GB1566430A - Self-opening rotatable screw thread cutting head - Google Patents

Description

(54) SELF-OPENING, ROTATABLE SCREW THREAD CUTTING HEAD (71) We, GUSTAV WAGNER MAS CHINENFABRIK, a German Company of Opfersteinstrasse 11, 7410 Reutlingen, West Germany, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns a rotatable, selfopening, screw thread cutting head. There is known, for example as disclosed British Patent No. 402,887, a rotatable, selfopening, screw thread cutting head which suddenly springs open after reaching a pre-determined length of thread and has tangentially arranged thread cutters.In a cylindrical base body of the head which has a central bore for the work-piece, there are equi-angularly arranged around the bore on a common pitch circle several, preferably, four, bores which receive the pivot pins of radially displaceable thread cutter holders.

The thread cutter holders are located to one side of the base body and there are arranged on the holders, thread cutters which lie tangentially to the work-piece and are adjustable radially of the work-piece.

Disposed concentrically around the base body is a ring assembly movable to a limited extent axially relative to the base body but constrained from moving rotationally relative to the base body. The assembly has an adjustable cam ring, releasably clamped to the remainder of the ring assembly, the cam ring having a number of spirally curved cam faces corresponding to the number of thread cutter holders. The cam ring can be unclamped so as to be rotated to, adjust the setting of the holders and re-clamped. On these spirally curved cam faces are supported cam follower surfaces of the thread cutter holders, these follow surfaces normally being defined by slide pads (which can be exchanged when worn) which overlap the cam ring and the thread cutter holders are pressed radially outwards by spring force applied to pressure pistons which engage pins inserted in the cutter holders.The pins are adjustable to suit different thread diameters After the head has cut the desired length of thread, the ring assembly is displaced to a limited extent in relation to the body until bevel surfaces adjacent the cam surfaces of the cam ring meet corresponding bevel surfaces on the slide pads whereupon the thread cutter holders, pressed by the pressure pistons, swing so far outwards that the thread cutters are moved away from the work-piece. The screw thread cutter head, which is located for example on a drive spindle cam, without change of direction of rotation, can now be drawn back in rapid traverse.

On the base body there is located concentric with the axis of rotation, a short tubular extension whih is integral with the body or is inserted as a separate bush, which has at the front a collar. This collar engages in corresponding grooves of the thread cutter holders, and the collar is radially so wide and the respective grooves in the thread holders so deep that the thread holders cannot move axially relative to the body unless there is displacement of the ring assembly to such an extent that outward movement of the holders is not longer constrained by the cam ring, when the holders can be drawn out from the base body.

The screw head cutter heads of this construction have a higher degree of rigidity in respect of the cutting forces acting on them and have, because of their simple and robust construction, found widespread use.

Recent manufacturing developments have led however to additional requirements and uses and the continual shortening of time cycles increases the stressing of the devices.

This invention is based on the problem of providing a screw thread cutting head which springs open considerably more rapidly than the known head and opens with certainty after cutting of the desired length of thread.

According to the invention there is provided a self-opening, rotatable screw-thread cutting head having a defined axis of rotation and comprising a base body, thread cutter holders pivotally mounted on said body and adapted to support tangential thread cutters, spring loaded holder opening devices urging the holders to pivot open to move thread cutters thereon away from the axis of rotation of the head and clear of the workpiece so that the head can be moved in a rapid traverse, a control ring assembly mounted for rotation with the base body, said control ring assembly comprising a cam ring having spiral cam surfaces which engage cam follower surfaces of said holders to hold the holders against said pivoting open of the holders, said cam ring being clamped to the remainder of the assembly but being releasable so that it can be rotated to adjust the setting of the holders by cam action through said cam surfaces, said ring assembly being displaceable axially relative to said base body to a limited extent to release the hold on the holders so that they can spring to an open position in which bevel surfaces of the holders engage bevel surfaces of the cam ring preventing further opening of the holders, the body further including pivot levers which are spring loaded to pivot outwards relative to the axis of rotation about axes which are transverse to said axis of rotation said levers being held in an inwardly pivoted position when the ring assembly is positioned so that the cam ring holds the holders in the closed position and being free to swing outwardly to a limited extent when the ring assembly is displaced to allow the holders to move to the open position, said levers having inclined wedge surfaces which engage corresponding wedge surfaces on the ring assembly to assist the displacement of the ring assembly to allow the holders to move in the open position.

