GB2181373A - Support assembly for use in machining - Google Patents

Abstract

A body 12, preferably annular, has radial apertures in which threaded inserts 20 are displaceable and lockable with desired extends of projection by lock nuts 32. The projecting inserts 20 provide supports for workpieces, e.g. against the deforming tendency of gripping jaws, and can be used in place of a range of spacer rings and for skimming soft jaws. With an annular body 12, the inserts 20 can project into the central cavity to support a workpiece externally. <IMAGE>

Description

SPECIFICATION Support assembly for use in machining The present invention relates to a support assembly which may be useful in many engineering (and other) applications, particularly in connection with machining.

It is often necessary to grip an article, e.g.

to allow it to be machined. But it is often difficult to achieve a suitably firm grip without damaging the article, particularly if it is a thinwalled section. Use may be made of a support, e.g. a pad (which may be a metal ring) which is inserted into the bore of a tubular article that is to be gripped externally. But this is very inconvenient since it depends on finding or producing an accurately dimensioned pad.

An article may be gripped externally by means of soft jaws which are held in a selfcentering chuck and have been cut to size as follows. The jaws are closed until they grip a pad which is selected so that the jaws define a surface which is rather smaller than the article to be gripped. They are then machined ("skimmed") to the precise outside dimension of that article. They can then be used to grip the article, but, for a thin-walled article, they can grip only very lightly or they will still distort it. Similarly, if a hollow article is to be gripped internally, soft jaws are opened until restrained by a ring; and the external surface which they define is then machined. These operations are not ideal, and depend on a range of rings being available, so that differently sized articles can be accommodated without excessive machining of the jaws.

Another difficult problem is how to support a long tube internally at a distance from its mouth, for vibration and fall are hard to control. Conventionally, it is particularly difficult to provide a reliable support in a tube on an axis which has a controlled eccentricity.

Some or all of these problems may be ameliorated by means of embodiments of the present invention.

A support assembly according to the invention may comprise a body having a plurality of radially extending apertures and a plurality of inserts which are at least partly receivable in respective apertures so as to project from them to a degree which is variable. The body has a surface comprising portions defining a cylinder and a multiplicity of portions defining nut abutment faces (generally flats) in which the apertures open. The portions defining a cylinder desirably facilitate gripping the assembly, e.g. with soft jaws. This is useful for adjusting and setting the assembly. Furthermore, a body which is largely cylindrical tends to be easier to produce than one that is, for example, basically polygonal.Thus while there might be, for example, a cylindrical surface portion axially adjacent a flat-providing portion, there is more preferably a cylindrical surface interrupted by the flat-providing portions, which preferably occupy only a minor proportion.

Projecting end portions of the inserts may provide support surfaces. The inserts and apertures may have corresponding threads to permit the variation. The thread in the aperture may be provided by the body or by a nut which is rotatably mounted in the body, with its threaded aperture in line with the body's aperture, so that rotation of the nut acts to vary the degree of projection of the insert.

There are preferably means, such as locknuts, for locking the inserts.

The inserts may be engageable in the apertures so as to project radially outwardly from the body.

The surface may be an exterior, generally convex surface or an interior face. The body may have surfaces of both types. Thus it may have a central cavity, and the inserts may be engageable in the apertures so as to project radially inwardly into it. Preferably the body is annular and the apertures pass right through it, so that inserts can project selectively either inwardly or outwardly (or both). Preferably the body has three or four apertures symmetrically arranged so as to correspond to the jaws of conventional chucks. There may be a larger number of apertures, arranged so that, for example, symmetrical groups of three or four can be selected.

In other aspects the invention provides a method of gripping an article by means of such a support assembly, and a method of machining an article which is so gripped.

Some embodiments of the invention will now be described in greater detail with reference to the accompanying drawings in which: Fig. 1 is a front elevation of a first embodiment of a support assembly according to the invention, arranged for supporting a tubular workpiece internally; Fig. 2 shows an embodiment similar to that of Fig. 1, but in use to support a workpiece externally; Figs. 3 and 4 are views similar to Figs. 1 and 2 respectively but showing an embodiment with three apertures and inserts; Fig. 5 is a diagram for illustrating a large number of alternative designs for inserts and lock-nuts; Fig. 6 is a side elevation of the assembly shown in Fig. 1 including a central location piece; Figs. 7 and 8 are front and side elevations of the central location piece shown in Fig. 6; Fig. 9 is an elevation of a setting fixture; Fig. 10 is an elevation of a body distance piece; and Fig. 11 is a front elevation of an adjusting nut.

