TOOL-BIT HOLDER AND METHOD OF MANUFACTURING SAME

Abstract: In a tool-bit holder (1) for e.g. tool bits (3, 5) of cemented carbide or other hard material, in which the tool-bit holder has vibration-damping properties, the novel feature is that the tool-bit holder (1) in all essentials consists of a material, e.g. mild steel, with vibration-damping properties. The effect achieved is that the tool-bit holder may be made in one piece, in contrast to prior-art tool-bit holders consisting of two separate parts of e.g. tool steel with a tubular intermediate layer of rubber. The vibration-damping properties makes it possible to place the bits (3, 5) in a manner which would otherwise cause instability and consequent machining marks on the work-piece.

Description: TOOL-BIT HOLDER AND METHOD OF MANUFACTURING SAME 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 A tool-bit holder of the kind referred to is disclosed in GB patent specification No. 1,299,750. With a view to achieving vibration-damping properties, the tool-bit holder thus known is divided into two mutually coaxial rigid parts with an intermediate layer of "anti-vibration material", such as rubber. It will be obvious that, com- pared to the manufacturing of conventional tool-bit hol¬ ders, known normally to be manufactured in one single piece of material, this construction causes a considerable increase in the cost of the manufacturing process. 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 to achieve vibration- damping properties by extremely simple means, and this object is achieved by means of the feature set forth in the characterizing clause of claim l. By manufacturing the tool-bit holder in the form of one single piece of homo¬ geneous material with vibration-damping properties, a manufacturing process is achieved, that is no more com- plicated or expensive than the process of manufacturing the conventional tool-bit holders from e.g. tool steel. It will be evident that a tool-bit holder manufactured from a material with considerably lower surface hardness than the hitherto known materials, such as tool steel, will be more vulnerable to wear from the chips produced during the machining of the workpiece concerned. This drawback is avoided by additionally providing the tool- bit holder with the feature set forth in claim 4. The invention also relates to a method of manufacturing a tool-bit holder according to the invention, and this method is characterized by the steps set forth in claim 7. By proceeding in this manner, it is avoided that also the surfaces of the sockets, in which the tool bits are to be received, are given an increased surface hardness and consequently become less capable of "gripping" the bits. Advantageous embodiments of the tool-bit holder and said method are set forth in claims 2, 3, 5 and 6 and 8, re¬ spectively. 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 the combination of a tool-bit holder with vibration-damping properties and a positioning and orientation of the tool bit or bits, that would other¬ wise cause instability, are the subject of claims in the co-pending international patent application No (B,S & Co. ref. 54827) 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), said holder having vibration-damping proper¬ ties, c h a r a c t e r i z e d in that the tool-bit holder (1,21) in all essentials consists of a material with vibration-damping properties. 2. Tool-bit holder according to claim 1, c h a r¬ a c t e r i z e d in that the material is mild steel. 3. Tool-bit holder according to claim 2, c h a r¬ a c t e r i z e d in that said material is steel of the type C15, 9 SMnPb 28K. 4. Tool-bit holder according to one or more of the claims 1-3, c h a r a c t e r i z e d in that at least those surfaces during use being subjected to influence of chips produced in the machining have a hardness at least corresponding to the highest surface hardness of the chips. 5. Tool-bit holder according to claim 4, c h a r¬ a c t e r i z e d in that the hardness of the surfaces mentioned is produced by surface treatment of the material with vibration-damping properties referred to. 6. Tool-bit holder according to claim 5 and claim 2 or 3, c h a r a c t e r i z e d in that the surface treatment is constituted by a case-hardening process. 7. Method of manufacturing a tool-bit holder according to any one or any of the claims 4-6, c h a r a c t e r¬ i z e d in a) that the tool-bit holder is given the shape desired by machining a workpiece consisting of a material with vibration-damping properties, and b) that, subsequently, the tool-bit holder is sub¬ jected to a surface treatment causing an increase in the hardness of the surfaces of the tool-bit holder, while the socket or sockets adapted to receive the bit or the bits are kept suitably covered to prevent an increase in the hardness of the surfaces in said socket or sockets. 8. Method according to claim 7, c h a r a c t e r¬ i z e d in that during step b, in each socket there is placed a tool bit or a body with at least the same capa¬ bility of covering the surfaces in the socket.

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