GB2079642A - Tool feed attachment for machine tools - Google Patents

Abstract

For machining slots or keyways on milling machines, or for extended machining including taper cutting of workpieces on lathes e.g. capstan lathes, a tool (24) is carried on a tool accessory attachment device (40) which includes a reciprocally-movable tool carrier (45) and an accommodating housing (41); the carrier and housing (41) include a guideway system (50) allowing linear to and fro motion to the carrier (45). The accessory device (40) incorporates an integral motor unit e.g. a double-acting ram (60) for reciprocating the carrier (45) and hence for moving the tool (24) through a cutting stroke limited by stops (72). <IMAGE>

Description

SPECIFICATION Tool accessory attachment for machine tools The present invention relates to a tool accessory fattachment for machine tools.

The turning of workpieces on a turret or capstan lathes is subject to certain limitations, amongst which are the restricted length of workpiece periphery machinable and the fineness of finish attainable. Moreover, the freedom to taper a work piece on such a lathe is limited.

Peripheral shaping and tapering can be accom plished on conventional capstan lathes by one of two methods. Firstly, a specially ground cutting tool can be mounted in a roller box secured in one of the tool holders of the capstan. Secondly, plunge cutting can be employed, using a specially shaped tool mounted on the cross slide of the lathe.

Setting up a roller box is an awkward and time-consuming trial and error process. Automatic operation of the lathe cannot continue indefinitely because tool wear necessitates frequent resetting of the roller box if dimensional tolerances are to be observed. Disappointingly poor surface finishes are common and may even prevent use of a roller box for high quality work. Poor finish is the result of tool chatter occasioned by vibration of the capstan, which is supported merely by the lathe saddle, and aggravated by the overhang of the roller box from the capstan. If one merely wished to machine a workpiece exterior to an elongated right-cylindrical form, this can be accomplished with a roller box by appropriately feeding the capstan along the lathe turning axis. However, the problem of surface finish would remain.Generally, it is difficult with a roller box to secure dimensional accuracies better than + 1 to 2 thou (0.025 - 0.051 mm).

Better accuracy and surface finish is attainable by plunge cutting, accuracy to 0.1 thou t0.002 mm) being possible. Plunging involves feeding the cutting tool radially into the workpiece by lengthwise movement of the cross slide. The cross-slide cannot move along the lathe turning axis, so the machinable length of workpiece periphery will be determined by the width of the cutting tool. As is known, tool width - or cutting edge length - is finite and limited inter alia by the lathe power available and by the size and strength of the workpiece.

As a rough guide, peripheral machining and cutting of long, shallow tapers on a conventional small workshop capstan lathe is usually limited to lengths (measured along the turning axis) of less than one inch or so.

Extended machining on an automatic capstan lathe could be achieved by repeated steps of machining and feeding workpiece stock incremental ly through the lathe chuck. Clearly, accuracy of concentricity would suffer. The alternative would be to machine on a centre lathe instead, but this might well be inconvenient if numerous, identical work pieces of complex shape are to be produced, for which a capstan lathe would ordinarily be regarded as the proper tool to use.

An object of this invention is to provide an accessory for a capstan lathe which can remove or alleviate the foregoing problems.

Cutting acceptable tapers on centre lathes is also not without difficulties. The tool post, mounted atop the compound slide, is carried by an indexable head slide. Once set to the required angle accurate tapers can be produced, but surface finish leaves much to be desired inasmuch as lengthwise movement of the head slide can only be effected manually. The accessory to be described hereafter can usefully be added to a centre lathe to obtain improved taper cutting.

Keyways and slots are frequently formed by milling. Whilst milling cutters of numerous shapes and sizes are available, it may be that a keyway or slot is required which does not conform to the shape of any available cutter. Unless a purpose-made cutter is obtained, the machinery required may involves numerous operational steps, possibly including careful re-mounting of a workpiece on the mill slide after other milling operations have been performed. The accessory according to the invention is expected to offer substantial advantages when mounted on a milling machine, since keyways and slots of virtually any profile can be formed using a simple, appropriately-ground cutting tool.

