US3837758A

US3837758A - Means for damping vibrations of tools in drilling machines or the like

Info

Publication number: US3837758A
Application number: US00283232A
Authority: US
Inventors: P Streicher
Original assignee: TIEFBOHR TECHNIK GmbH
Current assignee: Tiefbohr Technik & Co dt GmbH; TIEFBOHR TECHNIK GmbH
Priority date: 1971-08-25
Filing date: 1972-08-23
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24
Also published as: FR2151355A5; GB1390544A; IT964230B; JPS4831575A; CA981491A; CH541376A; PL76081B1; DE2142549B2; DE2142549A1

Abstract

A drilling machine wherein two parts which are rotatable relative to each other are connected by an elastic coupling which serves to reduce or eliminate vibrations, especially torsional oscillations, of the tool during removal of material from a stationary or rotary workpiece. The coupling may be installed between two parts of the supporting structure for workpieces, between two parts of the tool, between two parts of the tool supporting structure, or between the tool and its supporting structure. The coupling may consist of one or more elastic elements and one or more damping elements, such as eddy current brakes.

Description

United States Patent 1 1 Streicher Sept. 24, 1974 MEANS FOR DAMPING VIBRATIONS OF TOOLS IN DRILLING MACHINES OR THE LIKE [75] Inventor: Peter Streicher, Gebersheim,

Germany [73] Assignee: Tiefbohr-Technik GmbH & Co.,

Dettingen, Germany [22] Filed: Aug. 23, 1972 [21] Appl. No: 283,232

[30] Foreign Application Priority Data Aug. 25, 1971 Germany 2142549 [52] U.S. Cl. 408/143 [51] Int. Cl B23b 47/02 [58] Field of Search 82/2; 408/143 [56] References Cited UNITED STATES PATENTS 2,108,699 2/1938 Walther 408/143 2,432,383 12/1947 Colwell..... 408/143 X 2,458,995 l/l949 Hummer 408/143 X 3,557,646 l/197l Agnew 82/2 3,663,116 5/1972 Muller et al. 408/143 FOREIGN PATENTS OR APPLICATIONS 1,238,311 4/1967 Germany 408/143 564,825 3/1944 Great Britain 408/143 Primary Examiner-Leonidas Vlachos Attorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT A drilling machine wherein two parts which are rotatable relative to each other are connected by an elastic coupling which serves to reduce or eliminate vibrations, especially torsional oscillations, of the tool during removal of material from a stationary or rotary workpiece. The coupling may be installed between two parts of the supporting structure for workpieces,

between two parts of the tool, between two parts of v the tool supporting structure,.or between the tool and its supporting structure. The coupling may consist of one or more elastic elements and one or more damping elements, such as eddy current brakes.

25 Claims, 8 Drawing Figures PAIENIEDSMW saw; 758

SHEET 10F 4 PAIENTEDSEPZMBH 3,837. 758

v sum 30 Fig. 5

MEANS FOR DAMPING VIBRATIONS OF TOOLS IN DRILLING MACHINES OR THE LIKE BACKGROUND OF THE INVENTION The invention relates to machine tools in general, and more particularly to machines wherein a tool is movable relative to a workpiece and/or vice versa to remove material from the workpiece. Still more particularly, the invention relates to improvements in a device for eliminating or reducing vibrations, especially torsional oscillations or vibrations, which develop during removal of material and affect the finish of workpieces and/or the useful life of material removing tools. The vibration clamping device of the present invention can be used with advantage in drilling or boring machines wherein a tool rotates relative to the workpiece and/or vice versa to provide the workpiece with a relatively deep bore or hole.

It is already known to provide the shank of a metal cutting drill with supporting surfaces which abut against and are guided by the surface surrounding a bore while the head of the tool penetrates into a metallic workpiece. As a rule, a thin layer of lubricant is maintained between the surface surrounding the bore and the supporting surfaces of the shank. The supporting surfaces are intended to cooperate with the surface around the bore in order to reduce the tendency of the tool to vibrate relative to the workpiece and/or vice versa.

It is also known to utilize in a drilling machine a tool whose shank consists of two concentric tubes one of which surrounds the other. The tubes are coupled to each other for transmission of torsional stresses and carry rolling elements which engage and travel along the surface surrounding a bore in the workpiece.

