GB2164276A - Axial clamping connection - Google Patents

Abstract

The connection between a tool and a tool holder has on the tool a centring stud 27 followed by a chuck shoulder 28 which is divided by a transverse groove open towards its end face 29 into two chuck fingers 32, 33 which extend symmetrically of the longitudinal axis 18 of the tool. The chuck fingers are provided with key-like oblique faces 38, 36 which co-operate (Figure 3) with corresponding oblique faces 59 of chuck cylinders 57, 58, which are removed toward each other within a radial bore 56 in the tool holder 12 by means of a retaining screw 78. Corresponding to the centring stud 27, the tool holder 12 has a centring bore 52 adjacent to which is a free space 53 into which the chuck shoulder 28 can penetrate and which is traversed by the radial bore 56. The retaining screw 78 is constructed as a differential screw of which the oppositely disposed thread ends engage in correspondingly oppositely threaded bores in the chuck cylinders 57, 58. <IMAGE>

Description

SPECIFICATION Axial clamping connection The invention relates to an axial clamping connection between a tool holder and a tool in accordance with the preamble to claim 1.

An axial clamping connection of this type is known for example from German Patent Specification No.

31 08439. Since on the one hand the tool housings on the spindles of drilling and milling machines differ considerably in construction, there being not only tapered work tool holders with all manner of cone angles but also special models and since on the other hand there are various types of tools such as milling cutters, reamers and various sizes of drill, all of which shou Id be usable with the utmost versatility, it is customary to fit the tools together after the fashion of a unit construction system. And then for specific jobs, the appropriate tool head is fitted, together with a tool holder appropriate to the tool housing which is required. Even then, the length can be varied by interposing connecting pieces of different lengths.

The prior art construction comprises in a radial bore of the fitting pin a radially displaceable connecting bolt which has at both ends a conical shoulder or conical depression. Held in the tool holder diametrically thereto are two retaining screws in radial threaded bores which have corresponding conical depressions or shoulders on their inwardly directed end faces. The common axis of the two retaining screws is thereby somewhat axially offset in relation to the axis of symmetry of the radial connecting bolt so that when the retaining screws are screwed in, the conical shoulders accordingly enter the conical depressions in a staggered arrangement and by virtue of this key effect the radial force brought about by the retaining screws is converted to an axial clamping force.Indeed, the radially freely movable connecting bolt guarantees that the fitting stud suffers no radial loading in the fitting bore of the tool holder, thus ensuring that the annular face and the bearing surface are in all-over contact with a high pressure of application in order in this way to establish a reliable frictional joint.

What is unfavourable in this case, however, is the flow of force, since on the one hand the clamping force is transmitted from the tool holder through the retaining screws to the connecting bolt and thence to the fitting stud of the tool. In other words, this means that the force flow passes through a plurality of structurally weak points. One of these weak points is the housing of the retaining screws in the tool holder since namely the inter-engaging thread flanks are braced on each other for practical purposes only in lines of contact which are created by pure chance, because no thread makes a complete all-over contact. Another weak point is the contact zone which occurs as a linear contact zone and then only in the most favourable circumstances, between the conical shoulders and the corresponding axially offset conical depression.If, namely, the cone angles exactly agree, then this constitutes the most favourable circumstance, in which the zone of contact extends only along a line or, by virtue of Hertzian pressure, is deformed into a very narrow surface. In this case, this leads easily to an overloading and thus to a yielding effect, so that the reliability of the clamping connection is adversely affected, particularly in the case of a vibrating tool with changing load peaks.

Wear phenomena can occur which lead to premature failure of the device. Furthermore, both retaining screws must be tightened relatively strongly in order to establish the necessary firm connection, which may in certain circumstances damage the screwthread or the thread in the threaded bore in the tool holder. Since with increasing tightening and by virtue of the key action serving as a reaction on the clamping force, the retaining screw is subjected increasingly to unilateral oblique pressure against the forward area of the threaded bore and by virtue of the more random and linear contact points it is impressed into the flanks of the screwthread so that a major part of the torque needed for secure clamping is used up here so that in most cases, an adequate axial clamping force can be applied only when the device is new.Furthermore, an evident disadvantage is that in order to change tools both diametrically opposed retaining screws have to be turned backwards until they release the radial bore of the fitting pin. This is a cumbersome operation.

