| CLAIMS 1 . A workpiece-holding jig for a lathe, comprising: a faceplate provided on the reverse thereof with means for attachment to a lathe shaft and on the face with a central plain bore and three sets of threaded bores extending outwardly therefrom, the bores in each set being spaced along two lines extending parallel to and equidistantly spaced from a radial line extending from the centre of the faceplate, the radial lines being spaced one from another around the central bore by 120 degrees of arc, each set being spaced from the central bore by a different distance; a first support member having a support plate presenting a support face extending normally to the faceplate and an attachment plate extending from said support plate on the opposite side from said support face, the attachment plate having two bores therethrough each alignable with a threaded hole in a respective one of the two lines of any of the three sets, whereby screws passed through the plate and into the threaded bores may secure the first support member with the plane of the support plate thereof extending at right-angles to the radial line of the set; a second support member attachable to the support plate of the first support member and extending at right-angles thereto; clamping means securable to the first support member for clamping a workpiece against said first and second support members; a centralising rod insertable into the central plain bore and shaped such that the portion of the rod projecting from the bore presents a flat face in a plane normal to the faceplate and passing through the axis of the rod, an alignment bore passing through the said portion of the rod normal to the flat face, the axis of the bore intersecting the axis of the rod, the flat face providing a reference face against which slip blocks may be temporarily positioned for locating the support members at a desired radial distance from the centre of the faceplate; and an alignment rod having a shape and size corresponding with that of the alignment bore in the centralising rod so as to be a sliding fit in said bore. 2. A workpiece-holding jig according to Claim 1 , wherein at least one keyway groove is provided extending along the support face of the first support member parallel to the surface of the faceplate, and the second support member has at least one key attached thereto, slidable in the keyway, or each slida- ble in a respective one of the keyways. 3. A workpiece-holding jig according to Claim 1 or 2, further comprising an auxiliary workpiece support securable to the second support member, the auxiliary workpiece support presenting two support surfaces extending normally to the surface of the faceplate and containing an angle between them. 4. A workpiece-holding jig according to Claim 3, wherein said angle is 90 degrees. 5. A workpiece-holding jig according to Claim 3 or 4, wherein the second support member is provided with at least one keyway groove extending parallel to the surface of the faceplate, and the auxiliary workpiece support has at least one key attached thereto, slidable in the keyway, or each slidable in a respective one of the keyways. 6. A workpiece-holding jig according to any preceding claim, wherein the threaded bores in each line in the faceplate are equally-spaced one from another. |
[0001] This invention relates to a lathe workpiece-holding jig, particularly, but not exclusively, for use in the precision machining of small components.
Background to the Invention
[0002] Conventional faceplates for lathes have been provided with a pattern of radially-extending slots for adjustable attachment of components for holding workpieces being machined. This type of arrangement is time-consuming to set up precisely, especially for small components, and has been largely superseded by lathe chucks having a plurality, typically four, of radially movable, lockable, jaws. While chucks are convenient for many applications, they can present difficulties with the accurate positioning of small and irregularly-shaped workpieces, and there is the risk of damage from the jaws marking surfaces of the work- pieces.
Summary of the Invention
[0003] The invention provides a workpiece-holding jig for a lathe, comprising: a faceplate provided on the reverse thereof with means for attachment to a lathe shaft and on the face with a central plain bore and three sets of threaded bores extending outwardly therefrom, the bores in each set being spaced along two lines extending parallel to and equidistantly spaced from a radial line extending from the centre of the faceplate, the radial lines being spaced one from another around the central bore by 120 degrees of arc, each set being spaced from the central bore by a different distance;
a first support member having a support plate presenting a support face extending normally to the faceplate and an attachment plate extending from said support plate on the opposite side from said support face, the attachment plate having two bores therethrough each alignable with a threaded hole in a respective one of the two lines of any of the three sets, whereby screws passed through the plate and into the threaded bores may secure the first support member with the plane of the support plate thereof extending at right-angles to the radial line of the set; a second support member attachable to the support plate of the first support member and extending at right-angles thereto;
clamping means securable to the first support member for clamping a workpiece against said first and second support members;
a centralising rod insertable into the central plain bore and shaped such that the portion of the rod projecting from the bore presents a flat face in a plane normal to the faceplate and passing through the axis of the rod, an alignment bore passing through the said portion of the rod normal to the flat face, the axis of the bore intersecting the axis of the rod, the flat face providing a reference face against which slip blocks may be temporarily positioned for locating the support members at a desired radial distance from the centre of the faceplate; and
an alignment rod having a shape and size corresponding with that of the alignment bore in the centralising rod so as to be a sliding fit in said bore.
[0004] Preferably, at least one keyway groove is provided extending along the support face of the first support member parallel to the surface of the faceplate, and the second support member has at least one key attached thereto, slidable in the keyway, or each slidable in a respective one of the keyways.
