TOOL-BIT HOLDER

Abstract: In a tool-bit holder (1) for e.g. tool bits (3, 5) of cemented carbide or other hard material, the novel features are a) that the tool-bit holder (1) has vibration-damping properties, and b) that the bits (3, 5) are placed and oriented in a manner which would cause instability and consequent machining marks on the workpiece, if feature <u>a</u> were not present. With this arrangement, it is possible to achieve faster machining without risk of "chatter".

Description: TOOL-BIT HOLDER TECHNICAL FIELD The present invention relates to an elongated tool-bit holder of the kind set forth in the preamble of claim 1. BACKGROUND ART As will be well known by persons skilled in the art of drilling and boring in metal by using a drill or boring bar comprising an elongated tool bit holder and at least one tool bit of very hard material, such as cemented carbide, the speed of machining, i.e. the amount of ma¬ terial removed per unit time, depends on the positioning and orientation of the cutting edges of the tool bits re¬ lative to the tool-bit holder and/or the article being machined. When adjusting said positioning and orientation with a view to achieving higher machining speeds, critical val¬ ues, at which instability occurs, may be reached, and to avoid any risk of instability, it is common practice to keep said parameters on the safe side of the critical values. This, of course, entails a reduction in the speed of machining and hence of the profitability of the machi¬ ning operations concerned. DISCLOSURE OF THE INVENTION On this background, it is the object of the invention to provide a tool-bit holder of the kind referred to above, with which it is possible by extremely simple means to achieve high machining speeds without any risk of instability, and this object is achieved by means of the features set forth in the characterizing clause of claim 1. By using a tool-bit holder with vibration-damping properties, and placing and orienting the bit or bits in a manner causing the critical values to be exceeded, any tendency to instability is prevented, at the same time as the high speed of machining normally associated with such a tendency is achieved. Advantageous embodiments of the tool-bit holder are set forth in claims 2 - 4. BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention is explained in more detail with reference to the exemplary embodiments of tool-bit holders according to the invention shown in the drawing, in which Figure 1 is a front view in the direction of the arrow I in Figure 2 of a drill in the form of a drill-bit holder with clamped-on tool bits, together with the hole being drilled in a workpiece, Figure 2 is a side view in the direction of the arrow II in Figure 1 of the drill shown in Figure 1, Figure 3 shows a boring bar intended for use in a lathe, seen in the direction of the arrow III in Figure 4, and Figure 4, at a reduced scale, shows the boring bar of Figure 3, seen in the direction of the arrow IV in Figure 3. DESCRIPTION OF THE PREFERRED EMBODIMENT Figures 1 and 2 show the front end of a drill consisting of an elongated drill-bit holder 1, of which only the front end 2 is shown, and which in a roughly well-known manner supports two tool bits, viz. a first bit 3 with its associated first cutting edge 4 and a second bit 5 with its associated second cutting edge 6. The tool bits 3 and 5 are in a manner known per se gene¬ rally shaped like equilateral triangles, in which the corners are rounded and the sides are broken outwardly on the middle so as to give the cutting edges 4 and 6 a flattened V-shape. The bits 3 and 5 are secured to the drill-bit holder 1 in a manner known per se (not shown) so that they can be removed and turned and/or replaced. As will be seen from Figure 1, the first cutting edge 4 lies in a meridian plane 7 and extends from a position close to the drilling axis 8 to an outermost corner 9 at an appreciable distance from the periphery 10 of the drill support. The second cutting edge 6 lies in an axial plane 11 inter¬ secting the meridian plane 7 at the outermost corner 9 at an angle 12 of between 1° and 4°, the second cutting edge 6 extending from a position at an appreciable dis¬ tance from the drilling axis 8 to an outermost corner 13 defining the periphery 14 of the hole being or having been drilled. As will appear from Figure 2, the two bits 3 and 5 are mutually axially offset in such a manner that the first bit 3, as reckoned in the feed direction 19 of the drill, is lagging by a small distance 20, i.e. that the load on the second bit 5 becomes greater. In addition, the bits are oriented about their central axes in such a manner that the innermost half of the first cutting edge 4 forms an angle 15 of between 8° and 10° with a radial plane 16, whereas the outermost half of the second cutting edge 6 forms an angle 17 of between 5° and 7° with this radial plane. The positioning of the second bit 5, partly in the feeding direction 19 in front of the first bit 3, partly in the direction of rotation 18 in front of a symmetrical posi¬ tion relative to the first bit 3, causes the greatest cutting force to be on the second bit 5. If the drill- bit holder 1 consists of a material without vibration- damping properties, e.g. ordinary tool steel, the posi- tioning of the second bit 5 relative to the first bit 3 as shown and described would make the drill consisting of the drill-bit holder 1 and the two tool bits 3 and 5 unstable, i.e. it would most probably execute torsional vibrations during a drilling operation, in a manner known per se causing the formation of machining marks in the periphery 14 of the hole being drilled and - not least - an intolerable noise and risk of damage to the tool bit. Vibrations of this kind are avoided in the drill-bit holder according to the invention, since this holder is manufactured from a material with inherent vibration- damping properties, e.g. mild steel. Tests have shown that steel corresponding to C 15, 9 SMnPb 28K has such vibration-damping properties that vibrations of the kind referred to are avoided, leaving the periphery 14 of the hole drilled completely smooth. Other types of steel with similar vibration-damping properties may, of course, also be used. To prevent wear on the drill-bit holder 1 due to the contact with the chips produced, the drill-bit holder may be treated to make its surface sufficiently hard to avoid such wear arising. If the drill-bit holder 1 con¬ sists of mild steel as mentioned above, this may easily be achieved by conventional case hardening, e.g. at a depth of approx. 0.5 mm and to a Rockwell-hardness of between 55 and 60. A further effect of this is that the chips slide more easily on the surfaces concerned, this being important especially in the case of deep holes, in which a "burning-on" may easily take place. The invention may be used with the same effect on e.g. a stationary boring bar for use in a lathe, as also dealt with in the above-mentioned GB patent specification No. 1,299,750, and an example of this will now be described with reference to Figures 3 and 4. Thus, Figures 3 and 4 show a boring bar 21, to the front end 22 of which a single tool bit 23 is secured in the usual manner. As will appear from Figure 3, the cutting edge of the bit 23 forms an angle 25 of between 3° and 11° with a diametral plane 27 through the radially outermost edge of the bit, said bit lying in a plane generally paral¬ lel to the axis 24 of the boring bar 21, said axis 24 during use being substantially parallel to the rotation axis of the rotating workpiece (not shown) , that the radially innermost corner of the cutting edge, as seen in the direction of rotation, lies somewhat ahead of the outermost one. Such a positioning of the tool bit causes a good con- veyance of the chips through the axially extending chip groove 26, but increases the risk of vibrations. Also in this case, however, this risk may be avoided by making the boring bar 21 fully or partly from vibration-damping material and possibly hardening certain surfaces, as explained above in the discussion of the exemplary embodi¬ ment shown in Figures 1 and 2. The features relating to damping of vibrations are the subject of claims in the co-pending international patent application No (B, S & Co. ref. 54794). LIST OF PARTS 1 Drill-bit holder 2 Front end 3 First tool bit 4 First cutting edge 5 Second tool bit 6 Second cutting edge 7 Meridian plane 8 Drilling axis 9 Outermost corner 10 Periphery 11 Axial plane 12 Angle 13 Outermost corner 14 Periphery 15 Angle 16 Radial plane 17 Angle 18 Direction of rotation 19 Feed direction 20 Distance 21 Boring bar 22 Front end 23 Tool bit 24 Axis 25 Angle 26 Chip groove 27 Diametral plane

