WO1994008744A1

WO1994008744A1 - Collet with translating jaws for automatic lathes

Info

Publication number: WO1994008744A1
Application number: PCT/IT1992/000145
Authority: WO
Inventors: Gianfranco Clerici
Original assignee: Gianfranco Clerici
Priority date: 1992-10-16
Filing date: 1992-11-19
Publication date: 1994-04-28
Also published as: ITMI922388A1; AU3093992A; IT1255885B; EP0664737A1; ITMI922388A0

Abstract

Collet (20) for automatic lathes comprising externally conical jaws (21), three coaxial cup-like structures (50, 60, 70) consisting of a collar (51, 61, 71) and of longitudinally elastic tongues (55, 62, 72) acting on the jaws (21), and a reaction provoking ring (40) having a double internal taper (44, 45) which encircles the top (24) of the jaws (21) and the edge of the first cup (50) which is external and has a double internal taper (53) and external (52) and which in turn encircles the rear zone (25) of the jaws (21) thus producing a translating movement of the jaws (21) both during the closing phase of the collet (20), due to action by the edge of the first cup (50) and during the opening phase of the collet (20) due to elastic reaction by the tongues (62, 72) of the second and third cups (60, 70).

Description

COLLET WITH TRANSLATING JAWS FOR AUTOMATIC LATHES The invention concerns automatic lathes and like machines. In automatic lathes the bar to be processed must repeated¬ ly be first held and then released by a collet inside a chuck through which said bar is made to pass.

The jaws of the collet are formed of a cylindrical body the inside surface of which is cylindrical and the outer one conical . By means of longitudinal cuts the faces of said cylindri- cal body are divided into strips whose positions correspond to those of the various jaws.

The collet closes by a centripetal movement of said jaws pressed by thrusting means. As this centripetal motion is produced by bending the strips of the cylindrical supporting body contact between jaws and bar is confined to a limited area of said bar. Additional pressure by the jaws against the bar could gra¬ dually increase the area of contact between bar and jaws if the latter's supporting strips were fully elastic, but too much elasticity would be unlikely to ensure jaws of adequate rigidity.

The supporting strips could be more elastic if the jaws were made in blocks separate from the cylindrical support¬ ing body and of a material different from that of said body and subsequently fixed to it.

It is clear however that the supporting cylindrical body can never be sufficiently elastic to ensure complete ad- herence between the inner surface of the jaws and the bar. But again, as pressure on the external conical surface of the jaws is generally made by thrusting means which also have conical surfaces, in order to secure perfect match¬ ing between jaws and bar not only would there have to be extreme precision between the conical surfaces of the thrusting means and the jaws, but also between said sur¬ faces and that of the bar. Bearing in mind how impossible it is to achieve, and maintain, small tolerances in mechan¬ ical parts of this kind, similarly would it also be impos- sible to ensure absolute precision in work done by automa¬ tic lathes .

The above invention eliminates, or reduces, these drawbacks as will now be explained in what follows. Subject of the invention is a collet for chucks on auto- matic lathes having jaws that make a translating movement. Said collet comprises three coaxial cylindrical cup-like structures, called 'cups' for simplicity, fitted one in¬ side the other, whose upper ends act on the collet, and a reaction provoking ring, with a cylindrical outer surface, that encircles the top of the jaws and the top of the outermost cup . The jaws have a front zone and a rear zone, both external¬ ly conical, whose diameter decreases towards the back of the. collet.

The upper internal part of the reaction ring matches with the upper external part of the jaws against a surface of equal taper but tapering in the opposite direction. The upper edge of the first cup has an internal taper that allows it to match with the lower external part of the jaws, and an external taper, in the opposite direction to that of the inner one, which matches with the lower internal conical part of the reaction ring.

