| 摘要 |
An improved drill bit for wood boring or boring in other relatively soft material, having a generally cylindrical shaft (20), with a flattened blade portion at one end (24). The blade portion (24) is broad and flat with essentially parallel side surfaces (41,42) and having negatively beveled edges along the length of such side surfaces, such side surfaces giving way to a modified end edge. The modified end edge includes a center spur that is of rectangular cross section, with a length of one half to several times the thickness of the blade, and said spur (34) is centered on the end edge and is made with a concave tip (35). The edges of the center spur are parallel from vertex (36) to base. Outer spurs of rectangular cross section (29 and 30) with a negative bevel away from the leading edge are located on the lateral extremities of the end edge. Radially extending cutting surfaces (45 and 46) with a negative bevel away from the leading edge (37 and 38) extend at right angles from the base of the center spur to the inside edge of the outer spurs.
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