Twist drill

Abstract

A twist drill has a shaft and a flute portion, which extends between a drill tip and the shaft and has at least two flutes, which run helically around it at an angle of twist, are separated from one another by two webs and have a land extending between the flutes on the circumference of the flute portion. In order to provide a twist drill that has the features mentioned at the beginning, has better lubrication of the round bevels, less wear, improved guidance and improved concentricity, at least two round bevels that are spaced apart from one another are provided on each land and extend on the land at an angle of inclination in relation to the drill axis that is greater than the angle of twist but less than 90.

Claims

1. A twist drill comprising a shank and a flute portion which extends between a drill tip and the shank and has at least two flutes which peripherally extend helically at a twist angle and which are separated from each other by two webs and have a land extending at a periphery of the flute portion between the flutes, wherein provided on each land are at least two respective mutually spaced margins which extend on the land at an angle of inclination relative to a drill axis, that is larger than the twist angle but less than 90, wherein the twist angle and the angle of inclination are measured from the drill axis in the same direction, and wherein the diameter of the flute portion, defined by the margins, starting from the drill tip, continuously narrows within a distance (A) from the drill tip towards the shank.

2. A twist drill as set forth in claim 1, wherein the angle of inclination is at least 5 larger than the twist angle and less than 85.

3. A twist drill as set forth in claim 2, wherein the angle of inclination is less than 80.

4. A twist drill as set forth in claim 1, wherein within a short portion behind the drill tip the lands including the margins have a relief angle>1.

5. A twist drill as set forth in claim 1, wherein the narrowing is between 0.1 and 0.8 mm per 100 mm of length of the narrowing portion.

6. A twist drill as set forth in claim 1, wherein the distance (A) is at least three times the drill diameter and at a maximum corresponds to the length of the flute portion.

7. A twist drill as set forth in claim 1, wherein the distance (A) is less than the length of the flute portion and the diameter of the flute portion including any margins is constant in the region between the distance (A) and the length of the flute portion and corresponds to the diameter of the narrowed portion at the distance (A) from the drill tip.

8. A twist drill as set forth in claim 1, wherein the width of the margins, measured perpendicularly to the longitudinal extent thereof, is between 0.2 and 5 mm.

9. A twist drill as set forth in claim 8, wherein the width of the margins, measured perpendicularly to the longitudinal extent thereof, is between 0.5 and 1.5 mm.

10. A twist drill as set forth in claim 1, wherein the internal spacing between adjacent margins is at least 0.2 and at a maximum 5 mm.

11. A twist drill as set forth in claim 10, wherein the internal spacing between adjacent margins is between 0.5 and 1.5 mm.

12. A twist drill as set forth in claim 1, wherein the depth of the recess between adjacent margins is between 0.01 and 0.5 mm.

13. A twist drill as set forth in claim 12, wherein the depth of the recess between adjacent margins is between 0.05 and 0.2 mm.

14. A twist drill as set forth in claim 1, wherein the drill comprises solid carbide metal.

15. A twist drill, comprising: a shank; and a flute portion, wherein the flute portion extends between a drill tip and the shank and has at least two flutes, which peripherally extend helically at a twist angle and which are separated from each other by two webs and have a land extending at a periphery of the flute portion between the flutes, wherein each land includes at least two respective mutually spaced margins that extend on the land at an angle of inclination relative to a drill axis that is larger than the twist angle but less than 90, wherein the twist angle and the angle of inclination are measured from the drill axis in the same direction, and wherein the diameter of the flute portion, defined by the margins, starting from the drill tip, continuously narrows within a distance (A) from the drill tip towards the shank.

Description

(1) Further advantages, features and possible uses of the present invention will be apparent from the description hereinafter of a preferred embodiment and the accompanying Figures in which:

(2) FIG. 1 shows a side view of a twist drill according to the invention,

(3) FIG. 2 shows a side view of the tip portion of the twist drill of FIG. 1,

(4) FIG. 3 shows an end plan view on to the tip of the twist drill of FIG. 1, and

(5) FIG. 4 diagrammatically shows the contour of a twist drill according to the invention.

(6) FIGS. 1 through 4 firstly show a twist drill denoted generally by reference 1, comprising a shank portion 2 and a flute portion 3 which extends between a tip 4 which is of a wedge-shaped or cone-shaped configuration in side view, and the shank portion 2. As can be seen from the end plan view in FIG. 3 the twist drill 1 has two flutes 5 separated from each other by two webs 6. At the tip 4 of the drill the webs 6 end in relief surfaces 8 which define the main cutting edges 7 along an intersection line with the inside surfaces of the flutes 5.

