GB2215648A - Engagement of accessories on machine tools - Google Patents

Abstract

A spindle holder 10 has a retractable plunger 20 for use in engaging accessories such as a coolant feed block. To allow engagement with both standard European accessories requiring 6mm retraction and other accessories requiring more, the plunger has two coaxial retractable parts: a rod 28 and a collar 30. Retraction force on the rod 28 compresses a spring 39 so the rod 28 retracts, carrying the collar 30 with it, until after 6mm of travel the latter abuts the holder body. Further retraction of the rod 28 is possible if a greater force is applied so as to compress also a spring 48 engaged between the rod 28 and the collar 30. <IMAGE>

Description

ENGAGEMENT OF ACCESSORIES ON MACHINE TOOLS The present invention relates to the engagement of accessories on machine tools. It particularly relates to machine tools having spindle holders for use with tool holding products that require outrigger support. The tools may be machining centres. It is particularly applicable to NC and CNC machine tools, and primarily (though not exclusively) to machine tools having automatic tool changing devices.

A known type of machine tool has a multiplicity of spindle holders carrying respective tools. The holders which are not in use are in an accessible store, e.g.

provided by a carousel which can be indexed to enable a desired holder to be selected and moved to the working position.

A spindle holder may be required to be engaged with an accessory, e.g. a coolant feed accessory, any of various electrically operated accessories, or any of various mechanical accessories such as angle heads, drill and tapping heads, and speed increaser and decreaser units. A widely-used mode of engagement makes use of spindle holders which have mounting plungers. A plunger may project from the front end of the body of the spindle carrier, parallel to the conical shank thereof. It may engage a connector block which has an opening in which an end portion of the accessory engages when the holder is moved #- into the engagement position. During the engagement, the travel of the accessory relative to the gauge plane of the spindle holder must be within prescribed limits.It may be required to displace the plunger so that it is released from a rotational lock relative to the spindle. A prescribed displacement may also be required to render an accessory operative, e.g. to bring a coolant supply port into communication with a coolant inlet of the spindle holder. Much apparatus employs plungers with a maximum displacement of 6mm. But this requires a spindle holder to be accurately matched to the accessory system and to the machine tool. Furthermore not all countries observe this standard. For example, in standard U.S. tools, all dimensions are in inches and do not readily convert to the metric standards. As a result of this, the cooling blocks used on U.S. equipment may not fit equipment used elsewhere; and non-U.S. cooling blocks may not fit U.S. tools.

It would be convenient to have a system that permitted wider tolerances. Furthermore, there are moves towards systems that require displacements of greater than 6mm - - The present invention provides a machine tool component such as a spindle holder having a plunger assembly which comprises a first part displaceable relative to a second part; the assembly being retractably urged in one longitudinal sense to project; and the first part being retractably urged in the same sense to project beyond the second part.

Preferably the arrangement is such that when the assembly is in a fully projecting configuration, a force causing retraction of the first part causes the second part to retract with it for a predetermined distance (e.g.

6mm); whereafter further retraction of the second part is restrained, but further retraction of the first part is permitted, preferably requiring a greater force. Thus a part of the plunger assembly can be displaceable by a standard amount (such as 6mm), whereas a greater travel is possible for a component abutting the plunger assembly.

For example, there may be first resilient means that resist retraction of the first part over its full range of movement. The second part may be coupled to the first part via a second resilient means such that, when retraction of the second part is restrained, retraction of the first part is still permitted, but against the urging of both resilient means.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side view of a spindle holder embodying the invention; Fig. 2 is an end view of the spindle holder of Fig.

1; and Figs. 3 to 5 are longitudinal sections in the plane of Fig. 1, showing the plunger assembly in different configurations.