A drawback of the just described tools is that their initial cost is very high and also that their supporting surfaces or rolling elements generate friction which contributes to higher energy requirements of the prime mover. Moreover, frictional engagement between the shank of the tool and the internal surface of the workpiece generates heat which must be removed by intensive cooling. Still further, the supporting surfaces or the rolling elements are likely to adversely affect the finish of the surface around the bore so that the workpiece must be subjected to costly and time-consuming aftertreatment. Finally, it was found that such construction of drilling tools cannot insure a satisfactory reduction and/or elimination of vibrations, especially torsional oscillations. Stray movements of the tool and/or workpiece produce readily detectable chatter marks and reduce the useful life of the tool owing to premature dulling of cutting edges. Also, vibrations invariably cause the tool to drill a hole or bore whose diameter exceeds the desired diameter so that the aforementioned supporting surfaces or rolling elements become useless since they are received in the bore with excessive radial clearance.

lt was further proposed to provide the shank of a drilling tool with a mass or weight which rotates with the tool and is maintained in close proximity to that surface of the workpiece which is to be formed with a bore. The shank is movable axially relative to the weight so that the head of the tool can penetrate into the material of the workpiece. Such weights cannot reduce the vibrations, particularly torsional oscillations, especially if the tool is to drill a relatively deep bore. Moreover, in

order to insure proper balancing of the tool, the clearance between the weight and the tool shank must be minimal which contributes to the manufacturing cost.

Since, the weight is to remain close to the exposed surface of the workpiece, it interferes with convenient positioning of the tool and with manipulation of the machine because it overlies the outer end of the bore.

SUMMARY OF THE INVENTION An object of the invention is to provide novel and improved means which is capable of substantially reducing or completely eliminating vibrations (especially torsional oscillations) which tend to develop during removal of material from workpieces, especially during such removal which is necessary during drilling of deep bores or holes into rotating or stationary metallic workpieces.

Another object of the invention is to provide vibration eliminating means which can be mounted at or close to the locus where the vibrations originate.

A further object of the invention is to provide vibration eliminating means which is simpler, more rugged, more reliable, more effective, longer lasting and less expensive than heretofore known vibration damping means.

An additional object of the invention is to provide vibration damping or eliminating means which can be built into many existing machines with minor alterations and at a reasonable cost.

Still another object of the invention is to provide vibration reducing or eliminating means which occupies little room in a drilling or like machine and which requires no attention on the part of the user.

The invention is embodied in a machine tool, particularly in a drilling machine which comprises first supporting means for workpieces, tool means, and second supporting means for the tool means. At least one of the supporting means is movable relative to the other supporting means to effect the penetration of tool means into a workpiece which is mounted in the first supporting means. The tool means and the two supporting means together constitute an assembly which includes rotary first and second portions one of which is turnable relative to the other portion. In accordance with the invention, the machine further comprises elastic vibration damping coupling means which connects the first and second portions to each other.

The second supporting means may include a tool holder and the two portions may form part of the tool holder, i.e., a first portion of the tool holder is connected with a second portion of the tool holder by way of the coupling means.

The tool means may include a cutting device, a head for the cutting device and a shank for the head, and the coupling means may be installed between two relatively movable portions of the cutting device, head or shank. It is also possible to construct the machine in such a way that the coupling means connects a tool holder of the second supporting means with the shank of a tool means, the shank with the head or the head with the cutting device.

The second supporting means may include a rotary tool spindle having two portions which are connected to each other by the vibration damping coupling means. Also, one portion of the aforementioned assembly may constitute the tool means and the other portion may constitute a spindle of the second supporting means whereby the coupling means connects the tool means with the spindle.

The coupling means may comprise one or more elastic elements in the form of metallic springs or blocks consisting of natural rubber or a synthetic plastic material having the characteristics of rubber, and one or more damping elements, such as a mechanical damper, a pneumatic or hydraulic cylinder and piston unit, or an eddy current brake. It is also possible to use coupling means which includes one or more elastic blocks which not only transmit torque but also serve to damp vibrations developing when the cutting device of the tool means removes material from the workpiece.

