GB2143446A - Drill bit - Google Patents

Abstract

A solid drill bit having a reversing plate 13 mounted on the end face of the shank 12 is, in contrast to the prior art, so constructed that the cutting edge 27 projecting at the head end and extending to the radially outermost cutting corner 29 is aligned at a right- angle to the longitudinal axis 32 of the shank. The adjacent cutting edge 28 is somewhat oblique thereto but is only partially active. The resulting transverse force is compensated by a corresponding component in the region of the cutting corner 29. The main chip 17 is lifted off in the direction of feed and can be carried away without trouble via a chip clearance 17 which is widened out further behind the reversing plate 23 and which comprises planar portions 22 18, 22 and a wall 24. The bit is suitable for drilling in a diameter range of 12 to 14 mm with a form error of only 5 mu m and a roughness depth of 3 to 5 mu m. <IMAGE>

Description

SPECIFICATION Solid drill bit The invention relates to a solid drill bit of the type mentioned in the preamble to Claim 1, in other words having a single reversing plate. Such commercially available and practically employed drill bits are ideal for producing bores of 14to 18 mm diameter. In this respect, the reversing plate is so disposed that the two cutting edges which enclose an obtuse angle with each other cut simultaneously and are in each case oriented to the shank axis at an angle which is other than 900.

The object on which the invention is based is to provide a solid drill bit of the type mentioned but which is suitable for diameters of 12 to 14 mm, achieving a high drilling quality and permitting of high cutting outputs.

This problem is resolved by the characterising features of Claim 1.

The resultant cutting edge geometry leads to a smooth cutting action and a chip form which can be carried away largely without problem. Furthermore, the forces reacting against the feed force are largely compensated so that lateral deflection of the shank is minimised. It is possible therefore even to provide a more slender shank while increasing the drilling quality and therefore also machine diameters of 12 to 14 mm. The chip runs off parallel with the drill bit axis. The chip clearance opens to the rear and gives the chip a straight and free run outwards from the bore hole. It is possible to achieve bore holes to a depth of 2.2 x the bit diameter, whereas in the prior art only 1.5 times the bit diameter is possible.

The further developing features of Claims 2 to 9 indicate dimensions which are particularly adapted to this range of application.

With the features of Claim 10, it is furthermore possible considerably to increase the drilling depth.

While conventional drills can be used up to a drilling depth which is 1.5 times the drill bit diameter, the solid drill bit according to the invention can be used to drill to a depth of 2 to 3 times the bit diameter as a result of this design of the chip clearance.

Claims 11 and 12 indicate dimensions suitable for this.

In a type of operation where the drill bit stands still and the tool rotates, the positioning indicated in Claim 3 is recommended because chips are carried away with the least effect on the drilling quality.

The invention is explained in greater detail hereinafter with reference to an embodiment illustrated in the accompanying drawings, in which: Fig. 1 shows a solid drill bit according to the invention enlarged to twice its natural size; Fig. 2 shows the front part of the shank in Fig. 1, on an enlarged scale; Fig. 3 is a view in the direction of the arrow 3 in Fig. 2, simplified in that only the details in the region of the end face are shown; Fig. 4 shows the cutting edge area of the solid drill bit according to Fig. 1 at the commencement of the cutting process; Fig. 5 is a view corresponding to that in Fig. 4 but with the cutting process rather more advanced, and Fig. 6 is a view corresponding to Fig. 5 when the cutting process is advanced.

The solid drill bit according to Fig. 1 consists of a clamping shank 11,the construction of which may vary in known manner and which is designed to be gripped in a chuck or other housing in a machining unit. This is followed by the actual shank 12 with a reversing plate 13 mounted on the end face thereof.

In the embodiment illustrated, there is in the clamping shank 11 an axial bore 14 into which discharges an oblique bore 16 in the shank 12.

Cooling liquid is carried to the cutting zone through this passage. Also constructed in the shank 12 is a chip space or clearance 17, the configuration of which is described hereinafter with reference to Figs. 2 and 3.

