GB2057931A

GB2057931A - Drill grinding machine

Info

Publication number: GB2057931A
Application number: GB8025890A
Authority: GB
Original assignee: MEGOMAT AG
Current assignee: MEGOMAT AG
Priority date: 1979-09-06
Filing date: 1980-08-08
Publication date: 1981-04-08
Also published as: CH640165A5; JPS6354511B2; GB2057931B; JPS5645355A; DE3028960C2; DE3028960A1

Abstract

A carriage (22) displaceable on a rail (20) is connected to a carrier (28) on which a swivel arm (29) is disposed which is pivotable about a pivotal axis (B). A cantilever arm (32) is disposed on a branch (29') of the swivel arm (29) extending horizontally for pivoting about a pivotal axis (A). The cantilever arm (32) carries a chuck (34) for holding the drill to be ground. The axis of the chuck (34) which coincides with the axis of the drill to be ground, and the two pivotal axes (A, B) intersect in the grinding plane (18') of a grinding wheel (18) independently of all adjustments. The second pivotal axis (B) is offset by an amount (x) in relation to the axis (C) of the grinding wheel (18). The arrangement renders it possible to grind the pointing surfaces of a twist drill in addition to the relief surfaces and the flanks of the drill without re-chucking the drill. <IMAGE>

Description

SPECIFICATION Drilling grinding machine The invention relates to a drill grinding machine such as serves, in particular, for resharpening twist drills.

A drill grinding machine known through DE PS 839.908 comprises a rotary table which is pivotable about a vertically disposed pivotal axis and which is mounted in a base plate. A stand disposed on the rotary table contains a bearing for a horizontally disposed pivotal arm pivotally mounting a holder. In the known device, the horizontal pivotal axis is in one plane with the axis of the grinding wheel. The grinding wheel is adapted for feeding in towards the drill to be ground, in its axial direction, and can be pivoted backwards and forwards, parallel to the grinding plane defined by the grinding surface, by means of a lever, for the purpose of grinding. With this known drill grinding machine, four surfaces can be ground at the drill tip, namely the two relief surfaces determining the angle of cut and the two flanks adjoining the relief surfaces and determining the clearance angle.As a result of the axial adjustability of the grinding wheel, however, there is no assurance that the vertical pivotal axis always extends in the grinding plane, so that the grinding plane can also lie outside the course of the vertical pivotal axis, depending on the chucking length of the drill. If it lies outside, then it is not possible to machine the relief surfaces and the flanks of a drill without axial readjustment either of the grinding wheel or of the drill between the two grinding operations.

An even greater disadvantage of the known drill grinding machine is the restriction of the grinding possibilities to the said four surfaces of the drill tip. The most favourable cutting performance of a drill with a low feed pressure can only be achieved, however, if the drill is pointed. For the pointing, pointing surfaces must be ground which adjoin the flanks or, if these are omitted, the relief surfaces. As a result of the pointing, the centreline between cutting edges of the drill is shortened and a positive cutting angle is imparted thereto.

This known drill grinding machine is not suitable for grinding the pointing surfaces because the drill would have to be brought into a different position in relation to the grinding wheel for this purpose than during the grinding operations first mentioned.

In other known drill grinding machines, either the drill has to be re-chucked or a second grinding wheel is provided to grind the pointing surfaces. When the drill is rechucked, experience has shown that a great deal of precision is lost and furthermore an additional expenditure of time is necessary for this. The loss of precision has a particularly disturbing effect on drills of small diameter. A second grinding wheel, on the other hand, increases the cost of the machine considerably, because a separate drive is generally necessary due to the unfavourable angular position of the second grinding wheel in relation to the first grinding wheel.

It is therefore an object of the invention to provide a drill grinding machine, which, with a single grinding wheel and without re-chucking the drill, is capable of grinding the pointing surfaces as well as the cutting surfaces and the flanks of a twist drill.

According to the invention, a drill grinding machine comprises a grinding wheel having a plane grinding surface, a chuck for holding a drill to be ground, the chuck being mounted for pivoting about two pivotal axes which always intersect one another at a right angle, the axis of the chuck, which coincides with the axis of a drill mounted in the chuck, intersecting the point of intersection of said two pivotal axes in said plane grinding surface and one of said two pivotal axes always extending in the plane of the grinding surface and means for moving the chuck and said grinding wheel relative to one another in a direction parallel to said plane grinding surface, said one of the said two pivotal axes being radially offset with respect to the axis of rotation of the grinding wheel, the path of relative movement of the chuck and the grinding wheel extending beyond the periphery of said plane grinding surface.

