Drill

摘要

A guide portion prevents the drilling hole from curving due to a skipping rope phenomenon, and also prevents the inner wall face of the drilling hole from being damaged, so that its surface roughness can be improved.;Chip evacuating flutes 4 are formed in the periphery of a drill body 1 which has a stick shape and is rotatable on its axis O, from its front flank 3 toward the rear side.;Cutting edges 2A are formed along ridge lines where the front flanks 3 intersect with wall faces 4A which are in the chip evacuating flutes 4 and face in a drill rotational direction T.;A cutting edge section 2, where the cutting edges 2A are formed, is provided in the front side of the drill body 1. A cutting edge section 2 has an external diameter which is smaller toward the rear side in the axis O direction than the external diameter D at the cutting edges 2A.;A guide portion 6 has a maximum external diameter part 6A at the front periphery side, and is provided to the rear side of the cutting edge section 2. ;An external diameter at the maximum external diameter part 6A is larger than the external diameter at the rear of the cutting edge section 2, and is smaller than or equal to the external diameter D at the cutting edges 2A.;The maximum external diameter part 6A of the guide portion 6 shows a smooth convex curve shape in a rotatory figure obtained by rotating it on the axis O.

主权项

1. A drill comprising a drill body which has a stick shape and is rotatable on an axis; wherein:
chip evacuating flutes are formed in a periphery of the drill body from front flanks toward a rear side; cutting edges are formed along ridge lines where the front flanks and wall faces intersect with each other; the wall faces are in the chip evacuating flutes and face in a drill rotational direction; a cutting edge section in a front side of the drill body has an external diameter smaller toward the rear side in the axis direction than an external diameter at the cutting edges; a guide portion is provided to the rear side of the cutting edge section; the guide portion has a maximum external diameter part on the front periphery side thereof; an external diameter at the maximum external diameter part is larger than the external diameter at the rear of the cutting edge section, and is smaller than or equal to the external diameter at the cutting edges; and characterized by: the maximum external diameter part of the guide portion shows a smooth convex curve shape in a rotatory figure obtained by rotating the drill body on the axis, wherein a plurality of the guide portions are provided to the rear side of the cutting edge section, each of the guide portions having the same shape and size in the rotary figure, wherein the rear of each guide portion has an external diameter smaller than the external diameter at the maximum external part, and wherein the shape is: a convex arc with a radius from the rear of the cutting edge section to the maximum external diameter part of the next rearward guide portion, and the external diameter thereof increases radially outward in proportion to the rear direction; the convex arc with the radius from the maximum external diameter part to a proximity point extremely close to the point, and the external diameter thereof slightly decreases radially inward in proportion to the rear direction; a straight line, which is smoothly connected with the convex arc at the proximity point and goes toward the rear side, from the proximity point toward the rear side, and the external diameter thereof decreases radially inward in proportion to the rear direction; and another convex curve shape from the rear of the guide portion to the maximum external diameter part of the next rearward guide portion.