GB2233058A

GB2233058A - Lockable nuts

Info

Publication number: GB2233058A
Application number: GB8913922A
Authority: GB
Inventors: Anthony P Wyatt
Original assignee: Crawford Collets Ltd
Current assignee: Crawford Collets Ltd
Priority date: 1989-06-16
Filing date: 1989-06-16
Publication date: 1991-01-02
Anticipated expiration: 2009-06-16
Also published as: GB8913922D0; GB2233058B

Abstract

A threaded nut 10 suitable for use as a closure nut for the retention of a collet on a machine spindle or a tool in a toolholder during a machining process has a threaded locking ring 38 capable of limited axial movement relative to the remainder of the nut 10. Pins 54 and grub screws 58 are provided on the nut for selectively axially moving the backing ring 38 so that when the nut is engaged with a complementary thread, the threads are locked together preventing the nut 10 from slipping during the machining process. The locking ring 38 is urged by a spring 40 into abutment with axially adjustable alignment pins 44, so that the threads of the locking ring 38 and the nut 10 are aligned. The spring 40 acts against an insert 42 screwed into the nut 10. <IMAGE>

Description

LOCKING NUT The invention relates to locking nuts and in particular to locking nuts in the form of closure nuts for the retention of a collet on a machine spindle or a tool in a toolholder during a machining process.

There are a variety of designs of collet closure nut in common use for the retention of a collet on a machine spindle or a tool in a tool holder, the collet in turn gripping and retaining a particular tool, often a milling cutter or extension piece. Early designs of closure nut were constructed as one piece resulting in a high percentage of the tightening torque experienced by the closure nut not being translated into an axial closing force on the collet but rather being lost in friction at a front bearing taper or collet nose.

Later designs incorporated a secondary pressure ring enabling the axial force to be maximised by relieving radial friction by the use of an intermediate roller thrust bearing race or ball bearing race. There still remains a problem with this design, however, due to the tendency of modern machine tools to operate at high rotational speeds and be provided with regenerative or induction braking. Under inertial conditions exacerbated by the use of high speeds and this type of braking system, a bearing race which has assisted in amplifying the axial closing force is counterproductive and causes the nut to loosen. Any loosening of the closure nut in this way may allow the tool to slip in the toolholder causing possible damage and the interruption of the machining process.

According to the present invention there is provided a threaded nut having a section of the thread capable of axial movement relative to the remainder of the nut, means being provided on the nut for selectively axially moving said section, so that when the nut is engaged with a complementary thread, axial movement of the threaded section locks the threads tether.

A closure nut embodying the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a closure nut on the line D-D of Figure 2.

Figure 2 is an end elevation of the closure nut of Figure 1 and; Figure 3 is a cross-sectional view of the closure nut of Figures 1 and 2 on the line C-C of Figure 2 with details of a closing ring of the nut being omitted for clarity; and The closure nut includes a body 10 of generally cylindrical shape having a bore 12, which has a central thread adapted to engage a spindle of a toolholder (not shown) having a complimentary thread. Six slots 14 are provided on the exterior surface of the body 10 parallel to the threaded bore 12 to cooperate with a C-spanner so that the closure nut may be rotated and tightened on the spindle.

As may be most clearly seen from Figure 1, one unthreaded end of the bore 12 of body 10 is provided with a groove 15 of generally semi-circular cross-section and extending around the nut in a plane normal to the axis of the bore 12. A closure ring 24 is received within this unthreaded part of the bore 12. The ring 24 has a centrally threaded bore 26 and is provided with a groove 28 on its outer surface. The groove 28 is generally of semi-circular cross-section, the groove being aligned with the bore groove 15 so as to form a race 30 to contain a plurality of ball bearings 32. The ball bearings 32 are inserted into the race 30 by means of an opening 34 in the body 10, which is subsequently sealed by means of a grub screw 36. The bearings 32 serve to retain the closure ring 24 within the bore 12 of the body portion 10 whilst allowing relative rotational movement.