In the drawings, corresponding elements of different embodiments are referred to by the same reference numbers.

Referring first to Fig. 1, the support assembly 10 has an annular body 12, suitably of steel. The inner and outer radial surfaces 14,16 are generally cylindrical. Four apertures 18 pass through the body 12 radially, in a symmetrical array. Each aperture is threaded, and receives a correspondingly threaded insert 20. Where each aperture 18 opens into the inner surface 14, there is a slot 22. At the outer surface 16 there is a flat 24 (seen more clearly in Fig. 2) surrounding each aperture.

Each insert 20 has a threaded shank 26 and an enlarged head 28 at one end. (Fig. 1 shows a number of different head types. In practice, a set of identical inserts 20 would normally be used, with heads suitable for the intended use.) At the other end 30, the shank is tapered, the apical angle being slightly less than 360/n degrees, where n is the number of inserts 20. In Fig. 1, n = 4, so the angle is slightly under 900. This is to allow the inserts 20 to be screwed in as far as possible, with their ends 30 fitting together as shown.

In this configuration the inserts 20 are screwed inwardly as far as they can go, with their heads 28 sandwiching lock-nuts 32 against the flats 24. Thus the four heads 28 define a convex support surface S of the minimum dimension achievable with this particular assembly. In order to define a larger surface S, the inserts are unscrewed to the necessary degree, and locked in place by means of the nuts 32 (which are screwed down against the flats 24). The maximum size of surface S achievable with the assembly is attained when the four inserts 20 are screwed outwardly until the amount of the threaded shanks 26 remaining in the apertures 18 is the minimum for reliable engagement. But a still larger surface S can be achieved by then exchanging them for inserts 20 with longer shanks 26. A plurality of sets of shanks 26 can be provided, such that a large range of sizes can be achieved.The sets are dimensioned so that there is no gap between them. That is, the maximum dimension achievable with one set is the same as, or slightly greater than, the minimum dimension achievable with the next set.

Fig. 2 shows a similar assembly, but with the inserts 20 reversed in order to grip a workpiece W which passes into the central cavity of the body 12. The figure shows the maximum size of workpiece W that can be gripped. The slots 22 are provided so that this size is equal to the size of the cylindrical surface 14, less a tolerance. Of course, a simpler body 12 could be produced without such slots 22 if the loss of maximum size of workpiece did not matter (e.g. if it were only intended for use in the mode shown in Fig. 1; in which case the body 12 could be substantially solid, rather than annular). The inserts 20 shown in Fig. 2 differ from those shown in Fig. 1 in that the ends 30 remote from the heads 28 have formations 34 engageable by implements (e.g. screwdrivers or Allen keys).

Figs. 3 and 4 show a further embodiment in which the body 12 has three apertures 18 arranged at 1200 intervals. Otherwise the assemblies are very similar to those of Figs. 1 and 2. They are shown supporting three-jaw self-centering chucks J, internally (Fig. 3) and externally (Fig. 4).

Fig. 5 shows some of the alternative forms for the ends of inserts 20 and the lock-nut 32. Figs. 5a to 5q show ends of inserts 20.

The ends of Figs. 5a to 5i and 5k are intended for providing support surfaces. It will generally be desirable for the supporting or gripping end to be profiled such that the surface to be supported does not touch the outer edge of the insert. Thus, 5a and 5c show hexagonal heads 28 which are radiused, completely in the case of Fig. 5a, and on a stub 42 in Fig. 5c. Fig. 5d shows how a head 28 can be machined with a step 44 for location at an edge of a workpiece. Figs. 5i,j and k show internal ends 30, for coming together as shown in Fig. 1. Usually the conical form of Fig. 5j is preferred, though 5i and 5k have the advantage of being usable also as support surfaces as mentioned above.Figs. 51 to 5q show alternative driving formations 34 for the external end 30 of an insert remote from the head (i.e. in use as in Fig. 2 or 4). They show, respectively, a cavity for a hexagonal key drive; a cavity for a slot drive; flats for a spanner; transverse apertures for receiving a tommy bar; openings for a C-spanner; and a spline drive.

The lock-nuts 32 shown in Figs. Sx,y and z are respectively; a lock-nut with a knurled outer diameter, intended to be tightened by hand; a castle-shaped outer diameter for engagement by a special spanner when only limited spanner movement is possible; and a standard hexagonal lock-nut.

