WO1998002789A1

WO1998002789A1 - Programmable steady rest

Info

Publication number: WO1998002789A1
Application number: PCT/AU1997/000445
Authority: WO
Inventors: Patrick John Mccluskey
Original assignee: Anca Pty. Ltd.
Priority date: 1996-07-16
Filing date: 1997-07-16
Publication date: 1998-01-22
Also published as: AUPO106796A0

Abstract

A programmable steady rest (1) adapted for use in conjunction with a CNC machine (2) comprises a base assembly (10), a workpiece supporting bush (4) fitted thereto and a programmable control (50) wherein the base assembly is automatically movable relative to the CNC machine in the direction of a separately programmable positioning axis (P-axis) which extends parallel to a principal programmable axis (e.g. the X-axis) of the CNC machine. The steady rest (1) may be programmed to remain stationary relative to the workpiece (5) and/or the grinding wheel (8), or to move relative to the workpiece (5) and/or grinding wheel to provide optimum support for the workpiece (5) during machining operations.

Description

PROGRAMMABLE STEADY REST This invention relates to computer numerically controlled (CNC) machine tools and in particular to a programmable steady rest for use in conjunction with such CNC machine tools. The development of multi-axes and multi-function machine tools in conjunction with the development of sophisticated computer controlled operations has facilitated the emergence of a generation of very high speed precision machine tools capable of complex multi-step operations from one machine.

Such machine tools typically hold a workpiece in a controlled position whilst a movable "cutting tool" is made to act upon the workpiece to perform the desired task. As used herein, the term "workpiece" refers to a blank or machinable element and the term "cutting tool" refers to the portion of the machine which acts on the workpiece to modify the shape or properties of the workpiece. Such cutting tools may include grinding wheels, end-mills, turning tools, laser cutting beams, plasma beams, punch tools etc.

The conventional axis nomenclature of CNC machine tools will be herein adopted by reference to the three orthogonal directions or axes (X, Y and Z) and the three rotary axes (A, B and C) as described in International Patent Application

No. WO92/22024 pertaining to the improved control of CNC machine tools which is incorporated herein by reference.

Typically a CNC machine is controlled by a computer program, called a "part program", which serially instructs the machine to perform a sequential series of discrete operations in a predetermined sequence so that the movable operative part moves along a programmed path determined by the part program. Each individual instruction is termed a "block" and may constitute a determining command for an axis or a combination of controllable axes. For example, a block may instruct a grinding wheel to move 5mm in the Y axis at a given velocity or instruct a grinding wheel to rotate and move forward 0.05 mm in the X and Y axis at a given velocity. The blocks, once programmed into the computer, are then fixed in a set sequential order. The whole set of sequential blocks may then be automatically operated by the CNC machine which then operates from start to finish of the part program.

CNC machines conventionally include a trajectory interpolator and a position controller. The trajectory interpolator produces interpolated position commands from inputs representing a feedrate specification, i.e. all the data required to determine the desired feedrate or speed along the programmed path, and high level motion commands, the machine's internal numeric representation of the data required to interpolate the machine along the desired path to the end point of the current block. The interpolation mode comprises a specification for the geometric path to be traversed by the cutting tool from the programmed start point to the programmed end point.

Once suitably programmed, such CNC machine tools can perform complex machining tasks with a high degree of accuracy and speed. However, when the machining of a workpiece requires the use of a steady rest, which is often desirable to minimise vibration and sometimes essential to prevent distortion when, for example, an elongate workpiece is being machined, the range of steady rests available for use in conjunction with CNC machine tools is very limited. In particular, the currently available steady rests are limited in their capacity to be programmed to act under computer numerical control and therefore are not capable of being integrated for co-operative interaction with a programmed CNC machine tool. Accordingly, in some situations where a steady rest is required, the full potential of a CNC machine tool is not realised as the steady rest must be manually controlled, necessitating an interruption to the automated action of the machine tool. To date, currently available steady rests fall into two categories, which are described with reference to Figures 1 and 2 of the accompanying drawings.