According to the present invention, there is provided an accessory tool attachment for a machine tool comprising a tool holder slidably received in a housing adapted to be mounted on a machine tool, the tool holder being linearly reciprocal along a guideway of the attachment, and the attachment having an integral motor unit operable to move the tool holder at a controlled speed to and fro along the guideway between limit stops spaced-apart along the guideway.

The attachment can be employed with various machine tools as the foregoing indicates, but its preferred application is for use on a turret or capstan lathe. Accordingly, the invention comprises a turret or capstan lathe having a cross slide movable to and fro in one direction transverse to the lathe turning axis and located adjacent a workpiece chuck of the lathe, and mounted on the cross slide there is an accessory tool attachment comprising a tool holder slidably received in a housing adapted to be mounted on a machine tool, the tool holder being linearly reciprocal along a guideway of the attachment, and the attachment having an integral motor unit operable to move the tool holder at a controlled speed to and fro along the guideway between limit stops spaced-apart along the guideway, controls of the lathe being arranged to activate the motor unit for reciprocating the tool holder in timed relation with operating movements of the cross slide.

Preferably the motor unit is energised hydraulically and is a cylinder and piston device.

For ease of taper cutting, the housing can be mounted on a sub-base member to rotate or index about a vertical axis; a suitable graduated angle scale will be provided to enable the user to select any required angle.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings, in which: Figure 7 is a simplified diagrammatic side elevation of a capstan lathe which can embody the present invention, Figure 2 is a further simplified top plan view of certain elements of the lathe, showing the tool accessory attachement according to the invention mounted thereon, Figure 3 is an end elevation of the tool accessory attachment seen in Figure 2, and Figure 4 is a cross-sectional view taken on the line IV-IV of Figure 3.

The capstan lathe 10 shown in Figure 1 is conventional, and may be an automatic machine programmed to perform an elaborate sequence of machining operations on a workpiece. Upon completion of the workpiece, such a lathe severs the worpiece, adv ancesfresh workpiecestocktothe machining position and then repeats the machining sequence. As is conventional the lathe 10 has a chuck 1,e.g. a collet chuck, mounted to rotate on a driven shaft - not shown - which is rotated by a motor drive within housing 12. longitudinally-extending ways 13 parallel to the lathe turning axis 14 extend from the housing 12 to a support pedestal 15.A capstan saddle 16 is movable along the ways 13 by means of a manual drive 17, which is used merely to set the capstan 18 approximately to the required position relative to the chuck 11, depending on the workpiece length. The capstan 18 runs on a longitudinallyextending capstan slide 19 mounted on the saddle 16 for power-driven to and fro motion, and is indexable to bring any one of its tools (not shown) to a machining position on the turning axis 14.

Extending normal to ways 13 the lathe has a cross-slide 20 carried by transverse ways 21. The ways 21 and the cross-slide 20 are in a fixed position relative to the turning axis. The cross slide 20 carries a tool mounting 22 illustrated by way of example in Figure 1 as a tool post. The cross slide 20 can only move at right angles to the axis 14 and is used for plunge cutting using a tool 24 ground e.g. to the exactworkpiece profile required. Movements of the slide 20 along ways 21 are very accurately governed by adjustable limit stops, not shown. Machining to dimensional tolerances of the order of 0.1 thou is readily attainable, better by a factor of ten than is within the usual capability of a roller box mounted on the capstan 18.Surface finish obtainable by plunge cutting is significantly better than by use of a roller box, too, owing to the rigidity of the slide 20 and ways 21, and to the rigid support of the tool 24 atop the slide. The slide is able to mount two cutting tools one of which may be used for parting-off.

However, parting-off will commonly be performed by a parting-off tool carried in a vertically movable slide mounted on housing 12 over the chuck 11.

