TOOLHOLDERS FOR MACHINE TOOLS

Abstract: A toolholder for holding a cutting tool such as a tap in the spindle of a machine tool includes a torque-limiting clutch to prevent excessive load being applied to the cutting tool. The clutch comprises at least one ball (98) located in sockets (90, 104) in the driving and driven members (15,24) but there is an arrangement, whereby, at a predetermined critical torque, the ball (98) moves axially out of engagement with the one of the driving and driven members to discon­ nect the drive, and a deflecting device (106) engages with the ball (98) and moves it to a position where it does not encounter the socket from which it has been released or any similar sockets. This prevents wear on the clutch. The tool holder also comprises a conduit system (130, 132) for cutting fluid being fed into a bore in the cutting tool. The conduit extends through a telescopic part of the toolholder and includes a flexible part (132) deviating from a straight linear form, so that it can extend by tending to straighten, in order to accommodate telescopic extension of the toolholder.

Description: The invention relates to an axially tapper according to the precharacterizing past of claim 1, of US-A-4514115. One problem associated with the use of rotary type toolholders in machine tools is that of supplying cutting fluid to the tool under relatively high pressure (say of the order of 300 lbs. per square inch). In tapping for instance, it is desirable to force cutting fluid through the tap itself (and taps are bored to provide a canal for the cutting fluid) so that the fluid emerges from the tool in the hole which is being tapped, where, if it is under a sufficiently high pressure, it forces swarf produced by the tapping operation out of the hole. Obviously, it is necessary to supply the cutting fluid under pressure through the toolholder, but a problem which has been encountered in practice is that the high pressure fluid creates internal forces acting on the components of the toolholder itself. This problem is exacerbated in the case of an axially telescopic tapper, because the high pressure fluid tends to force the movable part of the tapper out of the stationary part. The object of the invention is to provide an axially telescopic tapper with means for satisfactorily supplying cutting fluid under high pressure to the tap itself. According to the invention, an axially telescopic tapper for use in a machine tool comprises: a stationary part adapted to be held in the machine spindle and a movable part adapted to receive the tap or a tap adapter, there being provision for limited axial displacement of the movable part relatively to the stationary part, characterized in that a cutting fluid supply system inside the tapper includes a flexible conduit attached to one end to the stationary part and at the other end to the movable part, the flexible conduit deviating from a straight linear form, so that it is capable of extension by tending to straighten. By confining the cutting fluid into a conduit where it passes through the tapper, it is ensured that the fluid does not pressurise the relatively movable components of the tapper. Moreover, the fluid will not contaminate the internal mechanism of the tapper. In the preferred construction, the flexible conduit has at least a part helical formation and preferably the flexible conduit makes at least one complete convolution which provides the required variable length of conduit to accommodate the permitted extension of the tapper in use. The flexible conduit is preferably made of plastics materials, such as nylon. Preferably there is provided within the stationary part of the tapper a tubular retainer which is formed with an abutment for a compression spring adapted to resist extension of the tapper, and the flexible conduit is attached at one end to this tubular retainer, so that the retainer provides a part of the cutting fluid passage through the tapper. One construction of a tapper for use in a machine tool, and incorporating the various aspects of the invention outlined above, will now be described by way of example only, with reference to the accompanying drawing, showing a longitudinal section through a tapper holder. The tapper has a machine-tool spindle-engaging part 2, generally referred to as the holder, and an adapter which receives the tap itself (not shown). The spindle-engaging part of the tapper includes a body 10 which has a tapered shank 12 adapted to fit in conventional manner into the tapered socket of a machine tool spindle (not shown) and to form a tapper lock in the spindle, so that the spindle is then able to rotate the tapper about its own longitudinal axis. The body 10 forms a "stationary" part of the tapper, in the sense that once locket in the machine