[0005] The jig may further comprise an auxiliary workpiece support secura- ble to the second support member, the auxiliary workpiece support presenting two support surfaces extending normally to the surface of the faceplate and containing an angle, most suitably 90 degrees, between them. The second support member is preferably provided with at least one keyway groove extending parallel to the surface of the faceplate, and the auxiliary workpiece support has at least one key attached thereto, slidable in the keyway, or each slidable in a respective one of the keyways.
[0006] The threaded bores in each line in the faceplate are preferably equally-spaced one from another, with the spacing of each set from centre suitably differing by increments of 3mm.
[0007] The jig of the invention simplifies the mechanical alignment of the workpiece in the three orthogonal directions, thereby enhancing accuracy. The time taken to set up a workpiece is substantially reduced, and this accurate setup is readily repeatable for production. The jig of the invention can handle a wide range of sizes of workpiece, from very large industrial manufacture down to the smallest model-making units, all with the same degree of accuracy. Damage to workpieces by chucks during set-up and machining is avoided.
Brief Description of the Drawings
[0008] In the drawings, which illustrate an exemplary embodiment of the invention:
[0009] Figure 1 is a plan view of the faceplate (considered flat on a horizon- tal surface before installation on the lathe, whose shaft will be horizontal);
[0010] Figures 2a, 2b and 2c are top plan views of the base portion and supporting portion of the first support member, and an end view of one of two brackets for joining the base portion to the supporting portion;
[0011] Figures 3a, 3b, and 3d are top plan views of the base portion and supporting portion of the second support member, and an end view of one of two brackets for joining the base portion to the supporting portion;
[0012] Figure 4 is an end view of the assembled second support member;
[0013] Figure 5 is a perspective view of the assembled jig with workpiece in place; and
[0014] Figures 6a and 6b are top plan and side views of a V-block attachable to the support members to facilitate the machining of cylindrical or irregularly- shaped workpieces.
Detailed Description of the Illustrated Embodiment
[0015] Referring to Figure 1 , the faceplate 1 comprises a circular steel plate having on the reverse face (not shown) means for attachment to the lathe in conventional manner. In the front face, the faceplate is provided with a central unthreaded bore 2 on the axis of rotation of the faceplate. Three sets 3, 4 and 5 of threaded bores are each arranged in two parallel lines 3a, 3b, 4a, 4b, 5a, 5b of the bores equally-spaced apart in each line. The lines in each set are parallel not only to each other, but also to a radial line from the centre, and the radial lines are each at 120 degrees of arc from the adjacent ones. The three sets are each positioned at a different distance from the centre than the other two, for example one set will commence at x mm from the centre, the next at x+3 mm and the third at x+6 mm. Additional threaded holes 6, 7 and 8 are provided along the radial lines.
[0016] The first support member 9, whose components are illustrated in Figures 2a, 2b and 2c, is L-shaped in section, with the two branches of the L-shape exactly at 90 degrees to each other. A base portion 9a, which is curved in plan, serves for fixing to the faceplate and has three elongate fixing holes 10 spaced apart by distances equal to the spacing of the threaded bores in any of the sets of bores in the faceplate. It is formed with projecting tabs 109 which are received in slots 1 10 in the rectangular, supporting, portion 9b of the first support member. The supporting portion 9b has three plain alignment holes 1 1 therethrough, on a centre line 12 of the member, six sets of attachment holes 13, three sets on each side of the centre line 12, and two rectangular section keyway grooves 14 extending along the supporting portion 9b and parallel to the base portion 9a, between the sets of attachment holes 13. The holes 13 have two functions: attachment of the second support member, as hereinafter described; and attachment of a clamp for the workpiece. The base portion 9a is also provided with a pair of rectangular slots 1 1 1 to receive a tab 1 12 projecting from a respective one of two right-angle brackets 1 13 (Figure 2c), while the supporting portion is provided with a pair of longer slots 1 14 for receiving the second tabs 1 15 projecting from the brackets 1 13. The second tabs 1 15 are provided with a cut-out 1 16 corresponding with the lower keyway groove 1 14. Assembly of the components is achieved by locating the tabs 1 12 in the slots 1 1 1 , and then mounting the base portion 9a on to the supporting portion 9b with the tabs 109 in the slots 1 10 and the bracket tabs 1 15 in the slots 1 14. The components can then be secured together by welding.
[0017] The second support member 15 is illustrated in Figures 3a, 3b, 3c and 4, and again consists of an L-shaped member in section, with the two branches of the L-shape exactly at 90 degrees to each other. A base portion 15a has three elongate slots 16 therethrough for receiving fixing screws permit- ting attachment of the second support member 15 to the first support member 9. Two rectangular slots 17 extend transversely, between the slots 16. Three smaller rectangular slots 18 are provided in the base portion 15a, extending parallel to the longer side thereof. The supporting portion 15b of the second support member is provided with two sets of two holes 19, for optional attachment of the V block, hereinafter described with reference to Figures 6a and 6b. Three tabs 300 extend from the edge of the supporting portion 15b, corresponding in size and shape with the slots 18 in the base portion 15a, and into which they are received on assembly. Two transverse slots 301 pass through the supporting portion between the holes 19 in each pair. A pair of brackets 302 (Figure 3c) are used to hold the two components 15a and 15b rigidly together, each having a longer tab 303 to be received in one of the slots 18, and a shorter tab 304 to be received in one of the transverse slots 301 . Assembly is in the same manner as for the first support member, as hereinbefore described. Fig- ure 4 illustrates an end view of the assembled second support member, from which it can be seen that the longer tabs 303 are dimensioned to project beyond the rear face of the base portion 15a, thereby permitting them to act as keys engageable in the keyways 14 on the first support member 9 so that the second support member 15 is held in accurate alignment with it as it is slid along the first support member into its desired position as hereinafter described.
[0018] Figure 5 illustrates the jig in a working configuration thereof, the first and second support members having been positioned and secured together as hereinafter described, and with a clamp 20 attached to clamp the workpiece 21 in position, ready for machining. A balance weight 22 is also attached to the faceplate 1 to balance the eccentric forces generated when the lathe is operated, due to the off-centre positioning of the jig components and workpiece.
[0019] The clamp 20 consists of a slotted block 23, one end of which bears against the workpiece, a nut and bolt 24 passing through the slot and through one of the holes 13 in the first support member 9 to urge the block 23 into en- gagement with the workpiece, while a spacing post 25 extends between the block 23 and the face of the support member 9 to ensure that the block 23 is pressed firmly and evenly on the surface of the workpiece, thereby minimising the likelihood of marking of the surface of the workpiece.
[0020] The jig is set up as follows. First, the first support member 9 is positioned so that the face of the supporting portion 9b is at the correct distance from the centre of the faceplate 1 to position the workpiece in a first orthogonal axis. This is done by locating in the central unthreaded bore 2 a centralising rod (not shown) which is a close rotating fit in the bore 2 and which is shaped such that the portion of the rod projecting from the bore presents a flat face in a plane normal to the faceplate and passing through the axis of the rod. An alignment bore passes through the projecting portion of the rod normal to the flat face, the axis of the bore intersecting the axis of the rod, and an aligning rod is passed through this bore and through one of the alignment holes 1 1 in the supporting portion 9b of the first support member 9, thus ensuring that the first support member 9 is correctly aligned with the centre of the faceplate and extends at right-angles to a radius from the centre of the faceplate. A slip block having the desired dimension for the spacing of the first support member from the centre is then interposed between the flat face of the centralising bore and the face of the first support member, beneath the aligning rod, and pressing the first support member towards the centre to hold the slip block firmly in place, it is rotated with the aligning rod about the centralising rod until the fixing holes 10 align with holes in one of the sets 3, 4 and 5 in the faceplate. Because the holes in each set are uniformly spaced apart, the three sets are displace radially one from another, and the fixing holes 10 are elongated, there will always be one position at which alignment, and hence accurate fixing, can be achieved.
[0021] The aligning rod can then be removed for the next set up stage, in which the second orthogonal positioning is achieved by locating the keys extending from the second support member, as hereinbefore described, in the keyways 14 on the face of the first support member 9, positioning a suitably- dimensioned slip block between the flat face of the centralising rod and the supporting portion 15b of the second support member. With the second support member 15 firmly pressed against the slip block, which in turn is pressed against the centralising rod, the base portion 15a of the second support mem- ber is secured to the supporting portion 9b of the first support member 9 by a suitable set screw 26, either engaged with a thread in one of the holes 13, or secured by a nut to the rear of the supporting portion 9b if the holes are unthreaded.
[0022] The workpiece 27 is then positioned against the adjacent faces of the first and second support members 9 and 15, the third orthogonal positioning of the workpiece being achieved by placing a slip block of suitable dimension between the underside of the workpiece and the faceplate. The workpiece is then clamped by locating the clamp in position and tightening the bolt 24 to hold the workpiece firmly in the desired position for machining. The balance weight 22 can be attached to the faceplate using a screw engaging one of the holes in the sets 3 to 7 to compensate for the uneven or eccentric loading of the faceplate due to the attachment of the support members and workpiece.
[0023] Referring now to Figures 6a and 6b, the V-block 30 is generally rec- tangular, but has in its front face 31 a deep V-shaped groove presenting two flat faces 32 and 33 at right-angles to each other, with a rectangular-section channel 34 at the apex of the groove. Threaded fixing holes 35 are provided in the sides 38 of the block. The fixing holes 35 are used in conjunction with a pair of holes 19 in the second support member 15 to receive screws securing the V- block to the face of the supporting portion 15b of the member. The workpiece can then be located against the faces 32 and 33 and clamped in position by means of a suitable clamp attached to the first support member 9.