As shown in Figure 2, the slide 20 presents two tool-mounting tables 28,29 separated by a gap, the tables 28,29 being movable to and fro in unison.

Adjacent the gap 30 each table is traversed by a plurality of slots 31 for tool mounting bolts. The slots 31 allow for limited adjustment along the axis 14 of tools mounted on the tables 28, 29.

As discussed above, the ability of a capstan lathe to machine workpiece peripheries, e.g. so as to produce shallow, elongated tapers is limited. To overcome this drawback, an accessory device 40 has been developed. Device 40 is mounted on the cross-slide 20 so as to benefit from the positional accuracy which, as mentioned, is a feature of the cross-slide. The device 40 is bolted to table 28 (or 29) and is in an attitude for cutting a shallow taper on a workpiece. The device is shown in more detail in Figures 3 and 4, to which attention is now directed.

The device 40 comprises a base 41 which is slotted at 42 for bolts 43 which locate in the slots 30 of the cross slide 20 for clamping the device to the chosen table 28, 29. The base 41 provides an open-topped housing 44 for a tool holder 45, housing 44 being substantially U-shaped as seen from the end view (Figure 3) of this example. The tool holder 45 is recessed at 46 to accommodate a tool 24 which is clamped in the recess 46 by bolts 49.

The tool holder 45 is slidably supported by the base 41 in the housing 44 for reciprocal movement in one direction. Movement of the tool holder is guided by a close4itting guideway system 50. The guideway system comprises a rail and groove structure, the rail being part of one of the members consisting of the tool holder and housing, the groove part of the other member. As shown, the guideway system 50 is formed by two rails 51 projecting laterally in opposite directions from opposite sides of the holder 45; the rails extend the length of the holder 45; the rails extend the length of the holder 45. The rails 51 are received in two inwardly-opening housing grooves formed in the housing 44 by rebates 52 and retention plates 53. The rebates 52 extend the length of the housing.

Movement of the tool holder 45 is accomplished by a motor unit integral with the device 40. As shown, movement is produced hydraulically by a double-acting piston and cylinder device 60. As shown, the cylinder 61 is formed by a bore in the holder 45. At one end, cylinder bore 61 is closed by a blanking plate 62, and at the other end by an apertured plate 63. The piston 64 has a piston head 66 fitting bore 61 and a piston rod 67 which extends through the apertured plate 63 to an anchoring member 68 non-displaceably fastened in any convenient manner to the base/housing 41,44. Since the piston 64 is immovable, the base/housing being securely bolted to the table 28, 29, appropriate hydraulic signals will cause the tool holder 45 to travel to or fro within the housing 44. Hydraulic pressure is fed to opposite sides of the piston head through conduits shown chain dotted in Figure 4 which lead from two nipples 69. Hydraulic lines, not shown, connect the nipples with a hydraulic supply unit.

Two end plates 70 are secured to the base 41, each closing a respective one of the ends of the housing 44. (No end plate is shown in Figure 3 for clarity of illustration.) Positively-acting means to control the throw or stroke of the movable tool holder 45 are incorporated in each end plate 70. The strokecontrolling means comprise elongated adjustable abutments 72 screw-threaded into openings in the end plates 70, locking nuts 74 serving to retain the screw threaded abutments in their chosen settings. The abutments 72 are directly engageable by the tool holder 45. Equivalent stroke controlling means could, in an alternative design, be adjustably se cured to the tool holder 45; movement of the latter would be arrested when one or other of the said means strikes the associated end plate.In another arrangement, the holder 45 could include a lug running along a threaded bar fast with the housing, said bar carrying spaced-apart threaded nuts serving as the limit stops.

In use, the device 40 is mounted on the cross-slide 20 with the guideway system 50 extending parallel or at a chosen inclination to the turning axis 14, and is clamped tightly in place. The required cutting operation is attained by (a) feeding the slide towards the workpiece until arrested at a predetermined stop position and (b) traversing the tool 24 along the workpiece by hydraulically shifting the tool holder 45 along the guideway system 50.

