AU618131B2

AU618131B2 - Collet intended to carry a tool, particularly a tapping tool

Info

Publication number: AU618131B2
Application number: AU41587/89A
Authority: AU
Inventors: Charles Gerard Willen
Original assignee: PCM Willen SA
Current assignee: PCM Willen SA
Priority date: 1988-09-30
Filing date: 1989-09-20
Publication date: 1991-12-12
Anticipated expiration: 2009-09-20
Also published as: ATE114522T1; AU4158789A; EP0360947A1; KR900004448A; DK480989A; JPH0741470B2; JPH0295503A; DE3852309T2; DK480989D0; EP0360947B1; DE3852309D1; KR940004789B1

Abstract

The collet comprises an outer body (1) provided with a cylindrical bore (2), and a sleeve (3) which can move axially inside the bore (2). The sleeve (3) comprises screws (8) for holding the cutting tool. The outer body (1) and the sleeve (3) are provided with prismatic surfaces (9, 10) connecting them kinematically in rotation, and means (5, 11, 12) limiting the axial displacement of the sleeve (3) inside the bore (2). A spring (4) arranged inside the bore (2) makes it possible to return the sleeve (3) into a predetermined rest position. This tool- holding collet permits autonomous axial compensation of the difference between the liner feed movement imposed by the machine and that which the tool has, for example a tap. <IMAGE>

Description

r FORM 10 6 8 F 1 702 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class 4 4 4, 4s 4 44 Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address 4 4, 4 -l 4 4 of Applicant: PCM Willen S.A.

Route du Stand, 14 1844 Villeneuve

SWITZERLAND

Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Collet Intended to Carry a Tool, Particularly a Tapping Tool The following statement is a full description of this invention, including the best method of performing it known to me/us 9 .J 5845/7 COLLET INTENDED TO CARRY A TOOL, PARTICULARLY A TAPPING TOOL.

ABSTRACT OF THE DISCLOSURE The collet comprises an external body formed with a cylindrical bore and a socket which is movable axially within the bore The socket (3) includes screws for holding the cutting tool. The external body and the socket are provided with prismatic surfaces 10) which couple them together for rIi rotary movement, and with means 11, 12) limiting the S axial displacement of the socket within the bore I A spring arranged within the bore enables the socket to be returned to a predetermined rest position. This tool-carrying collet enables automatic I I axial compensation for the difference between the linear feed applied by the machine and that of the tool itself, for example a tap.

Figure 1 st -1 FIELD OF THE INVENTION The present invention relates to a collet intended to carry a tool, particularly a tapping tool, subject on the one hand to a rotary movement about its axis, and on the other hand to an axial displacement.

A cutting tool which is subject on the one hand to a rotary movement, and on the other hand to an axial displacement, being movements wich are imparted to it by anl appropriate machine, is subjected under certain conditions to its own axial movement resulting from the rotation of -the tool and from friction on the surface to be machined, which is particularly the case with a tapping tool but the same phenomenon can arise for other kinds of machining.

PRIOR ART The majority of present-day machines cannot ensure exact and constant synchronization of the axial movement of the tool itself, for example a tap, relative to the axial movement of the machine, which is in step with the rotation of the headstock. The magnitude of its owni axial movement in the case of a tap is a function of the pitch of the tap. In fact, even if present-day digital controls permit exact synchronization during the tapping operation, a greater or lesser desynchronization occurs at the instant of reversal of the direction of11 rotation, when the a desired depth of tapping is reached. The differences depend on the speeds of rotation, and they also result from the difference in inertia between tne headstock of the machine and the carriage or the component causing the axial movement imparted by the machine to the tool, causing different accelerations or decelerations as the case may be. Even if machines with digital control have enabled one to do away with mechanical play, which is another source of desynchronization, absolutely constant control throughout the reversal of the direction of rotation, which is necessary in a tapping operation, can only be guaranteed by certain rare machines. The problem -2

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IIr 00 I l *I I 4141 1144 up to the present day has been met by special apparatus for tapping, of widely varying constructions, which themselves take up the differences in the axial movements but have the disadvantage of being only tapping apparatus, which are on the one hand bulky and on the other hand equipped solely for tapping. Certain of these apparatus, with or without built-in reversal of the direction of rotation, have independent travel throughout the whole taping operation. Sometimes tapping machines are provided with a mechanical system called a "pattern" for ensuring constant synchronisation, which is acceptable at low or medium speeds.