The structures of the three cups virtually consist of a collar and of longitudinal elastic tongues. The upper ends of the second cup, inside the first one, and of the third cup inside the second, are arranged respective¬ ly in positions corresponding to the front and back zones of the jaws and fit into seats made for them behind the conical faces of said jaws. Therefore, during the closing phase of the collet, movement of the first cup towards the jaws, making frontal contact with the head of the chuck, causes simultaneous movement, due to the effect of the conical surfaces of the edge of said cup opposite respectively to the conical surface of the reaction ring and to the conical surface of the jaws, of the rear zone of the jaws towards the axis of the collet and of the reaction ring towards the front of the collet. As a consequence, the effect produced by the opposing con¬ ical surfaces of the ring and of the front of the jaws is to move this latter part towards the axis of the collet. Movement of the jaws towards the inside of the collet causes bending of the tongues of the second and third cups. During the opening phase of the collet, withdrawal of the first cup leaves the reaction ring free to withdraw as well. Consequently the elastic tongues of the second and third cups are free to resume their original positions thus mov- ing both the front and the rear parts of the jaws away from the axis of the collet.

Between the tongues of the first outer cup there are lon¬ gitudinal rectangular spaces of equal width and placed at equal centre distances. The second cup consists of a cylindrical collar whose dia¬ meter is slightly smaller than the internal diameter of the cylindrical body formed by the first cup, from which collar depart a number of longitudinal tongues, equal in number to the tongues of the first cup, placed at equal distances and of a width slightly less than that of the spaces between the tongues on the first cup.

In its rear conical area each jaw has a central longitudi¬ nal channel which extends from the lower edge of said jaw to a niche formed behind the jaw's front conical area. The position of an internal face of said niche corresponds to the bottom of the channel, there being an opposite face, farther out, parallel to the first and behind the conical surface at a distance from the first face slightly greater than the thickness of the ends of the tongues of the se- cond cup to allow said tongues' ends to enter the niche. Therefore when, during the collet's opening phase, said tongues return to their original position, their action against the external face of the niche causes the front of the jaws to move away from the collet's axis. The third cup, inside the second one, is formed of a cylin¬ drical collar also carrying longitudinal tongues. The external diameter of the third cup, measured at the ends of the tongues, is such as will create sufficient space, between said tongues and those of the second cup, to permit entry of the fin-shaped rear end of the jaws. During the collet's opening phase, therefore, when the tongues of the third cup resume their original positions, their action against ss . d fin causes the rear end of the jaws to move away from the axis of the collet. Between a projecting annular edge inside the lower end of the collar of the first cup and the lower end of the second cup, there is a helical compression spring placed to ensure the correct reciprocal positions of the first and second cups and at the same time the relative move¬ ments between said cups while the collet is closing. In some executions there are six, or else three, jaws of equivalent angular value.

In one execution the jaws are connected by an elastic ring fitted inside a specially made transversal annular groove in said jaws. A section of this ring, opposite the spaces between one jaw and another, may be smaller than that of the groove so that, when the collet is closed, said section may form an undulation inside said groove to an extent correspond¬ ing to the reduction in the groove's length. In one type of execution it is advantageous to have the reaction ring moderately elastic to allow it to expand, then automatically contract again when the collet closes, inside the cylindrical cavity in the chuck containing it. Such elasticity in the reaction ring can be advantageous- ly produced by a series of alternating transversal cuts on the front and back edges of the ring, which cuts extend nearly to the opposite side so as to create a kind of fretted edge which, by its very nature, assists elastic alteration of the form along its axis. The advantages of the invention are evident. The effect of the reaction provoking ring, during the closing phase of the collet, is to create a double in¬ clined plane system that acts practically on the ends of the front and back of the jaws which become pressed against the bar to be firmly held, parallel to themselves until they adhere completely to said bar.

In the opening phase the jaws are similarly pressed front and back and are compelled to move away from the axis of the collet by translating parallel to themselves, ensur¬ ing that the jaws open completely. With the elastic reaction ring, closure of the collet is accompanied by full pressure of the jaws both on the in¬ ner cylindrical surface of the chuck and on the surface of the bar to be processed, there being automatic compen¬ sation of errors of tolerance and of construction, as well as of the effects of wear during use.

The expanding type is therefore particularly advantageous in the case of second-hand lathes where there has been wear on the seats in the chuck for the collet and for the thrusting means. To the above advantages may be added greatly improved pre¬ cision, a more functional machine and higher output. Characteristics and purposes of the invention will become still clearer from the following example of its execution illustrated by diagrammatically drawn figures. Fig. 1 Perspective view of the collet partly cut away. Fig. 2 Perspective of an exploded view of the collet. Fig.3 Longitudinal section in detail of the open collet. Fig.4 The same section showing the acting forces. Fig.5 As Fig. 3, during the closing phase. Fig.6 The same showing the acting forces. The chuck 10 has a cylindrical body 11 and head 15 connec¬ ted by threading 12 on each.

