BORING TOOL

Abstract: The invention relates to a boring tool comprising a boring bar (1) having a centre axis (C) which at the top is arranged to be connected to a machine tool, and where the boring bar (1) at the bottom along the centre axis (C) is slit into two legs (3, 4) which by means of an adjusting screw (6) are movable towards or from each other for exact adjustment of the position of the cutting tool (10) in relation to the centre axis (C). The tool is arranged in such a way that a joint through bar (7) is detachably attached to the bottom of each of the legs of the boring bar (1), said joint through bar is extending essentially perpendicular to the slit (2) and the centre axis (C), where the cutting tool (10) is provided at the end of the bar (7). Hereby an especially simple tool is obtained which by means of well-known means can be adjusted extremely precisely for fine machining of holes.

Description: Boring tool The invention relates to a boring tool comprising a boring bar with a centre axis, which at the top is arranged to be connected to a machine tool, and where the boring bar at the bottom along the centre axis is slit into two legs which firstly outermost have means for securing a tool with a cutting edge and secondly are movable by means of an adjusting screw towards or away from each other for exact adjustment of the position of the cutting edge of the tool in relation to the centre axis. Such a boring tool which is also called a boring head is used at formation of large holes where a hole is formed initially by means of e.g. a drill, a miller or by casting. Before fine machining, it is machined to a small undersize. After this the tool must be positioned precisely within the desired tolerance, and this is done by adjusting the adjusting screw after which the clearance between the two legs can be altered to put the cutting edge of the tool in a desired position. A boring tool of this kind is known from GB A 2 128 117. It appears in this document that it is difficult to make the exact adjustment of the position of the cutting edge before the final chip is cut as it is difficult to determine the achieved diameter change by adjustment of the adjusting screw. In reality, this is only possible by measuring with a micrometer or slide gauge directly on the cutting tool but a measuring of this kind will always have some uncertainty, and the quality will largely depend on the experience and professional qualifications of the person doing the measuring. There are other types of boring tools where the cutting tool is on a carriage, the movement of which is controlled by screw mechanisms and where the displacement of the carriage is read directly on a divided scale. An example of this is seen in US A 3685917. This type of boring tools include fine mechanics which are very sensitive to dirt and which require regular greasing and other forms of maintenance in order to function, and the accuracy is furthermore often not sufficiently great. The object of the invention is to provide a boring tool of the kind mentioned in the opening paragraph that permits machining with finer tolerances and where there is no substantial demand for maintenance, and where the structure is simple and heavy- duty and the mechanical stability is very high. This is obtained with a boring tool of the kind where a joint through bar is detachably attached to the bottom of each of the legs of the boring bar, said joint is extending essentially perpendicular to the slit and the centre axis, where the cutting edge is provided at the end of the bar. The through bar can then be displaced to the sides in relation to the legs by means of the detachable attachment. A suitable detachable attachment can for example consist of a retaining screw. Because of the fact that the bar can be secured to both legs at the same time, a given setting of the spreading of the legs can be maintained during the machining. Because of the fact that one can choose between securing to one of the legs or the other during the adjustment, there will at the same time arise a number of choices of adjusting the cutting diameter : The retaining screw on the leg farthest from the cutting edge is loosened and the legs are spread by means of the adjusting screw, whereupon the retaining screw is retightened. An increased diameter size is hereby obtained. - The retaining screw on the leg next to the cutting edge is loosened and the legs are spread, whereupon the retaining screw is retightened. A reduced diameter size is hereby obtained. The retaining screw farthest from the cutting edge is loosened and the legs are brought together, whereupon the retaining screw is retightened. A reduced diameter size is hereby obtained. The retaining screw next to the cutting edge is loosened and the legs are brought together, whereupon the retaining screw is retightened. An increased diameter size is hereby obtained. A boring tool according to the invention is utilised in machine tools at boring of holes where the boring tool is rotated in relation to a stationary work piece in which the hole is made, and in boring machines where the boring tool is stationary whereas the work piece is rotated. The tool is furthermore utilised as tool holder in e.g. lathes which hereby will have an additional adjustment possibility. As stated in claim 2, for determining the positional change of the cutting edge upon adjustment of the adjusting screw, an opening is provided in one of the legs with means for securing a gauge so that this gauge through the opening can contact the side of the opposite leg that faces the slit with a view to determine the change in clearance between the two legs. By determining the change of the width of the slit in this way, a very precise measurement for the adjustment of the machining diameter can be obtained at the same time as the adjustment is done. The measuring of the intermotion of the legs can be done in other ways, e.g. by determination of the angle of rotation of the adjusting screw. As stated in claim 3, it would be expedient if the opening is shaped as a bore hole