There exist tapping apparatus, and also quickchange tool holders, with interchangeable extension pieces of several types. These extension pieces can perform several functions, but never built-in axial compensation within the dimensions of the basic interchangeable extension piece. Moreover the extension piece is added on to its support, which increases the length of the total bulk.

SUMMARY OF THE INVENTION The object of the present invention is to present a tool-carrying collet enabling automatic compensation of the differences in axial movements of a cutting tool, avoiding the need to use special and bulky apparatus for the machining, and in particular tapping operations with automatic machines with digital control.

The collet according to the present invention comprises an external body formed with a cylindrical bore and the external shape of which matches the shape of the collet holder, and provided with a socket movable axially within the bore and provided with means for holding the cutting tool; wherein the external body and the socket are provided with means which couple them together for rotary movement, and with means limiting the axial displacement of the socket within the bore; and wherein resiliently deformable means are provided for returning the socket to a predetermined rest position.

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44, i By equipping the tool-carrying collet wit-h an external body, the shape of which corresponds to a 'isual collet intended to be supported by a known collet carrier, while placing in a bore in this body a socket which will hold the cutting tool and be able to perform an Ixial displacement within the bore in the external body, between predetermined limits and against deformable resilicnt means returning the socket to a predetermined rest position, one obtains automatic axial compensation of an amount which is of course limited by the construction and the dimensions of the collet.

This compensation in relation to the rest position of the socket can be made in one direction or in the other or in both, as will be explained in the discription.

The advantages of this collet with built-in axial compensation are as follows The collet according to the invention enables one to provide, in addition to the gripping function, the function of uni- or bi-directional compensation within the same dimensions as those of standard collets which solely provide the gripping of the tool. They can be mounted within standard collet carriers without any adaptation being needed and without increasing the length occupied as is the case with interchangeable extension pieces; it is no longer necessary to arrange the gripping collet in specific apparatus which are special and bulky, for compensation of the differential axial displacement between the cutting tool and the axial displacement to which it is subjected by the machine tool; the machining operation, particulary a tapping operation, can be carried out with standard collet carriers of different lengths and sizes, thus permitting one to adapt to the differing shapes of the workpieces to be machined, much better than with conventional apparatus; it is very economical and practical to be able to use the same collet carriers for similar operations, for example boring, reaming and tapping; 4 with CNC turrets with 3, 4 or 5 controlled shafts or even more, tapping operations often have to be performed on an alignment. and in a direction different from the axis of the workpiece, and one often has to carry out several radial or axial tapping operations, even oblique ones, on the same workpiece, and in this case specific apparatus called driven tool carriers perform the functions of boring, reaming and tapping. The driven tool carriers for tapping, having to provide for axial compensation, are of a relatively complicated construction as mentioned above; they are expensive and bulky and can only be used for tapping. The collet for tapping according to the invention enables one to carry out this last operation i oO with the tool carriers for drilling or reaming, this 0* making unnecessary the special installation of a complete 0 r specific apparatus for tapping; the tool-carrying collet according to the invention S likewise simplifies the equipping of a workshop with tool carriers and gives to the user great flexibility of use because, since the machines have various attachments for !the tool carriers, these can only shift from one machine to another in a relatively limited way, which is not the l case with the collets according to the invention which are |i not bound to the attachment of the tool carrier and which can thus be fitted to any machine whatever. This collet system thus offers the possibility of rationalizing almost completely the equipment of a workshop as regards i different machining operations, especially those performed on CNC turrets, machining centers and CNC reaming machines. Hence the economic advantage is considerable.

The design of the collet makes it a simple and robust accessory which in practice withstands without harm any incorrect actuations or accidents which may occur only the means wich do the gripping of the tool, which are preferably screws arranged radially in the socket, need to be replaced from time to time, and of course the cutting tool itself.