One embodiment of the cutting head according to the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a longitudinal section through the screw thread cutting head along the line IV - IV of Figure 2; Figure 2 shows a cross section through the screw thread cutting head along the line I - I of Figure 1; and Figure 3 shows a further longitudinal section through the screw thread cutting head according to the invention along the line II - II of Figure 2.

The screw thread cutting head is shown in the three figures in the closed and therefore ready for cutting, position. Referring to Figure 1, the screw thread cutter holders 3 are pivotally mounted in the base body 1 by means of pivot journals 2 and are secured by the radial projections 4 against axial displacement. The base body 1 has a bore for the workpiece, and the axis of this bore defines the axis of rotation of the head. The screw thread cutters 6 are firmly clamped on the screw thread cutter holders by means of clamping plates 5 and clamping screws (not shown). The screw thread cutters can be subsequently adjusted by means of screw threaded pin 7 after loosening the clamping screws. The base body 1 is centered on and secured, by means of screws 9 to a working spindle (not shown) of an appropriate machine tool, such as a screw cutting lathe.

On the base body 1 there is mounted co-axially a control ring 10 which is connected at the front to a cam ring 11, the control ring 10 and the cam ring 11 forming a ring assembly. The ring assembly can move axially to a limited extent relative to body 1, this movement being limited to prevent complete pivoting out of the screw thread cutter holders 3, by the stop bolt 13 engaging in a groove 12 in the ring 10, which stop bolt is pressed outwards by the compression spring 14, but its outward movement is limited by the stop screw 15. The cam ring 11 is (see also Figure 2) prevented from moving axially relative to ring 10 by the holding pieces 18 and 20 engaging in annular groove 16 of ring 11. Pieces 18 and 20 are screwed by screws 17 and 19 to the ring 10.After rotational adjustment of the cam ring 11 by means of a bevel gear driver (not shown), which driver can engage the tooth section 21 of the ring 11 through a passage (not shown) in the ring 10, a clamping member 20 carried by the ring 10 is caused to be clamped by screws 22 against the walls of annular groove 16 of ring 11 whereby ring 11 is clamped to ring 10 in such a manner that relative rotation between ring 10 and ring 11 is prevented.

In the base body 1 there are disposed radially spring loaded pistons 24 which are acted upon by compression springs 23 and which press the screw thread holders 3 to pivot outwards by acting on pins 25 inserted in the holders until there is contact between cam follower surfaces 26 of the holders and spirally curved cam surfaces of the cam ring 11. A complete coming out of the bushes from the base body is prevented by means of pin screws 27.

In Figure 3 it is shown how, by means of a block 28 which is fixed to the base body 1 by a screw 29, the ring 10 is prevented from turning on the base body 1. In the block 28 is inserted a catch bolt 30 which is pressed radially outwards by means of compression spring 31 and a collar located on it limits its radial movement outwards. The outwardly pointing curved end engages in the bore 32 of the ring 10 and prevents an unintended rotational movement of the ring 10 and the cam ring relative to the body and thus an undesired adjustment of the screw thread holders.

Two opening levers 33 which are located diametrically opposite are located in corresponding recesses of the base body 1 and are mounted for pivoting about axes which are transverse to the axis rotation of the head by having ball formations 34, engaged in recesses in body 1. The levers 33 are pressed outwards by compression springs 35.