Figure 1 shows a workpiece support system for a CNC controlled tool and cutter grinding machine having a chuck or collet A in which one end of an elongate rotatable workpiece B is mounted, a grinding wheel C operable on the workpiece B and a "V" or halfmoon block steady rest D. The steady rest D is fixed relative to the grinding wheel C in the X-axis direction, i.e. the direction of the axis of rotation of the workpiece B and so when the grinding wheel moves relative to the workpiece B in the X-axis direction, the steady rest D moves by a corresponding distance relative to the workpiece B in the same direction. This type of steady rest is suitable for supporting the length of the workpiece when grinding flutes, but has limited flexibility for grinding the end face of the workpiece. Support is not provided when working on the end of the workpiece unless the steady is manually adjusted to a suitable position. This is time consuming and, as such, not optional in a CNC machine. Figure 2 shows another type of workpiece support system for a CNC controlled tool and cutter grinding machine having a "pop-up" steady rest E. The pop-up steady rest E is pneumatically, hydraulically or electrically driven up and down in the Z-axis direction and manually adjustable in the X-axis direction relative to the workpiece B. It is, however, required to be fixed relative to the collect A and workpiece B during actual machining operations. Thus, the pop-up steady rest E only supports the workpiece B at a fixed distance from the collet A during machining by the grinding wheel D. It does not interfere during end face grinding but can provide only limited support along the length of the workpiece during fluting operations. The main purpose of a steady rest is to protect the workpiece against vibration and deflection during grinding. The above steady rests have limitations. It is therefore desirable to provide a CNC machine tool and a method of operating a CNC machine tool wherein a numerically controlled steady-rest is movable in the direction of the X-axis to support the workpiece, regardless of whether the cutting tool is operating along the length of the workpiece or at its end, without interfering in the operation of the cutting tool.

According to a broad aspect of the invention, there is provided a programmable steady rest adapted for use in conjunction with a CNC machine, comprising a workpiece supporting means automatically movable relative to the CNC machine, and programmable control means adapted to control the position of the workpiece supporting means relative to the CNC machine.

According to another aspect of the invention, there is provided a CNC machine comprising workpiece mounting means for holding a workpiece, a cutting tool movable relative to the workpiece mounting means and operable upon a workpiece held by the workpiece mounting means, programmable control means for controlling the CNC machine, and a programmable steady rest including a workpiece supporting means which is automatically movable relative to the workpiece mounting means and the cutting tool under the control of the programmable control means. The programmable control means is preferably arranged to control the position of the workpiece supporting means in relation to at least one programmable positioning axis, herein called the P-axis, said P-axis being arranged to extend parallel to one of the existing principal programmable axes of the CNC machine.

According to a further aspect of the invention, there is provided a method of operating a CNC machine having a workpiece mounting means for holding a workpiece, a cutting tool movable relative to the workpiece mounting means for operating on the workpiece, a steady rest including workpiece supporting means for supporting the workpiece and programmable control means programmed with a plurality of principal programmable axes for controlling movement of the cutting tool relative to the workpiece, said method comprising the steps of: programming the CNC machine with at least one separately programmable positioning axis for the steady rest, said positioning axis extending substantially parallel to one of the principal programmable axes; and automatically controlling the position of the workpiece supporting means in relation to the workpiece mounting means and the cutting tool by moving the steady rest in the direction of the separately programmable positioning axis.