5 According 'o one embodiment, the means providing for the coupling between the two basic components of the collet for rotary movements are matching polygonal surfaces formed on the outer part of the socket and a part of the bore.

According to another variation, these means can be matching toothed surfaces provided on the external surface of the socket and the bore.

According to another variation, the means for Vcoupling for rotary movement comprise at least one key.

According to another embodiment, two matching flat surfaces formed on the external surface of the socket and Si the bore provide for the coupling for movement between the t outer body and the socket.

-According to another embodiment, balls rolling in axial, inclined, or helical grooves, made on the one hard in the external surface of the socket and on the other hand in the bore, provide for the coupling for movement between these two components.

According to another embodiment, the axial di.splacement of the socket within the bore is limited on the one hand by an added component arranged on the extremity of the socket and on the other hand by respective matching i shoulders provided in the bore and on the socket.

The means which are resiliently deformable can be either springs, or resilient washers, or a body of K resiliently deformable material.

According to another variation, if axial compensation is required to be provided in both directions, opposed resilient means should be provided to cause the return of the socket to its predetermined rest position.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described in more detail, with the help of the accompanying drawing showing two preferred embodiments of the invention.

Figure 1 is a view in partial axial section of a first embodiment of the invention.

Figure 2 is a view in axial section of a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The collet of Figure 1 is arranged for compensation of axial displacement solely in one direction, namely that indicated by the arrow F.

It is constituted by three essential components, namely :an external body 1 formed with a bore 2, in the interior of which there is a socket 3, and a spring 4 arranged between the socket 3 and the !Dore 2 agains a shoulder 5 of the bore 2 and a shoulder 6 of the socket.

The general construction of the (-ollet and more I t particularly of the external body 1 is not tied to one particular type or shape of collet and it is similar to, or at least compatible with, the gripping collets available on the market. It enables one to fix the cutting tit$ tool, the shank of which corresponds to the bore 7 of the Socket 3 and is gripped by screws 8 arranged radially in the rear part of the sockets 3 and acting against the driving square or against one or more f lats machined on the shank of the tool.

The coupling between the external body 1 and the socket 3 for rotary movement is obtained by means of a first prismatic surface 9 of the socket with a corresponding prismatic surface 10 of the external body 1 These same surfaces serve also for axial guidance, during the compensating displacement, of the socket 3 within the body 1 The maximum independent displacement of the socket 3 within the body 1 is determined on the one hand by a shoulder 11 of the socket which abuts against the shoulder of the bore, and on the other hand by a ring 12 f ixed in a groove of the socket 3 and which, in the rest position, abuts against the internal surface of the body 1 and particular abuts at the bottom of a recess 13.

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.8 I t Instead of using prismatic surface to provide the coupling between the body 1 and the socket 3 for rotary movement, other means can be envisaged such as keys, toothed outlines, balls rolling in axial, or inclined, or helical grooves, formed on the one hand in the external surface of the socket and on the other hand in the interior of the bore. In place of the spring 4, one can use resilient washers or a body of resiliently deformable material.

The operation on the collet of Figure 1 with a tapping tool is as follows the linear feed of the machine is adjusted so that it is slightly less than the feed of the tap itself, which is defined on the one hand by the speed of rotation and on the other hand by the pitch of the thread of the tap. Thus during cutting the tap performs its own compensating displacement, that is to say the socket 3 shifts in the direction F as the tapping operation proceeds. At the end of the tapping operation, during the reversal of the rotation, desynchronization can occur between the axial feed applied by the machine and the feed of the tap itself, and it is compensated by the possibility for the socket to shift in one direction or the other. The feed of the machine is preferably adjusted to 95 of the feed of the tap itself, thus at the instant of synchronized reversal of the rotation of the headstock and of the feed motion one is at approximately the middle of the compensating travel. The return movement of the machine is adjusted to the value of the return movement of the tap itself, so that the gripping collet remains well within its compensation travel, avoiding all constraint on the tap. The longer the compensation travel of the collet, the simpler is the operation of adjustment. In accordance with the characteristics of the machines and the speed of the tapping operation, a hesitation may be necessary during reversal of the rotation and of the linear feed.