When the head is closed, the opening levers 33 lie with their part cylindrical surfaces 36 lying with their axes on the axis of the bore of the ring 10. In use, the head moves with the machine tailstock in the direction of the axis of the bore of the body 1 whilst cutting of the screw thread on the workpiece takes place. As soon as the desired length of thread of the workpiece is almost reached, the opening of the screw thread cutting head is effected by a stop (not shown) on the machine tool or as in this embodiment by means of a switch fork (not shown) which is engaged in the annular groove 37 of the ring 10 and which at the appropriate time, holds the ring 10 and ring 11 from progressing further in the feed direction, whilst the base body 1 which for example is screwed on to the tailstock in the region of its recess 8, proceeds further with the screw thread cutter holders 3.The base body 1 and the screw thread holders 3 now continue further until the bevelled edges 38 adjacent the faces 26 (Figure 1) meet the corresponding bevelled edges 39 adjacent the spiral cam surfaces of the cam ring 11.

At this moment also, the inclined faces 40 on the opening levers 33 meet the corresponding inclined faces 41 in the ring 10 which respectively lie at an angle of 60 to the axis or rotation of the screw thread cutting head, and the holders spring to the open position in which the bevel faces 39 and 38 are in engagement.

According to the embodiment of the invention, the opening of the holders 3 is accelerated and the relative return movement of the ring 10 and the ring 11 axially in respect of the base body is facilitated due to the fact that on the one hand the compression springs 35 act via the faces 40 and 41 on the levers 33 and ring 10 to accelerate the relative axial movement of the ring assembly considerably in the holders opening operation and on the other hand levers 33 due to their faces 40 spaced from the pivot points of the levers oppose with less resistance the closing of the thread cutter head than catch bolts radially disposed and provided with the same inclined faces and with the same ring force.

WHAT WE CLAIM IS: 1. A self-opening, rotatable screwthread cutting head having a defined axis of rotation and comprising a base body, thread cutter holders pivotally mounted on said base body and adapted to support tangential thread cutters, spring loaded holder opening devices urging the holders to pivot open to move thread cutters thereon away from the axis of rotation of the head and clear of the workpiece so that the head can be moved in a rapid traverse, a control ring assembly mounted for rotation with the base body, said control ring assembly comprising a cam ring having spiral cam surfaces which engage cam follower surfaces of said holders to hold the holders against said pivoting open of the holders, said cam ring being clamped to the remainder of the assembly but being releasable so that it can be rotated to adjust the setting of the holders by cam action through said cam surfaces, said ring assembly being displaceable axially relative to said base body to a limited extent to release the hold on the holders so that they can spring to an open position in which bevel surfaces of the holders engage bevel surfaces of the cam ring preventing further opening of the holders, the body further including pivot levers which are spring loaded to pivot outwards relative to the axis of rotation about axes which are transverse to said axis of rotation, said levers being held in an inwardly pivoted position when the ring assembly is positioned so that the cam ring holds the holders in the closed position and being free to swing outwardly to a limited extent when the ring assembly is displaced to allow the holders to move to the open position, said levers having inclined surfaes which engage corresponding inclined surfaces on the ring assembly to assist the displacement of the ring assembly to allow the holders to move in the open position.

2. A head according to claim 1, wherein the pivot of each of said pivot levers is defined by a ball formation at one end of the lever which ball formation is located in a recess in the base body.

3. A head according to claim 1 or 2, wherein there are two of said pivot levers located diametrically opposite relative to the axis of rotation of the head.

