GB1562229A

GB1562229A - Cutting drill

Info

Publication number: GB1562229A
Application number: GB43910/76A
Authority: GB
Original assignee: Walter Montanwerke GmbH
Current assignee: Walter Montanwerke GmbH
Priority date: 1975-12-12
Filing date: 1976-10-22
Publication date: 1980-03-05
Also published as: ATA847276A; AT350873B; DE2555979C2; IT1072210B; CH618368A5; FR2334456B1; FR2334456A1; DE2555979A1

Abstract

Pocket-like recesses (4, 5) into which indexable inserts (6) are inserted are formed on the root of two opposite chip grooves (3). The indexable inserts (6) are of rhombic configuration with four main cutting edges (7). On account of the rhombic configuration, the main cutting edges (7) enclose angles other than 90 DEG with one another. One indexable insert (6) is arranged so as to project with its main cutting edge (7) beyond the drill axis (12) and to intersect the drill axis so that the material is also cut in the centre and no peg of material is left behind. In order to permit better chip disposal, the indexable inserts (6) have ground-in or sintered-in chip breaker grooves (15) adjoining the main cutting edges. These indexable inserts (6) are designed as through-hole inserts and are releasably fastened to the drill body (1) by means of a screw (10). This permits maximum utilisation of the expensive indexable inserts. <IMAGE>

Description

(54) IMPROVED CUTTING DRILL (71) We, MONTANWERKE WALTER GmbH, a German Company, of 7400 Tübingen Derendingedstr. 53 West Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a drill having a drill body and at least one reversible cutter mounted in the body.

German Offenlegungschrift No. 23 58 048 describes a cutter drill whose overall cut width is defined by the operative edges of two cutters so that one attacks roughly a radially outermost portion of the cut width and the other cutter roughly a radially innermost portion of the cut width, the cutters being welded to the drill body.

Moreover, the cutters are disposed to operate at small positive axial and radial rake angles with the radially innermost cutting edge lying to one side of the drill axis. This leaves a residual pin of workpiece material coaxial with the drill axis, and which must be continuously removed.

Special measures are also required to obtain satisfactory chip removal.

Welding cutters to the drill body, is an inefficient use of metal in these expensive cutter plates, as only one cutting edge is usable. In addition, chip removal is a critical factor in this prior drill.

It is an object of the present invention to obviate or mitigate the above disadvantages.

According to one aspect of the present invention there is provided a drill for metallic materials and plastics comprising a rotary drill body, a reversible cutter located in a recess in the drill body and having a plurality of cutting edges, the cutter being inserted in the body such that an operative one of the cutting edges is inclined at an angle outside the drill body of less than 90" to the drill axis, and has one end located outside the drill body said operative cutting edge defining the entire cut width, the cutter being located with said operative cutting edge intersecting and projecting beyond the rotational axis of the drill body, so that the other end of the cutting edge is located on the opposite side of the drill axis to said one end and means for releasably securing the cutter in the recess of the drill body.

According to another aspect of the present invention there is provided a drill for metallic materials and plastics, comprising a rotary drill body, a plurality of reversible cutters located in corresponding recesses in the drill body, each cutter having a plurality of cutting edges, the cutters being inserted in the body such that operative ones of the cutting edges of the cutters are inclined at an angle outside the drill body of less than 90" to the drill axis, the operative cutting edge of one cutter having an end located outside the drill body while the operative cutting edge of another cutter intersects the axis of the drill body, the entire cut width being defined by said operative edges, and means for releasably securing each cutter in its respective recess of the drill body.

Preferably the or each cutter has a chip guide surface adjacent a respective cutting edge.

Preferably further the cutter is in the form of an apertured plate and the releasable securing means comprises screw means which passes through the aperture.

The present invention provides a drill fitted with interchangeable reversible cutters and is usable in drills having small diameters of 20 mm and less: the present invention enables good chip-removal even under difficult operating conditions.

In the drill an operative cutting edge passes through the drill axis, so that chips are clearly removed from the workpiece material over the entire width of cut and no pin of material remains.

Surprisingly, it has been shown that the approach to zero of the cutting speed in the region of the drill axis does not impair the working result.

The reversible cutters may be removed, turned or interchanged by simple removal of screws, so that the cutting edges can be used in sequence. Clamping parts necessary and conventional with other reversible cutters can be eliminated: these parts hinder the movement of the chip at small drill diameters (20 to 50 mm).

The formation of the reversible cutters as apertured plates, in conjunction with ground chip-guides which act as chipbreakers, provides a simple and effective solution to some of the above disadvantages of prior drills.

In the case of very small drill diameters (smaller than 20 mm), the provision of several reversible cutters to provide the desired width of cut can result in the cutters becoming too small. In this case it is preferable to provide a drill satisfying the first aspect of the invention.

For a drill with more than one cutter the reversible cutters, lying at different radial spacings relative to the drill axis are preferably located so that the reversible cutters, when beginning to cut, penetrate in sequence into the material. In this connection it has proved advantageous if the radially innermost reversible cutter projects axially a small amount beyond the radially outermost cutter, so that the radially innermost reversible cutter penetrates first with its cutting corner into the material.

