GB1574657A - Boring bar - Google Patents

Description

(54) BORING BAR (71) We, KOMET STAHLHALTER-UND WERKZEUGFABRIK ROBERT BREUNING GmbH, a joint'stock company organised under the laws of the Federal Republic of Germany, of 7122 Besigheim, Auf dem Kies 3, Federal Republic of 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 parti cularly described in and by the following statement: The invention relates to a boring bar, and especially, although not exclusively, to a boring bar for working metal.

A known boring bar (U.S. Patent Specifi cation 2,630,725), has a bit holder which is of substantially rectangular form as seen in plan view. An exchangeable polygonal bit is fixed at one corner of this rectangle by means of a clamping screw which is passed through a central bore in the bit. In the region of the diagonally opposite corner, the bit holder has a threaded bore for screwing in a retaining screw by means of which it is fixed to the boring bar. This known bit holder is relatively large and requires a correspondingly large opening in the boring bar. As a result, the boring bar is greatly weakened, in particular when, for the ar rangement of a ring of bit holders substan tially in a cross-sectional plane of the boring bar, a plurality of such openings is required.

Moreover, the bit holders and the openings therefor in the boring bar are difficult to produce because of their rectangular and par4lelepipedal shapes.

According to the present-invention there is provided a boring bar having at least one ex changeable polygonal bit held against abut ment surfaces in a recess provided in a bit holder by means of a clamping screw passed through the said bit, 'the boring bar having an opening'shaped to receive the bit holder in which the bit holder is fixed to the boring bar by means of a retaining screw, wherein the opening is a blind- -bore extending. sub stantially pcrpendicularlqi to the axial direc tion of the boring bar - and - having a cylin drical wall and a substantially plane bottom, the bit holder having a rear cylindrical part of a circular cross-section fitting into the blind bore and, adjacent thereto, a front part of substantially semi-circular cross-section of the same diameter as the rear part, the recess for the bit being provided in the dia metric surface of this front part, a bore for the retaining screw extending parallel to the axis of the bit holder being provided in that zone of the rear part which projects laterally beyond the bit, and a threaded bore for the retaining screw being provided in the bottom of the blind bore.

The blind bore can be produced in simple manner, and so also can the partly cylin drical and partly semi-cylindrical bit holder.

Moreover, the bit holder can have relatively small dimensions, so that the opening or blind bore in the boring bar also has small dimensions and, consequently, the cross section of the boring bar is not substantially weakened. Finally, the blind bore offers a good and secure support for the bit holder.

In order to keep these dimensions of the bit holder and also of the blind bore as small as possible, that zone of the rear cylindrical part which projects laterally be yond the bit borders advantageously directly on the bit and is in the form of a semi circular disc which'is narrow in the axial direction.

The invention will now be described in more detail, solely by way of example, with reference to the accompanying drawings in which Fig. 1 is a partial side view of the boring bar; Fig. 2 is a cross-section on the line 11-Il of Fig. 1; and Ag. 3 is a partial longitudinal section on the line IIIIII- of Fig. 1.

In The drawings, there is shown a boring bar 1 which has a circular cross-section. The boring bar may be equipped with one or more exchangeable polygonal bits or cutting inserts 2. The bits 2 arse formed of hard metal. In the embodiment shown in the draw three such bits are arranged in a so-called cutting-edge ring, their cutting edges being disposed in a common-cross sectional plane of the boring bar. Since all three bits 2 are connected to the boring bar in the same way, only the connection of one of these parts-is described hereinafter.

A bit holder '3 serves to fix the bit 2 to the boring bar 1, the holder being arranged in a blind bore 4 with a cylindrical wall 4a and a substantially plane bottom 4b in the boring bar 1. The bit holder 3 has a rear cylindrical part 3a with a circular cross-section fitting into the bore 4, and a front part 3b with a substantially semi-circular cross-section of the same diameter as the cylindrical part 3a Both the parts 3a and 3b have - the same diameter as the bore 4, A recess 5 with abutment surfaces 6 for the bit 2 is provided in the front part 3b. The bit 2 is provided with a central bore 7 through which there extends a clamping screw 8 which is screwed into a threaded bore 9 in the bit holder 3.

The -bit holder has in that zone 31a of the rear part 3a which projects beyond the bit 2 a bore 10 extending parallel to the axis of the bit holder 3. A threaded bore 11 in line with the bore 10- is provided in the bottom 4b of the bore 4. A retaining screw 12 passed through the bore 10 is screwed into this bore 11 and serves to fix the bit holder 3 in the bore 4. Since the retaining screw 12 is arranged eccentrically with respect to the axis of the bit holder 3 and to the blind bore 4, the retaining screw 12 also serves as a means securing the bit holder 3 against twisting. As can be seen in particular from Fig. 2, the bit holder 3 is supported well and securely alomost over its entire length in the blind bore 4.

Advantageously, that zone 31a of the rear cylindrical part 3a which projects beyond the bit 2 borders directly thereon and is in the form of a semi-circular disc which is narrow in the axial direction. In this way, very small dimensions of the bit holder are obtained in conjunction with very great stability.

So that the boring bar 1 may be weakened as little as possible by the bit holder or holders, the diameter D of the blind bore 4 and of the bit holder 3 is advantageously approximately as great as its length L.

In order also to ensure reliable chip removal, the boring bar 1 has above the bit a recess 13 extending perpendicularly to the axis of the blind bore 4. Due to this recess 13, the clamping screw 8 is accessible from above without the bit holder having to be taken out of the boring bar 1.

The axis of the blind bore':4 e-xtends--sub- stantially perpendicularly to the axis of the boring bar 1 and intersects the axis of the boring bar. It would also be conceivable, however, to arrange the axis of the blind bore at a distance from the axis of the boring bar. The axis of the bit holder 3, however, always extends substantially parallel to the top of the bit 2, unless the bit is inclined a little with respect to the axis of the bit holder in order to produce a positive or negative cutting angle.

Claims (5)

WHAT WE CLAIM IS:

1. A boring bar having at least one exchangeable polygonal bit held against abut ment surfaces in a recess provided in a bit holder by means of a clamping screw passed through the said bit, the boring bar having an opening shaped to receive the bit holder in which the bit holder is fixed to the boring bar by means of a retaining screw, - wherein the opening is a blind tore extending sub stantially perpendicularly to the axial direc tion of the boring bar and having a cylin drical wall and a - a-substantially plane bottom, the bit - holder having a rear cylindrical part of a circular cross-section fitting into the blind bore and, adjacent thereto, a front part of substantially semi-circular cross-section of the same diameter as the rear part, the recess for the bit being provided in the dia metric surface of this front part, a bore for the retaining screw extending parallel to the axis of the bit holder being provided in that zone of the rear part which projects laterally beyond the bit, and a threaded bore for the retaining screw being provided in the bottom of the blind bore.

2. A boring bar according to claim 1, qherein that zone of the rear cylindrical part which projects laterally beyond the bit borders directly on the bit and is in the form of a semi-circular disc which is narrow in the axial direction.

3. A boring bar according to claim 1 or 2, wherein the diameter of the blind bore and of the bit holder is approximately as great as the length of the latter.

4. A boring bar according to claim 1, wherein the boring bar has above the bit a recess extending perpendicularly to the axis of the blind bore.

5. A boring bar according to claim 1 and substantially as described hereinbefore with reference to and as shown in the accompanying drawings.