Finally, there is a further restriction which is that the connecting bolt should be guided in the radial bore of the fitting pin with the least possible clearance, as otherwise the transmission of force from it to the walls of the bore would likewise take place only by linear contact. Therefore, compared with the fitting pin, the connecting bolt only has freedom of movement in one dimension, which means that the threaded bores in the tool holder and the radial bore in the fitting pin, when viewed in the longitudinal direction of the tool axis, must coincide exactly, as otherwise the zone of contact between the conical elements is no longer in a central plane but is laterally offset, with the result that then, once again, the fitting pin is drawn obliquely into the fitting bore on one side.This offset of the plane of force transmission naturally also occurs if for example the conical depression in one of the retaining screws is offset eccentrically. The prior art construction therefore requires highly accurate manufacture in order to achieve the desired effect.

The object of the present invention is to provide an axial clamping connection of the type described, in which the connection between tool holder and tool is not subject to a one-sided loading, this aim being achieved with less complication in terms of manufacture and maintained for a longer period of use, so that by reason of better application of pressure between annular face and bearing surface, a reliable and stable connection is guaranteed even after repeated actuation of the clamping connection.

Furthermore, it is intended to facilitate handling.

According to the invention, this problem is resolved by the characterising features according to claim 1.

Advantageous further developments and embodiments will become evident from the features in the sub-claims.

The invention is described in greater detail hereinafter with reference to an embodiment shown in the accompanying drawings, in which: Figure 1 is a plan view of a device according to the invention when the tool and tool holder are separate; Figure 2 is a side view of the device inthe direction of the arrow 2 in Figure 1; Figure 3 is an enlarged view of the device according to Figure 1, illustrated in the clamped condition; Figure 4 is an enlarged frontal view of the tool holder viewed in the direction of the arrow 4 according to Figure 1;; Figure 5 is an enlarged rear view of the tool in the direction of the arrow 5 according to Figure 1, whereby for illustration purposes the retaining screw and a chuck cylinder are illustrated in their relationship thereto, and Figure 6 is a view of a chuck cylinder in the direction of the arrow 6 according to Figure 5.

According to Figure 1, reference numeral 11 denotes a tool, namely a drill, which is arranged to be inserted into a tool holder 12 which is in turn held by its splined journal 13 in a tool housing 14 which is indicated only by broken lines. This tool housing 14 may be a fixed or rotatingly driveable chuck or the tool holder of a turret head of a machining centre.

Reference numeral 16 relates to a scale of length which illustrates a measurement of 10 cm for purposes of comparison.

The tool 11 which is illustrated is of known construction in its region which extends from the collar 17 leftwardly in the longitudinal axis of the tool and carries at the end faces an outer cutting tip 19 and an inner cutting tip 21. Behind each of the cutting tips there emerges a coolant passage 22, 23, the said passages merging rightwardly into a common axial passage 24.

On its rightwardly directed side, the collar 17 has a bearing face 26 and a centring stud 27 projecting from it coaxially of the longitudinal axis 18 of the tool. Adjacent to it is a chuck shoulder 28. In the view shown in Figure 2, it is evident that this chuck shoulder 28 is divided into two chuck fingers 32 and 33 which extend symmetrically of the longitudinal axis 18 of the tool by a transverse groove 31 which is open towards its end face 29. In respect of a plane of symmetry identified by reference numeral 34 in Figure 4 and corresponding to the plane of Figure 2, the chuck fingers 32 and 33 have diametrically opposite first oblique faces 36,37,38 and 39 which diverge towards the end face 29.In the view shown in Figure 1, the first ends faces 36 and 37 as well as 38 and 39 are disposed in each case serially and in pairs and Figure 2 illustrates that the two aligned oblique faces, e.g. 38 and 39, are constructed as flat or plane surfaces which lie in a common oblique plane. Of the first oblique faces, short mutually parallel free faces 41,42,43 and 44 emerge in pairs of third oblique faces 46,47,48 and 49 which diverge tow33rds the centring stud 27. Also the aforementioned surfaces are, in the view shown in Figure 1, aligned in pairs and are constructed as plane surfaces which lie in a common plane. This construction can be very easily achieved with an angled milling cutter which is passed radially over the chuck shoulder. It will be understood that the free faces 41 to 44 may also be constructed as transition curves.

Expediently, the first oblique faces 36 to 39 enclose with the third oblique faces 46 to 49 an angle of about 900 and are inclined at 450 in relation to the axis 34 of symmetry.

