GB2098105A

GB2098105A - Means for securing a reversible cutting insert to tool holder

Info

Publication number: GB2098105A
Application number: GB8213339A
Authority: GB
Original assignee: Fried Krupp AG
Current assignee: Fried Krupp AG
Priority date: 1981-05-09
Filing date: 1982-05-07
Publication date: 1982-11-17
Also published as: FR2505220A1; JPS57194803A; DE3118467A1

Abstract

A cutting insert (2) is retained in a tool holder (1) by a clamping member (3) which extends through a bore (4) in the insert which is parallel to but has its axis offset from the axis of the bore in the tool holder which receives the clamping member. The clamping member has a head (3a) with a conical undersurface, which subtends an obtuse angle ( beta ) and bears against a corresponding surface on the insert to urge the insert against a base seat (12) and a lateral seat (11) on the tool holder. <IMAGE>

Description

SPECIFICATION Means for securing a reversible cutting insert to tool holder The invention relates to means for securing a reversible cutting insert to a tool holder. The clamping member used has a head and a shaft and can be passed through a countersink and a bore in the insert. The shaft of the clamping member can, for example, be screwed into a bore in the tool holder.

The insert and the tool holder are so disposed that the axes of the bores are mutually offset. The insert is locked in position, so that it abuts against a base supporting surface and at least one lateral abutment surface, by the head of the clamping member, when its shaft is fixed in the tool holder, bearing against the countersink in the insert and pressing the insert against the base supporting surface and the lateral abutment surface.

Inserts with negative geometry must, in contrast to those with clearance angles, be clamped against the lateral abutment surface only. The insert therefore normally has a cylindrical attachment hole.

Inserts which must be clamped both against a lateral abutment surface and a base surface are normally provided with a countersink adjoining the cylindrical bore.

An attachment of this kind is described in Gebrauchsmuster 7237608. The insert has a conical bore enlarged conically at its upper end. The screw used as a clamping member has a corresponding countersunk head which presses the insert into the recess in the tool holder when the screw is tightened. To change the insert the screw must be entirely withdrawn which is disadvantageous. Apart from the fact that exchange of the insert is time consuming, there is also the risk of losing the comparatively small screw when it is withdrawn. This disadvantage is avoided by the arrangement described in German Specification 2333240.The releasable clamping member has a thread extending in a direction inclined, as viewed perpendicular to the bore supporting member when the insert is resting on said surface, at an angle less than 90 to the axis of the bore, its head having a curved clamping surface corresponding to the curvature of the inner wall of the bore in the insert which rests at a pressure point of limited peripheral extent on the inner wall of the bore to the insert, the centre of curvature of conical clamping surface of the head of the clamping member lying eccentrically with respect to the longitudinal axis at least along part of the peripheral surface of the head.This mode of attachment, in which the head of the clamping member is smaller than the minimum diameter of the hole in the insert allows exchange of the insert by partial unscrewing only of the clamping member out of the hole in the tool holder. As in the Gebrauchsmuster referred to above, the cone angle of the part of the head which abuts the insert when clamped is substantially less than 90 . The insert is therefore mainly clamped against the lateral abutment surface and only lightly against the bore surface. This has the disadvantage that, because of unavoidable tolerances in the dimensions of inserts and tool holders, the point of engagement between the head and the insert can vary so that no consistent clamping conditons can be attained.Also the clamping member is skew to the seating of the insert which can result in a further possibility of displacement of the point of engagement. Finally the clamping member is subjected to severe bending stress due to the relatively small cone angle of its head. In contrast to the head described in Gebrauchsmuster 7237608, the surface of which is pressed practially competely against the corresponding recess in the insert, the arrangement of German Specification 2333240 involves the risk of breakage of the clamping member due to its inability to stand the high tension and particularly bending stresses.

It is therefore the object of this invention to provide means for attaching a reversible cutting insert to a tool holder by means of a clamping member which ensures firm seating of the insert on the holder, renders possible rapid exchange of the insert and which subjects the clamping member to tension and bending stresses which are as low as possible.

This is achieved by the means claimed in claim 1.

Preferably the conical portion between the head and the shaft, by which the clamping force is applied to the insert, is such that the major component of the clamping force acts on the base supporting surface and the minor component towards the lateral abutment. The bending stress on the clamping member is then very small because it is subjected to practically no lateral deflection on clamping. Finally the bores both of the insert and the tool holder can be directed perpendicular to the base supporting surface which facilitates manufacture. In addition the advantage of rapid exchange of the insert after freeing of the clamping member is retained.

According to a feature of the invention the cone angle of the conical portion between the head and the shaft is 100-160 . The insert has a through bore with a countersink corresponding to this conical portion. Preferably, to facilitate rapid exchange of the insert, the clamping member has a thread of coarse pitch, preferably 0.2 to 0.4 times the thread diameter.

According to a further feature of the invention the head and/or the opposite end of the clamping member may be engageable by a spanner, e.g. by means of a hexagon socket therein, which also facilitates rapid exchange of the insert.

It has been found sufficient for attachment of the clamping member to the tool holder for the cylindrical shaft to have a thread at its lower end only.

It is also possible to provide between the tool holder and the insert a removable supporting plate, which is secured in the bore of the tool holder by a threaded bush having a bore to receive the clamping member.

According to a further feature of the invention it is advantageous, instead of using a screw thread, to stress the clamping member in a readily releasable manner by a helical or plate spring. For this the shaft of the clamping member has an annular collar supporting the spring which is disposed axially on the shaft. The other supporting surface for the spring is on the tool holder so that the compressed spring urges the clamping member and the insert firmly against the tool holder.

