can be positioned between the piston  130  and a shaft  410 , expands to a decompressed state. In turn, when the piston  130  is advanced to re-feed the cutter  140 , the piston  130  contacts the spring washer  405 , causing advancement of the piston  130  and, ultimately, the cutter  140 , to slow. As air pressure in the positive feed drill continues to advance the piston  130 , the spring washer  405  compresses at a defined compression rate until the spring washer  405  is fully compressed and the cutter  140  is back into contact with the machining surface  150 . Accordingly, the one or more spring washers  405  situated in the piston  130  absorbs the energy of the advancing cutter as it nears the machining surface  150 , so that the cutter  140  does not re-contact the machining surface  150  with damaging force. This process typically occurs in a span of several microseconds, such that the overall pecking and machining operation is not slowed by the addition of the cushion mechanism. In an exemplary embodiment, this advancement is slowed less than one-tenth of a one second. It should be noted that the compression rate of the spring washer  405  may be customized to lengthen or shorten the dampening effects of the cushion mechanism. The compression rate required is chosen according to the force from the cylinder  135  divided by the distance over which you want the energy to be dissipated. In an exemplary embodiment, the spring washer  405  may comprise rubber, metal, or plastic. The size and material of the spring washer  405  may determine its compression rate. 
       FIGS. 5   a  and  5   b  illustrate a positive feed drill  500  equipped with a cushion mechanism according to an alternative exemplary embodiment of the present invention. As illustrated in the exploded view of  FIG. 5   b , a compression spring  505  is inserted in the forward section of the shaft  510 , in front of the gear  125 , in order to impede the forward progress of the cutter  140  when the spindle  110  is advanced during a pecking operation. As with the spring washer  405  (explained with reference to  FIGS. 4   a - b ), the compression spring  505  expands when the spindle  110  is retracted and provides counter force to slow down the advancement of the cutter  140  just prior to it coming back into contact with the machining surface  150 . The speed reduction of the cutter  140  is achieved based on the placement of the compression spring  505 , which is situated so that the piston  130  must engage the compression spring  505  before re-engaging the axial gear  125 . 
       FIG. 6  illustrates yet another positive feed drill  600  equipped with a cushion mechanism according to another alternative exemplary embodiment of the present invention. As illustrated in  FIG. 6 , a hydraulic damper  605  slows the advance of the cutter  140  during a pecking operation. A rear holder  606  of the hydraulic damper  605  is coupled to the outside of the axial-moving shaft  610 , while a forward holder  615  is coupled to a static location  615  on the drill  600 . When the shaft  610  moves backwards during the chip clearing operation, the hydraulic damper  605  will expand. Then, when the shaft  610  moves forward to re-feed the cutter  140  into the machining surface, the hydraulic damper  605  impedes the advancement of the drill shaft  610  (and hence the cutter  140 ) just prior to contact with the machining surface  150 . Alternatively to the hydraulic damper  605  illustrated in  FIG. 6 , the hydraulic damper  605  may also be configured inside the piston  130  to provide the same benefit as the one shown in  FIG. 6 . Further, the hydraulic damper  605  can be replaced with a pneumatic damper (not illustrated). 
     As with the other embodiments illustrated above, the hydraulic damper  605  allows the positive peck feed drill to more efficiently and safely resume cutting operation with the machine surface  150 , while reducing the tendency for the cutter  140  to be damaged during the pecking operation. 
     Although specific embodiments of the invention have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects of the invention are described above by way of example only and are not intended as required or essential elements of the invention unless explicitly stated otherwise. Various modifications of the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of this disclosure, without departing from the spirit and scope of the invention defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.