The bore 12 of the closure nut is provided with a rebate of increased diameter at the end remote from the grooved end. As may be seen from Figure 1, in this rebate are received a locking ring 38, a Belleville washer 40 and an insert 42. The locking ring 38 and insert 42 are provided with threads of the same pitch and diameter as the thread of the bore 12. The insert 42 is also provided with an external thread 50 to engage the corresponding thread in the rebate, so holding the locking ring 30 and the Belville washer 40 in the rebate. A butting surface 52 provided on the insert 42 prevents any overtightening of the external thread 50 by abutting against a surface of the body 10 of the locking nut. This also ensures that the internal thread is aligned with the thread of the bore 12.

The internal thread of the locking ring 38 is held in alignment with that of bore 12 of the body portion by the action of the Belleville washer 40 and by means of three spiral pins 44 that are arranged parallel to the axis of the nut, pass through openings 46 in the locking ring 38 and are received in bores 48 within the body portion 10. The spiral pins 44 have ends that lie in a common plane normal to the axis of the nut to engage the locking ring and define the aligned position. Thus despite the fact that threads are provided separately on the body 10, the locking ring 38 and the insert 42, the assembled locking nut may be readily threaded on to a spindle of a toolholder having a complimentary thread.

The closure nut is additionally provided with three actuating pins 54 contained within openings 56 in the body portion 10 that extend parallel to the threaded bore 12. One end of each of the actuating pins 54 engages a grub screw 58 while the opposite end 60 is for engagement with the locking ring 38.

In use, the closure nut is threaded onto the spindle of a toolholder having a complimentary thread as has been previously described, and rotated until a collet is clamped firmly in position. The pins 54 are retracted using the grub screws 58, so allowing the thread on the locking ring 38 to be aligned by the spiral pins 44, the Belville washer 40. The grub screws 58 are then rotated to cause axial movement of the actuating pins 54, and so cause axial displacement of the locking ring 38 toward the insert 42 against the action of the Belleville washer 40. This axial displacement of the locking ring 38, away from the spiral pins 44, results in a temporary misalignment of the internal thread of the locking ring 38 relative to that of the bore 12 of the body 10 and the insert 42. Further rotation of the grub screws 58 in the same sense causes a temporary elastic deformation of the locking ring 38 to further the locking action of the nut, so preventing the tool from slipping when in use. After the machining process has been completed the grub screws 58 may be slackened off, allowing the locking ring 38 to resume its unstressed position, and the locking nut may then be removed by means of a C-spanner or other suitable means in engagement with the grooves 14.

Claims

1. A threaded nut having a section of the thread capable of limited axial movement relative to the remainder of the nut, means being provided on the nut for selectively axially moving said section, so that when the nut is engaged with a complementary thread, axial movement of the threaded section locks the threads together.

2. A nut in accordance with claim 1 wherein the threaded section is in the form of a threaded locking ring moveable axially between a position in which the thread thereof is in threaded alignment with the remainder of the thread and a position in which the thread locks with the complimentary thread.

3. A nut in accordance with claim 2 wherein, in said aligned position1 the locking ring is urged by spring means into engagement with an alignment member to position the locking ring.

4. A nut in accordance with claim 2, wherein the alignment member is formed by a plurality of pins extending parallel to the axis of the nut and having co-planar ends for engagement with the locking ring, the axial positions of the pins being adjustable.

5. A nut in accordance with claim 5 wherein said spring means acts between the locking ring and an insert carried by the remainder of the nut.

6. A nut according to claim 5 wherein the insert is annular and is in external threaded engagement with a rebate provided at the end of the nut.

7. A nut according to claim 6 wherein the insert is provided with an internal thread corresponding to said thread on the nut and is threadedly aligned with said nut thread by engagement of an abutment on the insert with the remainder of the nut as said external thread is engaged with the rebate thread.

8. A nut in accordance with any preceding claim wherein the means for moving the section axially is at least one actuating pin carried by the nut and having an end engagable with said section, the or each actuating pin being axially movable to move said section.

9. A nut in accordance with claim 8 wherein the or each actuating pin is moved by a grub screw engaging the actuating pin.

10. A nut in accordance with any preceding claim including a closing ring.

11. A nut substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.

12. A machine tool including a toolholder wherein a tool is retained in the toolholder by a closure nut formed by a nut in accordance with any of claims 1 to 10.