Fig. 6 is a side view of the assembly shown in Fig. 1, including a central location piece 40 which is shown in more detail in Figs. 7 and 8. This has the form of a disc. One face has a central locating aperture 46 adapted to accept the centre of a machine tool. The other face has a plurality of radial channels 100 corresponding to a set of apertures 18 of a body 12. Thus in this example there are four channels 100 at 900 intervals. Centrally there is a recess 102. This is surrounded by an annular projection 104 (interrupted by the channels 100) whose radially outer surface is a sliding fit within the internal surface 14 of the body (into which it extends only a short way, so as not to interfere with the inserts 20). The outer sector portions 44 then lie flat against an end face of the body 12. The locating aperture 46 is thus located concentrically with the body 12 (which will in turn be concentric with the article being supported, if the inserts 20 are symmetrically arranged. Alternatively, the article may be eccentric to a predetermined degree.).

There may be apertures 106 in the sector portions corresponding with threaded apertures in an end face of the body 12 so that the location piece 40 can be secured to a body 12 by screws 108.

Many different forms of location piece are possible. The channels 100 and/or recess 102 are not always necessary, but are desirable when the piece might otherwise foul or impede adjustment of inserts 20, particularly inserts with large heads and/or locking nuts when these are within the internal cavity of the body 12 (note the head visible in the centre of Fig. 6, in relation to the recess 102). Variants include: a location piece which locates only by means of a central projection; and a location piece with one or more projecting dowels to locate in apertures in a body instead of or in addition to the central projection 104 and/or the screw apertures 106.

Location pieces are not the only axial attachment pieces. Thus there may be setting fixtures for providing support for adjustment of the assembly; and body distance pieces.

These may have formations for coupling to a body in the same manner as a location piece.

Thus Fig. 9 shows a setting fixture 110 having two engagement faces 112,114 each of which has similar formations to the body engaging face of the location piece 40 shown in Figs. 6 to 8. They are of different sizes to accommodate different bodies. The face 112 shown uppermost is provided on a raised portion, the outer margin 116 being lower so that it is not fouled by the heads of inserts projecting radially beyond a body mounted thereon. This outer margin, which projects beyond a body mounted thereon, has marks corresponding to the angular distribution of the clamping apertures.When a body is mounted on one face 112 or 114, the assembly may stand on a level surface, perhaps steadied by bars (parallels) placed beneath it to counteract any tendency to rock owing to the central projection. (Of course, a simpler setting fixture with only a single engagement face could be planar beneath.) Fig. 10 shows an example of a body distance piece 120. Two coaxial attachment portions 122 each resemble a central location piece, having formations for engaging bodies: in this example, a central projection 124 and screw apertures 126. The portions 122 are spaced by a neck portion 128. This could be a simple surface on which the roller bearing of a machine tool's steady could run. However the distance piece 120 incorporates a rotatable bearing sleeve 130, engageable by a steady that uses stationary friction pads.

Use of a body distance piece coupled to two bodies enables steadies to be used with workpieces which would not normally be suitable. For example, an eccentric workpiece can be steadied by adjusting the inserts 20 of the bodies so that the distance piece runs smoothly and concentrically.

Now that a range of components have been described, some uses will be explained.

If a tubular article is to be gripped by jaws, a support assembly embodying the invention can be used to counter the tendency to distortion. Thus if the article is to be gripped externally by four jaws, an assembly as shown in Fig. 1 may be provided within the article. Provided it is correctly mounted within the bore of the article, with the inserts 20 in line with the jaws, the risk of distortion of the article is minimised. Similarly, distortion due to four jaws urged radially outwardly against the interior of a tubular article can be minimised using an assembly as shown in Fig. 2. Figs. 3 and 4 show assemblies that can be used similarly with chucks using three jaws. The article can then be machined. Since the assembly can be accurately centred and made symmetrical about the axis, rotation of the article by the chuck can proceed smoothly.It may no longer be necessary to machine soft jaws after over-adjusting them against a spacer ring. It is enough to place a support assembly where required, and then close or open the jaws until they abut the article. In any case, the assembly can replace a whole range of spacer rings to great advantage. Since it is axially short, jaws that are gripping it can be machined over a substantial proportion of their gripping surfaces, thus producing stepped jaws suitable for supporting an article adjacent an axial end thereof, with the step abutting the end face of the article.

