Multi-blade self feed bit

The invention relates to self feed bits and more particularly to a self feed bit having a plurality of cutting edges.

Self feed bits for cutting large diameter holes in wood for pipe, conduit and other applications are known. These types of bits include a shank that has one end adapted to be connected to a chuck of a rotary tool such as a drill or power driver. The opposite end of the shank supports a cutting head having an annular cutting edge. A screw tip is provided for feeding the cutting member into and through the wood. A cutting member is disposed between the cutting edge and the tip. The bit is rotated at high speed such that the teeth score the edge of the hole and the cutting member bores the interior of the hole.

An improved self-feed bit is desired.

A drill bit comprises a shank defining an axis of rotation. A cutting head is attached to the shank. A plurality of cutting blades defining a plurality of cutting edges extend from adjacent the axis of rotation to the edge of the cutting head. The cutting edges are disposed at different angles to a plane perpendicular to the axis of rotation.

FIG. 1 is a front view of one embodiment of the drill bit of the invention.

FIG. 1A shows the screw tip used in the embodiment of FIG. 1 .

FIG. 2 is a partially exploded side view of the embodiment of the drill bit of FIG. 1 .

FIG. 3 is a perspective view of the embodiment of the drill bit of FIG. 1 .

FIG. 4 is a top view of the embodiment of the drill bit of FIG. 1 .

FIGS. 5A-5C are partial section views taken along lines 5 A- 5 C, respectively, of Fig. showing the orientation of the blades of the embodiment of the drill bit of FIG. 1 .

Referring to the Figures an embodiment of a drill bit is shown generally at 1 and comprises a shank 2 having a quick coupling 4 disposed at a first end thereof. The quick connect coupling 4 may comprise a plurality flat faces 4 a adapted to be received and retained in a chuck of a rotary tool such as a power screwdriver, drill or other power driver. A recess 4 b may be formed around the circumference of the shank to be releasably engaged by the quick connect coupler of the rotary tool. Other configurations of shank 2 may also be used for coupling the drill bit to a rotary drive tool.

A generally cylindrical, cup shaped cutting head 6 is formed on the opposite end of shank 2 from quick connect coupling 4 . The cutting head 6 comprises an annular wall comprising three wall portions 10 a , 10 b and 10 c connected to shank 2 by a base 12 . Each of the wall portions 10 a , 10 b , and 10 c have an arcuate profile that together form a circular cutting edge. While the wall portions each define a portion of the circular cutting edge, it is to be understood that when the drill bit rotates the wall portions circumscribe and cut a round hole. Formed on the distal edges of the wall portions 10 a , 10 b and 10 c are a plurality of teeth 14 that create the cutting edge. When the drill bit 1 is rotated about the rotational axis B-B the teeth 14 score the material being cut to create a clean cut around the periphery of the hole being drilled. A screw tip 15 is formed along the rotational axis B-B of the bit that engages the material being cut to feed the bit through the material.

The screw tip 15 may be made removable from the remainder of the bit. The screw tip 15 may include a relatively long stem 15 a as shown in FIG. 1A that extends into an axially aligned bore in the cutting head 6 and shank 2 . A set screw 19 engages a notch 15 b in the stem 15 a to retain the screw tip 15 in place. In an alternate embodiment, the screw tip 15 may include external screw threads 11 , FIG. 2 , that mate with internal screw threads 17 on the bit to allow the screw tip 15 to be inserted on or removed from the bit.

A plurality of cutting blades or lifters 20 a , 20 b and 20 c are formed on the cutting head 6 . When the drill bit is rotated at high speed in the direction of arrow A, the cutting blades 20 a , 20 b , and 20 c lift the material from the interior of the hole being drilled. Troughs 21 a , 21 b and 21 c are formed between wall portions 10 a , 10 b and 10 c and in base 12 in front of the cutting blades 20 a , 20 b and 20 c to create open areas for the wood chips to be ejected from the drill bit during the drilling operation. The troughs 21 a , 21 b and 21 c comprise gaps in the base 12 and gaps between the wall portions 10 a , 10 b and 10 c . The troughs are located in front of the leading or cutting edges of cutting blades 20 a , 20 b and 20 c , the leading edges or cutting edges being the forward edges of the cutting blades as the blades rotate in the direction of arrow A. In one embodiment, three such cutting blades are provided offset from one another 120° such that the cutting blades are evenly spaced about axis B-B. The cutting blades are arranged such that the inner portions of each of the blades at least partially circumscribe screw 15 .

Referring to FIGS. 5A-C each of the cutting blades 20 a , 20 b and 20 c are formed with a different orientation relative to the drill bit to increase the cutting efficiency of the bit. A reference spur height line C represents the plane defined by the distal edges of the spurs 14 and is oriented perpendicular to the axis of rotation B-B of the bit. Cutting blade 20 a has a cutting edge 25 that is oriented at an angle relative to the reference spur height line C. The inner corner 25 a of the cutting edge 25 is disposed below the reference spur height line C a greater distance D a than the distance d a that the outer corner 25 b of the cutting edge is disposed below the reference spur height line C. As used herein inner corner refers to the portion of the cutting edge nearest the center axis B-B of the bit and the outer corner refers to the portion of the cutting edge nearest the spurs 14 . Further, “below” as used herein means in the direction towards base 12 . Cutting blade 20 b has a cutting edge 27 that is oriented at an angle relative to the reference spur height line C where the inner corner 27 a of the cutting edge 27 is disposed below the reference line a lesser distance D b than distance d b that the outer corner 27 b of the cutting edge 27 is disposed below the reference spur height line C. Cutting blade 20 c has a cutting edge 29 that is oriented parallel to the reference spur height line C where the inner corner 29 a of the cutting edge is disposed below the reference line the same distance D c as the outer corner 29 b of the cutting edge. In one embodiment D c is dimensioned between d a and D b and D a and d b . In one embodiment d a is equal to D b and d b is equal to D a . Further, in one preferred embodiment d a and D b equal approximately 0.01 inches; d b and D a equal approximately 0.072 inches; and D c equals approximately 0.026 inches. The blades may be investment cast blanks of approximately 55 HRC and machined to the finished configurations.

When the bit is rotated the screw thread 15 feeds the bit 1 through the material being cut, the teeth 14 score the circumference of the hole being cut to create a smooth edge and the cutting blades 20 a , 20 b and 20 c cut or lift material from the interior of the hole being cut. Using three blades distributes the cutting forces more equally around the bit. Also, by grinding the blades to have the orientations previously described with respect to FIGS. 5A-5C , each blade cuts a different segment of the hole. Blade 20 a cuts the outer periphery of the hole, blade 20 b cuts the inner portion of the hole and blade 20 c cuts the middle portion of the hole between the outer periphery and the center portion. By spreading the forces around the bit and having the blades cut only a portion of the hole, the drill bit runs smoother than other designs and is safer for the operator to use.

Specific embodiments of an invention are disclosed herein. One of ordinary skill in the art will recognize that the invention has other applications in other environments. Many embodiments are possible. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described above.