In a machine in accordance with the invention as defined in the immediately preceding paragraph, the working range of the machine during a grinding operation is along a line traced by the point of intersection of the three axes mentioned, which line is offset with respect to the axis of rotation of the grinding wheel. As a result, it is possible to grind the pointing surfaces of a drill, when the drill, while gripped in the chuck, is brought against the periphery of the grinding wheel in a direction parallel to the plane grinding surface of the wheel, from outside the periphery of the wheel. For this purpose, the drill tip must penetrate by a small amount through the plane grinding surface of the grinding wheel and be brought into the required angular position by adjustment of the chuck about the two pivotal axes as will hereinafter be explained.

Preferably the chuck is mounted for rotation about its axis and is secured to an arm which in turn is mounted for pivoting about said two pivotal axes, a first of which intersects the chuck axis at right angles, and the second of which extends horizontally and constitutes said one of said two pivotal axes, the axis of rotation of the grinding wheel also being disposed horizontally, said second pivotal axis being offset radially upwards from the axis of rotation of the grinding wheel said path of relative movement of the chuck and the grind- ing wheel extending rectilinearly parallel to the second pivotal axis.

With this arrangement, with the axes of the grinding wheel horizontal and the second piv otal axis disposed above it, the grinding oper ation can best be observed. It is also preferred that the tangent at the point of intersection between the periphery of the grinding wheel and said second pivotal axis makes an angle of 40 to 70 .

This angle is decisive inter alia for the grinding of the pointing surfaces of a drill, as will again be hereinafter described, the chuck with the drill mounted in it, should be adjusted about the second, preferably, horizontal, pivotal axis so that the drill faces upwards with its point at an angle of about 45".

A specific embodiment of-the invention will now be described in detail by way of example with reference to the accompanying drawings, in which:~ Figure 1 shows a drill grinding machine according to the invention in front view, Figure 2 shows the drill grinding machine in plan view, Figure 3 shows the drill grinding machine in a side view, partially in cross-section through a stationary part, Figure 4 shows the tip of a twist drill illustrated in perspective, and positioned for grinding by the grinding wheel of the machine and Figure 5 shows the twist drill of Fig. 4 during the grinding of one of the pointing surfaces.

With reference to the accompanying drawings, the drill grinding machine illustrated in Figs. 1 to 3 comprises a supporting frame 10 with a base plate 12. Disposed in the supporting frame 10 is an electric motor 14 which drives a grinding wheel 18 through a belt 16.

The base plate 12 comprises a rail 20 on which a carriage 22 is disposed for displacement parallel to the end grinding surface or plane 18' of the grinding wheel 18. Disposed on the carriage 22 is an angled carrier 28 in which, at its upper end, a bearing 30 is disposed. An angled swivel arm 29 is mounted in the bearing 30 for pivotal movement about a horizontal pivotal axis 13. The angular position of the swivel arm 29 in relation to the carrier 28 can be read off on a scale 48.

Disposed on the horizontally extending lower branch 29' of the swivel arm 29 is a bearing 25 defining a pivotal axis A, hereinafter termed the first pivotal axis, which always extends at right angles to the pivotal axis B, hereinafter termed the second pivotal axis. A cantilever arm 32 is mounted in the bearing 25 for pivoting about the first pivotal axis A and carries, at its upper end, a chuck 34 for holding a drill to be ground. The axis D of the chuck 34 always extends at a right angle to the first pivotal axis A.

The first pivotal axis A, the second pivotal axis B and the axis D of the chuck 34 have a common point of intersection A-B-D, which always lies in the end grinding plant 18' of the grinding wheel 18 regardless of the angular positions set at a scale 26 showing the angular position of the arm 32 in relation to the branch 29' of the arm 29 about the first pivotal axis A and the scale 48 showing the angle of adjustment about the second pivotal axis B. This point of intersection A-B-D is adjustable along the second pivotal axis B by displacement of the carriage 22 on the rail 20. The second pivotal axis B lies by an amount x above the axis C of the grinding wheel 18, which amount x is smaller than the radius of the grinding wheel 18.The amount x is substantially so dimensioned tha the second pivotal axis B intersects the grinding wheel 18 in a region in which the tangent of the grinding wheel 1 8 to the second pivotal axis B has an angle between 40 and 70 , preferably of 55 .