tool spindle, it has no motion other than the rotary motion with the machine tool spindle. A collar 14 is formed on the body 10. Internally, the body 10 has a large bore 16 to accommodate a sleeve portion 8 of a movable part 20, which is adapted to be displaced axially within limits relatively to the stationary body 10. As will hereinafter appear, the mounting of the movable part 20 within the body 10 provides for the transmission of torgue from the body 10 to the movable part 20, so that whenever the body 10 is rotated by the machine tool spindle, this rotary motion is transmitted to the movable part 20. At its forward end, the movable part 20 has a large bore 22, and when the part 2 and the tapper are assembled, the inner end of a generally cylindrical driven member of the tapper is received within the bore 22, the part of the driven member which is thus received in the bore 22, being a sliding fit thereon. The driven member has a bore which includes a square cross-section part within which is received a correspondingly square cross-section end of the shank of the tap (not shown). Hence, when the adapter is fitted into the bore 22 of the movable part 20, the tapper is complete, and ready to receive a tap to perform a tapping operation. The tap is retained in the adapter by a known type of retaining sleeve which does not form part of the invention. A quick release mechanism is provided for releasably holding the adapter unit 2 in the movable part 20, and this quick release mechanism comprises a ball 30 located in a radial bore in the wall of the movable member 20, and engageable in an annular groove formed near the inner end of said driven member. A release-collar 34 is slidably mounted on the exterior of the movable part 22 near to the outer end of the part, and a compression spring 36 acting between an external rib 38 on the part 20 and an internal rib 40 in the release collar 34 urges the collar inwardly, to a locking position indicated in the Figure, wherein a circlip 42 within the collar 34 engages with the outer face of the rib 38. In this locking position, the internal rib 40 is aligned with the hole in which the ball 30 is located, and as shown in the Figure, prevents outward movement of the ball 30 from a position, where it would engage in the groove 32 of the driven member. A relatively deep annular recess 44 in the inner end of the release collar 34 can be moved into alignment with the ball 30, by pulling the release collar 34 outwardly, against the action of the spring 36. When the release collar is pulled into this position, the ball 30 can move radially outwards so that it is partly in the groove 44, and in this position, it will allow said cylindrical driven member to pass. In order to effect a connection between the adapter unit and the movable part 20, the release collar 34 is pulled outwardly by hand, to bring the groove 44 into alignment with the ball 30, and then the inner end of the driven member is slid into the bore 22. The ball 30 will be pushed outwardly to allow this connecting movement to take place, but once the unit has been fully inserted into the movable member 20, the release collar 34 can be released, so that it moves inwardly under its spring loading, and an inclined face of the groove 44 engages with the ball 30, pressing the ball inwardly into engagement with the groove of the driven member. Once the releaseable collar arrives at the position illustrated in the Figure, the ball 30 cannot thereafter move outwardly, and consequently, the adapter unit becomes axially locked within the movable part 22. At its outer end, the movable part 20 is formed with dogs 46, which in the assembled position engage with dogs on the driven member and establish a torque transmitting connection between the movable member 20 and the driven member. This driven member 50 forms part of a torgue-limiting clutch within the adapter unit which function is to transmit torgue to the driven member, which receives the actual tap. Reverting now to the connection between the body 10 and the movable part 20, which it will be recalled has to transmit torgue, whilst permitting some axial displacement of part 20 relative to the body 10, it should be mentioned that it is know to provide tappers with this kind of facility. The purpose of allowing the movable part 20 to be pulled out of the body 10, arises from the fact that once the tap has started to cut into the workpiece, continued rotation of the tap causes it to cut an internal screw-thread within a bore of the workpiece, and involves an axial feed of the tap. It is impracticable to match the rate of feed of the machine tool spindle precisely to the feed of the tap due to its cutting action. In practice the spindle is usually underfed, that is to say, the rate of feed due to cutting