Inside the cylindrical body 11 the inner cylindrical face 14 may be seen and, forward of that, the cylindrical seat 13 of a larger diameter. In the head 15 there is an axial hole 17 to receive the end of the collet 20, said hole having an internal edge 18. The collet 20 comprises six substantially equal jaws 21 made from six coaxial cy1indrico-conical sectors, the reac¬ tion ring 40 and a first cup 50. On the jaws there is an inner cylindrical face 22 with which to grip the bars (not shown), an upper cylindrical end 23 that will enter the hole 17 in the head of the chuck, the front zone 24 with an external back-ward inclined coni¬ cal face 26 and the rear zone 25 with a conical face 27 this too inclined backward.

The projecting front edge 28 of the jaws makes contact with the edge 18 of the hole 17 in the head 15 of the chuck 10. Between zones 24 and 25 there is an arched transversal groove 29. The external cylindrical surface 42 of the reaction ring 40 is intended to fit into the cylindrical seat 13 of the chuck. Inside said ring 40 is a conical face 44 at the front and a conical face 45 at the back,both inclined towards the out¬ side of the ring. The cylindrical cup 50 can slide freely within the chuck 10 and consists of a collar 51 at its base and of six longitu¬ dinal tongues 55 set at the same angular distance one from another forming a cylindrical body with equal intermediate rectangular spaces 56.

Close to its forward edge said cup 50 has an external co¬ nical surface 52 whose taper practically corresponds to that of the face 45 of the ring 40 matching it, and an in¬ ternal conical surface 53 whose taper practically corres¬ ponds to that of the conical face 27 of the jaw 21 that matches with it .

Inside the first cup 50 there is a second cup 60 consist- ing of a cylindrical collar 61 at the base from which de¬ part six longitudinal rectangular tongues 62 whose width is slightly less than that of the spaces 56 between the tongues 55 of the first cup 50.

Said tongues 62 form a cylindrical body whose external diam- eter is greater than that of the collar 61 and substantially equal to the external diameter of the cylindrical body formed by the tongues 55 of the first cup 50. In the conical face 27 of the rear zone 25 of the jaws 21 there is a longitudinal rectangular channel 30 virtually parallel to the axis of the internal cylindrical face 22, its width being greater than that of the tongues 62 on the second cup 60.

The bottom 31 of said channel connects, with practically no interruption, with the internal face of a niche 32 with an outward face 34 parallel to the internal face.

Said niche 32 lies behind the conical face 26 of the front zone 24 of the jaws.

At the lower end of the rear zone 25 of the jaws there is a recess 35 behind the conical face 27 forming the fins 36. The ends 63 of tongues 62 of the second cup 60 are narrower than the width of the niches 32 in the jaws. The length of said tongues is such that said ends 63, fitted into the channel 30, penetrate inside the niches 32. Inside the second cup 60 is a third cup 70 consisting of a cylindrical collar 71 at its base which carries longitu- dinal tongues 72 forming a cylindrical body.

The external diameter of said cylindrical body is smaller than the internal diameter of the cylindrical body of the second cup 60 and this creates a space between the tongues of the second and third cups sufficient to receive the fins 36 formed at the lower ends of the jaws.

Sufficient elasticity is assured for the tongues 55, 62, 72 of the three coaxial cups 50, 60, 70 by their thickness and by the material used to make them. The lower edge of the first cup 50 projects inside the cup o form an annular seat 57. Between this seat 57 and the second cup 60 is a helical compression spring 65 that ensures maintenance of a correct position between the two cups when not engaged, and at the same time permits their necessary movements during the closing phase of the collet 20. The collet functions in the following way.

Fig. 1 shows the collet when idle and fully open. The bar to be processed, not drawn in the figure, is put in determinining by means of force A translation of the cup 50 towards the head 15 of the chuck 10 and then simultaneous action by the conical surfaces 52 and 53 respectively on the conical surface 55 of the ring 40 and on the conical surface 27 of the rear zone 25 of the jaws 21 as indicated in each case by the arrows B and C (Figs. 3 and 4). Force B creates a component Bl towards the face 13 of the chuck while force C creates a component Cl towards the bar. Following further translation of the first cup 50, force B divides again into a second component D which moves the reaction ring 40 towards the front of the collet. This movement by the reaction ring 40 in turn determines action by the conical surface 44 against the upper conical surface 26 of the jaws, as shown by the arrow E.

