Self-feed wood bit

A large diameter self-feed wood bit is provided including a feed spur having a coarse spur thread of approximately 1.75 millimeters and a 20-degree main cutting edge relief angle. The main cutting edge relief angle complements the coarse self-feed thread pitch for faster, more efficient drilling of large diameter holes in wood.

FIELD OF THE INVENTION

The present invention relates to a self-feed wood bit, and more particularly, to a self-feed wood bit having a feed spur having a coarse spur thread.

BACKGROUND AND SUMMARY OF THE INVENTION

Self-feed wood bits are used for boring a hole through wood. The typical self-feed wood bit includes a fine thread feed spur and one or more main cutting edges extending radially outward from the center and including scoring perimeter teeth. The feed spurs are typically provided with a fine thread which acts somewhat like a screw in order to draw the self-feed wood bit into the wood so that the main cutting edge cuts away the surface of the wood. The feed spur is typically provided with a fine thread in order to limit the speed at which the main cutting edge is drawn into the wood in order to prevent binding of the wood bit which occurs if the wood bit is drawn inward too quickly. It is desirable in the art of wood bits to provide a wood bit which provides faster drilling, improved efficiency, and improved self feeding. These and other objects are obtained by providing a self-feed wood bit with a coarse thread on the feed spur and with an approximately 20 degree relief angle on the main cutting edge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1-5 , the self-feed wood bit 10 according to the present invention will now be described. The self-feed wood bit includes a cutting body portion 12 and a shank 14 extending from the main body portion 12 . The main body 12 includes a pair of main cutting edges 16 and a pair of following cylindrical wall portions 18 , each of which include a plurality of scoring perimeter teeth 20 . The pair of main cutting edges 16 each include a rake face 22 having a rake angle b of approximately 30 degrees. As can best be seen in FIGS. 4 and 5 , the substantially planar surface of the rake face 22 extends throughout the overall vertical depth of the main body portion 12 . The main cutting edges 16 also include a relief face 26 (best shown in FIG. 1 ) having a main cutting edge relief angle a (shown in FIG. 1 ) from about 15 degrees to about 25 degrees and preferably approximately 20 degrees.

The scoring perimeter teeth 20 extend a distance c approximately {fraction (1/32)} of an inch longer than the main cutting edge 16 as best shown in FIG. 3 . As seen best in FIG. 1 , the scoring perimeter teeth 20 are regularly disposed on the following cylindrical wall portion 18 except that the regular disposition of the scoring perimeter teeth 20 are interrupted by the relief angle a of the main cutting edges 16 . As seen best in FIGS. 4 and 5 , the cylindrical wall portion 18 terminates at an angle which is open relative to the other, opposing rake face 22 . As best seen in FIG. 2 , the main body portion 12 also includes a horizontal top wall portion 19 associated with the cylindrical wall portion 18 which terminates at an angle which is open relative to the other, opposing main cutting edge 16 . The main body portion 12 and shank 14 are provided with an axial bore 30 which receives a feed spur 32 therein. The feed spur 32 includes a shank portion 32 a and a self-feeding spur portion 34 . The shank portion 32 a of the feed spur 32 is retained in the bore 30 by a set screw 36 which is received in a threaded bore in the side of the shank 14 of the self-feed wood bit 10 . The feed spur 32 can be a double-ended feed spur as shown in FIG. 6 or a single-ended feed spur as shown in FIG. 7 . The double-ended feed spur shown in FIG. 6 includes two self-feeding spur portions 34 and 34 . The double-ended feed spur of FIG. 6 can be provided with a feed spur 34 having a coarse thread, according to the principles of the present invention, and a feed spur 34 having a fine thread. Alternately, as shown in FIG. 7 , the feed spur 32 can be provided with a single self-feeding spur portion 34 which may have a coarse thread according to the principles of the present invention as will be described in greater detail herein.

As shown in FIG. 8 , the thread detail of the self-feeding spur 34 will now be described. As shown in FIG. 8 , the spur 34 is provided with a thread 40 on a conical base portion 42 . The pitch distance between the threads 42 defines a coarse thread. For purposes of this application, the term coarse thread is used to define a thread having a pitch distance from about 1.65 millimeters to about 1.85 millimeters and preferably about 1.75 millimeters. The feed spur includes a thread length on the spur portion that extends into the cutter body to provide self-feeding action throughout completion of the hole (i.e., out the back side of the surface being cut).

Experimental Results

A course thread feed spur was tested with a self-feed wood bit having a main cutting edge relief angle a of 20 degrees and a pitch distance of the thread of the feed spur of 1.75 mm. The test was performed with a 2 9/16 inch diameter wood bit and compared with three other commercially available fine spur thread wood bits. The wood bit, according to the present invention, performed a cutting operation in approximately 5.8 seconds in comparison with each of the other commercially available bits which performed the same cut through the same material in approximately 7.1, 7.7, and 7.2 seconds, respectively. Accordingly, the coarse thread self-feed wood bit, according to the present invention, was approximately 18 percent faster in performing a cut than the commercially available finer thread wood bits. The main cut edge relief angle is 20 degrees to complement the coarse self-feed thread pitch of 1.75 mm for faster, more efficient drilling of large diameter holes in wood.