JP2522758Y2 - Gun drill - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gun drill used for deep hole drilling.

[0002]

2. Description of the Related Art As a drilling tool used for deep hole drilling of a work, as shown in FIG. 8, a cemented carbide is formed in a cylindrical shape having a diameter larger than that of the shank 1 at the tip side of a shank 1 having a hollow shaft shape. The cutting edge tip 2 is coaxially joined by brazing, and the shank 1
A chip discharge groove 3 having a substantially V-shaped cross section is formed in an outer peripheral portion of the cutting edge, and an intersection between a wall surface 4 of the chip discharge groove 3 facing the tool rotation direction and a front end surface 6 of the cutting tip 2 is formed. A gun drill having cutting edges 7 and 8 formed on a ridge line is known. In such a gun drill, the rear end of the shank 1 is mounted on a tool grip of a machine tool via a driver (not shown) so that the front end of the cutting tip 2 faces a work (not shown). Thereafter, the cutting edge tip 2 is pushed toward the tip side in the tool axis direction with respect to the workpiece, and is relatively driven to rotate around the tool axis with respect to the workpiece. Thereby, as shown in FIG. 9, the cutting blades 7, 8 are cut into the work W, and the work W is pierced. At this time, a guide bush G is disposed adjacent to the workpiece W, and the cutting edge tip 2 is guided by the guide hole G1 of the guide bush G, thereby maintaining the straightness of the processing.

[0003]

By the way, in the above-mentioned gun drill, since the cutting tip 2 is formed to have a larger diameter than the shank 1, the outer peripheral portion 2a of the rear end of the cutting tip 2 is formed at these joints. It is inevitable that it protrudes radially beyond the outer peripheral surface of the shank 1.

[0004] Therefore, after the cutting tip 2 is pushed in the axial direction to machine the cutting tip to a predetermined depth, the tool is pulled back to the rear end side in the axial direction (the direction of the arrow A in FIG. 9) to form the cutting tip 2 through the hole formed. When removing 2, remove the guide bush G
Guide hole G1 and the cutting edge tip 2 are eccentric and the cutting edge tip 2
The outer peripheral portion 2a of the rear end collides with the mouth of the guide hole G1, which may cause the chip 2 to be chipped or the guide bush G to be damaged. In this regard, the intersection ridge 2c between the wall surfaces 4, 5 of the chip discharge groove 3 and the outer peripheral surface 2b of the cutting edge chip 2 is a sharp corner, and therefore, is particularly likely to be chipped. The guide hole G1 colliding therewith is also sharply damaged.

The present invention has been made under such a background, and has as its object to provide a gun drill which can prevent chipping of a rear end of a cutting edge tip and does not damage a guide bush.

[0006]

In order to solve the above-mentioned problems, a gun drill according to the present invention includes a cutting edge at a rear end side of an intersection ridge between an outer peripheral surface of a cutting edge chip and each wall surface of a chip discharge groove. To form a chamfer that gradually retreats toward the center in the radial direction toward the center to reach the joint between the cutting edge tip and the shank, and the surface of this chamfered portion is aligned with the axis of the cutting edge tip. It is configured by a curved surface that draws a convex curve in a cross-sectional view perpendicular to the cross section.

Here, the curved surface has various curved shapes such as a conical surface curved in an arc shape in a sectional view perpendicular to the axis of the cutting edge tip, and an elliptical curved shape in the sectional view. Is included. Further, the degree of curvature of the chamfer may be constant from the front end to the rear end, or may be changed so that the degree of curvature becomes gentler toward the rear end of the chamfer.

[0008]

According to the above construction, the intersection ridge line between the outer peripheral surface of the cutting edge tip and the wall surface of the chip discharge groove is retreated toward the center in the radial direction at the chamfered portion, and the amount of protrusion of this portion from the outer peripheral surface of the shank is reduced. Decrease. For this reason, the possibility that the intersection ridgeline between the outer peripheral surface of the cutting edge tip and the wall surface of the chip discharge groove contacts the guide bush is reduced. Also, since the chamfered portion is retracted toward the center in the radial direction as it approaches the rear end side of the cutting edge tip, the cutting edge tip is eccentric when the cutting edge tip is pulled back, and the chamfered portion is formed in the guide hole of the guide bush. Even when it comes into contact with the surroundings, the chamfered portion is drawn into the guide hole while sliding on the mouth portion of the guide hole, and the eccentric state is gradually eliminated. Therefore, the cutting edge tip is smoothly drawn in without being caught by the guide bush. Furthermore, since the surface of the chamfered portion is formed by a curved surface, the center in the circumferential direction of the chamfered portion relatively protrudes as compared with the case where the surface of the chamfered portion is formed by a flat surface. The cross-sectional shape of the take part is closer to the shape of the opening of the guide hole of the guide bush. For this reason, a possibility that both ends of the chamfered portion are in intensive contact with the mouth of the guide hole and chips or the like are concentrated on such a portion is also eliminated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, the overall configuration of the gun drill according to the present embodiment will be described with reference to FIG.
Reference numeral 0 denotes a cylindrical driver 11 mounted on a tool holding portion of a machine tool, a hollow shaft-shaped shank 12 coaxially fitted into a center hole 11a of the driver 11, and a coaxial shaft at the tip of the shank 12. Cutting edge tip 1 brazed jointly
3 and a chip discharge groove 14 having a substantially V-shaped cross section is formed on the outer peripheral portion from the tip of the cutting edge tip 13 to the shank 12, and the wall surfaces 15, 16 of the chip discharge groove 14 are formed.
Among them, the wall surface 15 facing the tool rotation direction and the cutting edge tip 13
In that the cutting blades 18 and 19 are formed at the intersection ridge line portion with the tip surface 17 of the conventional art.