Preferably, the workpiece supporting means is movable in the direction of a programmable positioning axis which is arranged to extend parallel to a linear axis (herein called the X-axis) of the CNC machine. The present invention is particularly applicable to a CNC machine having workpiece mounting means in the form of a rotatable chuck or collet for holding and rotating a workpiece, and a cutting tool operable upon the workpiece, the axis of rotation of the workpiece constituting the orthogonal X-axis for the CNC machine. In a particularly preferred embodiment, the programming of the steady rest is co-ordinated and/or integrated with the primary programming of said CNC machine so that the steady rest can be automatically moved in the direction of the P-axis to compensate for the relative movement of the cutting tool and workpiece fitted to said machine whilst under the control of the primary program. The co-ordination of the steady rest may be effected by programming the steady rest to move in response to commands from the trajectory interpolator and position controller of the CNC machine. In a particularly preferred embodiment, the steady rest is programmed to move in the direction of the P-axis under closed loop control. The movement of the steady can be fully controlled and programmed to maintain an optimum distance between the cutting tool and the steady rest. The distance between the cutting tool and the steady rest can be varied in accordance with the desired task including operations performed on the end of the workpiece. The steady rest most preferably incorporates a cylindrical bush as the workpiece supporting means to provide optimum linear and rotational support.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a prior art workpiece support system; Figure 2 is a schematic diagram of another prior art workpiece support system;

Figure 3 is a section through a steady rest in accordance with the invention; Figure 4 is a plan view of the steady rest of Figure 3; Figure 5 is an end view of the steady rest of Figure 3; Figure 6 is a schematic block diagram of a control system for a programmable steady rest in accordance with the invention; and Figures 7 to 10 are side views of the steady rest at different positions during a machining cycle.

The steady rest 1 of Figures 3 to 5 comprises a base assembly 10 and a workpiece supporting means 4. The base assembly 10 is mounted on a saddle 3 which is slidably movable on a bed 2 of a CNC multi-axis grinding machine. The grinding machine includes workpiece mounting means in the form of a collet 6 in which a workpiece 5 is adapted to be mounted, a headstock 7 for feeding a workpiece 5 into the collet 6 to project therefrom, and a cutting tool in the form of a grinding wheel 8. As shown in Figure 3, the workpiece 5 is in the form of an elongate, cylindrical piece of stock, having a forward part which is fed out of the collet 6 and a rear part which is adapted to be held by the collet 6. The collet 6 is rotatable to rotate the workpiece 5 about its longitudinal control axis, hereinafter called the orthogonal X-axis of the CNC machine.

As shown in Figures 3 and 4, the workpiece supporting means is in the form of a cylindrical bush 4 having forward and rear spaced ring members 41 and 43, each having a circular opening 44 for receiving the cylindrical workpiece 5. However, the form of the workpiece supporting means may vary for different applications. It may, for instance comprise a single bush or ring member, or a V- shaped or half-moon shaped supporting block. The base assembly 10 of the steady rest includes a base plate 11 fixed to the saddle 3, and a bush mounting slide 12. The slide 12 has a lower ramp part 13 with an inclined upper ramp surface 14 and an upper slide part 15 on which the bush 4 is mounted by four socket head cap screws 16. The upper slide part 15 is mounted for sliding movement on the inclined surface 14 of the ramp part 13 by an adjustment screw 17 to allow the height of the bush 4 in the Z-axis direction to be adjusted manually. The position of the base assembly 10 on the saddle may be adjusted laterally in the Y-axis direction by two screws 39 located on the side of the saddle.

The lower ramp part 13 remote from the collet 6 is mounted on a horizontal pivot shaft 18 of the base plate 1 1 so as to be pivotally movable about a horizontal axis extending substantially perpendicularly to the axis of rotation of the workpiece 4, and an adjustable spring loaded screw 19 is provided for fixing the rear end of the lower ramp part 13 to the base plate 11. This allows the relative heights of the front and rear ends of the bush 4 to be adjusted by the adjustable screw 19. The steady rest 1 includes a target assembly 20 having a pop-up workpiece stop block 22 which is movable relative to the base assembly 10 in a substantially vertical direction perpendicular to the longitudinal axis of rotation of the workpiece. The target stop block 22 is retained in position by a keeper plate 24 secured to the front end of the upper part 15 of the bush mounting slide 12 by end screws 25, and a pneumatic target cylinder assembly 26 is provided below the keeper plate 24. An actuator rod 28 connected to the piston of the pneumatic target cylinder assembly 26 extends vertically upwards out of the cylinder to engage the lower end of the target stop block 22 for raising or lowering the target stop block 22.