The tool holder 12 has an annular face 51 directed at the tool and, coaxial with the longitudinal axis 18 of the tool a centring bore 52 into which the centring stud 27 is fitted. Adjacent to the centring bore 52 is an ideally likewise cylindrical free position 53 which provides space for the chuck shoulder 28. Also discernible in Figure 1 is a coolant passage 54 which leads farther down rightwardly and which, in a bore indicated by broken lines in Figure 3, leads to a point of contact (not particularly shown) with the tool housing. In the region of the free position 53, the tool holder 12 is traversed by a continuous radial bore 56, as illustrated by the views in Figures 1,3 and 4. The radial bore 56 is orientated at a right-angle to the plane of symmetry 34 and is thus parallel with the transverse groove 31.In the radial bore, on either side of the aforesaid plane of symmetry 34, there is a chuck cylinder 57, 58 which is guided for radial displacement and the inwardly directed end faces are constructed as second oblique faces 59 or 61 and 62 according to Figures 3, 5 and 6, corresponding to the first oblique faces. Figures 5 and 6 clearly show that these oblique faces, which are aligned one behind the other in the direction of view of the plane of symmetry 34, are with reference to the example of the second oblique faces 61 and 62, constructed as plane surfaces which lie in a common oblique plane.

Accordingly, this plane face is likewise inclined at 450 in relation to the longitudinal axis 18 of the tool.

On grounds of symmetry and stability, the chuck cylinders 57 and 58 also point to fourth oblique faces 63 or 64 and 66 which correspond to the third oblique faces 46 to 49, so that the chuck cylinders are constructed symmetrically in respect of a first radial plane 67 parallel with the annular face 51.

As Figure 4 shows, particularly, the chuck cylinders 57 and 58 have on their outer periphery a flattened surface 68 which does not extend as far as the oppositely disposed end faces 69,71,so that this flattened portion acquires the character of a groove which is bounded at both ends in a radial direction.

According to Figure 4, there is in the region of the flattened surfaces on both chuck cylinders in each case a locking pin 72,73 which projects inwardly radially in relation to the radial bore 56, the locking pins preferably taking the form of a screwthreaded pin which is rotated into a corresponding screwthreaded bore 74. The said locking pin 72,73 secures the associated chuck cylinder 57, 58 against rotation and also against its being unscrewed too far from the radial bore 56.

The chuck cylinders 57 and 58 are according to Figure 4 provided with mutually aligned threaded bores 76 and 77 which have the same pitch but oppositely directed screwthreads.

A retaining screw 78 shown as a component in Figure 5 and constructed as a differential screw, comprises accordingly at the two terminal screwthreaded parts an external screwthread 79 and 81 of opposite thread. The threadless middle shank 82 is of reduced diameter in the manner of a conventional tensioning bolt and in comparison with the inside diameter of the transverse groove 31 of the chuck shoulder 28 (Figure 2) it is at least some 2 to 3 mm smaller, so that, in the assembled state, the gap which exists between the middle shank and the chuck fingers 32 and 33 is sufficiently large not to inhibit the flow of coolant. Tensioning bolts with a slender middle shank are commercially available and are known to be capable of accommodating extremely high tensile loadings.Both ends of the retaining screw 78 comprise a hexagonal socket head 83, 84, so that the retaining screw can be actuated from either end by means of a suitable tool.

This has the advantage that regardless of the particular rotary position of the tool holder 12, one of the hexagonal sockets is always available in a position which is favourable. Also, if necessary, two tools may be applied in order for example to slacken off a retaining screw which is excessively tight.

Figure 1 shows the tool holder 12 in the slackened condition i.e. the chuck cylinders 57 and 58 are displaced radially outwardly by actuation of the retaining screw 78 to such a degree that the inner end faces 71 are spaced apart sufficiently from each other sufficiently that, widening out like a hammer, the chuck shoulder 28 can fit between them. In this position, therefore, it is possible to introduce the tool 11 into the tool holder 12, care naturally being taken to see that the tool 11 assumes such a relative rotary position that the middle shank 82 of the retaining screw 78 can penetrate the transverse groove 31 in the chuck shoulder 28.As shown particularly in Figure 2, this is ensured by a positioning 87 held in the annular face 51 of the tool holder 12 and axially parallel in a bore 86, the positioning pin being capable of plunging into one of corresponding positioning bores 88,89 offset by 1800 in respect of one another in the bearing surface 26 of the tool 11.

When the tool 11 with its chuck shoulder 28 and the centring stud 27 is pushed into the centring bore 52 and the free position 53 sufficiently for the bearing surface 26 to bear on the annular face 51, the retaining screw 78 is optionally rotated from one of its two ends so that, by virtue of the opposite screwthread, the two chuck cylinders 57 and 58 move towards each other. During the course of this movement, the two oblique faces of the chuck cylinders encounter the first oblique faces of the chuck fingers (in Figure 3, the second oblique faces 59 and 61 and also the first oblique faces 38 and 36 can be seen), so that the chuck fingers are axially tightened by the onset of keying action of the oblique faces sliding on one another.The chuck cylinders 57 and 58 have freedom of movement along the radial bore 56, in other words at a right-angle to the plane of symmetry 34 and, sliding on one another, the oblique faces, by virtue of their plane construction, provide freedom of movement between the chuck fingers and the chuck cylinders in the direction of the plane of symmetry, so that even with an offset of the central axis of the radial bore 56, it is nevertheless guaranteed that the chuck shoulder 28 is tightened solely with an axial clamping force.