This action sets up a component El which thrusts the upper part 24 of the jaws towards the bar (Figs. 5 and 6). From the foregoing it is clear that, subsequent to longitu¬ dinal application of force A to the cup 50, forces Cl and El effect radial translation of the six jaws towards the axis of the collet and therefore towards the bar to be processed, which bar is thus held firmly by pressure spread equally all over the surface of contact with the collet, giving au¬ tomatic compensation of structural and positional tolerances between the inner surface of the chuck and the surfaces of the bar, of the jaws and of the reaction ring.

Jaw translation towards the collet's axis bends the tongues 62 of the -second cup 60 towards the collet's axis by means of face 34 of niche 32 in the jaws, and bends the tongues 72 of the third cup 70 by means of the fins 36 on said jaws. Arrow 4 (Fig .6^" ) .

During the opening phase when the first cup 50 withdraws, the tongues 62 of the second cup 60, resuming their original po¬ sition, press against the face 34 of the niche 32 in the jaws causing the upper part of the jaws to move away from the axis of the collet. (Arrow G, Fig. 6).

At the same time the tongues 72 of the third cup 70, resuming their original position, press against the lower fins 36 on the jaws causing the lower part of the jaws to move away from the axis of the collet.

Claims

1. Collet (20) with translating jaws (21) for chucks ( 10) in automatic lathes characterized in that it comprises three coaxial cylindri- cal cup-like structures, called cups (50, 60, 70) one fit¬ ting into another and pressing with their upper ends on the jaws (21), and a reaction provoking ring (40) whose outer cylindrical surface (42) surrounds the top (26) of the jaws (21) and of the first external cup (50), the jaws (21) having two . zones, a front one (24) and a rear one (25) both conical externally (26, 27) their diameters decreasing towards the rear zone of the collet (20), the upper internal zone of the reaction ring (40) matching with the upper external zone (26) of the jaws (21) by means of a conical surface (44) tapering in the opposite direction and of equal value, the upper edge of the first cup (50) having an internal taper (53) matching with the lower external zone (27) of the jaws (21) and an ex¬ ternal taper (52) in the opposite direction to the internal taper (53)matching with the lower internal conical zone (45) of the reaction ring (40),each of the three cups (50, 60, 70) substantially consisting of a collar (51, 61, 71) and of longi tudinal moderately elastic tongues (55, 62, 72), the upper end (63) of the second cup (60), inside the first one (50), and of the third cup (70)inside the second one being placed to corres pond respectively with the front (24) and rear (25) zones of the jaws (21) within the seats (32 35) behind the conical fa¬ ces (26, 27) of said jaws (21) so that during the closing phas of the collet (20), movement of the first cup (50) towards the jaws (21) making frontal contact (28). with the head ( 15) of the chuck ( 10), causes simultaneous movement, due to the ef¬ fect of the conical surfaces (52, 53) of the edge of said cup (5 respectively opposite to the conical surface (45) of the reaction ring (40) and to the conical surface (27) of the jaws (21), of the rear zone (25) of the jaws (21) towards the axis of the collet (20) and of the reaction ring (40) towards the front of the collet (20) and, conse¬ quently, due to the effect of opposing conical surfaces (44, 26) of the ring (40) and of the front (24) of the jaws, a corresponding movement of said latter zone (24) towards the axis of the collet (20) and therefore elastic bending of the tongues (62, 72) of the second (60) and third (70) cups towards the axis of the collet (20) while, in the opening phase of the collet (20), withdrawal of the first cup (50) leaves the reaction ring (40) free to move back so that the elastic tongues (62, 72) of the second (60) and third (70) cups are free to resume their original positions moving both the front (24) and rear (25) zones of the jaws (21) away from the axis of the collet (20) thus ensuring that in both the opening and closing phases of the collet (20), movements of the jaws (21) will be made practically parallel one to another and ensuring, in the closing phase, that the whole length of the jaws (21) will match up with the bar to be held firm¬ ly and processed and, in the opening phase, withdrawal of the whole length of the jaws (21) from the axis of the collet (20).