The reversible cutters can be inserted with axial and radial angles of substantially 00. Cases are also possible in which a small positive axial angle is present.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a double-edged drill according to the present invention, in perspective view; Figs. 2, 3 and 4 show the drill according to Fig. 1, in three different side views; Figs. 5 and 6, show the drill according to Fig. 1, in two fragmentary side views in section and to a larger scale; and specifically showing the individual cutters of the drill; Fig. 7. shows the drill according to Fig. 1, in front end elevation, and to a larger scale; Fig. 8 shows a single-edged drill according to a further embodiment of the invention in partial side elevation; Fig. 9 shows a drill according to Fig. 8, in front end view and to a larger scale, and Fig. 10 shows a reversible cutter of the drill according to Fig. 9 in plan view.

The drills shown in Figs. 1 to 7 in doubleedge form and in Figs. 8 and 9 in singleedged form, have a rotary drill body 1, provided with a conventional tapering shank 2. In the case of the double-edge form. there are formed in the drill holder 1, at two diametrally-opposed locations on the periphery, two chip grooves 3, on whose base there are formed pocket-like recesses 4, 5 into which reversible cutters 6 are inserted. The reversible cutters 6 consist of hard metal or high-speed steel; they are rhomboid in the example shown, with four cutting edges 7. Adjacent edges 7, because of the rhomboid form, of the reversible cutters 6, form with each other angles slightly greater than and slightly less than 900 respectively.

Each reversible cutter 6 has a throughbore 8, (Fig. 7), countersunk at 9, and into which there is fitted a correspondinRlv shaped screw 10, which is screwed into a tapping 11 in the drill body 1, and holds the cutter 6 securely in its recess 4 or 5.

As can be seen in Figs. 3 and 7, the reversible cutters 6 provided in the drill according to Figs. 1 to 7, are located at differing radial spacings from the drill axis 12, in such a way that the total width of cut is provided by the two operative cutting edges, of the two reversible cutters 6. The radially outermost reversible cutter 6, located in recess 5, extends with a chamfered cutting corner 13 slightly beyond the periphery of the body. The operative cutting edge 7 of this cutter is inclined to the drill axis 12, to be set at an angle A1 (Fig. 3) less than 90" (for example 86 ) Thus.

because of the rhomboid shape of the reversible cutter 6, the cutting corner 13 is relieved at the periphery of the drill.

The radially innermost reversible cutter 6 (Fig. 6) is likewise set at an angle p2 of less than 90 , for example 2=860. The operative cutting edge 7 of this cutter intersects the drill axis 12 and extends beyond it at 14. By virtue of the setting angles ofthe cutters, the portion of the edge at 14 projecting beyond the drill axis 12 does not come into contact with the material being drilled.

The cutters 6 are located such that the innermost reversible cutter 6 projects with its outer cutting corner by an amount indicated by a2 in Fig. 6, which is greater than the projection of the cutting corner 13 of the outermost reversible cutter 6 in Fig.

5, where this projection is indicated by a,.

This means that the outer cutting corner of the innermost reversible cutter on commencement of drilling, is the first to come into contact with the material. Cases are also imaginable, in which the circumstances are reversed, i.e. a1 is greater than a2.

The reversible cutters 6 are provided with chip guide surfaces 15, associated with each of the cutting edges 7, and are located at a depth of 0.5 mm in the case of a cutter thickness of about 5 mm for example. The chip guide surfaces (15) are ground into the reversible cutters 6; the surfaces (15) with the connecting free surface 16, defining the edges 7. The free surfaces 16 are inclined relative to the base surface in the manner of conventional truncated-pyramidal reversible cutters.

As can be seen in Fig. 9, the chip guide step surfaces (15) are provided substantially parallel with the base surface of the reversible cutters 6. Forms are also possible, in which the chip guide surfaces (15) are in the form of troughs.

In order to guarantee a trouble-free seat for the reversible cutters 6 in their recesses 4, 5, the drill body 1 is provided in the region of the inwardly-lying corner of the recesses with a through bore indicated at 17.

The two reversible cutters 6 are located at different radial spacings from the drill axis 12, and consequently their operative cutting edges operate at different cutting speeds due to this arrangement, the cutting speed at cutting edge 7 of the radially-innermost reversible cutter 6 approaching zero at the drill axis. For reasons of simplicity, both reversible cutters are as a rule made of the same material; it is however also possible for the cutters to be made of different materials, for example hard metal and high speed steel, in accordance with the differing cutting speed of their cutting edges 7.

Both cutters 6 operate at an axial angle y (a) and a radial angle y (r) of 0 in each case.

It is also possible for the cutters 6 to operate with a small positive axial angle y (a) of about 3 , and it is also possible for both cutters to have different cutting geometries.

It would be possible for the drill to have more than two cutters for larger drill diameters.