According to Fig. 2, the chip clearance 17 has as the first defining wall a first sagittal plane 18 extending approximately 0.2 mm below a central plane of the shank 12 and into which the reversing plate 13 is let so as to be substantially flush with the surface thereof. The reversing plate 13 is reversibly fitted by a screw 19 which engages a threaded bore 21 in the shank 12. The first sagittal plane 18 extends in a radial direction over about 5/8ths of the shank diameter and is widened out further by some 1 to 2 mm towards the end face. In an axial direction it is followed by a step leading to a second sagittal plane 22 which extends some 1.2 mm below the central plane. This has substantially the form of a portion of a circle having a radius of 15 to 20 mm.At the point 23 of its greatest radial extension, it penetrates somewhat farther into the shank than the largest part of the first sagittal plane 18. This construction results in what is indeed only a negligible widening out of the chip face at a critical location, but the result is significant in the efficacy of the tool. The axial distance from the location 23 to the end face of the shank 12 corresponds approximately to the drilling depth and in this example amounts to twice the nominal drilling diameter.

The chip clearance 17 is further defined by a second limiting wall 24 oriented at an angle of some 1150 in relation to the first wall and the contours of which follow from the end face of the shank, Therefore it has approximately the form of an elongated J in the view in Fig. 2. In contrast to conventional spirally twisted chip spaces, there is thus on the one hand a flexion resistant form of the shank 12 and on the other the chips are carried away without changing direction.

In known manner the reversing plate 13 has a plan view in the form of a hexagon wherein at every second cutting corner 26 the adjacent cutting edges 27 and 28 enclose an obtuse angle of, for instance, 1580. The other cutting corners 29 have a rounding with a small radius of some 0.6 mm and extending over a sector of approx. 980. The cutting edges 27 and 28 are straight over a length of approx. 4 mm.

The reversing plate 13 is approx. 2.5 mm thick.

Constructed radially of the centre of the reversing plate behind the cutting edges 27, 28 and cutting corners 29,26 is a fillet approx. 1 mm wide and approx.0.3 mm deep.

As Fig. 2 shows, the reversing plate 13 is form lockingly fixed in the shank 12. Its location is thereby so chosen that the cutting edge 27 protruding at the end and extending in each case to whichever is the radially outermost cutting corner 29 is at a rightangle to the longitudinal axis 32 of the shank.

The outermost edge of the radially outermost cutting corner 29 is at a radial distance of 6 to 7 mm from the longitudinal axis 32 of the shank, according to the drilling diameter desired. Preferably, the stepping is in steps of 0.25 mm each. Following known principles, the reversing plate 13 is of hard metal.

Figs. 4 to 6 show the reversing plate 13 or the end face of the shank 12 of a solid drill bit according to Fig. 1 enlarged to the scale according to Fig. 2 and in various phases of the cutting process. In the initial phase according to Fig. 4, virtually only the cutting edge 27 is engaged with the workpiece 33. Since the cutting edge 27 is directed at a right-angle to the longitudinal axis 32 of the shank, no laterally deflecting forces occur in the zone of the cutting edges. As cutting proceeds (Fig. 5), both the cutting corner 29 and also a small part of the cutting edge 28 will become active. Here, transverse forces occur which are, however, largely self-compensating.

When finally the initial phase is completed, the cutting edge 28 has approximately half of its length working and the resulting transverse deflection is compensated by the fully engaged cutting corner 29. It could be deduced from the view in Fig. 6 that the leftwardly acting transverse deflection resulting from the greater proportion of the cutting edge 28 would exceed the oppositely directed transverse deflection at the cutting corner 29. However, a wedge effect becomes operative in the region of the rounding of the cutting corner 29 and this provides a compensating influence.

In current metal cutting technology, choosing an optimum cutting edge geometry, a suitable material or material alloy can ensure that the chip breaks as quickly as possible because short, scale-like chips can be carried out without complication.

Nevertheless, skimming off the individual chips has a decided significance with regard to drilling quality.

As Fig. 6 illustrates, the chip cut off by the cutting edge 27 is lifted off in the direction of feed, guided parallel with the tool axis and is thus carried away without trouble.