2. Collet (20) as in claim 1, characterized in that the first external cup (50) has, be¬ tween one longitudinal tongue (55) and another, rectangular spaces (56) of equal width and set at equal distances, in that the second cup (60) consists of a cylindrical collar (61) whose external diameter is slightly smaller than the internal diameter of the cylindrical body formed by the first cup (50), from which a number of .longitudinal tongues (62), equal to the number of tongues (55) of the first cup (50) stand up at equal distances, the spaces between them being slightly narrower than the width of the spaces (56) between the tongues (55) of the first cup (50), the exter¬ nal diameter of the cylindrical body created by the tongues (62) on the second cup (60) being practically the same as the external diameter of the cylindrical body formed by the tongues (55) of the first cup (50) so that by fitting the second cup (60) into the first cup (50) the tongues (62) of the second cup (60) can freely lodge into the spa¬ ces (56) between the tongues (55) of the first cup (50).

3. Collet (20) as in claim 1, characterized in that on the rear conical zone (25) of each jaw (21) there is a central longitudinal rectangular channel (30) which extends from the lower edge of said jaw (21) as far as a niche (32) formed beind the front conical zone (24) of the jaw (21), said niche (32) having an inner face corresponding to the bottom of the channel (30) and an opposite face (34), farther out, parallel to the first face and situated behind the conical surface (26) at a distance from the first face slightly greater than the thickness of the end (63) of the tongue (62) on the second cup (60) to allow said end (63) to fit inside the niche(32) so that when , during the opening phase of the collet (20), said tongues (62) return to their original position, their action against the outermost face (34) of the niche (32) causes the front zone (24) of the jaw (21) to move away from the axis of the collet (20).

4. Collet (20) as in claim 1, characterized in that the third cup (70), internal in re¬ lation to the second cup (60), consists of a cylindrical collar (71) from which depart longitudinal tongues (72), the external diameter of said third cup (70), at the ends of the tongues (72), being such as to create between said tongues (72) and those (62) of the second cup (60), a space sufficient to permit entry of the fin-shaped rear end (36) of the jaw (21) so that when, during the opening phase of the collet (20), the tongues (72) of the third cup (70) resume their original position, their action on said fin (36) is such as to move the rear zone (25) of the jaws (21) away from the axis of the collet (20).

5. Collet (20) as in claim 1, charac erized in that between a projecting annular edge

(57) inside the lower edge of the collar (51) of the first cup (50) and the lower end of the second cup (60) there is a helical compression spring (65) to ensure the precise reciprocal positions of the first cup (50) and of the se- cond cup (60) and at the same time allow movements between said cups (50, 60) to be made during the closing phase of the collet (20).

6. Collet (20) as in claim 1, characterized in that the upper ends of the tongues (55) (72) of the first cup (50) and of the third cup (70) lie at practically the same level in relation to the base of the collet (20) so that they reach a position correspond¬ ing to that of the rear conical zone (25) of the jaws(21) while the tongues (62) of the second cup (60) reach a higher level corresponding to that of the front conical zone (24) of the jaws (21).

7. Collet (20) as in claim 1, characterized in that there are six jaws (21) of equal angular value .

8. Collet (20) as in claim 1, characterized in that there are three jaws (21) of equal angular value .

9. Collet (20) as in claim 1, characterized in that the jaws are connected by an elastic ring mounted inside a specially made transversal groove in said jaws .

10. Collet (20) as in claim 9, characterized in that there is a segment of said elastic ring, in a. position corresponding to the space between one jaw and another, whose cross section is smaller than that of the above groove, this in order to allow said segment, when the collet is completely closed, to form an undulation inside the groove to an extent corresponding to the reduc¬ tion in length of said groove.

11. Collet (20) as in claim 1, characterized in that the reaction ring (40) is moderately elastic so that it may expand, and automatically contract again when the collet (20) is closing, inside the cylindri¬ cal cavity (13) of the chuck ( 11) in which it is placed.

12. Collet (20) as in claim 1, characterized in that the reaction ring (40) is made elas^¬ tic by a series of alternate transversal cuts on the front and back edges of said ring (40), which cuts extend almost to the opposite edge so creating a fretted line which, by its very nature, helps to promote elastic bending in a longitudinal direction.