It is further possible to install the coupling means between the frame of the machine and the first supporting means or to employ first supporting means having two portions which are connected to each other by the vibration damping coupling means.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved coupling means itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic fragmentary axial sectional view of a drilling machine wherein the elastic vibration damping coupling means comprises discrete elastic and damping elements and connects the tool spindle with the tool holder;

FIG. 2 is an .end elevational view as seen from the left-hand side of FIG. 1;

FIG. 3 is a fragmentary partly elevational and partly axial sectional view of a second machine wherein the coupling means comprises an eddy current brake;

FIG. 4 is a transverse vertical sectional view as seen in the direction of arrows from the line Ill-III of FIG.

FIG. 5 is a fragmentary axial sectional view of a machine wherein the coupling means comprises a single part mounted between the tool spindle and the tool holder;

FIG. 6 is a fragmentary axial sectional view as seen in the direction of arrows from the line VI-VI of FIG. 7 and illustrates a portion of a machine wherein the coupling means comprises four discrete elastic blocks;

FIG. 7 is a sectional view as seen in the direction of arrows from the line VII-VII of FIG. 6; and

FIG. 8 is a fragmentary axial sectional view of a further machine which constitutes a modification of the machine shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 and 2, there is shown a portion of a drilling machine which includes first supporting means (not shown) constituting a holder for a metallic workpiece; a drilling tool which serves to remove material from a workpiece held in the first supporting means and includes a cutting device with one or more cutting edges (not shown), a head (not shown) for the cutting device, and a shank 2 for the head; and second supporting means which mounts the tool shank 2 and includes a rotary tool spindle l and a tool holder 3 which is rotatably mounted in an axial recess 7 of the spindle l and is rigidly connected with the shank 2. The recess 7 is surrounded by a cylindrical internal surface of the spindle l. The housing in which the spindle l is rotatable is of conventional design. Also, the exact construction of the prime mover means (e.g., an electric motor) which rotates the spindle 1 forms no part of the invention.

The two supporting means and the drilling tool together constitute an assembly extending between the workpiece in the first supporting means and the prime mover for the spindle 1. This assembly includes two portions (namely, the spindle 1 and the tool holder 3) which are rotatable relative to each other. The improved coupling means serves to transmit torque from the first portion (spindle l) to the second portion (tool holder 3) of the assembly. When the head of the tool bears against a workpiece so that the cutting device penetrates into the material of the workpiece, the rear end face 10 of the holder 3 abuts against the adjacent surface in the bottom portion of the recess 7 in the spindle l. The shank 2 is preferably hollow to define an axial passage which communicates with an axial passage in the holder 3 and with an axial bore 6 in the spindle 1 for admission of a suitable fluid coolant into the area where the cutting device removes material from the workpiece. The front end face of the spindle 1 carries a retaining disk 8 which is secured thereto by means of screws or other suitable fasteners, not shown. The central portion of the disk 8 serves as a retainer to prevent accidental removal of the holder 3 from the recess 7. This central portion is provided with an opening 9 through which the elements of the coupling means extend. These elements include a helical spring 4 one end of which is secured to the disk 8 (and hence to the spindle 1) and the other end of which is secured to the holder 3 (and hence to the tool shank 2), and a damping element 5 (e.g., a dashpot having a cylinder mounted on the disk 8 and a piston having a piston rod connected to the holder 3). The opening 9 of the disk 8 further serves to permit unobstructed passage of the shank 2. The dashpot 5 constitutes but one of a variety of damping elements which can be used in the improved coupling means; for example, the coupling means may embody an electrical, hydraulic, pneumatic or mechanical damping element which counteracts the tendency of the tool to vibrate during penetration of its cutting device into the material of the workpiece. The element 4 may constitute a metallic spring or a block consisting of elastomeric material (such as natural rub ber or a synthetic plastic material having the characteristics of rubber). The construction of the damping element 5 may be such that its damping action is constant or adjustable within a desired range. The same applies for the elasticity of the elastic element 4.

The recess 7 and the holder 3 are long enough to eliminate the likelihood of any bending or flexing of the holder 3 when the spindle l rotates and the cutting device of the tool penetrates into the workpiece. On the other hand, the holder 3 is rotatable in the recess 7 and has limited freedom of axial movement. The torque transmitting connection between the spindle l and the holder 3 is established exclusively by way of the elastic element 4 of the coupling means. The bottom surface in the recess 7 takes up axial stresses which develop when such bottom surface is engaged by the rear end surface of the holder 3 while the cutting device of the tool penetrates into the material of the workpiece.