The drawings show a spindle carrier assembly in the form of a drill chuck 10, adapted for connection to a coolant feed accessory. The chuck 10 has a tapered shank 12 at its front end, and a drill bit engaging opening 14 at the other end. It has an axis of rotation X-X, as shown in Fig. 1. A body 16 forms an eccentric collar around an intermediate portion of the chuck. It has an interior conduit (not shown) for supplying liquid coolant to the spindle. In use, the body of the chuck rotates within the body, which is stationary to enable the connection of a supply port to the conduit. In order to align the inlet of the conduit with the supply port of a cooling block, the cooling block is engaged with a location plunger assembly 20 (possibly via a location block). The plunger assembly 20 projects from the radially projecting part 18 of the body 16.This part 18 has a blind bore 22 in which the plunger assembly is mounted. The bore 22 has a uniform cylindrical crosssection, and the closed end 24 of the bore has a central conical recess 26. The plunger assembly has two principal parts: a piston 28 and a collar 30. The piston 28 has an outer cylindrical rod portion 32 and an inner body portion 34 of larger diameter such that it fits slidably and snugly within the bore 22. The inner region of the body portion 34 has a pair of axially spaced annular walls between which there is a portion 40 of reduced diameter, about which there is an annular recess 42. A lug 44 projecting from the wall of the bore delimits the possible travel of the piston. 28 by engagement with the walls 36,38.

A first compression spring 39 extends between the recess 26 in the bore and a connection to the piston 28.

The collar 30 is mounted slidably on the rod portion 32. It has a tubular portion 48 and an enlarged inner flange 50 which is stepped, with the step 52 facing away from the bore. The tubular portion 48 has an inner diameter larger than the rod portion 32, and the resulting annular space houses a compression spring 54. This is engaged between the shoulder between the tubular portion 48 and the flange 50, and a collar 56 fast with the rod portion 32. The collar 56 is dimensioned so that it can compress the spring 54 within the tubular portion 48.

The drill chuck 10 has an annular collar 58 having a radial projection 60 that extends adjacent the plunger assembly. It is spaced a predetermined distance forwardly of the body 16. As shown in Fig. 3, the forward travel of the collar 30 is limited by engagement of the projection 60 in the step 52. Travel of the collar 30 in the other direction is limited by abutment with the body 16.

Starting from the configuration shown in Fig. 3, if a component is urged against the front face of the piston rod portion 32, with sufficient force to compress the spring 39 in the bore 22, the piston 28 moves to the right in Fig. 3, carrying the collar 30 with it, past the configuration shown in Fig. 5. This continues until the collar 30 abuts the body 16, as shown in Fig. 4.

Generally it will be arranged that this corresponds to a travel of 6mm of the collar 30. The piston 28 can be moved farther to the right, though this requires compression also of the outer spring 54. In the illustrated embodiment, the piston rod 32 extends lmm forwardly of the gauge line in its fully extended configuration shown in Fig. 3; and the piston 28 may be depressed to a position llmm below the gauge line, thus providing Smm of compensating range beyond the normal 6mm of travel.

Claims (5)

CLAIMS:

1. A machine tool spindle holder assembly having a tapering shank and a mounting plunger assembly for engaging an accessory, the plunger assembly comprising a plunger projecting in the same direction as the shank and being resiliently retractable; and wherein the plunger assembly comprises first and second coaxial plunger parts mounted so as to be axially displaceable relative to each other and to the rest of the spindle holder assembly; the plunger being resiliently urged to project and the first part being adapted to project beyond the second part.

2. A spindle holder assembly according to claim 1 wherein abutment means are provided for limiting travel of the second plunger part and wherein retraction of the first plunger part relative to the rest of the spindle holder assembly is resisted by first resilient urgin#g means and retraction of the first plunger part relative to the second plunger part is resisted by second resilient urging means such that force on the first part causes both parts to retract with compression of the first resilient urging means until the second part engages said abutment means, whereafter further retraction of the first part is possible on application of a greater force sufficient to compress both the first and second resilient urging means.

3. A spindle holder assembly according to claim 2 wherein the possible retraction of the second part is substantially 6mm.

4. A spindle holder assembly according to any preceding claim wherein the first plunger part is a rod member and the second plunger part is a collar slidable on the rod member.

5. A machine tool spindle holder assembly substantially as herein described with reference to and as illustrated in the accompanying drawings.