Abstract:
A hole-finishing hole finishing tool includes a pilot cone within which a quarter round section is free to be displaced in an axial direction. The quarter round section is resiliently biased away from a workpiece. When the tip of the pilot cone is inserted into a hole in a workpiece and force is applied, the quarter round section having a cutting element at its tip is displaced forward into contact with the perimeter of the hole, whereby chamfering is performed. The use of a single lip quarter-round cutting edge permits the tool to be used on small holes.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to cutting tools and, more particularly, to tools for countersinking, chamfering and deburring holes. 
     When holes are made by drilling or punching in metal, ceramic or plastic, the holes are often rough at their entrances or exits. Conventionally, drill bits and the like are used as hole finishing tools to remove a small amount of material. Drill bits have the disadvantage that they are not adaptable to finishing small holes. In addition, especially when the holes are larger, tool chatter frequently produces roughness in the material. 
     A different type of hole finishing tool employs the hole in the material as a pilot hole into which is fitted a pilot piece. An angled cutting edge is guided by the pilot piece to remove a small amount of material at the entrance of the hole. Although the piloted hole finishing tool solves the problem of tool chatter, and consequent roughness of the cut, the pilot piece and cutting blades are relatively large, thus making the piloted hole finishing tool unsuitable for finishing small holes. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An object oft his invention is to provide an improved hole finishing tool for chamfering and deburring holes, particularly holes drilled or punched in metal. 
     Another object of this invention is to provide a hole finishing tool which offers the advantage of a piloted chamfering tool, but which is useable on large and very small holes alike. 
     A further object of this invention is to provide a dependable hole finishing tool suited for the manufacturing environment that is simple to use. 
     A still further object of the invention is to provide a hole finishing tool of simple design and construction that renders it relatively inexpensive to produce and therefore more cost effective to the end user. 
     Briefly stated, the present invention provides a hole-finishing hole finishing tool which includes a pilot cone within which a quarter round section is free to be displaced in an axial direction. The quarter round section is resiliently biased away from a workpiece. When the tip of the pilot cone is inserted into a hole in a workpiece and force is applied, the quarter round section is displaced forward into contact with the perimeter of the hole, thereby deburring, chamfering or countersinking is performed. The use of a pilot cone stabilizes the cutting element and a quarter round single lip cutting edge permits the tool to be used on small holes. 
     According to an embodiment of the invention, there is provided a hole finishing tool comprising: a support member, the support member having a shape that is fittable into a hole in a workpiece, a shank, an end of the shank passing through the support member, the end having a cutting element formed or fastened thereon, means for resiliently biasing the shank away from the support member sufficiently to withdraw the cutting element within a contour of the support member, and means for permitting the application of a force to the shank sufficient to extend the cutting element into working contact with a perimeter of the hole. 
     According to a feature of the invention, there is provided a hole finishing tool comprising: a pilot cone, the pilot cone including a slot passing axially therethrough, a shank, a section of the shank having a peripheral shape fitting through the slot, a cutting element at an extremity of the section, a resilient element axially biasing the shank away from the pilot cone sufficiently to withdraw the cutting element within a contour of the pilot cone, means for permitting the shank to be urged a predetermined distance forward by application of a force thereon, and the predetermined distance being sufficient to extend the cutting element into working contact with a perimeter of a hole in a workpiece. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a hole finishing tool according to an embodiment of the invention. 
     FIG. 2 is a perspective view of the hole finishing tool of FIG. 1 disassembled to enable description thereof. 
     FIG. 2 a  is an axial cross section of the tool of FIG. 1 showing the relationship of the elements thereof in its quiescent condition. 
     FIG. 3 is a side view of the hole finishing tool of FIG. 1 resting on the perimeter of a hole in a workpiece before downward force is applied. 
     FIG. 4 is a side view similar to FIG. 3 but taken while a downward force is applied to chamfer the perimeter of a hole in the workpiece. 
     FIG. 5 is an end view of a hole finishing tool that employs a number of support bars instead of a conical surface, Additionally shown in this view is an optimum angular relationship between the pilot support members stop screw and the tools cutting edge. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1,  2  and  2   a,  a hole finishing tool, shown generally at  10 , includes a shank  12  suitable for chucking in chuck of a drilling machine (not shown). A pilot cone  14  is slidably fitted on shank  12 . Longitudinal travel of pilot cone  14  along shank  12  is limited by a stop screw  13  which is accommodated in a notch  15  in shank  12 . 
     A spring stop collar  16  is affixed to shank  12  by any suitable means such as, for example, a set screw  18 . Set screw  18  bears against a flat  19  in shank  12  A coil spring  20  is biased between pilot cone  14  and spring stop collar  16 . A forward end of shank  12  is machined to a quarter round section  22 . A slot  24  longitudinally through pilot cone  14  permits longitudinal sliding of quarter round section  22 . A cutting edge  23  is formed in the rotationally leading edge of quarter round section  22 . 