When the spindle l is driven, the extent of relative angular movement between the spindle and the holder 3 is determined by the elastic element 4. At the same time the element 5 reduces or eliminates the tendency of the tool 2 to vibrate during removal of material from the workpiece. It was found that the illustrated coupling means is especially effective in elimination or substantial reduction of torsional oscillations.

It is clear that the coupling means 4, 5 can be installed between the holder 3 and the shank 2 of the tool, or that the spindle 1 may comprise two portions one of which is rotatable relative to the other portion and is connected with the other portion by a coupling means including the elements 4, 5 of FIGS. 1 and 2. Still further, the coupling means may be installed between two portions of the shank 2, between two portions of the holder 3, between two portions of the head of the tool, between two portions of the cutting device on the head of the tool, between the cutting device and the head, or between the head and the shank 2. Still further, and especially if the supporting means for the workpiece is rotatable in the frame of the drilling machine, the coupling means may be installed between the frame and the supporting means for the workpiece or between two relatively movable portions of the supporting means for the workpiece. It is equally within the purview of the invention to provide several coupling means, for example, a first coupling means between the spindle 1 and the holder 3 and a second coupling means between the holder 3 and the tool shank 2.

In the embodiment of FIGS. 3 and 4, the damping element 5a of the coupling means constitutes an eddy current brake and the elastic element of the coupling means is a composite structure consisting of four blocks 4a made of natural rubber or elastomeric synthetic plastic material.

The eddy current brake 5a comprises two pole shoes 11 (one shown in FIG. 3) which are formed on magnetizable cores 12 (one shown) and are located diametrically opposite each other with reference to the axis of the tool shank 2. The cores 12 are connected to a ring 13 by means of radially extending screws (one shown in the upper portion of FIG. 3) or analogous fasteners. Each of the cores 12 has a winding 14 which is connected with one of two stationary slip rings 15 by means of suitable conductor means, not shown. The slip rings 15 supply to the respective windings 14 d-c current from a suitable source, not shown.

The eddy current brake 5a is mounted in a hollow casing 16 which consists of non-magnetizable material and comprises two mirror symmetrical sections or

shells

17 and 18. The

sections

17, 18 of the casing 16 are connected to the ring 13 by axially parallel screws 19 or analogous fasteners so that the casing 16 rotates with the pole shoes 11. That portion of the section 18 which is remote from the section 17 has an axial extension 20 which is fixed to and rotates with the tool spindle 1 (not shown in FIGS. 3 and 4). The

sections

17, 18 accommodate antifriction roller bearings 21 the inner races of which are connected to and rotate with a sleeve 22. The central portion of the sleeve 22 (between the bearings 21) is rigidly connected with and is surrounded by an aluminum ring 23 which carries two magnetizable steel rings 24 located radially inwardly of one of the pole shoes 11. The pole shoes 11 are separated from the steel rings 24 by narrow air gaps. The rings 24 are separated from each other by a centrally located external flange of the aluminum ring 23.

The front end portion of the sleeve 22 (i.e., the lefthand end portion, as viewed in FIG. 3) has an externally threaded extension 25 which meshes with a nut 26 rigid with the shank 2 of the drilling tool. A liquid coolant can be supplied into the bore of the workpiece by way of a passage 6 including an axial bore in the extension 20 of the section 18 of the casing 16, an axial hole in the sleeve 22 and its extension 25 and an axial bore in the shank 2. The extension 20 of the section 18 receives a hollow sealing cylinder 27 surrounded by a sealing ring 32 to prevent the penetration of coolant into the right-hand antifriction bearing 21 of FIG. 3 or into the space which accommodates the eddy current brake 50.

That portion of the sleeve 22 which is immediately adjacent to the rear end of the nut 26 carries a twoarmed'lever 28 which is held against rotation relative to the sleeve 22 byone or more axially parallel pins or keys 29 (see also FIG. 4). The arms of the lever 28 extend into recesses 30 provided in the section 17 of the casing 16 and each thereof is flanked by two blocks 4a consisting of natural rubber or elastomeric synthetic plastic material. The blocks 4a together constitute the elastic element of the coupling means and are preferably secured to the section 17 by means of a suitable adhesive. A cupped cover 31 is threadedly connected with the section 17 to overlie and seal the lever 18, the recesses 30 and the elastic blocks 4a. The front end portion 3a of the nut 26 constitutes a holder for the shank 2.