is greater than the rate of feed of the spindle. Hence the movable part 20 has to move axially outwards, i.e. to the right as seen in Figure 1. Although the sleeve 1 is generally cylindrical, at one or more positions around its periphery, a groove 53 is machined in the outside ot fhe sleeve. An elongate ball race 52 is fitted around the sleeve 18 and engages in the bore 16 of the body 10, there being a multiplicity of balls arranged in several circles so that the sleeve 19 is both journalled and axially slideable quite freely in the body 10. At these positions a row of three larger balls 54 is fitted in the ball race 52, and these balls engage in the groove 53 of the sleeve 18 and in a matching groove 55 formed in the body 10. Although the larger balls can roll along the grooves 53 and 55 (thereby permitting axial motion of the sleeve 18 in the body 10) they act as keys transmitting rotary motion from the body 10 to the sleeve 18. It will be appreciated that the bearing arrangement just described permit the sleeve 18, and therefore the movable member 20, to slide axially within the body 10, but provides for torque to be transmitted from the body 10 to the movable part 20. At its outer end, the sleeve portion 18 of the movable part 20 is of slightly enlarged diameter, so that a small shoulder 58 is formed on the outside of the sleeve. A bearing ring 59 is located in the outer end of the body 10, and the enlarged diameter part of the sleeve 18 in this ring. An initial pressure ball 60 is located in a radial hole in the ring 59 and urged into engagement with the outside of the main portion of the sleeve 18 by a compression spring 62. A screw plug 64 acts on the spring 62 and provides a means of adjusting the spring pressure on the ball 60. When the tap firts encounters the workpiece in which the screw-thread is to be produced, the tap is arrested, but the body 10 continues to advance. The shoulder 58 strikes the ball 60 and the latter will only retract to allow the enlarged portion of the sleeve 18 to move further into the ring 59 when the force acting between the sleeve 18 and the ball 60 produces a radial component force acting on the ball sufficient to overcome the spring 62. Thus there is a very short period when the body 10 is applying a relatively strong force on the tap and this is adequate to enable the tap to bite into the workpiece to commence the tapping action. The strength of this threshold force can be present by adjusting the screw plug 64. For the purpose of controlling the permitted axial displacement of the movable part 20, there is a finger-like tubular retaining member 68 extending forwardly into the bore 16, and into a large bore 70 of the sleeve 18, from an internal flange 72 of the body. As shown in the Figure, the retaining member 68 is locked on to the flange 72 by a pair of circlips which engage with opposite sides of that flange, and there is a sealing ring 74 providing a liquid-tight seal between the internal flange 72 and the exterior of the retaining member 68. At its outer end, the retaining member 68 as an external lip 76, and a pair of annular pusher members 78 and 80 are slidably mounted on the outside of the retaining member 68. Outward motion of the outer pusher member 80 is limited by engagement of that member with the lip 76 as illustrated in the Figure, and inward movement of the inner pusher member 78 is restricted by engagement of that member with a circlip 82 engaged in the retaining member 68. A compression spring 84 extends between flanges of the pusher members 78 and 80, and holds those members apart, so that in the unloaded condition, the pusher members are engaged respectively with the circlip 82 and the lip 76 all as illustrated in the Figure. Externally, each of the pusher members 78 and 80 is a sliding fit within the bore 70 of the sleeve 18. Moreover, there are circlips 86 and 88 engaged in the bore 70 of the sleeve, which are also engageable respectively, within the outer ends of the pusher members 78 and 80. The operation of the connection between the body 10 and the movable part 20, which permits axial displacement of the latter, will now be described. In the ordinary operation of the tapper, if the conditions are such that the tap is advancing at a linear speed greater than that of the machine tool spindle, a pull is transmitted from the tap, through the adapter unit, to the movable part 20. The movable part is able to move outwardly, because its circlip 86 pushes on the pusher member 78 at the inner end of the sleeve 18, and the pusher member leaves the inner circlip 82. The outward motion of the pusher member 78 is resisted by the spring 84, which is compressed, since the outer pusher 80 cannot move outwardly due to its engagement with the lip 76. Therefore, the extension of the