Setting up the device 40 can be accomplished as follows. Suppose it is desired to machine parallel to axis 14. An accurately cylindrical bar is mounted in the chuck 11 and a dial gauge is attached to the tool holder 45 with its stem in contact with the bar. With the securing bolts 43 and their nuts slackened, the tool holder 45 is reciprocated along guideway sys tem 50 and the device 40 is bodily adjusted on table 28, 29 until the dial gauge reading is unchanging, whereupon the nuts are tightened on the bolts 43.

Clearly, an unchanging dial gauge reading indicates the guideway system 50 and tool holder movement are parallel to the surface of the bar and hence to the axis 14. To machine tapers, the device 40 is set up and adjusted in essentially this way, except the cylindrical bar is replaced by accurately tapered gauge bars of appropriate taper angles.

In a modification, the base 41 can be indexable about a vertical axis on a sub-base member, base 41 and sub-base member incorporating an index and angle scale. Setting up for a taper cutting exercise would involve adjusting the guideway system 50 for parallelism with the axis 14, clamping securely to the table 28, 29, and finally indexing the base 41 and tool holder 45 through the required angle indicated by the index and scale.

Feeding the slide and tool 24 of device 40 towards the workpiece for taking a cut and withdrawal thereof after completing the cut is a function of the lathe controls, and will not be described herein.

Automatic lathes programmable by pegboard or tape provide accessory control take-off signalling means which can be employed to activate move ments of the tool holder 45 in both directions along the guideway system 50. In one typical system for moving the tool holder, the cylinder and piston device 60 is connected in a control circuit including an hydraulic reservoir, a flow reversing valve and pumping means for the hydraulic fluid. Changing over the flow reversing valve reverses the hydraulic flow conditions to the cylinder and piston device 60, 64 and hence controls the direction of movement of the tool holder 45. The state of the flow reversing valve can be controlled by the accessory signalling means. Pumping the hydraulic fluid can convenient ly be achieved by a pneumatic ram, compressed air supplies being readily available in most workshops.

The signalling means can be used to control a pneumatic on/off valve to the pneumatic ram.

Rate of movement of the tool holder 45 along the guideway system 50 can be controlled by a manually-settable bleed valve in the line to the cylinder and piston device 60, 64.

As will be appreciated, sealing of the cylinder and piston device will be essential. Thus, seals will be required between plates 62 and 63 and the ends of the cylinder 61 of the tool holder 64, and a seal will be provided between the piston rod 67 and the aperture of plate 63. A seal will normally also be provided between the piston head 66 and cylinder bore 61.

If desired, the cylinder 60 could be integral with the base 41 when the piston would be fast with the tool holder.

A reversible electric motor/lead screw drive could be substituted for the hydraulic drive illustrated.

Speed of movement of the tool holder 45 along the guideway system 50 could be by controlling the voltage to the motor, or by a variable slip clutch interposed between the motor and the element driven thereby, i.e. the lead screw. A line or indication motor could conceivably be employed.

One method of controlling the device and lathe, using the lathe's control take-off signalling means has been mentioned above. Another method can involve use of a copy follower device. For example, a tracer mounted to respond to movements of the tool holder will be arranged to traverse the profile of a master of the shape which workpieces are required to reproduce. The tracerwill be arranged to operate two controls, one for controlling the position of the lathe cross-slide relative to the turning axis, and the other for controlling the supply of hydraulic fluid to the cylinder and piston device 60, 64. The use of copying devices is well known in the art and further detailed explanation here is believed to be unnecessary.

As best seen from Figure 4, the tool holder 45 is a sub-assembly of parts, 45a and 45b. Part 45a is recessed to take the tool 24 and is mounted atop part 45b. Part 45b incorporates the cylinder bore 61, the flow conduits and is furnished with the rails 51 and nipples 69. To assist setting up, e.g. after re-grinding tool 24 or after replacement thereof, part 45a is rotatable relative to part 45b and means is provided, not shown, to clamp the part 45a in any chosen setting upon the part 45b.