The target stop block 22 is raised at the start of each machining cycle so that the front end of the workpiece 5 which is fed out of the collet 6 contacts the target stop block 22 to set the position of the end of the workpiece 5 relative to the collect 6 for subsequent machining. The target stop block 22 preferably has an indent for receiving the front end of the workpiece to assist in more accurate setting of the position of the end of the workpiece 5. The saddle 3 includes a saddle plate 30 on which the base plate 11 of the steady rest is mounted, and downwardly extending limbs 31 received in longitudinal guide channels between guide rails 32 and a central section 33 of the bed 2.

The saddle 3 is automatically movable in a horizontal P-axis direction parallel to the X-axis of rotation of the workpiece 4 under the control of the CNC machine by a rotatable screw 34 extending through an internally screw-threaded downward extension 35 of the saddle and journalled for rotation in front and rear end bearings 36 provided at the front and rear of the bed 2 of the CNC machine. The screw 34 is rotated by a belt 37 extending around a pulley 38 at its rear end connected to an electric servo motor 40, called the P-axis motor. The programmable control means 50 for controlling movement of the grinding wheel 8 relative to the workpiece 5 and for controlling the movement of the saddle 3 and steady rest 1 mounted thereon in the P-axis direction relative to the bed 2 of the CNC machine is shown in Figure 6. The programmable control means 50 includes a part program 52 which defines a programmed path for the grinding wheel 8, a part program interpolator 54, a trajectory interpolator 56 and a servo position controller 58. The programmable control means 50 also includes, or is connected to, input means 51, for inputting data. The trajectory interpolator 56 receives path input signals 55 representing the programmed path from the part program interpolator 54, and steady rest position input signals 59 representing the required position of the steady rest 1 for each position of the programmed path of the grinding wheel 8. The trajectory interpolator 56 processes these input signals to generate interpolated motion command signals 61.

The servo position controller 58 is connected to an X-axis servo control drive 62 for controlling an X-axis motor 60 that causes movement of the grinding wheel 8 in the X-axis direction relative to the workpiece 5 mounted in the collet 6. This controlled relative movement may be achieved either by moving the grinding wheel 8 with respect to a fixed collet or by moving the collet with respect to the grinding wheel 8 which is fixed relative to the X-axis. Alternatively, both the grinding wheel 8 and collet 6 may be movable in the X-axis direction with the servo controller 58 co-ordinating the movements of both parts in accordance with interpolated trajectory commands from the trajectory interpolator 56.

The servo position controller 58 may also be connected to Y-axis and Z-axis servo control devices (not shown) for controlling Y-axis and Z-axis motors that can cause relative movement between the grinding wheel 8 and the workpiece 5 mounted in the collet 6 in the Y-axis and Z-axis directions respectively. Also, if movement of the grinding wheel is controllable relative to one or more rotary axes, the servo position controller 58 may be connected to one or more rotary axis servo control drives (not shown).

