GB2313333A - Preclamping ring - Google Patents

Description

PRECLAMPING RING FOR THE TURNING-OUT OF SOPT IWTFRCHANGAELE FALSE JAWS The invention relates to a clamping ring for preclamping the jaws of a three-jaw chuck in turning-out or outside diameter turning, having the features of the preamble of claim 1.

As a rule, in the machining of workpieces on a lathe a ttwKh of running of the order of magnitude of 0.01 mm is possible only if prior to the clamping of the workpiece, the clamping jaws of the chuck used are turned out from inside (in external clamping) or turned over from outside (in inside clamping). Moreover, in the case of workpieces which have already been completely machined at the clamping place, the clamping jaws must be so machined that the radius of the clamping surface corresponds to the radius of the workpiece to be clamped. This avoids damage to a completely machined surface at the clamping place.

In the machining of the clamping jaws, care must be taken to eliminate play from the clamping jaw drive.

To this end, for example, the Journal "Industriekurier", No. 22, 1955, page 45, discloses how to insert in the drilled holes of the attaching screws for soft interchangeable false jaws, clamping bolts in the same radial position in relation to the axis of rotation of the chuck, between which a clamping ring can be inserted. The three-jaw chuck is then preclamped against said clamping ring, and the soft interchangeable false jaws can be turned out from inside. In this procedure it is necessary to find a clamping ring which will enable the clamping jaws to be moved together to a clamping diameter which is smaller than the workpiece to be clamped. The interchangeable false jaws must then be turned out larger by a corresponding amount. One disadvantage of these devices is felt to be that the consumption of soft interchangeable false jaws is relatively high, since the clamping rings are available only in predetermined graduations of diameter.

US-PS 31 04 474 discloses an insert which can be inserted between the basic jaws of the three-jaw chuck and which consists mainly of a metal plate having three spirally outwardly extending zones offset by 120'. For the turning-out of the interchangeable false jaws, this device is introduced into the chuck - i.e., in the machining direction - behind the false jaws and between the basic jaws and is then clamped against the basic jaws by the use of a screwdriver-like tool. One disadvantage of this device is that the jaws can be preclamped only inwards, so that only the internal turning-out of the false jaws is possible, and the ancillary tool must be introduced into the chuck through the jaws to be machined.

Lastly, the Journal 'tWerkstattechnik", 58, 1968, Vol. 1, page 32, discloses a ring for the turning-out of jaws, wherein three slides are provided which are offset by 120 in relation to one another and are guided radially displaceably in a basic ring.

The slides are adjusted via a spiral toothing by the rotation of an adjusted ring in the radial direction, similarly to the drive of the clamping jaws in a three-jaw chuck. For the preclamping of the clamping jaws of the three-jaw chuck to be turned out, the slides are first adjusted to substantially the fitting radius, whereafter the slides are attached by screws in the attaching holes of the soft interchangeable false jaws, and finally the three-jaw chuck is preclamped against the slides. The soft interchangeable false jaws can then be turned out. In practice this operation is highly time-wasting. Moreover, the reclamping ring with the three slides and the slide-driving device represents a large weight, so that there is a high risk of accidents with the faulty handling more particularly of highspeed lathes. Due to their size, in many situations the turningout of the jaws is impossible.

Starting from this prior art, it is an object of the invention to provide for three-jaw chucks a clamping device which allows the simple stepless preclamping of the interchangeable false jaws of a three-jaw chuck both for internal turning-out and also external turning-over.

This problem is solved by a clamping ring having the features of claim 1. A set of clamping rings having the features of claim 11 also provides versatile applicability.

Since the outer and inner surfaces of the clamping ring each have surface portions which continually change in radius over an angular range of 120e in relation to the axis of symmetry, for the internal turning-out of the interchangeable false jaws the ring can be clamped between three clamping bolts disposed on the false jaws and caused by the rotation of its outer surface to bear against all three bolts. The clamping bolts are disposed in the same position as with the use of the known clamping ring as described in the aforementioned Journal 'tIndustriekurier". For the external turning-over of interchangeable false jaws, the ring is similarly laid on the outside over the clamping bolts and so rotated that the inner surface of the clamping ring bears on the outside against all three clamping bolts.

Since inner and outer surfaces changing continually in radius are provided in an annular preclamping device, in dependence on the dimensions of the clamping device, any desired preadjustments of the three-jaw chuck can be clamped. Since moreover the novel tool is annular in construction, it can be used both for internal turning-out and external turning-over. Finally, the novel tool is relatively lightweight, so that there is little risk of accidents, even with faulty handling.