For concentric machining of a tubular article, an assembly including a locating abutment piece 40 may be used. (Fig. 6 shows such a piece 40 in an assembly otherwise as shown in Fig. 1, though of course it could equally well be applied to any of the other assemblies.) The inserts 20 are screwed to produce the required dimension of supporting surface, and locked in place by the lock-nuts 32, which locate firmly and stably owing to the flats 24. Fine adjustments can be made to individual inserts to ensure that the assembly can be mounted within an article with the locating aperture 40 symmetrical about the centre line of a machine tool. This aperture can accept the centre usually associated with the machine tool, so that the article is supported thereby. Thus the functions of the machine tool centre are transmitted to the assembly.In effect, the body 12 serves to couple the inserts (and hence the support surface) to the central location piece 40 (and hence the machine tool centre). Once the assembly is mounted in an article, many operations can be performed on the article.

For some purposes a step may be machined on the head 28 of each insert 20 (c.f. Fig.

So), to correspond to a dimension that is to be given to the article. Such stepped heads 28 are particularly useful for supporting a heavy tube, since large forces can then be applied to its axial end face (without any risk of the support assembly being pushed along the tube) whereas radially only light, non-distorting forces are needed.

It is almost equally easy to provide eccentric support, merely by screwing different inserts 20 in or out to different extents. Variation of the eccentricity is easily achieved.

A modification for facilitating accurate adjustment of the inserts will now be described with reference to Figs. 1,6 and 11. As shown for the aperture 18 at the 6 o'clock position in Fig. 1, a slot 50 extends axially right through the body, symmetrically about the aperture 18, which in this case is not threaded. An adjusting nut 52 (Fig. 11) is insertable into the slot 50 with its threaded bore in line with the aperture 18 to receive an insert 20. The nut 52 has a knurled edge surface 54 which is accessible through the mouths of the slot 50 so that the nut 52 can be manually rotated to drive the insert 20 radially in either direction. It carries a scale 56 which can be read off against a reference on onthe body. Since the threads of the nut 52 and insert 20 are known, the scale 56 allows minute adjustments to be made accurately.After adjustment the lock-nut 32 is tightened, so that in use forces are not taken up by the adjusting nut 52, which might otherwise be deformed and made less accurate. Of course, all of the inserts may be provided with adjusting nuts 52 in this way. The radial apertures 18 of a body 12 for use with adjusting nuts 52 should not themselves have threads that engage the inserts. A body may have apertures, possibly of increased diameter, that can receive removable sleeves which provide internal threads (or smooth bores) when required. The 'sleeves' may be helical coils which provide external threads for engaging apertures, and internally may provide corresponding threads or be machined smooth. Sleeves may have formations engageable by tools whereby they can be screwed into and out of apertures.

For adjusting inserts 20 in either type of body, the assembly may be mounted in a jig, e.g. gripped by (preferably soft) jaws engaging its external cylindrical surface. It is then rotated so that the inserts 20 sweep past a dial test indicator to ensure concentricity (or a desired eccentricity). The diameter of the support surface they define can be checked with a micrometer. In place of jig mounting, the assembly may be mounted to a setting fixture 110, e.g. as shown in Fig. 9.

It will be appreciated that the foregoing embodiments are described only by way of example, and much variation is possible in the application of the invention. For example, a body 10 could have a different number of apertures 18. For example, there could be six apertures, arranged as if Fig. 3 were superimposed on Fig. 1, so that the same body could be provided with either four or three inserts 20 in the configuration of Fig. 1 or of Fig. 3.

Another configuration that may be useful is six apertures at 0,60,120,180,240 and 3000.

Claims (32)

1. A support assembly for use in machining comprising: (a) a body having a surface comprising portions defining a cylinder and a multiplicity of portions defining nut abutment faces; and a multiplicity of radially extending apertures opening in the nut abutment faces; (b) a multiplicity of threaded elongate inserts engageable in respective apertures so as to project from them to a degree which is variable, each insert having a workpiece engagement end portion; and (c) lock-nuts threadedly engageable on respective inserts so as to be lockable against respective nut abutment faces to which they are complementary.

2. A support assembly according to claim 1 wherein the body has a said surface such that cylinder portions and nut abutment face portions alternate.

3. A support assembly according to claim 1 or 2 wherein the nut abutment faces are flats, and the locknuts have flat faces for abutting them.