4. A head according to claim 1, 2 or 3, wherein the inclined surfaces lie at an angle of 60 to the axis of rotation.

5. A self-opening, rotatable, screwthread cutting head, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. of the ring 10 and prevents an unintended rotational movement of the ring 10 and the cam ring relative to the body and thus an undesired adjustment of the screw thread holders. Two opening levers 33 which are located diametrically opposite are located in corresponding recesses of the base body 1 and are mounted for pivoting about axes which are transverse to the axis rotation of the head by having ball formations 34, engaged in recesses in body 1. The levers 33 are pressed outwards by compression springs 35. When the head is closed, the opening levers 33 lie with their part cylindrical surfaces 36 lying with their axes on the axis of the bore of the ring 10. In use, the head moves with the machine tailstock in the direction of the axis of the bore of the body 1 whilst cutting of the screw thread on the workpiece takes place. As soon as the desired length of thread of the workpiece is almost reached, the opening of the screw thread cutting head is effected by a stop (not shown) on the machine tool or as in this embodiment by means of a switch fork (not shown) which is engaged in the annular groove 37 of the ring 10 and which at the appropriate time, holds the ring 10 and ring 11 from progressing further in the feed direction, whilst the base body 1 which for example is screwed on to the tailstock in the region of its recess 8, proceeds further with the screw thread cutter holders 3.The base body 1 and the screw thread holders 3 now continue further until the bevelled edges 38 adjacent the faces 26 (Figure 1) meet the corresponding bevelled edges 39 adjacent the spiral cam surfaces of the cam ring 11. At this moment also, the inclined faces 40 on the opening levers 33 meet the corresponding inclined faces 41 in the ring 10 which respectively lie at an angle of 60 to the axis or rotation of the screw thread cutting head, and the holders spring to the open position in which the bevel faces 39 and 38 are in engagement. According to the embodiment of the invention, the opening of the holders 3 is accelerated and the relative return movement of the ring 10 and the ring 11 axially in respect of the base body is facilitated due to the fact that on the one hand the compression springs 35 act via the faces 40 and 41 on the levers 33 and ring 10 to accelerate the relative axial movement of the ring assembly considerably in the holders opening operation and on the other hand levers 33 due to their faces 40 spaced from the pivot points of the levers oppose with less resistance the closing of the thread cutter head than catch bolts radially disposed and provided with the same inclined faces and with the same ring force. WHAT WE CLAIM IS:

1. A self-opening, rotatable screwthread cutting head having a defined axis of rotation and comprising a base body, thread cutter holders pivotally mounted on said base body and adapted to support tangential thread cutters, spring loaded holder opening devices urging the holders to pivot open to move thread cutters thereon away from the axis of rotation of the head and clear of the workpiece so that the head can be moved in a rapid traverse, a control ring assembly mounted for rotation with the base body, said control ring assembly comprising a cam ring having spiral cam surfaces which engage cam follower surfaces of said holders to hold the holders against said pivoting open of the holders, said cam ring being clamped to the remainder of the assembly but being releasable so that it can be rotated to adjust the setting of the holders by cam action through said cam surfaces, said ring assembly being displaceable axially relative to said base body to a limited extent to release the hold on the holders so that they can spring to an open position in which bevel surfaces of the holders engage bevel surfaces of the cam ring preventing further opening of the holders, the body further including pivot levers which are spring loaded to pivot outwards relative to the axis of rotation about axes which are transverse to said axis of rotation, said levers being held in an inwardly pivoted position when the ring assembly is positioned so that the cam ring holds the holders in the closed position and being free to swing outwardly to a limited extent when the ring assembly is displaced to allow the holders to move to the open position, said levers having inclined surfaes which engage corresponding inclined surfaces on the ring assembly to assist the displacement of the ring assembly to allow the holders to move in the open position.

2. A head according to claim 1, wherein the pivot of each of said pivot levers is defined by a ball formation at one end of the lever which ball formation is located in a recess in the base body.

3. A head according to claim 1 or 2, wherein there are two of said pivot levers located diametrically opposite relative to the axis of rotation of the head.

4. A head according to claim 1, 2 or 3, wherein the inclined surfaces lie at an angle of 60 to the axis of rotation.

5. A self-opening, rotatable, screwthread cutting head, substantially as hereinbefore described with reference to the accompanying drawings.