It has proved effective for the production of the clamping ring according to the invention if the surface portions of the inner surface extend over the angular range of 120- from a first, smaller inside radius ri to a second, larger inside radius Ri and the surface portions of the outer surface extend over the angular range of 120e from a first, smaller outside radius ra to a second, larger outside radius Ra.

Advantageously for the making and stability of the clamping ring, the larger inside radius Ri is smaller than the smaller outside radius ra, since in that case the remaining material crosssections maintain adequate dimensions. If the difference between the smaller inside radius ri and the larger inside radius Ri is in the range of 2 mm to 20 mm, more particularly between 5 mm and 10 mm, the result is a satisfactory compromise between the pitch of the inner surface and the number of clamping rings according to the invention, which cover the entire clamping range of a three-jaw chuck. The same thing applies if the difference between the smaller outside radius ra and the larger outside radius Ra is in the range of 2 mm to 20 mm, more particularly between 5 mm and 10 mm.

Particularly small cross-sections and therefore light weights of the clamping rings according to the invention are possible if the clamping ring is made from a through-hardenable steel, for example, anti-friction bearing steel.

The clamping rings according to the invention can be produced particularly precisely if the inner and outer surfaces are produced by laser cutting or milling.

A satisfactory compromise between strength and light weight is reached, the clamping ring has a thickness of 2 mm to 10 mm in the direction of its axis of symmetry, which during its use coincides with the axis of rotation of the three-jaw chuck.

Advantageously, the minimum thickness of the clamping ring between its inner surface and its outer surface in a direction radial in relation to its axis of symmetry is approximately 6 mm to 15 mm.

For the practical use of the invention, it, is more particularly advantageous to have a set of clamping rings of different diameter which is characterized in that each larger inside/ outside radius of a smaller clamping ring is larger than the next smaller inside/outside radius of the next following, larger clamping ring in the set. In this way a set of clamping rings according to the invention covers the entire clamping range of a three-jaw chuck occurring in practice (for example, up to approximately 400 mm diameter). At the same time it meets the requirements of practice if the inside radii of the clamping rings cover a range of 10 mm to 200 mm.

The invention will now be explained with reference to the drawings, which show: Fig. 1 a plan view of a clamping ring according to the invention in the direction of the axis of symmetry, Fig. 2 the clamping ring shown in Fig. 1 in its use for the internal turning-out of the soft interchangeable false jaws, and Fig. 3 the clamping ring according to the invention in its use for the external turning-over of soft interchangeable false jaws of a three-jaw chuck.

Fig. 1 is a view of a clamping ring 1 according to the invention in the direction of its axis of symmetry.

The clamping ring 1 has an inner peripheral surface 2 which is subdivided into three angular portions of 120e each. Each of the angular portions extends from a point 3 having the smallest inside diameter ri to a point 4 having the largest inside diameter Ri. At the place at which the smallest and largest inside diameters come closest together, the surface portions merge into one another in a groove 5. Between the point 3 and the point 4 the inside diameter ri continuously increases to the inside diameter Ri.

The outer surfaces 6 of the clamping ring 1 according to the invention are also subdivided into three segments of 1200 each in relation to the axis of symmetry of the clamping ring. The segments extend from a point 10 of smallest outside diameter ra to a point 11 of the largest outside diameter Ra, the radius continually increasing in relation to the axis of symmetry. At the transition between one angular segment and the next segment, as in the case of the transition adjacent the point 3, a groove 12 is provided which has a predetermined radius of curvature.

The grooves 5 and 12 are offset in relation to one another by a certain angle, so that an adequate material cross-section is left between the grooves for the clamping ring.

Fig. 2 shows a clamping ring according to the invention in its use the internal turning-out of soft interchangeable false jaws.

A three-jaw chuck 14 is shown in the direction of its intended axis of rotation. The chuck 14 bears three clamping jaws 15 of substantially identical construction which are formed in known manner by a basic jaw (not shown) and a soft interchangeable false jaw. The soft interchangeable false jaws are attached to the basic jaws by attaching screws, the screws being disposed axis-parallel with the axis of rotation of the three-jaw chuck.

Each interchangeable false jaw has a steel pin 16 in the same radial position in each drilled hole provided for the attaching screws of the soft interchangeable false jaws. The steel pin 16 of each interchangeable false jaw projects beyond said jaw by a certain amount in the direction of the axis of rotation. The clamping ring 1 according to the invention can be so inserted between the steel pins 16 that said pins bear against the outer surface of the clamping ring 1.

When used for the internal turning-out of the clamping jaws 15, the clamping ring 1 according to the invention operates as follows: A workpiece to be clamped is introduced between the clamping jaws 15, and the chuck is moved together as far as the workpiece.