Therefore, the bearing surface 26 is reliably and evenly pressed against the annular face 51. The flow of force passes from the chuck fingers through the chuck cylinders and their cylindrically smooth outer wall to the likewise cylindrically smooth inner wall of the radial bore 56 so that between the two parts which are to be clamped to one another, namely the tool and the tool holder, there is only inserted a single movable intermediate member, namely a chuck cylinder. Since the forces are transmitted by clearly defined smooth surfaces, the disadvantages entailed by linear contact are avoided and above all no screwthread is left in the way of the clamping force.The retaining screw 78 is only subjected to traction loading, while tilting moments in the chuck cylinders are absorbed by guidance of the chuck cylinders in the radial bore 56 which must be guaranteed by production techniques. Thus, no additional clamping forces occur in the region between the external screwthread and the threaded bore which could hamper operation of the retaining screw.

The function of centring is carried out by elements which are in an axial direction spatially separated from the clamping elements, so that machining them can be solely orientated at their intended function, for optimum results. For example, the centring bore 52 has a wall surface which is not interrupted by radial bores of any kind, so that ideal conditions for an accurately fitting finish are provided.

The illustration in Figure 3 shows that in the portion relating to the first and third oblique faces, the chuck fingers are symmetrical in respect of a second radial plane 91 parallel with the bearing surface 26, both radial planes 67 and 91 being, in the connected state illustrated, slightly offset in respect of each other in an axial direction to ensure that only the first oblique faces engage the corresponding second oblique faces.

If the positioning pin 87 according to the embodiment illustrated is fixed in the tool holder 12, this has the advantage that it is possible to economise on such pins since naturally the number of tool holders is less than the multiplicity of existing tools. The fact that two positioning bores 88 and 89 offset by 1800 in respect of each other are provided in the tool 11 and are associated with the positioning pin 87 has advantages in the case of the application with machining centres having what is known as a turret head. As already emerges from Figure 2, by virtue of its splined journal the tool holder 12 is committed to one specific position of installation which is naturally provided for in the tool housing. It can be natural for the tool housing not to be the same in all machines but to require tool holder positions which differ by 180% Now, however, when operating a drill, the endeavour is to have the outer cutting tip 19 (Figure 1) aligned horizontally (if the tool is held in a fixed position), because this guarantees better chip discharge and, after all, this outer cutting tip should as far as possible point towards the user because the latter then has the best view into the hole to be drilled. By reason of the fact therefore that the tool can be inserted into the tool holder 12 into either of two positions which are offset by 1800 in respect of each other, by reason of the two oppositely disposed positioning bores 88 and 89, it is possible to fulfil the foregoing condition regardless of the system used for fixing the tool holder 12 in the tool housing.

With regard to the abutting bearing surface 26 and annularface 51, it has been found to be advantageous to provide at least one of these faces with a so-called hollow ground surface of within 3 to 4 ijm, so that this surface may appear to be slightly conical when not in the clamped condition. In the clamped condition, however, the full area of both faces are pressed one against the other.

Claims (15)

1. Axial clamping connection between a tool holder and a tool such as a milling cutter, reamer or in particular a drill, the tool holder having a cylindrical centring bore coaxial with the longitudinal axis of the tool and an annular face directed at and aligned at a right-angle to the longitudinal axis of the tool, the said tool having an annular bearing surface adapted to be pressed against the annular face and, projecting therefrom and coaxial with the longitudinal axis of the tool, a centring stud which fits into the centring bore and, furthermore, in the region of the fitted-together parts of tool and tool holder, clamping elements are provided which comprise an externally operable radially disposed retaining screw and which are braced against the tool holder at one end and on the tool at the other and which convert a radial force brought about by the retaining screw into an axial clamping force which presses the bearing surface against the annular face, characterised in that integrally moulded on the tool (11) and adjacent the centring stud (27) there is a chuck shoulder (28) divided into two chuck fingers (32,33) extending symmetrically of the longitudinal axis (18) of the tool by a transverse groove (31) open at its end face (29), and in that the tool holder (12) has for the chuck shoulder (28) a coaxial free position (53) adjacent the centring bore (52) and in that the retaining screw (78) has a length projecting beyond the diameter of the chuck shoulder (28) while its ends which project radially on both sides beyond the chuck shoulder (28) are in the longitudinal axis (18) of the tool held inside a radial bore (56) which traverses the tool holder (12) in the region of the free position (53).