Embodiments of the invention are illustrated in the drawings, in which: Figure 1 is a cross-sectional view showing a reversible cutting insert held by a clamping member in a tool holder; Figure 2 shows an arrangement similarto that of Figure 1, including a supporting plate held in position by a threaded bush; and Figures 3 and 4 are cross-sectional views of tool holders carrying a reversible cutting insert, secured by a clamping member pressed against its seating by a spring.

The embodiment shown in Figure 1 consists essentially of a tool holder 1, a cutting insert 2 and a clamping member 3. The reversible cutting insert 2, which generally consists of hard metal, is accommodated in known manner in a corresponding recess in the tool holder 1. The through bore 4 in the insert 2 terminates at its upper end in a countersink 5. The clamping member 3 has a head 3a merging by a conical portion 3b into a shaft 3c having threads 6b at its lower end. The upper portion 6a of the shaft 3c is cylindrical and provides lateral guiding of the clamping member 3 in the tool holder. The bore 4 has a larger diameter than the head 3a of the clamping member 3.The axes of symmetry 7 of the clamping member 3 and 8 of the bore 4, i.e. their axial centre lines, extend parallel to one another so that the conical portion 3b abuts with its shoulder surface 9 against the conical surface 10 of the countersink when the clamping member 3 is tightend, thereby holding the insert 2 firmly in position due to the eccentric positioning of the clamping member 3. The clamping force exerted by the member 3 acts, owing to the obtuse cone angle p, which in the case illustrated is 1200, is directed mainly towards the tool holder 1. The arrangement shown in Figure 1 thus solves the problem underlying the invention of clamping the insert 2 both against the lateral abutment surface 11 of the tool holder 1 and also in particular against the base abutment surface 12 of the tool holder 1.

To exchange the insert 2, the clamping member 3 is unscrewed sufficiently to enable the bore 4 to be lifted clear of its head 3a. The new insert can be inserted in the reverse sequence, after which the clamping member 3 is screwed into the tool holder until the insert 2 is held by the force exerted on the surfacel0firmlyagainstthesurfaces 11 and 12 of the tool holder 1. The invention is particularly applicable to cases in which the surfaces 11 and 12 are inclined to one another at a right angle or an obtuse angle.

The embodiment shown in Figure 2 differs from that just described by the use of a supporting plate 13 interposed between the insert 2 and the tool holder 1. The supporting plate 13 is held in place by a threaded bush 14 which is screwed into a threaded bore in the tool holder 1. The clamping member 3 is screwed into a correspondingly formed bore in the bush. To ensure lateral and vertical seating of the plate 13, its bore 15 terminates at its upper end in a countersink 16, so that the correspondingly shaped portion of the bush presses down on the conical surface 17 of the plate 13 and urges it against the tool holder 1. The inclination of the surface 17 is preferably also such that it subtends an obtuse angle.

It is also possible, as shown in Figures 3 and 4, to lock the clamping member in position by a helical or plate spring 18 instead of by a screw thread, the spring being accommodated in a recess 19 in the tool holder and acting on a collar 20 on the clamping member 3 to press the insert 2 against the surfaces 11 and 12. This has the advantage over the embodiments shown in Figures 1 and 2 that no rotation of the clamping element in relation to the insert is required.

In the embodiment shown in Figure 4 the clamping element is bent through about 900 so that the force of the helical or plate spring 18 acts parallel to or at a small angle to the seating surface 12. This is to be recommended when the invention is to be applied to milling cutters. The insert is released by releasing the force ofthe spring 18, for example by a lever mechanism.

The invention is also appliable to multi-cut tools, such as millers, drills, and counterborers.

Claims

1. Means for attaching a reversible cutting insert to a tool holder having a base supporting surface and at least one lateral abutment surface by means of a clamping member having a head and a shaft which can be passed through a bore in the insert having a countersink and which can be fastened in a substantially cylindrical bore in the tool holder, for example by screwing into a thread in the cylindrical bore, the axes of symmetry of the bore in the insert and of the smaller bore in the tool holder being offset and parallel so that the head of the clamping member attached to the tool holder lies in the countersink and the insert is pressed against the base supporting surface and the lateral abutment surface, characterized in that the head of the clamping member, which in known manner is of smaller diameter than the minimum diameter of the bore in the insert has a larger diameter than the shaft of the clamping member and the clamping member has a conical portion between its head and its shaft, the surface of the conical portion defining in crosssection an obtuse angle.

2. Means according to claim 1, characterised in that the obtuse cone angle is 100-160 .

3. Means according to claims 1 and 2, characterised in that the shaft of the clamping member has a thread of coarse pitch, preferably 0.2 to 0.4 times as large as the diameter of the thread.

4. Means according to claim 1, characterised in that the head and/or the opposite end of the clamping member is engageable by a spanner, e.g.

by means of a hexagon socket therein.

5. Means according to claim 1, characterised in that the shaft of the clamping member is cylindrical and has a thread on its lower end only.

6. Means according to claim 1, characterised in that the tool holder contains a supporting plate between the insert and itself which, in known manner, is secured in the bore in the tool holder by a small bush which has a bore to receive the clamping element.

7. Means according to claim 1, characterised in that the shaft of the clamping member has an annular collar, against which presses a helical or plate spring surrounding the shaft and urging the clamping member in the direction of the axis of symmetry of the bore in the workpiece towards the abutment surface.