4. A support assembly according to any preceding claim wherein said surface is an exterior convex surface.

5. A support assembly according to claim 4 including inserts whose workpiece engagement portions are stepped so that the assembly can support a tubular workpiece internally adjacent a mouth thereof, the lower portions of the steps extending into the mouth to provide internal support and the upstands abutting the end of the workpiece.

6. A support assembly according to any preceding claim wherein the body has a central opening into which the apertures open.

7. A support assembly according to claim 6 wherein said apertures extend fully through an annular region of the body.

8. A support assembly according to claim 7 wherein the inserts are selectively mountable with their workpiece engagement end portions in the central opening or projecting radially outside the body.

9. A support assembly according to claim 7 or 8 including a multiplicity of inserts each having a workpiece engagement end portion at one end and being tapered at the other end, such that they can be engaged in apertures with the workpiece engagement portions at the exterior; the minimum external projection of the inserts corresponding to internal engagement of the tapered ends whose tapers are mutually adapted therefor.

10. A support assembly according to any of claims 6 to 9 wherein the central opening has portions defining a cylinder interrupted by radially extending recesses whose bases comprise flats into which the apertures open, such that inserts can be located with their workpiece engagement portions extending into the opening but not projecting inwardly of the cylinder; the lock-nuts being receivable within the recesses.

11. A support assembly according to any preceding claim wherein the apertures have internal threads complementary to the threads of the inserts.

12. A support assembly according to claim 11 wherein the internal threads are provided by removable elements.

13. A support assembly according to any preceding claim wherein at least one aperture houses a rotatable nut having an internal thread complementary to an insert and coaxial with the aperture; the nut being rotatable to displace the insert radially.

14. A support assembly according to claim 13 wherein the nut is graduated to facilitate predetermined displacements.

15. A support assembly according to any preceding claim having apertures at 0,120 and 2400 and/or at 0,90,180 and 2700 or at 0,60,120,180,240 and 3000.

16. A support assembly according to any preceding claim further including an axial attachment piece, the body and the attachment piece being mutually adapted so as to be connectable in axial alignment.

17. A support assembly according to claim 16 wherein the body has a central opening and the attachment piece has projection means engageable within the opening adjacent an axial mouth thereof.

18. A support assembly according to claim 16 or 17 wherein the body and the attachment piece have alignable screw fixing holes.

19. A support assembly according to claim 16,17 or 18 wherein the body and the attachment piece have complementary dowels and dowel receiving apertures.

20. A support assembly according to any of claims 16 to 19 wherein the attachment piece has a central locating formation for engaging with a centre of a machine tool, whereby a machine tool is engageable concentrically with the attachment piece and hence with the body.

21. A support assembly according to any of claims 16 to 20 including an attachment piece which has two attachment portions at opposite axial ends of a spacer portion, whereby two axially spaced bodies can be coupled together.

22. A support assembly according to claim 21 wherein the spacer portion provides a cylindrical surface on which a roller bearing of a machine tool's steady is runnable.

23. A support assembly according to claim 21 wherein the spacer portion is provided with a rotary bearing for engagement by stationary friction pads of a machine tool's steady.

24. A support assembly according to any of claims 16 to 23 including an attachment piece which is adapted to provide support for the support assembly for adjustment thereof, the support attachment piece having means for mounting to a horizontal surface.

25. A support assembly according to claim 24 wherein the support attachment piece is mountable to a horizontal surface in two orientations in which it exposes for use different respective connection means adapted for connection to different bodies.

26. A support assembly substantially as any herein described and illustrated with reference to the accompanying drawings.

27. A method of machining in which a workpiece is supported by a method which comprises providing a support assembly according to any preceding claim, engaging a multiplicity of inserts in apertures, and adjusting their degrees of projection so that their workpiece engagement end portions define a desired surface.

28. A method according to claim 27 wherein the adjusted support assembly is used to adjust soft jaws so that they define a desired surface for engaging a workpiece.

29. A method according to claim 27 or 28 wherein the body has a central opening into which the workpiece engagement end portions project to define a desired surface.

30. A method according to any of claims 27 to 29 wherein the body is releasably coaxially coupled to an axial attachment piece having a central locating formation whereby it is engaged with a centre of a machine tool which is thus concentric with the body.

31. A method according to claim 30 wherein different inserts are given different degrees of projection so that they define an eccentric surface.

32. A method of machining substantially as any herein described and illustrated with reference to the accompanying drawings.