The displacement path of the carriage 22 on the rail 20 extends over such a region that the point of intersection A-B-D goes beyond the outer edge of the grinding wheel 18 in both directions. As a result, it is possible to grind the tips of twist drills with a right-hand twist and left-hand twist. The setting of the drill grinding machine illustrated in Figs. 1 to 3 is intended for grinding drills with a righthand twist. If a twist-drill with a left-hand twist is to be ground, then the carrier 28 should be turned through an angle of 180 on the carriage 22 and the carriage 22 should be displaced to the left-hand side. The chuck 32 must then likewise be turned through an angle of 180 on the cantilever arm 29.

A stop arm 36, which can be swung into the path of displacement of the carriage 22, serves to limit the displacement path during the grinding of the pointing surfaces of the drill. In Figs. 1, 2 and 3, the stop arm 36 is illustrated in the swung out position in which it is inactive. The stop arm 36 can be swung into the displacement path of the carriage 22 so that it limits its displacement path in the direction of the centre of the grinding wheel 18. During the limiting, the fixed stop 38 disposed on the stop arm 36 and the adjustable stop 40, disposed on the carriage 22, meet. If the carriage 22 is displaced to the left-hand side for pointing twist drills with a left-hand twist, then a second stop arm 36' (Fig. 2) similar to the first stop arm 36 can be swung in so that the fixed stop 38' mounted on the left on this second stop arm 36' cooperates with the further adjustable counter stop 46 disposed on the carriage 22.

In Figs. 1 to 3, the chuck 34 for the drill to be ground is set at an angle of 1 80' on the scale 26 of the first pivotal axis A for the sake of better clarity in the drawings. The scale 26 is graduated so that the tip angle of the drill can be read off directly and this tip angle may amount to 11 8' for example.

The scale 48 related to the second pivotal axis B serves to adjust the cutting angle a and the clearance angle P. The values of these two angles cx and ss can be preset at the two adjusting knobs 50, 50' so that the chuck 34 strikes in the raised position with the preset angle a and in the lowered position with the preset angle ss. In order to grind the pointing surfaces, the angle of which is generally greater than the angle ss, for example 45 , the stop intended for the angle ss can be travelled over by actuating a release ring 53.

Offset at the corresponding parts at the periphery are identical scales to the two scales 26 and 48, which enable the operator to set the corresponding angles for grinding twist drills with a left-hand twist in the same manner. The chuck 34 for the drill to be ground is adjustable about its axis D. For this purpose, 1 80' offset detent positions are present, and a radial pin, not illustrated, engages in one side or the other of a groove. For release, the inner sleeve of the chuck has to be pushed forward against the force of a spring. In addition, by means of a further sleeve, disposed coaxially, any adjustment of the angle about the axis D can be effected, so as to turn the cutting edges of the drill with respect to the grinding plane. A spindle, not illustrated, for the axial feed of the drill is disposed in an outer sleeve 56.

The grinding machine being decribed ensures a rigid and always constant correlation of the pivotal axes A and B to the end grinding surface 18' of the grinding wheel 18, which correlation is independent of all adjusting elements. As a result, assurance is provided that the relief surfaces on the drill can be effected with the cutting angle a and the clearance angle P without axial readjustment of the drill.

For grinding all the surfaces at the tip of the drill, the drill tip is moved laterally towards and into contact with the grinding wheel 18, by displacement of the carriage 22. Whereas the stop arms 36, 36' remain swung out, that is to say inactive, for the grinding of the two relief surfaces, these stop arms are swung into the displacement path of the carriage 22 for the grinding of the pointing surfaces, so that the tip of the drill can then only be taken as far as the outer edge of the grinding wheel, the drill tip penetrating through the plane 18' of the grinding wheel 18'. The grinding wheel 18 has a cylindrical peripheral surface in the region of its outer edge. For the axial displacement of the drill, the chuck 34 has a fine adjustment device 58.

The surfaces and angles to be ground at the tip of a twist drill 62 will be explained with reference to Fig. 4 and Fig. 5 of the drawings.

A section of the grinding wheel is designated by 18". Fig. 4 shows the drill behind the section 18" of the grinding wheel, in perspective, seen at its tip. Fig. 5 shows the same position of the drill as in Fig. 4, but in side view. The drill 62 comprises two cutting edges 64, offset by 1 80' in its peripheral direction, which were produced by grinding the first relief surface 66 at the cutting angle.

The cutting angle a is related to a reference plane 70 which is at right angles to the axis of the drill 62. Adjoining the first relief surface 66 is a second relief surface 68 at an angle ss to the reference plane 70. The second relief surface 68 is the flank.