However, when the drill diameter is small, for example smaller than 20 mm, then an embodiment is preferably used as shown in Figs. 8 to 10. In this embodiment in the drill holder 1 there is inserted in a corresponding recess 40 in the base of the chip groove 3, one single reversible cutter 6, whose operative cutting edge 7 has its outer cutting corner located slightly outwith the periphery of the drill body, and, intersecting the drill axis 12 on the opposite side, extends beyond said axis 12 at 14. The reversible cutter 6 is inserted at a setting angle A smaller than 90 , for example 83". It is again attached by means of a screw 10 in the manner described for the previous embodiment. The cutter 6 operates at an axial angle y (a) and a radial angle y (r) of approximately 00; it can also be inserted with a small positive axial angle.

WHAT WE CLAIM IS: 1. A drill for metallic materials and plastics comprising a rotary drill body, a reversible cutter located in a recess in the drill body. and having a plurality of cutting edges, the cutter being inserted in the body such that an operative one of the cutting edges is inclined at an angle outside of the drill body of less than 90" to the drill axis.

and has one end located outside the drill body said operative cutting edge defining the entire cut width, the cutter being located with said operative cutting edge intersecting and projecting beyond the rotational axis of the drill body, so that the other end of the cutting edge is located on the opposite side of the drill axis to said one end and means for releasably securing the cutter in the recess of the drill body.

2. A drill for metallic materials and plastics, comprising a rotary drill body, a plurality of reversible cutters located in corresponding recesses in the drill body, each cutter having a plurality of cutting edges, the cutters being inserted in the body such that operative ones of the cutting edges of the cutters are inclined at an angle outside of the drill body of less than 90" to the drill axis, the operative cutting edge of one cutter having an end located outside the drill body while the operative cutting edge of another cutter intersects the axis of the drill body, the entire cut width being defined by said operative edges, and means for releasably securing each cutter in its respective recess of the drill body.

3. A drill as claimed in claim 1 or 2, wherein the or each cutter has a chip guide surface adjacent a respective cutting edge.

4. A drill as claimed in any one of claims I to 3, wherein the or each cutter is in the form of an apertured plate and the releasable securing means comprises screw means which extends through the aperture in the plate.

5. A drill according to claim 2, wherein the reversible cutters lie with different radial spacings relative to the drill axis and are inserted with different angular settings.

6. A drill according to claim 5, wherein a first one of the cutters, projects axially from the drill body beyond the other cutter, so that said one cutter engages the workpiece first on commencement of a cutting operation.

7. A drill according to claim 6, wherein the radially innermost cutter projects axially beyond the radially outermost cutter.

8. A drill according to one of the foregoing claims, wherein the or each reversible cutter is inserted with axial and radial rake angles of substantially 0".

9. A drill according to claim 1 or 2, wherein the or each reversible cutter is inserted with a small positive axial angle.

10. A cutting drill substantially as

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. conventional truncated-pyramidal reversible cutters. As can be seen in Fig. 9, the chip guide step surfaces (15) are provided substantially parallel with the base surface of the reversible cutters 6. Forms are also possible, in which the chip guide surfaces (15) are in the form of troughs. In order to guarantee a trouble-free seat for the reversible cutters 6 in their recesses 4, 5, the drill body 1 is provided in the region of the inwardly-lying corner of the recesses with a through bore indicated at 17. The two reversible cutters 6 are located at different radial spacings from the drill axis 12, and consequently their operative cutting edges operate at different cutting speeds due to this arrangement, the cutting speed at cutting edge 7 of the radially-innermost reversible cutter 6 approaching zero at the drill axis. For reasons of simplicity, both reversible cutters are as a rule made of the same material; it is however also possible for the cutters to be made of different materials, for example hard metal and high speed steel, in accordance with the differing cutting speed of their cutting edges 7. Both cutters 6 operate at an axial angle y (a) and a radial angle y (r) of 0 in each case. It is also possible for the cutters 6 to operate with a small positive axial angle y (a) of about 3 , and it is also possible for both cutters to have different cutting geometries. It would be possible for the drill to have more than two cutters for larger drill diameters. However, when the drill diameter is small, for example smaller than 20 mm, then an embodiment is preferably used as shown in Figs. 8 to 10. In this embodiment in the drill holder 1 there is inserted in a corresponding recess 40 in the base of the chip groove 3, one single reversible cutter 6, whose operative cutting edge 7 has its outer cutting corner located slightly outwith the periphery of the drill body, and, intersecting the drill axis 12 on the opposite side, extends beyond said axis 12 at 14. The reversible cutter 6 is inserted at a setting angle A smaller than 90 , for example 83". It is again attached by means of a screw 10 in the manner described for the previous embodiment. The cutter 6 operates at an axial angle y (a) and a radial angle y (r) of approximately 00; it can also be inserted with a small positive axial angle. WHAT WE CLAIM IS:

1. A drill for metallic materials and plastics comprising a rotary drill body, a reversible cutter located in a recess in the drill body. and having a plurality of cutting edges, the cutter being inserted in the body such that an operative one of the cutting edges is inclined at an angle outside of the drill body of less than 90" to the drill axis.

10. A cutting drill substantially as

hereinbefore described with reference to and as illustrated in Figs. I to 7 of the accompanying drawings.

11. A cutting drill substantially as hereinbefore described with reference to and as illustrated in Figs. 8 to 10 of the accompanying drawings.