The operation of the embodiment of FIGS. 3 and 4 is analogous to that of the structure shown in FIGS. 1 and 2. The damping action of the eddy current brake 5a can be regulated by changing the current which energizes the windings 14.

When the spindle 1 (not shown) rotates the casing 16, the latter rotates the lever 28 and hence the sleeve 22, nut 26 and tool shank 2 by way of two of the four elastic blocks 4a. The vibrations, especially torsional oscillations, which develop as a result of penetration of the cutting device into the material of the workpiece, are damped by the eddy current brake 5a to the extent determined by energization of the windings 14. Since the casing 16 is rigid with the spindle and the lever 28 is rigid with the holder 30 (which is rigid with the shank 2), the elastic element (blocks 4a) of the coupling means can be said to transmit torque from the spindle to the holder or from the spindle to the tool.

Referring to FIG. 5, there is shown a further embodiment of the coupling means which comprises a combined elastic and damping element in the form of a ring-shaped block 33 consisting of natural rubber or elastomeric synthetic plastic material. The tool holder 3b has a forwardly projecting cylindrical extension 34 which is secured to the internal surface of the ringshaped block 33. The external surface of the block 33 is secured to the internal surface of a nut 36 which is threadedly connected with the front end'portion of the tool spindle 1. The block 33 is received in a bore 35 of the nut 36. A radially inwardly extending flange of the nut 36 replaces the disk 8 of FIG. 1 and serves to prevent or limit axial movements of the holder 3b. The lat ter is rotatable in a bearing sleeve 37 provided ina recess 7b of the spindle lb. The passage 6 serves to deliver a liquid coolant to the innermost portion of the bore in the workpiece and includes axial bores in the spindle 1b, holder 3b and shank 2. The latter is rigidly connected with the holder 3b.

The operation of the structure shown in FIG. 5 is analogous to that of the structure shown in FIG. 1. When the spindle lb is driven by a motor, the holder 3b receives torque by way of the block 33 which at the same time serves as a means for damping vibrations or oscillations which develop as a result of penetration of the cutting device into the material of the workpiece.

FIGS. 6 and 7 illustrate a fourth embodiment of the invention. The shank 2 of the material removing tool is hollow and is received in a sleeve-like holder 3c which in turn extends into the recess 7c of the tool spindle 1c. The rear end portion of the shank 2 extends beyond the rear end face of the central portion of the holder 3c and has a circumferential groove for a split ring 40. A ringshaped collar of the holder 3c extends rearwardly beyond the split ring 40 and abuts against the surface 41 at the bottom of the recess 7c in the spindle 1c. In contrast to the construction shown in FIGS. 1-2, 3-4 and 5, the shank 2 of FIGS. 6 and 7 is rotatable in the holder 30 and the latter is held against rotation relative to the spindle by a screw 38 which makes with the axis of the spindle 10 an angle of about 70 and abuts against a flat surface 49 in a notch machined into the peripheral surface of the holder 3c. The major portion of the screw 38 is received in a tapped bore of the spindle 1c. The split ring 40 holds the shank 2 against extraction from the holder 3c.

The front end portion of the holder 30 is provided with an axial recess 42 bounded by a cylindrical surface and receiving a cruciform torque transmitting member 39 having two longer arms 44 and two shorter arms 43. The shorter and

longer arms

43, 44 are respectively located diametrically opposite each other. The shorter arms 43 alternate with the longer arms 44 and successive arms are angularly offset relative to each other by 90. The member 39 is rigidly secured to the shank 2, for example, by a ring-shaped seam of hard solder.

Each shorter arm 43 is received between two elastic blocks 45, and each longer arm 44 has an outer end portion which extends into one of two radial recesses or cutouts 47 provided in the front end portion of the holder 3c. The radially outermost portion of each of the four blocks 45 is received in a discrete recess 46 of the holder 3c. FIG. 7 shows that each cutout 47 is flanked by two recesses 46. The radially innermost portions of the longer arms 44 are flanked by pairs of elastic blocks 45; each of these blocks is preferably of T-shaped cross-sectional outline, as considered in a plane which is normal to the axis of the shank 2.