tapper unit is simply resisted by compression of the spring 84. When the tapping operation is complete, the machine tool spindle is reversed, so that it begins to wind the tap out of the screw-threaded hole formed in the workpiece. During this operation, the spring 84 pushes on the inner pusher member 78, which in turn pushes on the movable part 20 through the circlip 86, thereby returning the movable part 20 to its original axial location within the body 10. Supposing now that with the movable part in the unloaded position illustrated in the Figure, the machine tool spindle is fed towards a workpiece, and the tap carried by the tapper encounters a resistance (as would occur for instance, if the tap is not correctly aligned with the hole in which it is to cut a screw thread or when the tap reaches the bottom of a hole) then the arrangement which has been described will permit a limited contraction of the tapper by inward motion of the moving part 20 relatively to the body 10. In that case, the movable part 20 pushes on the outer pusher member 80 through the circlip 88, so that the pusher member 80 begins to move inwardly, leaving the lip 76. The inner pusher member 78 cannot move further inwardly, due to the circlip 82, and consequently, the spring 84 is again compressed as the pusher members 78 and 80 move towards each other. This, the spring 84 is used to resist both extension and contraction of the tapper, and this in itself is a very convenient arrangement. The tapper is also provided with means for supplying cutting fluid under high pressure, perhaps of the order of 2.10⁶ N/m² (300 lbs. per square inch), through a bore in the tap itself. For this purpose it has already been mentioned that the retaining member 68 makes sealing engagement with the internal flange 72 of the body, and it will be noted that the retaining member 68 has a lengthwise bore 130, which forms part of a passage for the cutting fluid. A flexible nylon pipe 132 is connected by a screw-threaded pipe connector 134 into the front end of the retaining member 68, and the forward end of the pipe 132 is connected to a nipple 136, which at its forward end is part conical and fits sealingly in the driven member-tapper. It is to be noted that the pipe 132 occupies a space in the sleeve 18 forward of the retaining member 68, and within that space, the pipe 132 is formed into two convolutions of a helix. During extension of the tapper by forward motion of the movable part 20, the helical part of the pipe 132 extends in length, to accomodate the forward motion, and conversely, if there is slight contraction in the length of the tapper, this can also be accommodated by contraction in the length of the helical portion of the pipe 132. The cutting fluid supply is connected into a screw-threaded bore 138 in the inner end of the body 10. From there, the fluid is prevented from entering the large bore 16, which contains the mounting mechanism for the movable part 20 of the tapper, but instead has to pass through the bore 130 of the retaining member 68. From there, it passes through the flexible pipe 132, to the nipple 136 and into the tap itself. The tap itself is bored axially and the cutting fluid is able to flow out through this bore in the tap, from which it issues near to the cutting position and in the hole which is being tapped. It is the provision of the flexible and extensible pipe 132 which enables a cutting fluid under relatively high pressure to pass through the tapper, without contaminating the working parts of the tapper, and without applying pressure for instance to the inside of the movable parts 20.

Claims: An axially telescopic tapper for use in a machine tool, comprising a stationary part (10) adapted to be held in the machine spindle and a movable part (20) adapted to receive the tap or a tap adapter, there being provision for limited axial displacement of the movable part (20) relatively to the stationary part (10), characterised in that a cutting fluid supply system inside the tapper includes a flexible conduit (132) attached at one end to the stationary part and at the other end to the movable part, the flexible conduit deviating from a straight linear form, so that it is capable of extension by tending to straighten. An axially telescopic tapper as claimed in claim 1, characterised in that the flexible conduit has at least a part helical formation (132). An axially telescopic tapper as claimed in claim 2, characterised in that the flexible conduit makes at least one complete convolution which provides the required variable length of conduit to accommodate the permitted extension of the tapper in use.

Inventors: PETRIE, LAURENCE ROSS
Applicants: HANDELSBOLAGET EMINENT SVEN HULTMAN AND CO.
Application year: 1985
Main classification: B23B31
IPC codes: B23B31