As shown in detail in FIG.
Is formed by forming a cemented carbide into a columnar body having a diameter somewhat larger than that of the shank 12, and fitting a mountain-shaped fitting portion 20 formed at the center of the rear end thereof to the tip recess 12 a of the shank 12. The shank 12 is brazed in the
It is firmly joined to.

As shown in detail in FIGS. 3 to 6, an intersection ridge line between the wall surfaces 15, 16 of the chip discharge groove 14 and the outer peripheral surface 13 a of the cutting tip 13 at the rear end of the cutting tip 13. The chamfered portions 21, 2 gradually retreat toward the center in the tool radial direction toward the rear end side of the cutting edge tip 13.
2 are formed. These chamfered portions 21 and 22 are formed such that the ridges at the intersection between the outer peripheral surface 13 a of the cutting edge tip 13 and the wall surfaces 15 and 16 are rounded along the circumferential direction of the cutting edge tip 13 and approach the joint with the shank 12. Each surface is formed by a curved surface that draws an arc-shaped convex curve in a cross-sectional view (FIGS. 4 to 6) orthogonal to the axis of the cutting edge tip 13. Have been. Then, the radius of curvature of each of the chamfered portions 21 and 22 is increased along the axial direction of the cutting edge tip 13 toward the rear end side of the chamfered portions 21 and 22, that is, R in FIGS. ₁ <is changed such that R ₂ <R _3.

Further, the chamfered portions 21 and 22 are arranged so that the cutting edge 13
The outer peripheral surface 13a and wall 15 and 16 that are formed in contact with the smooth both ends E _1, E _2. The rear end of each of the chamfers 21 and 22 is curved along the outer peripheral edge P of the shank 12.

The length S of the chamfers 21 and 22
Is appropriately changed according to the tool diameter D (see FIG. 1) and the length of the cutting blade tip 13, but preferably 0.2D
０．４0.4D is preferred. If it is less than 0.2D, the length of the chamfered portion 21 may be insufficient and the chipping prevention effect described later may not be sufficiently obtained. This is because there is a possibility that run-out at the time of processing excessively increases.

As shown in FIGS. 1 and 3, an annular chamfer 23 surrounding the cutting tip 13 is formed on the outer peripheral portion of the rear end of the cutting tip 13. Since 23 is formed at the intersection ridge line between the outer peripheral surface 13a of the cutting tip 13 and the rear end surface of the cutting tip 13, it is provided at the intersection ridge line between the outer peripheral surface 13a of the cutting tip 13 and the wall surfaces 15, 16. It is clearly distinguished from the chamfers 21 and 22 to be formed. 4 to 6, reference numeral 24 denotes the driver 1
An oil hole for discharging the cutting oil guided from the center hole 11a (see FIG. 2) into the shank 12 from the front end face 17 of the cutting tip 13, and 25 prevents run-out of the cutting tip 13 during cutting. It is a pad for doing.

In the gun drill 10 having the above configuration, the outer peripheral portion of the rear end of the cutting edge tip 13 is
In particular, since the chamfered portions 21 and 22 are formed at the intersection ridges between the wall surfaces 15 and 16 of the chip discharge groove 14 and the outer peripheral surface 13a of the cutting edge, the intersection ridges recede toward the center in the radial direction and the shank. 12, the amount of protrusion from the outer peripheral surface is reduced. For this reason, when the drill is pulled back to the rear end in the axial direction after the work is machined to a predetermined depth and the cutting tip 13 is removed from the hole formed in the work, even if the guide hole of the guide bush adjacent to the work and the cutting tip are used. 13 is eccentric, the outer peripheral surface 13a of the cutting edge tip and the wall surface 1
The possibility that the intersection ridge line portions 5 and 16 contact the periphery of the guide hole is reduced.