having a diameter corresponding to or slightly larger than the diameter of the shank part of a dial gauge. A dial gauge will here be easily mounted in the bore hole, and it is easy to secure it by means of a simple retaining device, e.g. a clamping screw. A dial gauge is a very conventional, well-known gauge, and it can be purchased having the necessary precision at a fair price as well. It is furthermore very easy to use, the resetting is simple and the reading can be done without difficulty. There is thus great advantages in designing the boring tool in such a way that the measuring of the diameter change can be done with a conventional dial gauge. As stated in claim 4, it is expedient if the bore hole in which the dial gauge can be placed is extending in an angle relative to the transverse axis of the boring bar, and where the point of abutment of the dial gauge on the side of the second leg is in the distance h from the plane of action of the tool perpendicular to the centre axis. The movement of the legs can be considered as a rotation about a centre of rotation situated at the upper end of the slit. For a given distance between this centre of rotation and the cutting edge the angle α and distance h can be chosen so that the deflection on the dial gauge during adjustment corresponds to the obtained diameter change during the subsequent machining. This is very advantageous as it is thus not necessary to convert from dial gauge deflection to diameter change. In the following an embodiment of the invention is described in detail with reference to the drawing, in which Fig. 1 is a draft of a boring tool according to the invention, seen from the side, and Fig. 2 is a partial sectional view through a boring tool with the dial gauge mounted. Fig. 1 shows the bottom part, namely the cylindrical boring bar 1 of a boring tool. In the boring bar 1 is a longitudinal slit 2 following the centre axis c of the boring bar. The slit 2 divides the boring tool into two legs 3,4 which are elastically movable relative to each other. Each leg then has a contour consisting of a half circle and a plane surface 13,14 where the plane surfaces 13,14 of the two legs, which are formed by the inside faces of the slit 2 are facing each other. Legs having other contours are possible within the scope of the invention, e.g. quadrangular or oval contours, as long as there is a longitudinal slit between them. In a transverse hole 5 at the bottom end of the leg 3 is introduced by means of a female thread a screw 6 which can be tightened to abut the plane surface 14 of the leg 4. By tightening the screw 6 against the plane surface 14, the two legs will elastically move away from each other. Transversely in relation to the slit 2 and at the bottom of the two legs 3 and 4 of the boring bar 1 is placed a bar 7 which is displaceable in a flute perpendicular to the slit. Outermost on the bar 7 is a cutting edge 10 which e.g. can be a conventional replaceable ceramic tip secured to the bar 7 by a screw 11 or it can be a hardened and sharpened end of the bar 7 which in itself expediently can be a conventional standard turning tool. The bar 7 can be fixed to each of the two legs by means of a retaining screw 8 and 9 each. In the leg 4 is a bore hole 12 extending from the outer side of the leg to the plane surface 14. In fig. 2 it is shown how a dial gauge 15 with the shank part 16 is mounted in the bore hole 12. Through the bore hole 12 the pin 17 of the dial gauge contacts the plane surface 13 of the opposite leg 3. In fig. 1 is seen a retaining screw 18 which is retaining the shank 16 of the dial gauge in the bore hole 12. In fig. 1 is also seen the handle of an Allen key 19 which is used at adjustment of the screw 6. At the top, the boring bar can be shaped with a conventional cone for mounting in a machine tool but a horizontal crossbar is generally built in between the boring bar and the cone so that the boring bar can be displaced sideways in relation to the rotational axis of the machine tool. The crossbar makes it possible to machine holes with widely different diameters. As can be seen in fig. 2, the bore hole 12 is made having a certain angle α in relation to the transverse axis T of the boring bar, and so that the pin of the dial gauge at mounting of the dial gauge in the bore hole will abut against the surface 13 in the vertical distance h to the point of action of the cutting edge. As a result of the angle , the travel of the dial gauge will be longer than the actual change of the clearance between the legs whereas the distance h for geometric reasons will give a smaller deflection on the dial than the horizontal travel of the legs in the point of attack of the cutting edge. By expedient choice of h and in relation to the length of the legs it can be ensured that the dial gauge indicates the change of the diameter when the screw 6 is adjusted before machining of a hole. In the current case the angle α is 28 degrees. In the following an example of how the boring tool according to the invention is utilised for the fine machining of a hole is gone through. At first the hole is roughly machined with a boring head so that it is 0.5 mm short of the diameter size. The fine machining must now be done in one or two steps in order to obtain size and surface quality as desired. In case it is done in two steps a test chip is initially prepared. A size of -0.04 mm in relation to the desired final Den efterfølgende opmaling viser nu, at hullet mangier 0,03 nun i forhold til det ønskede diametermal. Stalet skal altsa forskydes 0,015 mm for at na den ønskede diameter . Holdeskruen 9 løsnes, og bjaslken 7 er nu fastholdt af holdeskruen 8 til benet 3. Maleuret 15 onteres nu i boringen 12 og nuljusteres. Justeringsskruen 6 spasndes indtil maleuret viser en forøgelse af slidsen pa 0, 03 mm, hvilket aflasses direkte pa maleskiven. Herved vil bjaslken 7 forskydes 0.015 mm som ønsket. Holdeskruen 9 spaandes hvorved bjslken 7 nu igen fastholdes stabilt i den nu forskudte position, og maleuret og ombracconøglen fjernes hvcrefter den endelige bearbejdning kan foretages.