The spindle 1c has an axial passage 6 which can admit a liquid coolant to the innermost end of the bore in the workpiece by way of the hollow shank 2. Such coolant cannot penetrate into the space adjacent to the internal and external surfaces of the holder 3c due to the provision of sealing rings 48. As shown, the structure of FIGS. 6 and 7 employs two sealing rings 48 one of which is received in an internal groove of the spindle 1c and engages the peripheral surface of the holder 30. The other ring 48 is recessed into the internal surface of the holder 3c and engages the peripheral surface of the shank 2.

The illustrated inclination of the screw 38 relative to the axis of the spindle 1c insures that the holder 3c is biased rearwardly so that its rear end face engages the surface 41 in the recess 7c of the spindle.

When the spindle 1c is driven to rotate the holder 30 by way of the screw 38, the latter rotates the member 39 on the shank 2 by way of the coupling means including the four elastic blocks 45 which together perform the functions of elements 4 and 5 shown in FIGS. 1 and 2. Thus, the blocks 45 are yieldable elements to act not unlike the helical spring 4 of FIGS. 1 or 2, and their material is elastic and exhibits damping characteristics analogous to those of the dashpot 5 in FIGS. l-2 or the eddy current brake 5a of FIGS. 3-4. When the shank 2 offers a very high resistance to rotation, the outer end portions of the longer arms 44 on the member 39 come into direct contact with the surfaces bounding the respective cutouts 47; otherwise, the transmission of torque takes place by way of the elastic blocks 45. It will be noted that the coupling means of FIGS. 6 and 7 operates between the shank 2 of the tool and the holder 30.

FIG. 8 shows a spindle 1d having a recess 7d for a tool holder 3d which is rigid with the shank 2 of the drilling tool. The passage 6 delivers coolant into the bore of the workpiece, not shown. The front end portion of the spindle 1d has external threads and meshes with a cap 54 which prevents or limits axial movements of the holder 3d in the recess 7d.

The coupling means comprises a block 50 which consists of elastomeric material and is received in a recess 51 provided in the periphery of the tool holder 3d. A radial screw 53 which meshes with the spindle 1d has a pin-shaped extension 52 which is received in a radial hole of the block 50. The recess 51 may constitute a blind bore of the holder 3d and the block 50 is preferably secured to the holder by a suitable adhesive.

The coupling means of FIG. 8 operates between the spindle 1d and the holder 3d, the same as in the embodiment of FIGS. 1 and 2.

In the embodiments of FIGS. 1-2, 5 and 8, the holder can be said to form part of the tool, i.e., the coupling means is installed between the tool and the spindle. In the embodiment of FIGS. 6 and 7, the coupling means operates between the tool and the tool holder. Referring again to FIGS. 1 and 2, and assuming that the tool shank is mounted in a composite spindle including the portions 1 and 3, the coupling means 4, 5 can be said to operate between two relatively movable portions of a composite spindle.

An important advantage of the improved coupling means is that it either eliminates or reduces the vibrations (especially torsional oscillations) to such an extent that the wear upon the tool is much less pronounced than is heretofore known machines. Moreover, the surfaces surrounding the holes in the workpieces are at least substantially free of chatter marks so that the workpiece can be used without any or with minimal aftertreatment. Still further, and since the vibrations of the tool are either eliminated or at least greatly reduced, the tool can be made of materials which exhibit a very high resistance to wear but could not be used in presently known machines due to their low resistance to stresses which develop as a result of vibration of the tool and/or workpiece. Such highquality tools can be rotated and/or fed at a faster rate than conventional tools so that the treatment of workpieces (especially the drilling of deep holes) can be completed within shorter periods of time. Also, such high-quality tools can be used for drilling of holes in extremely hard and/or brittle workpieces and the treatment generates little noise.

It is preferred at this time to incorporate the coupling means in the supporting means for the tool, between the tool and the supporting means or into the tool proper. However, and as explained above, it is also possible to install the coupling means in the supporting means for the workpiece, i.e., between the frame and work holder or between two relatively movable portions of the work holder. The mounting of coupling means in the supporting means for workpieces is desirable and advantageous when the workpiece rotates while being engaged by the cutting device of the tool.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. In a drilling machine, a combination comprising rotatable spindle means provided with an axial recess; tool means held in said recess coaxially aligned with said spindle means and mounted therein rotatable relative thereto, said spindle means forming the only support of said tool means; and elastic coupling means between said spindle means and said tool means for transmitting a drive from said spindle means to said tool means while damping torsional vibrations.

