JPH034325B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in drills, and particularly to improvements in the shape of cutting edges of drills.

Recently, a so-called spiral blade drill has been known as a drill that improves the cutting performance of the center part of the drill. This has a spiral cutting edge formed in the center without a chisel, and this cutting edge in the center is continuous with a linear outer cutting edge formed in an extension of the helical groove. The outer cutting edge of this drill has a conical shape, but the center cutting edge has a flat surface, which makes it difficult to determine the center of the cut into the workpiece, resulting in center runout during machining. The problem is that it is easy.

On the other hand, in order to improve the rigidity of the drill, particularly the machinability of deep holes, it is preferable to increase the core thickness of the drill, that is, the thickness between the bottom surfaces of the helical grooves. Increasing the rigidity of the drill is preferable because it improves machining accuracy because center runout does not occur, especially in deep hole drilling, but as the core thickness increases, the radius of curvature of the center cutting edge increases in the spiral blade drill mentioned above. As a result, the flat surface also becomes larger, which makes it difficult to determine the center of machining for the workpiece, which has the disadvantage of not only starting the drilling process but also increasing center runout during machining. Become.

The present invention has been made in order to eliminate such conventional drawbacks, and is to increase the rigidity of the drill to improve cutting performance and to prevent core runout from occurring.

That is, the present invention provides a drill having a pair of helical grooves and a conical top surface, in which the core thickness between the bottom surfaces of the helical grooves is set to 1/4 or more of the diameter of the shank,
Near the axial center of the shank, first cutting edges that draw a convex curve in the direction of rotation when viewed from the bottom are formed in point symmetry with respect to each other, and the outer periphery is formed at the intersection of the extended surface of the helical groove and the flank surface of the top surface of the shank. A second cutting edge is formed on the
A substantially linear third cutting edge is formed between the first cutting edge and the second cutting edge, and the side shapes of the second cutting edge and the third cutting edge are substantially linear, The rotation locus circle of the first cutting edge is formed to be 1/5 to 1/20 of the diameter of the shank.

Embodiments of the present invention will be described below with reference to the drawings. A pair of twisted grooves 2 are formed in the shank 1 of the drill, and the top portion is formed in a conical shape. A pair of first cutting edges 3 that draw a convex curve in the direction of rotation are formed near the center on the top, and a second cutting edge 5 is formed at the intersection of the extension surface of the helical groove 2 and the flank surface 4. ,
A third cutting edge 6 is formed to connect the first cutting edge 3 and the second cutting edge 5. The third cutting edge 6 is formed substantially straight at the intersection with the concave surface 4 by cutting the bottom 20 of the helical groove 2 to form a rake surface 61. The first cutting edge 3 is formed by cutting the rake face with a radius of curvature r from the inner end of the third cutting edge 6 to the center point. Further, a lubricating oil supply port 8 for cooling the cut portion is formed in a portion of the back metal 7 at the rear of the flank 4 in the rotational direction.

The thickness B between the bottoms 20 of the twisted groove 2 is the diameter D
is set to 1/4 or more. Further, the diameter d of the circle drawn by the rotation locus of the first cutting edge 3 is set within the range of 1/5 to 1/15 of the diameter D of the shank 1. The range of the diameter d of the circle of the rotation locus of the first cutting edge 3 is a substantially flat surface, and the third cutting edge 6 and the second cutting edge 5 located outside this range have a substantially flat side surface shape. It is formed in a straight line. That is, the top of the shank is formed into a substantially conical shape by the second cutting edge 5 and the third cutting edge 6, and only the tip thereof is formed into a flat surface by the first cutting edge 3. ing. Note that if the core thickness B is less than 1/4 of the drill diameter D, the rigidity of the drill will be insufficient, and if the diameter d of the rotation locus circle of the first cutting edge 3 is more than 1/5 of the drill diameter D, core runout will occur. The prevention effect is not sufficient, and if it is less than 1/15, the cutting edge at the center is too small and the center cannot be cut well.

In the above configuration, the core thickness is very large, so the drill has high rigidity, and a cutting edge with a small radius of curvature is formed in the center instead of a chisel, so cutting in the center can be done well. . Also, the range of the first cutting edge 3 that forms a flat surface (range of diameter d)
is very small and is formed into a nearly conical shape by the second cutting edge 6 and the third cutting edge 5, making it easy to determine the center position during machining, resulting in less center runout and good cutting. It can be performed. Conventionally, since the cutting edge 60 is formed with a large radius of curvature as shown by the imaginary line, the diameter L of the flat surface formed at the top of the shank is very large, which makes it difficult to determine the center during machining. , center runout is likely to occur. On the other hand, if the flat surface at the tip is made smaller and the rigidity is improved as described above,
Since the drill performs stable cutting, cutting performance is significantly improved, and it is especially effective in deep hole drilling. Further, in the above configuration, when forming the cutting edge by cutting from the shank of cemented carbide or high-speed steel, the third cutting edge 6 is cut straight and its inner peripheral side is cut with a slight curve. This makes it possible to form the first and third cutting edges 3, 6, which is easier to process than the conventional case of forming cutting edges with a large radius of curvature. That is,
When the cutting edge wears out due to use, the flank surface 4 is ground down to shave the rake surface between the cutting edges 3 and 6, but in this case, the conventional cutting edge 60 cannot accurately machine the curved shape of the rake surface. However, in the present invention, most of the rake face is straight, so machining is easy. In particular, in the case of a drill with a small diameter shank, it is difficult to accurately process the center part, but with the above configuration, the center part can be easily processed, which is highly effective when manufacturing a thin drill.

As explained above, this invention increases the rigidity of the drill by setting a large core thickness, and also forms a cutting edge with a small radius of curvature at the center, and an outer peripheral cutting edge on the extension surface of the helical groove at the outer periphery. These two cutting edges are connected by a nearly straight cutting edge so that the top has a shape close to a conical shape, and the center runout of the drill during cutting is small, resulting in significantly superior cutting performance. It is something that

[Brief explanation of the drawing]

Fig. 1 is a side view showing an embodiment of the invention, Fig. 2 is a side view showing an embodiment of the present invention;
The figure is its bottom view. 1...Shank, 2...Twisted groove, 3...First cutting edge, 5...Second cutting edge, 6...Third cutting edge.

Claims (1)

[Claims] 1 In a drill with a pair of helical grooves and a conical top surface, the core thickness between the bottom surfaces of the helical grooves is set to 1/4 or more of the diameter of the shank, and there is a hole near the shaft center of the shank in the direction of rotation when viewed from the bottom. First cutting edges that draw convex curves are formed point-symmetrically with respect to each other, and a second cutting edge is formed on the outer periphery by the intersection of the extension surface of the helical groove and the flank surface of the top surface of the shank. A substantially straight third cutting edge is formed between the cutting edge and the second cutting edge,
The side shapes of the second cutting blade and the third cutting blade are formed into almost straight lines, and the rotation locus circle of the first cutting blade is formed to be 1/5 to 1/15 of the diameter of the shank. A drill characterized by: