GB2273452A

GB2273452A - A work piece steady for a lathe

Info

Publication number: GB2273452A
Application number: GB9324791A
Authority: GB
Inventors: Stephen Higgins
Original assignee: Caragh R & D
Current assignee: Caragh R & D
Priority date: 1992-12-21
Filing date: 1993-12-02
Publication date: 1994-06-22
Also published as: IES58598B2; IES922928A2; GB9324791D0

Abstract

A work piece steady (1) for mounting on a saddle of a lathe comprises a main support member (20) which carries a support bearing (37) for slidably supporting the work piece (2). A tool carrier (45) carries a cutting tool (47), and is vertically slidable in the main support (20) under the action of a cam follower (64) and a cam member (69). The cam member is rigidly secured in the tail stock of the lathe. As the work piece steady (1) is advanced longitudinally along the lathe, the radial position of the cutting tool (47) relative to the rotational axis (13) of the work piece (2) is controlled by the action of the cam follower (64) and the cam member (69). An adjustable taper forming profile surface (76) forms a taper on the work piece (2). <IMAGE>

Description

"A work piece steady for a lathe" The present invention relates to a work piece steady for supporting a work piece during turning in a lathe.

The invention also relates to a method for turning a work piece in a lathe using the work piece steady according to the invention, and further the invention relates to a component turned according to the method using the work piece steady.

In general, it is relatively difficult to turn components from a relatively long shaft with a reasonable degree of precision and accuracy in a lathe. This is particularly so where the shaft is of relatively small diameter. The action of the cutting tool on the shaft causes the shaft to deflect, unless the cutting tool is in engagement with the shaft relatively close to the chuck. To overcome this problem, work piece steadies are provided. Such work piece steadies may be mounted on the bed of the lathe, or on the saddle of the lathe. Such steadies, in general, support the work piece at a position intermediate the chuck and the cutting tool. While such steadies undoubtedly improve the precision and accuracy with which components can be turned from a shaft, in general, the degree of precision achievable is limited.Indeed, where it is desired to turn a taper on a component, such steadies have been found to be of little assistance, particularly, where a relatively high degree of precision is required. This is largely due to the fact that it is impractical for the steady to support the shaft sufficiently close to the region where the taper is to be formed to avoid deflection of the shaft adjacent the cutting tool.

Thus, where one wishes to turn a relatively long taper, considerable deflection of the shaft can occur adjacent the cutting tool. Needless to say, this leads to considerable inaccuracy and lack of precision in the turned component.

There is therefore a need for a work steady for supporting a work piece during turning of the work piece in a lathe which overcomes this problem. There is also a need for a method for turning a work piece in a lathe, and there is a need for a component turned in a lathe using the method.

The present invention is directed towards providing such a work piece steady, a method and a component.

According to the invention there is provided a work piece steady for supporting a work piece during turning of the work piece in a lathe, the work piece steady comprising a main support member, main mounting means for mounting the main support member on the lathe saddle, work piece support means carried on the main support member engageable with the work piece for rotatably supporting the work piece, the work piece support means defining the rotational axis of the work piece, tool mounting means for mounting a cutting tool on the main support member, the tool mounting means being slidable in the main support member in a direction transversely of the rotational axis of the work piece, follower means connected to the tool mounting means, and camming means for mounting on the lathe and co-operable with the follower means for determining the turned profile of the work piece.

In one embodiment of the invention the camming means comprises an elongated cam member for rigidly mounting in the lathe, and having a longitudinally extending cam profile for, in use, extending in a direction generally parallel to the rotational axis of the work piece, the cam profile defining at least portion of the profile to which the work piece is to be turned, and means for retaining the follower means in engagement with the cam profile of the cam member.

Preferably, the cam profile of the cam profile of the cam member is variable, and the work piece support means comprises a support bearing engageable with the outer surface of the work piece, and the tool mounting means carries the cutting tool so that the cutting edge of the cutting tool engages the work piece at a distance from the support bearing not greater than lOmm.

Preferably, the distance between the cutting edge of the cutting tool and the support bearing is not greater than 5mm. Advantageously, the distance between the cutting edge of the cutting tool and the support bearing is not greater than 3mm. Preferably, the distance of the cutting edge of the cutting tool from the support bearing is approximately lmm.

In one embodiment of the invention the tool mounting means carries the tool adjacent the work piece support means on the side of the work piece support means remote from the lathe chuck.

Advantageously, the means for retaining the follower means in engagement with the cam profile of the cam member is a spring means, and preferably, a compression spring acting between the main support member and the tool mounting means.

In one embodiment of the invention the follower means comprises a cam follower and preferably, the cam follower is rotatably mounted on the tool mounting means.

In one embodiment of the invention the tool mounting means is slidable vertically in the main support means, and the cutting edge of the tool engages the work piece at substantially the top dead centre position of the work piece.

In another embodiment of the invention the support bearing is provided by a ball bearing.

Additionally, the invention provides a method for turning a work piece in a lathe using the work piece steady according to the invention with the work piece slidably engaging the work piece support means, the method comprising the step of moving the work piece steady longitudinally along the lathe parallel to the rotational axis of the work piece with the follower means in engagement with the camming means for radially positioning the cutting tool relative to the rotational axis of the work piece as the work piece steady is moved longitudinally along the lathe.

Further the invention provides a component turned in a lathe using the method according to the invention and the work piece steady according to the invention.

The invention will be more clearly understood from the following description of a preferred embodiment thereof given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a work piece steady according to the invention, Fig. 2 is an end elevational view of the work piece steady of Fig. 1, Fig. 3 is a side elevational view of portion of the work piece steady of Fig. 1, Fig. 4 is a side elevational view of the portion of Fig. 3 illustrating the work piece steady in a different position to that of Fig. 3, Fig. 5 is a sectional plan view on the line V - V of Fig. 3, Fig. 6 is a front elevational view of a lathe illustrating the work piece steady of Fig. 1 mounted thereon, Fig. 7 is a perspective view of a component according to the invention turned in the lathe using the work piece steady of Fig. 1, Fig. 8 is a perspective view of a work piece prior to turning, Figs. 9(a) to 9(d) are diagrammatic end views illustrating a cutting tool of the work piece steady of Fig. 1 in use progressively turning a work piece, and Figs. 10(a) to 10(d) are diagrammatic side elevational views illustrating a cutting tool of the work piece steady of Fig. 1 in use progressively turning a work piece.

Referring to the drawings there is illustrated a work piece steady according to the invention indicated generally by the reference numeral 1 fòr supporting a work piece 2 during turning of the work piece in a lathe 3 to form a tapered turned component 6. The component 6 is of circular cross-section having a parallel portion 7 and a tapered portion 8 extending from the parallel portion 7 which terminates in a tip 9, see Fig. 7. The component 6 may be of any suitable material, in this case the component 6 is of steel.

Since the invention relates to the steady 1 only those parts of the lathe 3 relevant to the invention will be described. Briefly, the lathe 3 comprises a bed 10, and a chuck 11 rotatably mounted in a head 12 extending upwardly from the bed, see Fig. 6. The chuck 11 defines a rotational axis 13 which extends longitudinally of the lathe, and which coincides with the rotational axis of the work piece 2. A saddle 14 on which a cutting tool would normally be mounted for turning a work piece is carried on runners 15 and a lead screw 17 which in turn are carried in the bed 10.

In the case of the present invention the steady 1 is mounted on the saddle 14 A tail stock 16 is slidable on the runners 15.

Turning now to the steady 1, the steady comprises a main support member 20 of cast iron. The main support member 20 is of C-shape and comprises a base portion 21, an upstanding member 22 extending from the base portion 21 which carries a top cross member 23. Main mounting means for mounting the main support member 20 to the saddle 14 of the lathe 3 comprises a base plate 25 secured to the base portion 21 by screws 26, and which in use extends transversely of the rotational axis 13 of the chuck 11. Holes 28 in the base plate 25 receive screws (not shown) for securing the main support member 20 to the saddle 14.

A carrier housing 30 constructed of solid steel plates 31 is secured by screws (not shown) to the top cross member 23 of the main support member 20. A stabilising bar 32 extending through the upstanding member 22 of the main support member 20 locates and secures the carrier housing 30 in position on the main support 20. A carrier bracket 35 of steel is secured to the carrier housing 30 by screws 36 carries a work piece support means, namely, a support bearing 37 which is engageable with and supports the work piece 2 to prevent deflection thereof. The support bearing 37 is a ball type bearing, having an outer shell 38 which is a press fit in a bore 39 through the carrier bracket 35.An inner shell 40 of the bearing 37 defines a bore 42 which is a relatively tight sliding fit on the outer unturned diameter of the work piece 2 so that the bearing 37 is slidable longitudinally along the work piece 2. The bore 42 of the bearing 37, in use, defines the rotational axis 13 of the chuck 11 and, in turn, the rotational axis of the work piece 2.

Tool mounting means comprising a tool carrier 45 for carrying a cutting tool 47 is slidably mounted in the carrier housing 30. A guide groove 49 extending in the carrier housing 30 vertically of the steady 1 and transversely of the rotational axis 13 of the chuck 11 slidably engages a slider member 50 mounted on the tool carrier 45. A spacer 51 connects the slider member 50 to the tool carrier 45. A pair of clamp plates 53 secured to the carrier housing 30 by screws 54 slidably retain the slider member 50 in the guide groove 49, thereby constraining the tool carrier 45 to slide in a vertical direction, transversely relative to the rotational axis 13 of the chuck 11. The cutting tool 47 is welded to the tool carrier 45 so that a cutting edge 55 of the cutting tool 47 extends radially of the work piece 2 from the work piece axis towards the top dead centre position of the work piece 2.The cutting tool 47 is carried on the tool carrier so that the distance a between the cutting edge 55 and the face 57 of the support bearing 37 is as short as possible, and in this embodiment of the invention approximately lmm to minimize deflection of the work piece 2 during turning.

A guide rod 60 extending upwardly from the slider member 50 slidably engages a locating bracket 62 mounted to the main support member 20 by a screw 61.

Spring means comprising a compression spring 63 acting between the locating bracket 62 and the slider member 50 urges the tool carrier 45 vertically downwardly and in turn the cutting edge 55 of the cutting tool 47 into engagement with the work piece.

A follower means, namely, a cam follower 64 formed by a ball type bearing is rotatably carried on a bracket 66 which is secured to the tool carrier 45 by screws 65. A screw 71 secures an inner shell (not shown) of the cam follower 64 to the bracket 66. An outer shell 67 of the cam follower 64 rollably engages a camming means, namely, a cam profile surface 68 of an elongated cam member 69 for controlling the position of the cutting tool 47 for determining the profile to be turned on work piece 2. The cam member 69 comprises a mounting end 70 which is located and rigidly secured in the tail stock 16 of the lathe 3.

A cam portion 72 which forms the camming profile surface 68 is connected to the mounting end 70 by a link portion 73. The camming portion 72 extends generally longitudinally of the lathe 3 and parallel to the rotational axis 13 of the chuck 11 and work piece 2. A retaining guide groove 74 formed in the carrier housing 30 slidably engages the camming portion 72 of the cam member 69 for preventing lateral or vertical deflection of the cam member 69. The compression spring 63 as well as urging the cutting tool 47 into engagement with the work piece 2 also acts as a retaining means for urging and retaining the cam follower 64 in engagement with the cam profile surface 68 of the cam member 69.

The cam profile surface 68 may take up any shape depending on the turned profile to which the work piece 2 is to be machined. In this embodiment of the invention the cam profile surface 68 is provided with a variable taper forming profile surface 76 formed on a pivot member 77. The pivot member 77 is pivotally connected in a recess 78 formed in the camming portion 72 by a pivot pin 79. Adjusting means for permitting the angle of the taper forming profile surface 76 relative to the cam profile surface 68 to be varied comprises an adjusting screw 80 in a threaded hole (not shown) in the camming portion 72. A free end 82 of the adjusting screw 80 engages a free end 83 of the pivot member 77 for varying the angle of the taper forming profile surface 76. A lock nut 84 on the screw 80 enables the screw 80 to be secured in position for securing the pivot member 77 with the taper forming profile surface 76 at the desired angle.

In use, a cam member 69 with the appropriate cam profile surface 68 is selected and secured in the tail stock 16 of the lathe 3. The steady 1 is secured on the saddle 14. The camming portion 72 of the cam member 69 is engaged in the guide groove 74 with the cam follower 64 in engagement with the cam profile surface 68. Where a taper is to be turned on the work piece 2 the cam member 69 is selected so that when the cam follower 64 is in engagement with the cam surface profile 68, the lowest tip 87 of the cutting edge 55 of the cutting tool 47 coincides with the minimum radius of the taper. Where the taper is to terminate in an axial point, the lowest tip 87 of the cutting edge 55 of the cutting tool 47 should coincide with the rotational axis of the work piece when the cam follower 64 is in engagement with the cam profile surface 68.On the other hand, where the minimum radius of the taper is at a radial distance from the rotational axis of the work piece 2, then the lowest tip 87 of the cutting edge 55 of the cutting tool 47 should coincide with the minimum radius of the taper when the cam follower 64 is in engagement with the cam profile surface 68. The relationship between the position of the lowest tip 87 of the cutting edge 55 of the cutting tool 47 may also be achieved by adjusting the position of the cam follower 64 on the tool carrier 45, or alternatively by adjusting the position of the cutting tool 47 on the tool carrier 45.

On the cam member 69 being secured in the tail stock 16 and in the guide groove 74, the angle of the pivot member 77 is set by the adjusting screw 80 so that the taper forming profile surface 76 is set to give the desired angle of taper to be turned on the work piece 2. Prior to mounting the steady 1 on the saddle 14 a support bearing 37 having a bore 42 corresponding to the unmachined diameter of the work piece 2 to provide a relatively tight sliding fit on the work piece 2 is mounted in the carrier bracket 35. It may be necessary to provide a number of different carrier brackets 35 with different size support bearings 37 mounted therein to accommodate different diameters of work piece shaft.

Figs. 9 and 10 diagrammatically illustrate the action of the cutting tool 47 on the work piece 2 during turning of the taper 8 on the work piece 2. The saddle 14 is advanced rapidly longitudinally along the lathe towards the chuck 11 until the cutting edge 55 of the cutting tool 47 engages an end face 88 of the work piece 2, see Fig. 10(a). The position of the tail stock 16 is adjusted for moving the cam member 69 relative to the steady 1 until the cam follower 64 engages the cam surface profile 68 adjacent the taper forming profile surface 76. In other words, the cam follower should still be on the cam surface profile 68 but just ready to move onto the taper forming profile surface 76. The appropriate longitudinal feed speed of the saddle is selected, and the saddle drive is engaged to advance the saddle 14 towards the chuck 11.

Thus, the steady is advanced towards the chuck and the cam follower 64 engages the taper forming profile surface 76 so that as the steady 1 advances towards the chuck, the cutting tool is progressively moved radially upwardly away from the rotational axis of the work piece towards the top dead centre of the work piece. The progressive radial movement of the cutting tool from the rotational axis of the work piece forms the taper as can be seen in Figs. 9 to 10 (a) to (d).

As can be seen in Figs. 9(a) and 10(a) the lowest tip 87 of the cutting edge 55 of the cutting tool 47 coincides with the rotational axis 13 of the work piece 2 while the cam follower 64 is in engagement with the cam profile surface 68. The radial distance of the lowest tip 87 of the cutting edge 55 of the cutting tool 47 from the rotational axis of the work piece progressively increases as can be seen in Figs.

9 and 10 (b) to (d) as the cam follower progresses along the taper forming profile surface 76.

Accordingly, the angle of the profile of the taper 8 formed on the work piece 2 coincides with the angle of the taper forming profile surface 76 relative to the cam profile surface 68. In other words, the included angle of the taper 8 formed on the work piece 2 is half the acute angle which the taper forming profile surface 76 makes with the cam profile 68.

When the tapered portion 8 has been formed on the work piece 2, the work piece 2 is parted off by a suitable parting tool to form the component 6.

The advantages of the invention are many. However, the most important advantage is that use of the work piece steady according to the invention permits a taper to be formed on a component with a considerable degree of accuracy. This is by virtue of the fact that the work piece is supported almost precisely adjacent the point of engagement of the cutting tool with the work piece. In this embodiment of the invention as described above the cutting edge of the cutting tool engages the work piece at a distance of only lmm from the face of the support bearing.

While the cam profile surface 68 has been described as comprising a taper forming profile surface 76, the camming profile surface 68 may be of any desired profile depending on the profile to which the component is to be machined.

While the support means for supporting the work piece has been described as comprising a particular type of support bearing, any other suitable support means may be used. Needless to say, any other suitable follower means may be provided. It is also envisaged that instead of the tool carrier being vertically slidable, the tool carrier may be horizontally slidable, in which case, the camming profile surface would be arranged to facilitate horizontal sliding of the tool carrier.

The invention is not limited to the embodiment hereinbefore described which may be varied in construction and detail.

Claims

1. A work piece steady for supporting a work piece during turning of the work piece in a lathe, the work piece steady comprising a main support member, main mounting means for mounting the main support member on the lathe saddle, work piece support means carried on the main support member engageable with the work piece for rotatably supporting the work piece, the work piece support means defining the rotational axis of the work piece, tool mounting means for mounting a cutting tool on the main support member, the tool mounting means being slidable in the main support member in a direction transversely of the rotational axis of the work piece, follower means connected to the tool mounting means, and camming means for mounting on the lathe and co-operable with the follower means for determining the turned profile of the work piece.

2. A work piece steady as claimed in Claim 1 in which the camming means comprises an elongated cam member for rigidly mounting in the lathe, and having a longitudinally extending cam profile for, in use, extending in a direction generally parallel to the rotational axis of the work piece, the cam profile defining at least portion of the profile to which the work piece is to be turned, and means for retaining the follower means in engagement with the cam profile of the cam member.

3. A work piece steady as claimed in Claim 2 in which the means for retaining the follower means in engagement with the cam profile of the cam member is a spring means.

4. A work piece steady as claimed in Claim 2 or 3 in which the means for retaining the follower means in engagement with the cam profile of the cam member is a compression spring acting between the main support member and the tool mounting means.

5. A work piece steady as claimed in any of Claims 2 to 4 in which the cam profile of the cam member is variable.

6. A work piece steady as claimed in any preceding claim in which the work piece support means comprises a support bearing engageable with the outer surface of the work piece, and the tool mounting means carries the cutting tool so that the cutting edge of the cutting tool engages the work piece at a distance from the support bearing not greater than lOmm.

7. A work piece steady as claimed in Claim 6 in which the distance between the cutting edge of the cutting tool and the support bearing is not greater than 5mm.

8. A work piece steady as claimed in Claim 7 in which the distance between the cutting edge of the cutting tool and the support bearing is not greater than 3mm.

9. A work piece steady as claimed in Claim 8 in which the distance of the cutting edge of the cutting tool from the support bearing is approximately lmm.

10. A work piece steady as claimed in any of Claims 6 to 9 in which the support bearing is provided by a ball bearing.

11. A work piece steady as claimed in any preceding claim in which the tool mounting means carries the tool adjacent the work piece support means on the side of the work piece support means remote from the lathe chuck.

12. A work piece steady as claimed in any preceding claim in which the follower means comprises a cam follower.

13. A work piece steady as claimed in any preceding claim in which the cam follower is rotatably mounted on the tool mounting means.

14. A work piece steady as claimed in any preceding claim in which the tool mounting means is slidable vertically in the main support means, and the cutting edge of the tool engages the work piece at substantially the top dead centre position of the work piece.

15. A work piece steady for supporting a work piece during turning of the work piece in a lathe, the work piece steady being substantially as described herein with reference to and as illustrated in the accompanying drawings.

16. A method for turning a work piece in a lathe using the work piece steady according to any of the preceding claims with the work piece slidably engaging the work piece support means, the method comprising the step of moving the work piece steady longitudinally along the lathe parallel to the rotational axis of the work piece with the follower means in engagement with the camming means for radially positioning the cutting tool relative to the rotational axis of the work piece as the work piece steady is moved longitudinally along the lathe.

17. A method for turning a work piece steady in a lathe, the method being substantially as described herein with reference to and as illustrated in the accompanying drawings.

18. A component turned in a lathe using the method according to Claim 14 or 15 and the work piece steady of any of Claims 1 to 13.