2. A combination as defined in claim 1, and including tool holder means in said spindle means for mounting said tool means coaxially with said spindle means.

3. A combination as defined in claim 2, wherein said tool means is fixed to said tool holder means for rotation therewith and said tool holder means is turnably mounted in said spindle means, and wherein said coupling means transmits a drive from said spindle means to said tool holder means.

4. A combination as defined in claim 2, wherein said tool means is rotatably arranged in said tool holder means and the latter is fixed to said spindle means for rotation therewith, and wherein said coupling means transmits a drive from said tool holder means to said tool means.

5. A combination as defined in claim 1, wherein said coupling means comprises at least one elastic element and at least one damping element.

6. A combination as defined in claim 1, wherein said coupling means comprises at least one element having elastic and damping characteristics.

7. A combination as defined in claim 6, wherein said element is a block consisting of a material having the characteristics of rubber.

8. A combination as defined in claim 2, wherein said coupling means comprises at least one element consisting of elastomeric material and at least one damping element including an eddy current brake.

9. A combination as defined in claim 8, wherein said eddy current brake comprises at least one magnetizable core, an energizable winding on said core, and means for securing said core to said spindle means.

10. A combination as defined in claim 9, wherein said means for securing comprises a casing rigid with said spindle means and a ring connecting said core with said casing.

11. A combination as defined in claim 10, wherein said casing comprises two mirror symmetrical sections, said ring being disposed between and being rigid with said sections.

12. A combination as defined in claim 10, wherein said casing consists of non-magnetizable material.

13. A combination as defined in claim 9, further comprising antifriction bearing means provided in said casing for said tool holder means.

14. A combination as defined in claim 11, wherein said tool holder means is rotatable in said casing and includes a motion transmitting member having at least one radial arm, said elastic element comprising blocks consisting of elastomeric material, said blocks being mounted in said casing and flanking said arm.

15. A combination as defined in claim 14, wherein said casing has a recess for said blocks.

16. A combination as defined in claim 14, wherein said tool means has a shank rigid with said holder and said motion transmitting member is adjacent to said shank.

17. A combination as defined in claim 3, and further comprising a nut meshing with said spindle means and arranged to limit axial movements of said tool holder means relative to said spindle means.

18. A combination as defined in claim 17, wherein said coupling means connects said nut with said tool holder means. I

19. A combination as defined in claim 18, wherein said coupling means comprises a ring consisting of elastomeric material and having first and second surfaces respectively secured to said nut and to said tool holder means.

20. A combination as defined in claim 19, wherein said nut has an axial bore receiving said ring and said ring surrounds said tool holder means.

21. A combination as defined in claim 4, wherein said tool means includes a shank, said coupling means comprising torque transmitting means secured to said shank and at least one block consisting of elastomeric material and interposed between said tool holder means and said torque transmitting means to rotate said shank in re ponse to rotation of said tool holder means.

22. A combination as defined in claim 21, wherein said torque transmitting means comprises at least one relatively short and at least one relatively long arm extending radially of said shank, said block being interposed between said arms and said tool holder means.

23. A combination as defined in claim 22, wherein said tool holder means has a surface which is engaged by one of said arms in response to deformation of said block when said shank offers a predetermined resis tance to rotation with said tool holder means.

24. A combination as defined in claim 3, said coupling means including an elastic block secured to said tool holder means and a projection provided on said spindle means and arranged to rotate said tool holder means by way of said block.

25. A combination as defined in claim 24, wherein said tool holder means has a peripheral surface provided with a recess for said block, said projection being received in a hole of said block.

Claims

18. A combination as defined in claim 17, wherein said coupling means connects said nut with said tool holder means.

21. A combination as defined in claim 4, wherein said tool means includes a shank, said coupling means comprising torque transmitting means secured to said shank and at least one block consisting of elastomeric material and interposed between said tool holder means and said torque transmitting means to rotate said shank in response to rotation of said tool holder means.

23. A combination as defined in claim 22, wherein said tool holder means has a surface which is engaged by one of said arms in response to deformation of said block when said shank offers a predetermined resistance to rotation with said tool holder means.