8 In Figure 2 there is shown a collet for carrying a tool, comprising an external body 15 formed with a bore 16, in the interior of which can shift a socket 17, and two opposed springs 18 and 19 enabling axial displacement of the socket 17 from the rest position in the two ii directions F1 or F2. The spring 18 is housed in the interior of the bore and it abuts at one end against a shoulder 20 of the body 15 and at the other end against a shoulder 22 of the socket 17. The spring 19 abuts against !i the other face of the shoulder 20 of the body 15 and against a ring 23 screwed onto the extremity of the socket 17. The minimum axial displacement in the direction F1 is .limited by the. shoulder 24 of the socket 17, which the t, shoulder 20 abuts against. In the direction F2 the displacement is limited by the shoulder 25 of the ring 23, S which the front part of the external body 15 abuts against. The coupling between the external body 15 and the socket 17 for rotary movement can equally be achieved by Smatching prismatic surfaces made respectively in the back part of the external body and on the socket, or abreast of ithe central bearling 28. Screws 16 arranged radially hold Sthe shank of the tool in the interior of the bore 27 in (i ,the socket 17.

i, This collet with compensation of axial displacement in two directions is, of course, only an exemplary embodiment, and modifications can be made without going outside the spirit of the invention.

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Claims

1. A collet adapted to carry a tool which is subject to both rotary and axial movement, said collet being adapted for use with a standard collet carrier, said collet comprising: an external body having a cylindrical bore, said external body having an external shape which matches the shape of the standard collet holder; a socket, movable axially within said bore, said socket being provided with means adapted to hold the tool; a limiting means, adapted to limit the axial displacement of the socket within the bore; a resiliently deformable means adapted to return the socket to a predetermined rest position; a coupling means adapted to couple the external body and the socket 1 together; wherein said coupling means are adapted to allow relative axial linear movement between the external body and socket. :a~a

2. The collet as claimed in claim 1, wherein the coupling means comprises a prismatic surface formed on part at least of the external surface of the socket, cooperating with a matching prismatic surface j formed within the bore in the external body.

3. The collet as claimed in claim 1, wherein the coupling means comprises matching toothed outlines formed respectively on part of the external surface of the socket and within the bore in the external body.

4. The collet as claimed in claim 1, wherein the coupling means Sare constituted by at least one key.

5. The collet as claimed in claim 1, wherein the coupling means comprises two matching flat surfaces formed on the external surface of the socket and on the surface of the bore in the external body.

6. The collet as claimed in claim 1, wherein the coupling means comprise one or more balls rolling in axial, inclined, or helical grooves formed in the external surface of the socket and in the bore in the external body.

7. The collet as claimed in one of claims 1 to 6, wherein the limiting means comprise, for limitation in one direction an added component arranged on the socket, and for limitation in the opposite direction an internal shoulder in the bore in the external body, cooperating with a shoulder on the socket. 10 STA/1588w i ii

8. The collet as claimed in one of claims 2 to 7, wherein the resiliently deformable means comprises two opposed means opposed to each other, to permit axial displacement of the socket in two opposite directions in relation to its predetermined rest position.

9. The collet as claimed in one of claims 1 to 8, wherein the resiliently deformable means are helical springs.

The collet as claimed in one of claims 1 to 8, wherein the resiliently deformable means are resilient washers.

11. The collet as claimed in one of claims 1 to 8, wherein the resiliently deformable means are constituted by blocks of a resiliently deformable material.

12. The collet as claimed in one of claims 1 to 11, wherein the socket is provided with radial screws for holding the cutting tool. 0

13. The collet as claimed in one of claims 1 to 12, wherein the 0 tool is a tap.

14. A collet substantially as hereinbefore described with reference to Fig. 1 or Fig. 2. oo* 006a DATED this FOURTEENTH day of JUNE 1991 PCM Nillen S.A. 0o I Patent Attorneys for the Applicant S ,0 SPRUSON FERGUSON i -11 STA/1588w