GB2185699A - A bar puller for use on a CNC machine tool and a method of operating a CNC machine tool - Google Patents

Abstract

The bar puller comprises a support part (10) which can be supported by a turret of a computer numerically controlled machine tool and a bar gripping part (11) having at least one adjustable gripper (15) with a spring loaded detent (20). In order to operate the bar puller a circumferential groove is first formed in a bar (18) gripped by a chuck of the machine tool. The bar puller is then advanced toward the bar in a direction parallel to the axis thereof until the spring loaded detent of the or each gripper has ridden over the end of the bar and located in the said circumferential groove.The chuck is then caused to release its grip on the bar so that when the bar puller is retracted the bar is pulled to a new position. The chuck then grips the bar again and further retraction of the bar puller withdraws it from the bar. <IMAGE>

Description

SPECIFICATION A bar puller for use on a CNC machine tool and a method of operating a CNC machine tool The invention relates to a bar puller for use on a computer numerically controlled (CNC) machine tool and to a method of operating a CNC machine tool equipped with such a bar puller.

Known bar pullers for CNC machine tools grip the plain cylindrical surface of the bar and are relatively expensive.

The present invention seeks to provide a bar puller which can be made at a much reduced cost.

According to a first aspect of the invention there is provided a bar pullerfor use in a computer numerically controlled machine tool, comprising a supportpartwhich can be supported by a turret of the machine tool and a bar gripping part having at least one adjustable gripper provided with a spring loaded detent, so that in use when the gripper is correctly adjusted and the bar puller is moved towards a bar mounted in the machine tool in a direction parallel to the axis of the bar the spring loaded detentwill contact and ride over the end of the bar and locate in a circumferential groove provided in the bar.

Preferred and/or optional features of the first aspect of the invention are set forth in claims 2-9.

According to a second aspect of the invention there is provided a method of operating a computer numerically controlled machine tool equipped with a bar puller according to the first aspect of the invention, comprising the steps of: (a) forming a circumferential groove in a bar gripped by a chuck of the machine tool, (b) advancing the bar pullertowardsthe bar in a direction parallel to the axis thereof until the spring loaded detent of the or each gripper has ridden over the end of the bar and located in the circumferential groove.

(c) causing the chuck to release its grip on the bar and then retracting the bar pullerto pull the bar to a new position, (d) causing the chuck to grip the bar again and then further retracting the bar pullerto withdraw itfrom the bar.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which :- Figure 1 is an end view with a part shown in section, of one embodiment of a bar puller according to the first aspect of the invention, and Figure2 is a section taken along the line Il-Il of Figure 1.

Referring to the drawings, the bar puller shown therein comprises a tubular support part 10 and a gripping part 11.

The support part 10 can be supported at one ofthe stations of a multi-station turret of a computer numerically controlled (CNC) machine tool such asa CNC lathe.

The gripping part 11 has a cylindrical bore 12 therein which is of larger diameter than the bore of thetubular support part 10 and an hexagonal outer periphery 13 having sides which are alternately of longer and shorter length. Screw-threaded apertures 14 extend radially through the gripping part 11, one from each of the three shorter sides thereof.

However, the outer periphery 13 could be of any configuration, e.g. circular.

An adjustable gripper 15 is provided in each aperture 14. Each gripper 15 has a generally tubular body provided with an external screw-thread 16 which mates with the thread of its respective aperture and a stepped bore 17. The outer and larger diameter end ofthe bore 17 has an internal screw thread 19 over part of its length whereas the inner and smaller diameter end of the bore 17 is plain.

Each gripper 15 is provided with a detent 20 loaded by a compression spring 21. Each detent 20 has a hardened conical tip 22 at its inner end, a flange 23 at its outer end to hold it captive in the gripper, and a guide portion 24 intermediate its ends, the guide portion 24 being slideably disposed in the smaller diameter end ofthe bore 17. The spring 21 is interposed between the flange 23 and a load adjustment screw 25 which mates with the internal screw thread 19 and which has a screw-driver receiving slot in its outerfaceforadjusting the position of the load adjustment screw and thereby the load applied by the spring 21 to the detent 20.

The outer end of the tubular body of each gripper 15 also has two diametrically opposed screw-driver receiving slots for adjusting the position ofthe gripper in its respective aperture in the gripping part 11, although these slots could, for example, be replaced by a knurled knob.

The cone angle of each conical tip is preferably and as shown 900 or about 900 for a reason which will be explained hereinafter.

Associated with each gripper 15 is a locking screw 26 which operates on the gripper body by way of a nylon pad 27 to prevent unintentional adjustment of the gripper which may otherwise be caused by vibration.

In use the bar puller is located at one station of a multi-station turret of a CNC machine tool such as a lathe. When machining a plurality of components from a single bar 18,the bar puller is used to advance the bar each time a machine component is severed from the bar. In orderto advance the barthe CNC lathe is programmed to form a circumferential groove of say 1 mm depth in the bar. This groove is normally formed in the bar in a region where material isto be subsequently removed orwherethe machined component is ultimately to be severed from the bar. The turret is then indexed in orderto bring the bar puller into axial alignment with the bar.