As shown in Figure 6, the servo position controller 58 is independently connected to a P-axis servo control drive 42 for controlling the P-axis motor 40 for the steady rest 1. The P-axis motor 40, and thus the position of the bush 4 of the steady rest 1 in the P-axis direction is therefore controllable independently from, but concurrently with, the X-axis motor 60. The bush 4 of the steady rest 1 is preferably programmed to move in the direction of the P-axis under closed loop control, and a position/velocity transducer 46 is provided which senses the position of the steady rest 1 relative to the CNC machine and provides feedback signals to the P-axis servo control drive 42. The programmable control of the position of the steady rest 1 in the direction of the P-axis which is parallel to the X-axis of the CNC machine provides several advantages over conventional steadys. For instance, during one part of a machining cycle, when the grinding wheel 8 moves longitudinally relative to the workpiece in the X-axis direction to machine flutes of a drill bit, the position of the supporting bush 4 of the steady rest 1 may be synchronised to move in the P-axis direction with the grinding wheel 8 to provide maximum support for the part of the workpiece 5 being machined. During another part of the machining cycle when the grinding wheel 8 is required to operate on the end of the workpiece 5, the bush 4 of the steady rest 1 may be automatically moved to a position close to the end of the workpiece and maintained in that position stationary relative to the workpiece as the grinding wheel 8 operates on the end of the workpiece 5. The steady rest can thus be programmed to stay stationary relative to the grinding wheel and/or the collet 6, or to be positioned independently of the grinding wheel position.

In the set up and operation of the programmable steady rest, various parameters may be used by the programmable control means 50 to control movement of the steady rest 1 in the P-axis direction, including: blank length, a, being the total length of the workpiece 5; bush length, b, being the distance from the rear end 43 to the front end 41 of the bush 4; bush clearance, c, being the distance between the front end of the collet 6 and the rear end of the bush; overhang length, d, being the length of workpiece 5 which extends forwardly out of the collet 6 during machining by a cutting tool; minimum overhang length, e; and target indent parameter, f. Target indent parameter The depth of the indent on the pop up workpiece stop block 22 is used in the loading operation. This parameter is important as it sets the end of workpiece position for grinding if end of workpiece digitising is not selected.

The use of a programmable steady of the invention allows other aspects of a CNC machine tool to operate to full potential. For example, the automated loading and unloading of workpieces can be fully utilised without the steady interfering with such operations. Figures 7 to 10 show different positions of the steady rest during an automatic cycle of the CNC machine.

Figure 7 shows the initial loading phase with the steady rest in a position defining a minimum overhang, e, for the workpiece 5 which is loaded through the headstock 7 and collet 6 until it hits the target stop block 22. The minimum overhang, e, is equal to the bush length, b, plus the bush clearance, c. It is important to define a minimum overhang and bush clearance to ensure that in automatic operation of the CNC machine, the movable workpiece supporting bush

4 does not collide with the collet 6. After setting the minimum overhang, e, the steady rest 1 moves into the defined position for the correct workpiece length as shown in Figure 8. The workpiece 5 is then advanced until its forward end hits the target stop block 22.

The target stop block 22 is then moved downwards and the workpiece 5 is clamped by the collet 6 for rotation during a machining operation in which the grinding wheel 8 operates on the forward end part of the workpiece 5 which is supported by the bush 4 of the steady rest. During machining, the steady rest 1 is programmed to move in the P-axis direction relative to the collet 6 and the grinding wheel 8 to provide optimum linear and rotational support for the workpiece 5. For instance, during a fluting operation in which the grinding wheel 8 moves in the X-axis direction to grind flutes in the cylindrical surface of the workpiece 5, the steady rest 1 may be programmed so that the bush 4 is synchronised to move with the grinding wheel 8 relative to the collet 6 and workpiece 5. However, when the grinding wheel 8 operates on the forward end of the workpiece 5, the steady rest 1 may be programmed so that the bush 4 remains stationary relative to the collet 6 and workpiece 5 to support the workpiece 5 at a position close to its end without interfering with operation of the grinding wheel 8.

After grinding has finished, the steady rest moves into the position shown in Figure 9 for automatic removal of the workpiece 5 by a gripper 70. The gripper 70 is arranged to move over the workpiece 5 from a lateral position and has a pair of gripper jaws 72 operable to grip the finished workpiece 5 at a position along its length between the collet 6 and the bush 4. The following additional parameters may be used to program the movement of the bush 4 into the position of Figure 9; gripper length, g, being the length of the gripper jaws 72; gripper clearance, h, being the required clearance between the front end of the collet 6 and the rear end of the gripper jaws 72; and bush/gripper clearance, i, being the required clearance between the front end of the gripper jaws 72 and the rear end of the bush 4.