From the point of view of patent law, it is not necessary to indicate a theory underlying the advantages achieved. However, the foregoing remarks are intended to provide a guide for better illustration. The static and above all dynamic conditions which occur during the cutting process are so complicated that they cannot be dealt with in the short space available.

When using the solid bit drill in a machining unit in which the drill bit is stationary and the workpiece rotates, it has been shown to be expedient so to locate the solid drill bit that the first defining wall is horizontally aligned, the second defining wall projecting upwardly therefrom. The chips are better carried off in this way and the risk of some of them finding their way into the gap between the shank 12 and the wall of the bore hole is avoided. With this type of operation, the longitudinal axis 32 of the shank may be offset by up to 0.5 mm eccentrically in relation to the axis of rotation (drilling axis), so that a greater drilling diameter is achieved.

It is possible with the solid drill bit according to the invention to drill holes with a form error of only 5 lim and with a roughness of 3 to 5 pm depth.

Producing the chip clearance 17 presents no difficulty and can be made for example with a correspondingly shaped milling tool, a so-called Igel cutter, which simultaneously machines the first and second defining walls.

Claims (14)

1. Solid drill bit having a shank, with a reversing plate to be mounted on the end face of the shank and of which the plan view takes the form of a hexagon, whereby on every second cutting corner, the adjacent cutting edges enclose an obtuse angle, the other cutting edges having a rounding with a small radius and extending over a segment of more than 90 , and with chip clearance in the shank, characterised in that the cutting edge (27) which projects at the end and which extends to the radially outermost cutting corner (29) is orientated at a rightangle in respect of the longitudinal axis (32) of the shank.

2. Solid drill bit according to Claim 1, characterised in that the outermost edge of the radially outermost cutting corner (29) is at a radial distance of 6 to 7 mm from the longitudinal axis (32) of the shank.

3. Solid drill bit according to Claim 2, characterised in that the radial distance is subdivided into steps of 0.25 mm each.

4. Solid drill bit according to Claim 2, characterised in that the small radius of the cutting corners (29) of the reversing plate (13) measures about 0.6 mm.

5. Solid drill bit according to Claim 2 or 4, characterised in that the rounding with the small radius extends over a sector of about 980.

6. Solid drill bit according to Claim 5, characterised in that the obtuse angle amounts to about 1580.

7. Solid drill bit according to Claim 6, characterised in that the cutting edges (27,28) are straight over a length of about 4 mm.

8. Solid drill bit according to Claim 7, characterised in that the reversing plate (13) is about 2.5 mm thick.

9. Solid drill bit according to Claim 8, characterised in that radially of the centre of the reversing plate, there is behind the cutting edges (27, 28) and cutting corners (26,27) a fillet (31) of approx. 1 mm width and about 0.3 mm depth.

10. Solid drill bit according to one or more of the preceding Claims, characterised in that the chip clearance (17) has as its first defining wall a first sagittal plane (18) extending approx.0.2 mm below a central plane of the shank (12) and into which the reversing plate (13) is let so as to be virtually flushsurfaced, this first sagittal plane (18) extending radially over about 5/8ths of the shank diameter and being widened-out by a further 1 to 2 mm towards the end face, and in that this first sagittal plane (18) merges in an axial direction and via a step into a second sagittal plane (22) which extends about 1.2 mm below the central plane, takes substantially the form of a portion of a circle and at the point (23) of its greatest radial extension reaches somewhat farther than the first sagittal plane (18), and in that the chip clearance (17) has a second defining wall (24) aligned at an angle of about 1150 in respect of the first defining wall and the contours of which follow on from the end face of the shank.

11. Solid drill bit according to Claim 10, characterised in that the point (23) of greatest radial extension of the second sagittal plane (22) is provided in an axial direction from the end face at a distance ccorresponding substantially to about 2 to 3 times the nominal drilling diameter.

12. A solid drill bit according to Claim 10, characterised in that the radius of the portion of a circle measures about 15 to 20 mm.

13. Solid drill bit according to one or more of the preceding Claims, characterised in that it is arranged for location rigid with a machine so that the first defining wall is orientated horizontally, the second defining wall (24) rising upwardly therefrom.

14. A solid drill bit substantially as herein described herein with reference to the accompanying drawings.