(7) The particularities of the drill according to the invention can be seen primarily from FIG. 2. FIG. 2 shows an enlarged side view of a front tip portion of the twist drill 1 or the flute portion 3, and one of the webs 6 with a land 9 which extends between the two flutes 5. A plurality of parallel margins 11 extend on the land 9 at an angle of inclination relative to the drill axis 10, which in this embodiment is about 30 greater than the twist angle which defines the inclination of the flutes or the secondary cutting edges 12 relative to the axis 10 of the drill. The margins 11 are of a width (measured perpendicularly to their longitudinal extent (or at an angle -90 relative to the axis 10)) that is between 0.2 and 5 mm and preferably between 0.5 and 1.5 mm, wherein the spacing between the margins 11, that is to say the width of the recesses 14, is also in the range of between 0.2 and 5 mm and preferably between 0.5 and 1.5 mm.

(8) The margins 11 extend over the lands 9 at least within a spacing A from the drill tip 4, the spacing A being at least three times the nominal diameter D of the drill. In a tip portion which at a maximum is twice the nominal diameter of the drill, the land including the margins could be provided with a relief angle. The different diameters D.sub.N and D.sub.F (with D.sub.N>D.sub.F) in FIG. 3 however do not necessarily arise out of a relief angle in the peripheral direction, but inevitably also already occur by virtue of the fact that the diameter identified as D.sub.F is measured in a plane axially closer to the shank, than the diameter D.sub.N, wherein the outside contour of the drill overall narrows towards the shank and the margins extend inclinedly relative to the axis and the drill diameter is to be determined only where there are diametrally oppositely disposed margins.

(9) FIG. 4 once again diagrammatically shows the overall contour of the drill. The drill 1 comprises a shank 2 (which here is stepped) and the flute portion 3. The flute portion 3 narrows, starting from the maximum diameter D.sub.F at the cutting corners or radially outer ends of the main cutting edges 7, in the direction of the shank to a somewhat smaller diameter (respectively measured over the margins). The narrowing is in a range of for example between 0.1 and 0.8 mm per 100 mm of length of the flute portion 3, wherein the flute portion 3 can also go to a constant diameter again, as from a certain length of the narrowed region.

(10) It will be appreciated that the considerations relating to the diameter would similarly also apply for drills with an odd number of cutting edges, in which the diameter would be defined as double the radius from the axis to the outside surface of a round bevel, as the lands 9 and the margins 11 are then generally no longer disposed in mutually opposite relationship.

(11) In the region above the portion A the drill diameter remains constant, that is to say the outside surfaces of the margins 11 lie on a cylindrical surface around the axis 10 of the drill 10, with a radius which is somewhat smaller (for example between 0.1 and 0.3 mm) than the nominal radius of the drill.

(12) The lateral boundaries of the margins 11 do not form any cutting edges. Extending between the secondary cutting edge 12 and the rearward edge 13 of the land 9 are respective passages 14 which are formed by the recesses and which extend at the same angle of inclination relative to the axis 10 as the margins 11 and which provide for an improved supply of lubricant for the surfaces of the margins 11. Any drilling chips which pass into the passage 14 can be relatively easily and quickly transferred from the passage 14 into the next following flute 5 by way of the rearward edge 13 of the land, by virtue of the rotation of the drill and its angle of inclination of the margins 11.

(13) The inclination of the margins relative to the axis permits smooth operation of the drill in the hole and distributes the guide action of a round bevel on a shorter axial portion over a larger peripheral region than in the case of margins which follow the inclination of the flutes or the secondary cutting edges 12.

(14) At the same time however adjacent margins also overlap in the axial direction so that their lands at each axial position are supported against the wall of the drilled hole by way of at least two spaced margins.

(15) The margins can possibly be completely removed in the upper part of the flute portion 3 which is between the spacing A relative to the drill tip and the shank 2, in which case the land defines an outside radius which is for example between 0.1 and 0.3 mm below the nominal radius of the drill.

(16) Wear at the drill tip can be detected in particular by virtue of the position of a round bevel along the edge formed between the land 9 and the relief surface 8 moving in the peripheral direction with increasing wear of the relief surface 8. The twist drill according to the invention, the design configuration of which has advantages in particular for deep-hole drills, provides for reduced friction at the flute portion within the hole, with at the same time better guidance and smoother running operation of the drill. The quality of the drilled hole can also be further improved in that way.

(17) In regard to the drawings it should be noted that these admittedly on the one hand show realistic dimensional relationships, but are essentially to be interpreted as diagrammatic drawings, in particular in regard to the relationship of length to diameter of the drill, which in reality is generally markedly greater, but also in respect of the flute portion 3 and the portion A. The taper of the flute portion shown in FIG. 4 is also shown in markedly exaggerated form.

(18) For the purposes of the original disclosure it is pointed out that all features as can be seen by a man skilled in the art from the present description, the drawings and the claims, even if they are described in specific terms only in connection with certain other features, can be combined both individually and also in any combinations with others of the features or groups of features disclosed here insofar as that has not been expressly excluded or technical aspects make such combinations impossible or meaningless. A comprehensive explicit representation of all conceivable combinations of features and emphasis of the independence of the individual features from each other is dispensed with here only for the sake of brevity and readability of the description.