When the workpiece 5 has been gripped by the gripper jaws 72, the steady rest 1 and collet 6 move automatically into retracted positions as shown in Figure 10 to allow the gripper 70 to remove the finished workpiece 5. The retracted positions of the collet 6 and bush 4 may be defined by a gripper overhang parameter, j, and a tool clearance parameter, k, in addition to the gripper clearance, h.

The present invention provides several advantages over the current art, including: a) Programmable control of physical location of a steady rest relative to position of workpiece. That is, the steady rest moves in response to trajectory interpolator and position controller of grinding wheel. b) The physical location of steady rest does not interfere with operation of grinding wheel. c) The steady rest can support the workpiece both along its length and at its end point as required. d) The steady rest comprises a base assembly and interchangeable bush components for use with a wide range of workpieces, increasing flexibility. e) The steady rest may also act as a stop for positioning the workpiece. f) The independently programmable positioning axis (P-axis) allows for optimal positioning of the support point for any operation.

It will be appreciated that various modifications and alterations may be made to the preferred embodiment described above without departing from the scope and spirit of the present invention. For instance, different sizes and shapes of workpiece supporting means may be provided for different applications.

Claims

1. A programmable steady rest for use in conjunction with a CNC machine comprising a workpiece supporting means automatically movable relative to the CNC machine, and programmable control means adapted to control the position of the workpiece supporting means relative to the CNC machine.

2. A programmable steady rest according to claim 1 wherein the programmable control means controls the position of workpiece supporting means in relation to at least one programmable positioning axis, said programmable positioning axis being arranged to extend parallel to one of the existing principal programmable axes of the CNC machine.

3. A programmable steady rest according to claim 1 or claim 2 wherein the workpiece supporting means is movable in the direction of a programmable positioning axis which is arranged to extend parallel to a linear axis (herein called the X-axis) of the CNC machine.

4. A programmable steady rest according to claim 2 or claim 3 wherein the workpiece supporting means is mounted on a base assembly which is guided for longitudinal movement in the direction of the programmable positioning axis.

5. A CNC machine comprising workpiece mounting means for holding a workpiece, a cutting tool movable relative to the workpiece mounting means and operable upon a workpiece held by the workpiece mounting means programmable control means for controlling the CNC machine, and a programmable steady rest including a workpiece supporting means which is automatically movable relative to the workpiece mounting means and the cutting tool under the control of the programmable control means.

6. A CNC machine according to claim 5 wherein the programmable control means is programmed with a plurality of principal programmable axes and controls movement of the cutting tool relative to the workpiece mounting means in relation to the principal programmable axes, and the position of the workpiece supporting means is controlled by the programmable control means in relation to at least one programmable positioning axis, said programmable positioning axis extending parallel to one of the principal programmable axes of the CNC machine.

7. A CNC machine according to claim 5 or claim 6 wherein the workpiece supporting means is movable in the direction of a programmable positioning axis (P-axis) which extends parallel to a linear axis (herein called the X-axis) of the CNC machine.

8. A CNC machine according to claim 7 including X-axis drive means for causing relative movement of the cutting tool relative the workpiece mounting means in relation to the X-axis, and independently operable P-axis drive means for moving the workpiece supporting means of the steady rest in relation to the programmable positioning axis (P-axis).

9. A CNC machine according to claim 8 wherein the X-axis drive means and the P-axis drive means are controlled by the programmable control means of the CNC machine.

10. A CNC machine according to claim 9 wherein the programmable control means includes a trajectory interpolator for generating interpolated motion command signals for the X-axis drive means and for the P-axis drive means.