Claims: Claims 1. A boring tool comprising a boring bar (1) having a centre axis (C) which at the top is arranged to be connected to a machine tool, and where the boring bar (1) at the bottom along the centre axis (C) is slit into two legs (3,4) which firstly outermost have means for securing a tool with a cutting edge and secondly are movable by means of an adjusting screw (6) towards or away from each other for exact adjustment of the position of the cutting edge of the tool (10) in relation to the centre axis (C) , characterised in that a joint through bar (7) is detachably attached to the bottom of each of the legs of the boring bar (1), said joint through bar is extending essentially perpendicular to a slit (2) and the centre axis (C) , where the cutting edge is provided at the end of the bar (7) . 2. A boring tool according to claim 1, characterised in that for determining the positional change of the cutting edge upon adjustment of the adjusting screw (6), an opening (12) is provided in one of the two legs (3,4) with means (8) for securing a gauge (15) so that this gauge through the opening can contact the side (13) of the opposite leg (3) that faces the slit (2) with a view to determine the change in clearance between the two legs (3,4) . 3. A boring tool according to claim 1, characterised in that the opening is shaped as a bore hole (12) having a diameter corresponding to or slightly larger than the diameter of the shank part (16) of a dial gauge (15) . 4. A boring tool according to claims 1 and 2 , characterised in that the bore hole (12), in which the dial gauge (15) can be placed, is extending in an angle α relative to the transverse axis (T) of the boring bar (1) , and where the point of abutment of the dial gauge (15) on the side (14) of the second leg (4) is in the vertical distance h from the plane of action of the tool, where and h are chosen so that the deflection of the dial gauge for a given boring bar indicates the change in clearance between the legs in the plane of action of the tool . 5. A boring tool according to claims 1-4, characterised in that the boring bar (1) above the slit (2) preferably via a crossbar is connected to a cone arranged for attachment in a machine tool . AMENDED CLAIMS [received by the International Bureau on 17 October 2000 (17.10.00); original claims 1 - 5 replaced by new claims 1-5 (2 pages)] Amended claims 1. A boring tool comprising a boring shank (1) which has a centre axis (C) and at the top is arranged to be connected to a machine tool, and where the boring shank (1) at the bottom along the centre axis (C) with a slit (2) is slitted into two legs (3,4) which outermost have means for securing a tool with a cutting edge are movable by means of an adjusting screw (6) towards or away from each other for exact adjustment of the position of the cutting edge of the tool (10) in relation to the centre axis (C) , characterised in that for determining the positional change of the cutting edge upon adjustment of the adjusting screw (6), an opening (12) is provided in one of the two legs (3,4) with means (8) for securing a gauge (15) so that this gauge through the opening can contact the side (13) of the opposite leg (3) that faces the slit (2) with a view to determine the change in clearance between the two legs (3,4) . A boring tool according to claim 1, characterised in that the opening is shaped as a bore hole (12) having a diameter corresponding to or slightly larger than the diameter of the shank part (16) of a dial gauge (15) . 3. A boring tool according to claims 1 and 2 , characterised in that the bore hole (12), in which the dial gauge (15) can be placed, is extending in an angle α relative to the transverse axis (T) of the boring shank (1) , and where the point of abutment of the dial gauge (15) on the side (14) of the second leg (4) is in the vertical distance h from the plane of action of the tool, where and h are chosen so that the deflection of the dial gauge for a given boring shank indicates the change in clearance between the legs in the plane of action of the tool. 4. A boring tool according to claims 1, 2 or 3, characterised in thac a joint through bar (7) is detachably attached to the bottom of each of the legs of the boring shank (1), said joint through bar is extending essentially perpendicular to the slit (2) and the centre axis (C) , where the cutting edge is provided at the end of the bar (7 ) . 5. A boring tool according to claims 1-4, characterised in that the boring shank (1) above the slit (2) preferably via a crossbar is connected to a cone arranged for attachment in a machine tool .

Inventors: LARSEN ERIK, LARSEN, ERIK
Applicants: LARSEN ERIK, LARSEN TOOLING APS, LARSEN, ERIK
Application year: 2000
Main classification: B23B29
IPC codes: B23B29, B23Q17