Abstract:
A spade drill is provided including a V-shaped drill cutting end and a pair of reaming edges on each side thereof. The reaming edges have a relatively large radius of curvature and generally define a flat portion at the apex of the reaming edges. The junction between the drill cutting end and the reaming edges has a misblended radius.

Description:
This Application claims benefit of Provisional Application No. 60/119,436 filed Feb. 10, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The present invention relates generally to a spade drill, and more particularly to a spade drill having the ability to drill as well as ream a hole simultaneously. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     There are many circumstances in the manufacturing industry that require the task of drilling a hole while leaving the hole somewhat undersized and then following behind the drilling operation with a secondary operation with a reamer to size the hole to the desired size. The number of operations that are required to manufacture a part is directly related to the cost of the part. Thus, it is desirable to provide a drill with the ability to drill as well as ream a hole simultaneously. 
     Accordingly, the spade drill of the present invention has the ability to drill as well as ream a hole simultaneously thereby eliminating the requirement for a secondary reaming operation after a hole is drilled. The spade drill includes a V-shaped drill cutting and a pair of reaming edges on each side thereof. The reaming edges have a relatively large radius of curvature and generally define a flat portion at the apex of the reaming edges. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a side view of the spade drill according to the principles of the present invention illustrating the miss-blended radius between the drill section and sides; 
     FIG. 2 is a side view of the spade drill shown in FIG. 1, illustrating the reaming radius; 
     FIG. 3 is a side view of the spade drill shown in FIG. 1 illustrating the flats on each reaming section; and 
     FIGS. 4A and 4B are side and end views, respectively, of the tool holder for supporting the spade drill according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-5, the spade drill of the present invention will be described. 
     The spade drill  10  includes a generally V-shaped drill cutting end  12  with a first cutting edge  14  and a second cutting edge  16  on opposite sides of the spade drill. At the outer diameter of the cutting edges  14 ,  16  each opposing side  18  has a radius  20  that is not tangent to the cutting edge  14 ,  16  or the diameter of the side of the drill portion and is thus mis-blended on both portions of the cutting edge  14 ,  16  and on the sides  18 . This mis-blended radius  20  has two purposes; (1) it provides for the centering effect of the drill as the drill enters the workpiece in its rotational mode; and (2) it provides for a gradual breakdown or a barrier to prolong the natural wear that occurs as the drill endures through its normal breakdown. 
     In comparison with other shapes such as a full tangent radius, or angular edge, the outer edge tends to chip or break causing the drill to become unbalanced as well as unable to maintain its triangular indicated reading which is required to produce the self-centering effect. This also causes the diameter to be affected dimensionally, hence causing premature tool failure. 
     As shown in FIG. 3, the sides  18  of the spade drill have a reaming feature including a large radius “R” on opposing sides  18  of the spade drill which is not tangent “mis-blended” to the cutting edges  14 ,  16  of the drill section  12  and to the trailing end. The sides  18  perpendicular to the drill cutting face  12  has a flat  22  in the center of the farthest most distant diametrical point of the radius “R”. The radius “R” which is shown is greater than a width of the spade drill  10 . 
     As is commonly known in the art of reaming, a reamer must be allowed to pass through a hole that is smaller in diameter than the size of the reaming device. This in turn creates a wiping action or a burnishing effect which creates the hole size required. As shown in FIG. 3, the trailing side sections  18  are identical in design where the non-tangent radius “R” of the sides  18  expand the pre-drilled hole for the expansion of the hole by a distance X shown in FIG.  2 . Since the radius portion of the sides are not tangent, this provides a self-centering device. The identical flats  22  provided on the opposite sides  18  in effect act as wipers to burnish the whole diameter. 
     The length of the flats  22  are determined by the rotational versus linear insertion rate. The determining factor for the length of the flats  22  is that the rotation of the spade drill  10  correlates with the down feed such that the rotating flats  22  overlap as they are fed in a downward or upward direction effectively reaming the hole diameter. It should be noted that the sides  18  have a radiused portion  24 ,  26  on each side of the flats  22  so that the spade drill provides a reaming function both upon insertion and withdrawal of the spade drill  10  from the hole which has been drilled. 
     The spade drill  10  of the present invention is mounted in a holder  30  as shown in FIG. 4 which is provided with a V-shaped pocket for receiving the V-shaped base  32  of the spade drill  10 . The spade drill  10  is secured to the holder by a pair of threaded fasteners  34  which are inserted from opposite sides of the tool holder  30 . Cooling passages  36  are provided in the tool holder for blowing coolant at the drilling contact surface. The coolant passages also provide the function of assisting in removing metal fragments which are removed from the workpiece. The screws  34  which are inserted through holes  37  of the spade drill  10  have a head portion  38  which abuts directly against a recessed seat portion  39  surrounding the holes  37  of the spade drill  10  and a threaded portion  40  which extends into a head section  42  of the tool holder  30 . With this design, the screw head  38  does not interfere with the removal of the metal fragments which are removed by the spade drill insert  10  through the fluted sections  44  of the tool holder  30 . 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.