Figs. 4 and 5 show the drill 62 with the chuck 34, not illustrated in these Figures, with its axis D adjusted for grinding one of the two pointing surfaces 72. For this grinding operation, the holder is adjusted, for example, at the second pivotal axis B, to an angle of 45 and at the first pivotal axis A to an angle of 1 80'. The angle to be adjusted at the pivotal axis A may, however, be negative in relation to an angle of 1 80', for example 140 .

From Fig. 5, it can be seen that the tip of the drill 62 penetrates through the plane 74 of the end grinding surface 18' of the grinding wheel 18 by an amount a for the grinding of the pointing surface 72. For grinding all the surfaces, the drill 62 is brought up to the edge of the grinding wheel 18", from the outside, in the direction of the arrow 76 (Fig.

4). During the grinding of the pointing surface 72, the displacement distance in the direction of the arrow 76 is limited by the stops 38 and 40 (Fig. 1). The limitation corresponds to the position illustrated in Fig. 4.

The offsetting of the horizontal second pivotal axis B in relation to the axis C of the grinding wheel by the amount x is selected in such a manner that the drill 62 stands with its cutting edge 64 at an angle of about 30 to the tangent T-T of the edge of the grinding wheel for the grinding of the pointing surface 72. This leads to an angle to the tangent T-T of about 55 in relation to the horizontal.

In the embodiment illustrated, the first pivotal axis A, which is always at a right angle to the axis D of the chuck, extends vertically. An arrangement is also possible, however, in which the first pivotal axis extends horizontally. In such a case, the first horizontal pivotal axis would be pivotable about a vertical second pivotal axis and the vertical pivotal axis would then always extend in the grinding plane.

Claims

1. A drill grinding machine comprising a grinding wheel having a plane grinding surface, a chuck for holding a drill to be ground, the chuck being mounted for pivoting about two pivotal axes which always intersect one another at a right angle, the axis of the chuck, which coincides with the axis of a drill mounted in the chuck, intersecting the point of intersection of said two pivotal axes in said plane grinding surface, and one of said two pivotal axes always extending in the plane of the grinding surface and means for moving the chuck and said grinding wheel relative to one another in a direction parallel to said plane grinding surface said one of said two pivotal axes being radially offset with respect to the axis of rotation of the grinding wheel, the path of relative movement of the chuck and the grinding wheel extending beyond the periphery of said plane grinding surface.

2. A grinding machine as claimed in claim 1 wherein the chuck is mounted for rotation about its axis and is secured to an arm which in turn is mounted for pivoting about said two pivotal axes, a first of which intersects the chuck axis at right angles and the second of which extends horizontally and constitutes said one of said two pivotal axes, the axis of rotation of the grinding wheel also being disposed horizontally, said second pivotal axis being offset radially upwards from the axis of rotation of the grinding wheel said path of relative movement of the chuck and the grinding wheel extending rectilinearly parallel to the second pivotal axis.

3. A grinding machine as claimed in claim 2 wherein the tangent at the point of intersection between the periphery of the grinding wheel and said second pivotal axis makes an angle of 40 to 70 .

4. A grinding machine as claimed in any preceding claim wherein the means for moving comprises a displaceable carriage carrying the chuck.

5. A grinding machine as claimed in any preceding claim wherein the path of movement of the point of intersection of said two pivotal axes and the chuck axis extends beyond the outer periphery of said grinding surface at both sides.

6. A grinding machine as claimed in claim 5 wherein at least one removable stop means is provided for limiting the path of movement of the point of intersection of said two pivotal axes and said chuck axis in the direction of the centre of the grinding wheel when said point of intersection is in the vicinity of the periphery of the grinding wheel.

7. A grinding machine as claimed in claims 4, 5 and 6 wherein a stationary stop portion is formed by a member which can be swung into the path of said carriage and which cooperates with a counter stop which is adjustable and which is disposed on the carriage.

8. A grinding machine as claimed in claim 2 or claim 2 and any one of claims 3 to 7 wherein the arm is journalled in a first bearing which defines the first pivotal axis, the first bearing being carried by a swivel arm which in turn is journalled in a second bearing defining the second pivotal axis the second bearing being carried by a movable carrier.

9. A grinding machine as claimed in claim 2 or claim 2 and any one of claims 3 to 8 wherein the pivotal range of the chuck about the second pivotal axis is limited by at least one releasable stop means.

10. A grinding machine as claimed in claim 2 or claim 2 and any one of claims 3 to 9 wherein the chuck comprises a fine adjustment device for axially displacing the chuck.

11. A drill grinding machine substantially as herein before described with reference to, and as shown in, the accompanying drawings.