Then the turret is advanced in a direction parallel to the axis of the bar to cause the tips 22 of the spring loaded dete nts 20 to contact and ride overthe end of the bar and locate in the circumferential groove. The jaws of the chuck are then caused to release their grip on the bar and theturret is retracted sothatthe barpulleradvancesthe bar to a required position.

The jaws of the chuck are then caused to re-gripthe barwhereupon further retraction of the turret will withdraw the bar pullerfrom the bar. All ofthe aforesaid operations are carried out under computer control.

It has been found that a cone angle of or about 90" for each tip 22 is a good compromise enabling the tip to ride easily over the end ofthe bar and yet also provide an adequate grip when located in the circumferential groove. If the cone angle were to be much less the tip would not ride as easily overthe end ofthe bar, other circumstances being equal, and if the cone angle were to be much largerthegrip provided when located in the circumferential groove would not be so good.

The bar puller described above can be adjusted so asto co-operatewith bars which vary in diameter over a fairly large range such as 0-50mm and larger versions could be provided for co-operation with larger diameter bars. The bar puller unlike known bar pullers is able to co-operate with bars of very small diameter indeed, i.e. bars of less than Smm diameter.

Whilst the detents are said to be of hardened material they could instead be of any other appropriate material such as nylon. Nylon detents will be particularly suitable with, for example, aluminium or other relatively soft materials.

Moreover, the detenttip does not necessarily have to be conical; it could be of various other shapes, e.g.

chisel-shaped, or could be in the form of a ball.

The bar puller described above is given by way of example only and many modifications could be made to it without departing from the scope ofthe invention defined by the appended claims. For instance,the grippers do not necessarily have to be in screw threaded engagementwith the gripping part of the bar puller. Instead they could be pivotably mounted on the bar puller in such a waythatthey can be adjusted to co-operate with bars of different diameter. Also the grippers could be interconnected, such as by gearing, so that they can be adjusted simultaneously. Moreover, the bar puller need only have a single adjustable gripper and spring loaded detent provided that it also has a fixed part which is ableto co-operate with the spring loaded detent to grip the bar.

Claims (1)

1. A bar puller for use in a computer numerically controlled machine tool, comprising a support part which can be supported by a turret of the machine tool and a bar gripping part having at least one adjustable gripper provided with a spring loaded detent, so that in use when the gripper is correctly adjusted and the bar puller is moved towards a bar mounted in the machine tool in a direction parallel to the axis ofthe bar the spring loaded detentwill contact and ride overthe end of the bar and locate in a circumferential groove provided in the bar.

2. The bar puller of claim 1, wherein the spring loaded detent has a conical tip which in use contacts the bar.

3. The bar puller of claim 2, wherein the cone angle ofthe conical tip is 90 or substantially 90'.

4. The bar puller of any one of the preceding claims, wherein the gripping part has three or more angularly spaced adjustable grippers each provided with a spring loaded detent.

5 The bar puller of claim 4,wherein means are provided for adjusting all grippers simultaneously.

6. The bar puller of any one of the preceding claims, wherein the or each gripper and the gripping part have mating screw-threadswherebythe gripper or grippers can be adjusted in an in use radial direction with respect to the bar.

7. The bar puller of claim 6,wherein each screw threaded gripper has an associated locking device to prevent unintentional movementofthegripper relative to the gripping part.

8. The bar puller of any one ofthe preceding claims, wherein means are provided for adjusting the spring loadingonthedetentoftheoreach gripper.

9. A bar puller substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of operating a computer numerically controlled machine tool equipped with a bar puller according to any one of the preceding claims, comprising the steps of: (a) forming a circumferential groove in a bar gripped by a chuck of the machine tool, (b) advancing the barpullertowardsthe bar in a direction parallel to the axis thereof until the spring loaded detent ofthe or each gripper has ridden over the end of the bar and located in the circumferential groove, (c) causing the chuck to release its grip on the bar and then retracting the bar pullerto pull the bar to a new position, (d) causing the chuckto grip the bar again andthen further retracting the bar pullerto withdraw it from the bar.

11. A method of operating a computer numerically controlled machine tool equipped with a barpulleraccordingtoanyoneofclaimsl-9, substantially as hereinbefore described.

Amendments to be printed under Section 16(a) Printers instructions Application No.86/01314 Amendments to the claims have been filed, and have thefollowing effects: (a) Claims 1 above have been deleted ortextually amended.

(b) New ortextually amended claims have been filed asfollows: CLAIMS

1. Abarpullerforuseinacomputernumerically controlled machine tool, comprising a support part which can be supported by a turret of the machine tool and a bar gripping part having at least one adjustable gripper provided with a spring loaded detent adapted and arranged so that in use when the gripperis correctly adjusted and the bar puller is moved towards a bar gripped by a chuck of in the machine tool in a direction parallel to the axis of the bar the spring loaded detentwill contactand ride over the end ofthe bar and locate in a circumferential groove provided in the bar, when the chuck releases its grip and the bar puller is retracted the bar will be pulled bythe detent engaging inthe groove, and when the chuck grips the bar again and the bar puller is further retracted the detent will ride out of the groove and overthe end ofthe bar.