Claims: C L A I M S 1. Elongated tool-bit holder (1,21), at one end being adapted to be secured in a stationary or rotating part of a machine tool, e.g. a lathe and a drilling machine, respectively, and at its other end being adapted to hold securely at least one machine cutting tool, e.g. a tool bit (3,5,23), c h a r a c t e r i z e d in a) that said holder (1, 21) has vibration-damping properties, and b) that said tool bits (3, 5, 23) are placed and oriented in such a manner relative to the holder (1, 21) , that the tool consisting of said tool bits (3, 5, 23) and said holder (1, 21) would be unstable in operation, if said holder (1, 21) did not have said vibration-damping properties. 2. Tool-bit holder according to claim 1 and in the form of a drill-bit holder (1) with two tool bits (3,5) of cemented carbide or other hard material clamped at the front end (2), said tool bits (3,5) being mounted with their cutting edges (4,6) of flat V-shape facing generally forward in the direction (19) , in which the drill consisting of the drill-bit holder (1) and the bits (3,5) during the drilling operation moves through the hole (14) being drilled, said bits (3,5) also being positioned with the cutting edges (4,6) extending in such a manner that the cutting edge (4) of the first tool bit (3) extends in a diametral plane (7) from a position close to the drilling axis (8) to a position (9) at a distance from the periphery (14) of the hole being drilled, whereas cutting edges (6) of the second tool bit (5) extend from a position at a distance from the drilling axis (8) to said periphery (10) , c h a - r a c t e r i z e d in that the cutting edge (6) of the second bit (5) is situated in front of the cutting edge (4) of the first bit (3) , when considered in said direc¬ tion (19) , and also in front of a symmetrical position relative to the cutting edge (4) of the first bit (3) , when considered in the working direction of rotation (18) of the drill. 3. Tool-bit holder according to claim 2, c h a - r a c t e r i z e d in that the cutting edge (6) of the second bit (5) extends in an axial plane (11) tangent to the radially outermost point (9) of the cutting edge (4) of the first bit (3) and forms an angle (12) of 1-4° with a meridian plane (7) extending through said outermost point (9) . 4. Tool-bit holder according to claim 1 and in the form of a boring bar (21) having placed in the front end (22) a tool bit (23) , the surface of which lying for- wardmost in the direction of rotation lies in a plane parallel to the axis (24) of said boring bar, c h a ¬ r a c t e r i z e d in a) that the cutting edge of the bit (23) facing in the axial direction forms an angle (25) of 3°-ll° with a diametral plane (27) through the radially outer¬ most edge of the tool bit (23) , and b) that a chip groove (26) immediately adjoining the bit (23) extends through substantially the full active length of the boring bar (21) .

Inventors: HANSEN NIELS JOERGEN, HANSEN, NIELS, JOERGEN
Applicants: HANSEN NIELS JOERGEN, HANSEN, NIELS, JOERGEN
Application year: 1995
Main classification: B23B29
IPC codes: B23B51