Thereafter the workpiece is removed from the clamping jaws and a clamping ring 1 of suitable diameter is inserted between the steel pins. As shown in Fig. 2, the clamping ring is then caused to bear against the steel pins by anti-clockwise rotation. By the rotation of a cotter slot 17, the chuck can then experience the usual clamping force used in operation. The preclamping reduces to zero the play of the clamping jaw drive.

By the use of a suitable tool, the clamping jaws 15 can then be turned out from inside to the fitting diameter.

on completion of this operation the chuck is unclamped, the clamping ring 1 is removed, and the workpiece can be inserted between the clamping jaws 15. If the same clamping force is used as in the case of internal turning-out, the soft interchangeable false jaws engage the workpiece over its area, since their clamping surfaces have precisely the correct radius of curvature.

Moreover, the truth of running of a workpiece thus clamped is of the order of magnitude of 0.01 mm or better.

Fig. 3 shows the clamping chuck from Fig. 2 in a configuration having a larger clamping ring 1, which engages around the steel pins 16 on the outside. In this configuration the chuck 14 can be preclamped in the outward direction, to simulate the loading by a, for example, hollow workpiece to be clamped from inside.

In this configuration the clamping surfaces can lie, for example, at places 18 or 19, so that substantially any required diameters inside or outside the clamping ring can be turned over from outside. The advantages of this processing of the soft interchangeable false jaws are the same as already been described in relation to Fig. 2.

Special advantages are obtained if a graduated set of clamping rings 1 according to the invention is available which covers the entire possible range of diameters to be processed; the ranges of use of the individual clamping rings should overlap by approximately 10%, since any desired workpiece can be introduced between the clamping jaws, and whereafter the distance between two clamping pins 16 is determined, for example, using a slide gauge. Since the distance between two clamping pins 16 from one another is a clear indication of the incircle/circumcircle diameter bounded thereby, a suitable clamping ring can be assigned to each such dimension. The overall result in the use of the clamping rings according to the invention is an appreciable simplification of the internal/external processing of soft clamping jaws.

The continuously changing inside/outside radii of the clamping rings according to the invention also enables the diameter of the clamping jaws to be very precisely preadjusted, so that only the amount really required must be turned off the soft interchangeable false jaws. The consumption of soft interchangeable false jaws is in practice appreciably reduced in this manner. The device according to the invention also has advantages in the grinding-out of hard clamping jaws, in the case of which a similar procedure is called for.

In the foregoing the clamping rings according to the invention have been described from the example of a three-jaw chuck.

However, it is entirely possible to provide corresponding clamping rings for four-jaw chucks, in which case the angular subdivision of the clamping rings must be 90 , not 120 .

Claims (12)

1. A clamping ring for preclamping the jaws of a three-jaw chuck in turning-out or outside diameter turning, having a circumference side outer surface and an inner surface which are disposed substantially coaxially in relation to an axis of symmetry, characterized in that the outer surface and the inner surface each have surface portions which change continuously in radius over an angular range of 120 in relation to the axis of symmetry.

2. A clamping ring according to claim I, characterized in that the surface portions of the inner surface extend over the angular range from a first, smaller inside radius ri to a second, larger inside radius Ri, and the surface portions of the outer surface extend over the angular range from a first, smaller outside radius ra to a second, larger outside radius Ra.

3. A clamping ring according to one of the preceding claims, characterized in that the larger inside radius Ri is smaller than the smaller outside radius ra.

4. A clamping ring according to one of the preceding claims, characterized in that the difference between the smaller inside radius ri and the larger inside radius Ri is in the range of 2 mm to 20 mm, more particularly between 5 mm and 10 mm.

5. A clamping ring according to one of the preceding claims, characterized in that the difference between the smaller outside radius ra and the larger outside radius Ra is in the range of 2 mm to 20 mm, more particularly between 5 mm and 10 mm.

6. A clamping ring according to one of the preceding claims, characterized in that the clamping ring is made from throughhardenable steel.

7. A clamping ring according to one of the preceding claims, characterized in that the clamping ring is produced by milling.

8. A clamping ring according to one of the preceding claims, characterized in that the clamping ring is made by laser cutting.

9. A clamping ring according to one of the preceding claims, characterized in that the clamping ring has a thickness of 2 mm to 10 mm in the direction of the axis of symmetry.

10. A clamping ring according to one of the preceding claims, characterized in that the clamping ring has between its inner surface and its outer surface a minimum thickness of 6 mm to 15 mm in a direction radially to the axis of symmetry.

11. A set of clamping rings of different diameter according to one of the preceding claims, characterized in that in each case the larger inside/outside radius of a smaller clamping ring is larger than the smaller inside/outside radius of the next following, larger clamping ring in the set.

12. A set of clamping rings according to claim 11, characterized in that the inside radii of the clamping rings cover a range of 10 mm to 200 mm.