2. Axial clamping connection according to claim 1, characterised in that the chuck fingers (32, 33) have in relation to a plane of symmetry (34) orientated at a right-angle to the plane of the transverse groove (31), diametrically opposed first oblique faces (36, 37,38,39) which diverge towards the end face (29), and in that the radial bore (56) of the tool holder (12) is aligned at a right-angle to the plane of symmetry (34), and in that guided for radial displacement in the radial bore (56) on both sides of the aforesaid plane of symmetry (34) there is in each case a chuck cylinder (57, 58), on the end faces (71) of which, pointing towards the first oblique faces (36, 37,38, 39), there is in each case constructed corresponding second obliquefaces (59,61,62) and in that the retaining screw (78) is braced radially in respect of the longitudinal axis through the tool (18) in the two chuck cylinders (57, 58).

3. Axial clamping connection according to claim 2, characterised in that the retaining screw (78) is constructed as a differential screw while the chuck cylinders (57, 58) have mutually coaxial threaded bores (76,77) which are of the same pitch but which have an opposite direction of thread.

4. Axial clamping connection according to claim 3, characterised in that both ends of the retaining screw (78) are accessible from outside and have recessed hexagonal socket heads (83, 84).

5. Axial clamping connection according to claim 2, characterised in that the chuck fingers (32,33) have, diametrically opposed in relation to the plane of symmetry (34) and emanating from the first oblique faces short mutually parallel free faces (41, 42,43,44) and starting from these and diverging towards the centring stud (27) integrally formed third oblique faces (46, 47, 48, 49).

6. Axial clamping connection according to claim 5, characterised in that on the end faces of the chuck cylinders (57, 58) and also corresponding to the third oblique faces (46 to 49) there are fourth oblique faces (63,64,66), so that the chuck cylinders (57,58) are symmetrical in relation to a first radial plane (67) parallel with the annular face (51) while the chuck fingers (32, 33) are symmetrical in the portion relating to the first and third oblique faces and in respect of a second radial plane (91) parallel with the bearing surface (26), the first and second radial planes (67,91) being slightly offset in relation to each other axially when in the connected state.

7. Axial clamping connection according to one of the preceding claims, characterised in that viewed in the direction of the plane of symmetry (34) the first oblique faces (36,37,38,39) of the serially disposed chuck fingers (32,33) are aligned with one another in pairs, the aligned oblique faces (36137, 38/39) being constructed as plane faces which are located in a common oblique plane.

8. Axial clamping connection according to claim 7, characterised in that the second oblique faces (59, 61,62) of each chuck cylinder (57, 58) are constructed as plane faces located in a common oblique plane.

9. Axial clamping connection according to claim 7 or 8, characterised in that the oblique plane of the plane faces is inclined at 450 in relation to the longitudinal axis (18) of the tool.

10. Axial clamping connection according to claim 2 and claim 3, characterised in that the chuck cylinders (57, 58) are provided on their outer periphery with a flattened portion (68) which does not reach to the oppositely disposed end faces (69, 71) and in that there are in the radial bore (56) of the tool holder (12), in the region of the flattened surfaces (68) of both chuck cylinders radially inwardly projecting locking pins (72,73).

11. Axial clamping connection according to claim 3, characterised in that the retaining screw (78) comprises between the screwthreaded end portions (79,81) a reduced-diameter threadless middle shank (82).

12. Axial clamping connection according to claim 11, characterised in that the diameter of the middle shank (82) is at least 2 to 3 mm smaller than the inside diameter of the transverse groove (31) in the chuck shoulder (28).

13. Axial clamping connection in particular according to one of the preceding claims, characterised in that an axially parallel protruding positioning pin (87) is inserted into the annular face (51) of the tool holder (12) and in that corresponding positioning bores (88, 89) are provided in the bearing face (26) of the tool (11) in two positions which are offset by 180 in respect of each other.

14. Axial clamping connection according to claim 13, characterised in that the positioning pin (87) and the positioning bores (88,89) lie in the plane of symmetry (34).

15. Axial clamping connection between a tool holder and a tool such as a milling cutter, reamer or in particular a drill, as claimed in claim 1, substantially as described herein with reference to and as illustrated by the example shown in the accompanying drawings.