     Returning now specifically to FIG. 1, the end of pilot cone  14  includes a conical portion  26  extending approximately 180 angular degrees about the longitudinal axis of pilot cone  14 . The remainder of the forward portion of pilot cone  14  includes the angle consumed by quarter round section  22  and the angle consumed by a chip clearance area  28 . The leading part of quarter round section  22  is a portion of a cone  30 . The cone angle of portion of a cone  30  generally matches the cone angle of conical portion  26  of pilot cone  14 . A tip  32  of portion of a cone  30  lies immediately adjacent a tip  34  of conical portion  26 . In the quiescent condition shown in FIG. 1, quarter round section  22  is retracted by the urging of coil spring  20  to place tip  32  slightly inward of tip  34 . A relieved edge  36  at the leading perimeter of conical portion  26  permits conical portion  26  to rotate within a hole without interference or damage to the workpiece. 
     Referring now to FIG. 3, at the beginning of a machining operation of a hole  38  in a workpiece  40 , hole finishing tool  10  is lowered into position with tip  34  of conical portion  26  entering hole  38 . Tip  32  of portion of a cone  30  is retracted slightly from tip  34 . In this condition, cutting edge  23  remains out of contact with the edge of hole  38 . 
     Referring now to FIG. 4, when a downward force is applied to shank  12 , contact between conical portion  26  and the perimeter of hole  38  produces an upward force. This upward force compresses coil spring  20 , thereby permitting quarter round section  22  to advance. As quarter round section  22  advances with respect to pilot cone  14 , cutting edge  23  contacts the perimeter of hole  38  to debur or chamfer the same. 
     It is to be noted that the entire operation described above requires only the alignment of tip  34  with hole  38 , and then the downward urging of hole finishing tool  10  to complete the hole finishing operation. In a typical manufacturing situation, shank  12  of hole finishing tool is chucked in a drill press, and the entire operation is completed in a single feed of the drill press. This simplicity of operation promises a significant reduction in time and consequent cost of hole finishing. 
     One skilled in the art will recognize that, although the leading portion of shank  12  is characterized as “quarter round section  22 ”, neither the angular extent nor the shape of this element is limited by this characterization. Quarter round section  22  may have a shape in at least a portion of its extent that is other than quarter round. In addition, quarter round section  22  may occupy substantially more or less than 90 angular degrees. Also, the angular extent of conical portion  26 , although described as being approximately 180 angular degrees in extent, may be substantially more or less than this angular extent. The only factor governing the angular extent of conical portion  26  is that the angular extent be sufficient to support pilot cone  14  with cutting edge  23  out of contact with workpiece  40  in the absence of a downward force on shank  12 . 
     Referring now to FIG. 5, an embodiment of a hole finishing tool  10 ′ differs from the above-described embodiment in that the conical surface of pilot cone  14  is replaced with a plurality of support bars  26   a,    26   b  and  26   c.  Support bars  26   a - 26   c  perform the same supporting function as the conical surface of pilot cone  14 , but are separated by machined portions  42   a  and  42   b  which do not touch the workpiece in operation. As in the prior embodiment, support bars  26   a - 26   c  bear against the edge of the hole in the workpiece, thereby centering hole finishing tool  10 ′, and permitting the application of force to urge the tip of quarter round section  22  into cutting contact with the perimeter of the hole. 
     Shown also in FIG. 5 is the optimum angular relationship  50  between cutting edge  23  and stop screw  13  in pilot cone  14 . It is found that when angle  50  is kept between forty-five and two hundred and twenty five degrees measured counterclockwise from cutting edge  23  in FIG. 5, the overall length of tool  10 ′ can be kept to a minimum. If set screw  13  is located in a closer angular proximity to quarter round section  22 , notch  15  must be machined to close quarter round section  22 , whereby, thinning the cross section of shank  12  and weakening the quarter round section  22 . This not being desirable, notch  15  either must be moved farther back on shank  12 , which in turn would require that the length of cone pilot  14  be lengthened, in turn increasing the over all length of tool  10 ′, or be in the preferred optimum angular relationship  50 . 
     The embodiments are described in the environment of a chamfering tool. For this environment, the end of quarter round section  22  is a portion of a cone. Such a shape is not a necessary limitation on the present invention. For example, the present invention may be used in a counter bore. For a counterboring application, the end of quarter round section  22  is squared of at right angles to the axis of the tool, and cutting edge  23  is modified from its angled position to a position that extends generally radially outward from the axis of the tool. One skilled in the art will recognize that shank  12  must be withdrawn further away from tip  34  until the end of quarter round section is fully contained within the contour of pilot cone  14 . 
     Various other shapes may be substituted for the conical shape of pilot cone  14  without departing from the spirit and scope of the invention. Similarly, cutting edge  23  may have a shape that departs from a straight line. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.