11. A CNC machine according to claim 10 wherein the trajectory interpolator generates the interpolated motion command signals in response to path input signals representing a programmed path for the cutting tool, tool data input signals representing the required speed of movement of the cutting tool along the programmed path, and steady rest position input signals representing the required position of the steady rest for each position of the cutting tool on its programmed path.

12. A CNC machine according to claim 11 further including input means for inputting the steady rest position input signals to the programmable control means.

13. A CNC machine according to any one of claims 10 to 12 wherein the programmable control means includes a position controller for passing the interpolated motion command signals from the trajectory interpolator to the X-axis drive means and to the P-axis drive means.

14. A CNC machine according to any one of claims 6 to 13 wherein the workpiece supporting means is mounted on a base assembly which is guided for longitudinal movement in the direction of the programmable positioning axis (P- axis).

15. A CNC machine according to any one of claims 5 to 13 wherein the workpiece mounting means is adapted to hold and rotate a workpiece and the workpiece supporting means is mounted on a base assembly which is guided for longitudinal movement in a direction parallel to the axis of rotation of the workpiece.

16. A CNC machine according to claim 14 or claim 15 wherein the base assembly is guided for movement relative to a bed of the CNC machine under the control of a steady rest control motor.

17. A CNC machine according to any one of claims 14 to 16 wherein the steady rest includes a target member for defining the end of a workpiece mounted in and extending forwardly from the workpiece mounting means.

18. A CNC machine according to claim 17 wherein the target member is movable relative to the base assembly and the workpiece supporting means in a substantially peφendicular direction relative to the longitudinal direction of movement of the base assembly.

19. A CNC machine according to any one of claims 5 to 18 wherein the workpiece supporting means comprises a substantially cylindrical bush for receiving a workpiece of substantially cylindrical cross-section.

20. A method of operating a CNC machine having a workpiece mounting means for holding a workpiece, a cutting tool movable relative to the workpiece mounting means for operating on the workpiece, a steady rest including workpiece supporting means for supporting the workpiece, and programmable control means programmed with a plurality of principal programmable axes for controlling movement of the cutting tool relative to the workpiece, said method comprising the steps of: programming the CNC machine with at least one separately programmable positioning axis for the steady rest, said positioning axis extending substantially parallel to one of the principal programmable axes; and automatically controlling the position of the workpiece supporting means in relation to the workpiece mounting means and the cutting tool by moving the steady rest in the direction of the separately programmable positioning axis.

21. A method according to claim 20, wherein the programmable control means is programmed with a programmed path for the cutting tool, and the method includes the step of inputting steady position input signals representing positions of the steady rest for different positions of the cutting tool on its programmed path.

22. A method according to claim 21 including the step of inteφolating the steady position input signals with programmed path signals and cutting tool feed- rate specification signals to produce inteφolated motion command signals for controlling the position of the workpiece supporting means.

23. A method according to any one of claims 20 to 22 wherein the steady rest is programmed to move in the direction of the programmable positioning axis under closed loop control .

24. A method according to any one of claims 20 to 23 including the step of automatically loading a workpiece into the workpiece mounting means.

25. A method according to claim 24, wherein the step of automatically loading the workpiece includes feeding the workpiece from the workpiece mounting means until the forward end of the workpiece contacts a target of the steady rest.

26. A method according to any one of claims 20 to 25, including the step of automatically removing the workpiece after the cutting tool has operated on the workpiece.

27. A method according to claim 26, wherein the step of automatically removing the workpiece includes using a gripper to grip the workpiece, automatically retracting the workpiece mounting means and the workpiece supporting means from engagement with the workpiece, and moving the gripper and workpiece away from the workpiece mounting means and workpiece supporting means.

28. A method according to any one of claims 20 to 27 wherein the position of the steady rest is controlled in accordance with any one or more of the following parameters: length of workpiece; overhang of workpiece; length of workpiece supporting means; clearance between the workpiece supporting means and the workpiece mounting means; target parameters; and gripper parameters.