JPS6156044B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drill suitable for deep hole drilling.

Recently, so-called spiral blade drills have been proposed that improve cutting performance by eliminating the chisel part at the center of the drill and forming a cutting edge with a large curvature. Because of the large resistance encountered when passing through the shaped chip evacuation groove, good cutting performance could not be achieved in deep hole machining.

This invention was made to solve these conventional drawbacks, and the chip generated from the cutting edge is curled to a large curvature, thereby allowing it to pass smoothly through the discharge groove. It is something. That is, in the present invention, the pair of cutting edges have their starting ends near the center of rotation and are arranged substantially point-symmetrically with respect to each other when viewed from the bottom of the drill, and each cutting edge has a curved line convex with respect to the direction of rotation, and The cutting edge curve at the center has a larger curvature than the cutting edge curve at the outer periphery, and the chip discharge groove corresponding to each cutting edge is formed in a spiral shape in the shank. The curvature of the bottom surface on the front side in the rotational direction of the chip evacuation groove in the cross section in the direction substantially perpendicular to the cutting edge is greater than the curvature of the bottom surface of the portion closer to the cutting edge, and the tip of the chip along this curvature does not hit the inner wall of the machined hole. A protrusion is formed near the front end of the bottom surface of the groove in the drill rotation direction so as to have a curvature of the same size.

Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 1 to 3, 1 is a shank of a drill, and 2 is a tip. The tip 2 is attached to the head of the shank 1 by means such as brazing. A cutting edge 3 is formed on each of the chips 2, and the cutting edge 3 has a curved line convex in the direction of rotation when viewed from the bottom, has a constant large curvature at the center, and has a substantially straight line at the outer periphery. The cutting edge 3 may have a spiral curve whose curvature increases from the outer periphery toward the center. Further, the head of the shank 1 is formed into a conical shape, and each cutting edge 3 is formed point-symmetrically with respect to the center point 4 which is the apex thereof. The center point 4 may be eccentric to the extent of a manufacturing error, and the point symmetry is not strictly defined; it is sufficient that it is substantially point symmetric. Furthermore, both cutting edges may be discontinuous at the center point. In addition,
A supply port 50 for cooling oil during cutting is formed in the land portion 5 for receiving the force acting on the cutting edge 3.

The rake face 7 of each cutting edge 3 is formed continuously from the center to the outer periphery. Further, the protrusion 6 is formed so that the curvature of the bottom surface of the chip discharge groove 10 in the cross section in the direction substantially perpendicular to the cutting edge near the outer periphery is larger than the curvature of the bottom surface above it. In the illustrated example, the protrusion 6 is locally small, but the protrusion 6 may protrude over a wide range up to the outer periphery.

When drilling is performed with the above-mentioned drill, the chips 8 generated by the cutting blade 3 extend in a fan shape on the rake face and curl along the bottom surface of the groove 10, as shown in FIG. The tip is largely curled by the projection 6 and discharged along the length direction of the groove 10. That is, since the protrusion 6 is formed, the chips 8 are curled to a larger curvature than the curvature of the bottom surface of the groove 10, and therefore the chips 8 are smoothly discharged from the groove 10. In contrast, in conventional drills, the chips 9 formed in the groove 10 are smaller than the curvature of the groove due to the elasticity of the material. Therefore, it cannot pass through the groove 10 freely. Moreover, since the chips 9 extend along the bottom surface of the groove 10, the fourth
As shown by the imaginary line in the figure, the tip end touches the inner wall 80 of the machined hole. Therefore, the chips 9 are removed from the groove 10.
Even when the chip is being raised, it rubs against the inner wall 80 of the hole 80 and the bottom wall of the groove 10, creating a large resistance to ejection.As the hole becomes deeper, it becomes impossible to eject the chips, making it impossible to machine very deep holes. Ta.
However, if the chip 8 is curled with a large curvature, it can easily pass through the groove 10, making it possible to easily drill deep holes, which was previously considered impossible.

As explained above, this invention has projections formed in the groove for curling chips generated from the cutting edge, and has low chip ejection resistance.
It is especially suitable for drilling deep holes.

[Brief explanation of the drawing]

FIG. 1 is a front view of a drill showing an embodiment of the present invention, FIG. 2 is a side view thereof, and FIG. 3 is a bottom view thereof.
FIG. 4 is a sectional view taken along the line -- in FIG. 2. 1...Shank, 2...Chip, 3...Cutting blade, 6...Protrusion, 8...Chip, 10...Chip discharge groove.

Claims (1)

[Claims] 1 The pair of cutting edges have their starting ends near the center of rotation and are arranged approximately point symmetrically to each other when viewed from the bottom of the drill, each cutting edge forming a convex curve with respect to the rotation direction, and the cutting edge on the outer periphery The cutting edge curve at the center has a larger curvature than the curved line, and the chip discharge groove corresponding to each cutting edge is formed in a spiral shape in the shank. The curvature of the bottom surface on the front side in the rotation direction of the chip evacuation groove in the cross section in the orthogonal direction is larger than the curvature of the bottom surface of the part closer to the cutting edge, and the curvature is large enough that the tip of the chip along it does not hit the inner wall of the machined hole. A drill characterized in that a protrusion is formed near the front end of the bottom surface of the groove in the direction of rotation of the drill.