The device 40 has been described in its application to a capstan lathe for convenience. It could be mounted on a centre lathe, or on the head or even on the workpiece carriage of a milling machine, as has been mentioned hereinbefore.

With the unit 40, turning workpiece peripheries along a span of 13/4" or greater (45 mm) measured along the turning axis 14 is possible. Dimensional accuracies to 0.1 thou in diameter are readily attainable and surface finish equal to the finish possible with a well adjusted centre lathe can be obtained. As will be appreciated, the unit can be used to make the final finishing cuts after a workpiece has been roughed out by means of a suitably profiled plunge cutter mounted on the table opposite that on which the unit is mounted.

Claims (16)

1. An accessory tool attachment for a machine tool comprising a tool holder slidably received in a housing adapted to be mounted on a machine tool, the tool holder being linearly reciprocal along a guideway of the attachment, and the attachment having an integral motor unit operable to move the tool holder at a controlled speed to and fro along the guideway between limit stops spaced-apart along the guideway.

2. A tool attachment according to claim 1, wherein the guideway comprises a rail and groove system.

3. A tool attachment according to claim 2, wherein the tool holder has a pair of oppositely laterally projecting rails snugly received in two inwardlyopening housing grooves.

4. A tool attachment according to claim 1, 2 or 3, wherein the limit stops comprise adjustable abutments carried by the housing and engageable by the tool holder to arrest the latter and thereby control the throw thereof.

5. A tool attachment according to claim 1, 2, 3 or 4, wherein the motor unit is a double-acting pneumatic or hydraulic cylinder-and-piston device having its longitudinal axis parallel to the guideway.

6. Atool attachment according to claim 5, wherein the cylinder is a bore in the tool and the piston is non-displaceably secured to the housing.

7. A tool attachment according to claim 5 or claim 6, wherein the cylinder-and-piston device is connected in a hydraulic circuit including fluid pressurizing means, means for reversing the direction of fluid flow to opposite ends of the said device and a bleed valve operable to control the speed of movement of the tool holder along the guideway.

8. Atool attachment according to claim 1,2,3 or 4, wherein the motor unit comprises an electric motor and driven lead screw arrangement.

9. A tool attachment according to claim 8, wherein a variable slip clutch is coupled between the electric motor and the lead screw for controlling the speed of movement of the tool holder along the guideway.

10. A tool attachment according to any of claims 1 to 9, wherein the housing is indexably mounted on a sub-base member to rotate about a vertical axis, and includes an index and angle-setting scale.

11. An accessorytool attachmentfora machine tool, substantially as herein described with reference to and as shown in Figure 3 and 4 of the accompanying drawings.

12. A centre lathe fitted with a tool attachment according to any of the preceding claims for cutting tapers on workpieces.

13. A milling machine fitted with a tool attachment according to any of claims 1 to 11 for cutting keyways or slots in workpieces.

14. A turret or capstan lathe having a cross slide movable to and fro in one direction transverse to the lathe turning axis and located adjacent a workpiece chuck of the lathe, and mounted on the cross slide there is an accessory tool attachment comprising a tool holder slidably received in a housing adapted to be mounted on a machine tool, the tool holder being linearly reciprocal along a guideway of the attachment, and the attachment having an integral motor unit operable to move the tool holder at a controiled speed to and fro along the guideway between limit stops spaced-apart along the guideway, controlSof the lathe being arranged to activate the motor unit for reciprocating the tool holder in timed relation with operating movements of the cross slide.

15. A turret or capstan lathe according to claim 14, wherein the accessory tool attachment includes any of the features claimed in any one of the preceding claims 2 to 10.

16. A turret or capstan lathe substantially as herein described with reference to and as shown in the accompanying drawings.