Further, the chamfered portions 21 and 22 are
The rearward side of the guide hole retreats toward the center in the radial direction, so that even if the chamfered portions 21 and 22 come into contact with the periphery of the guide hole, the chamfered portions 21 and 22 close the mouth of the guide hole. The cutting edge tip 13 is pulled into the guide hole while sliding.
Eccentricity with respect to the guide hole is gradually eliminated. For this reason, the cutting edge tip 13 is smoothly drawn into the guide hole without being caught around the guide hole. As a result, the chipping of the cutting edge tip 13 is prevented and the guide bush is also prevented from being damaged.

Further, since the surfaces of the chamfers 21 and 22 are constituted by curved surfaces, the surfaces of the chamfers 21 and 22 are constituted by flat surfaces 30 as shown by a two-dot chain line in FIG. As compared with the case, the center portions in the circumferential direction of the chamfered portions 21 and 22 are relatively protruded, and thereby, the chamfered portions 21 and 22 are
Has a shape close to the mouth shape of the guide hole of the guide bush curved in an arc shape. Therefore, even when the chamfers 21 and 22 come into contact with the periphery of the guide hole, these chamfers 2
Only the both ends E ₁ and E _{2 of the first} and the _second 22 come into contact with the guide holes, and there is no possibility that chips are concentrated on these two ends E ₁ and E ₂ . In this regard,
When the flat surface 30 is used, the center of the chamfers 21 and 22 retreats toward the center in the radial direction, so that the chamfers 21 and 2
There is a great possibility that the _two ends E ₁ and E _{2 of the 2} will come into contact with the periphery of the guide hole in a concentrated manner, and chipping will occur at such a portion, so that the effect of the present invention cannot be exerted.

In the above embodiment, the chamfered portion 2
1 and 22 are formed in an arcuate cross section, but the present invention is not limited to this. For example, as shown in FIG.
22 may be configured. In addition, these chamfers 21 and 22
Is not necessarily to be formed into a curved surface in contact with the cutting edge tip outer peripheral surface 13a and wall surface 15, 16 at both ends E _1, E _2, the outer peripheral surface 13a and the like and discontinuous these ends E _1, E ₂ May be a curved surface that intersects. Furthermore, chamfer 2
The radii of curvature of 1 and 22 may be constant from the front end to the rear end.

[0019]

As described above, according to the gun drill of the present invention, the intersection of the outer peripheral surface of the cutting tip and the wall surface of the chip discharge groove forms the guide bush by the chamfer formed in the cutting tip. The risk of contact with the periphery of the guide hole is reduced, and even if they come into contact, the chamfered portion slides along the mouth of the guide hole, so that the cutting edge chip can be smoothly held without being caught around the guide hole. It is drawn into the guide hole. Further, since the surface of the chamfered portion is constituted by a curved surface, chips are not newly generated at both ends of the chamfered portion. Therefore, according to the present invention, there is obtained an excellent effect that the chipping of the cutting edge and the damage of the guide bush are reliably prevented, the tool life is improved, and the processing quality can be kept constant.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a cutting edge tip according to an embodiment of the present invention.

FIG. 2 is a side view showing the entire configuration of the embodiment of the present invention.

FIG. 3 is an enlarged view showing a joining portion between a cutting blade tip and a shank shown in FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a sectional view taken along line VV of FIG. 3;

FIG. 6 is a sectional view taken along line VI-VI in FIG.

FIG. 7 is a sectional view showing a modification of FIG. 6;

FIG. 8 is a view showing a configuration of a conventional gun drill.

FIG. 9 is a diagram showing a processing state by a gun drill.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Gun drill 12 Shank 13 Cutting edge chip 14 Chip discharge groove 15, 16 Wall surface of chip discharge groove 17 Cutting tip end surface 18, 19 Cutting edge 21, 22 Chamfer

Claims (2)

(57) [Scope of request for utility model registration] 1. A cutting tip having a diameter larger than that of the shank is joined to a tip end of the hollow shank, and a chip discharge groove having a substantially V-shaped cross section is formed on an outer peripheral portion from the tip of the cutting tip to the shank. Is formed, and a cutting edge is formed at an intersection ridge line between a wall surface of the chip discharging groove and a tip surface of the cutting edge tip, the outer peripheral surface of the cutting edge chip and the chip discharging surface. A chamfer at the intersection ridge line portion with each wall surface of the groove gradually retreating toward the center in the radial direction toward the rear end side of the cutting edge tip so that the rear end reaches the joining portion between the cutting edge tip and the shank. A gun drill wherein a chamfered portion is formed, and the surface of the chamfered portion is formed by a curved surface that draws a convex curve in a cross-sectional view orthogonal to the axis of the cutting edge tip. 2. The gun drill according to claim 1, wherein the surface of the chamfered portion has a curved surface whose degree of curvature becomes gentler toward a rear end side of the cutting edge tip. .