Patent GB-551553-A (GB)
Title: Thread cutting mechanisms
IPC: B23G7/00
Filed: 1941-07-24
Abstract: 551,553. Screwcutting dies and taps. LANDIS MACHINE CO. July 24, 1941, No. 9409. Convention date, Aug. 3, 1940. [Class 83 (iii)] A taper screw-thread cutting device has the radial movements of the cutters controlled by a cam bar coacting with an axially movable member and having spaced camming surfaces engaging longitudinally spaced surfaces on said member, the cam bar being adjustable by small increments to predetermine the degree of taper. The body 10 encloses a sliding pilot assembly including end plates 19, 20 spaced by bars 31, 32, the plate 20 being fitted with a stud 22 carrying a work-abutting member 24. A sine bar 34 is pivoted by a pin 33 to the bar 32 and is adjustable to different angular settings. The bar has a groove 43 connected by a pin and sliding block to a transverse cam bar 47 so that as the pilot assembly is moved rearwardly a transverse movement is imparted to the cam bar which has ai opposite ends cam grooves 48, 49 coacting with tongues secured to a cam ring 54 slidable on the body 10 and adjusted by a ring 57 screwing ovet a closing ring 58 to determine the cutting setting of the chasers. The rings 54, 58 are slidably keyed together by pins 59 and the ring 58 has camming prongs 63 which key it to the head 10. The cam ring 54 is constantly urged rearwardly by springs 67 passing through holes in the closing ring, this movement being normally resisted by the engagement of bar 47 with the surface 70 of a latch ring 71 having radially sliding latch members 73 coacting with a locking ring 76 screwing on the body 10. Normally the front of the bar 47 engages a pair of hardened members 79 secured to the body. A sealing ring 93 bridges the gap between the ring 58 and the head 65 of the body. Each chaser assembly comprises a slide 96, Fig. 2, of approximately rectangular form having oil grooves 101. Gib plates retain the slide in its recess against the bottom surface 81 thereof. The chaser-holders 113 are secured by screws 118 to the slides 96 and each holder has a recess to accommodate a tangential chaser secured by a clamp 122 by means of interlocking serrations as described in the U.S.A. Reissue Specification 20930. An integral lug 110 on the slide 96 resists radial movement of the chaser and to resist tangential thrust each gib plate is formed with a lug engaged by a vertical surface of the holder. In operation, the head is normally moved against the rotating work and after the chasers have started the cut the pilot assembly is progressively moved rearwardly to the position shown in Fig. 6 so that the cam bar acts to move the assembly consisting of rings 54, 57, 58 rearwardly to progressively open the dies and impart a taper to the thread. The sine bar may be adjusted to change the rate of taper or a different range of tapers may be cut by changing the bar 47 for one having differently inclined cam grooves. Such grooves may be vertical for cutting straight threads or the sine bar may be set parallel to the head axis. When a predetermined thread length has been cut trip members 135 carried by rods mounted between the plates 19, 20 are engaged by collars 136 on the rods to move the latches 73 outwardly so that they snap into recesses 150 in the locking ring to allow the ring assembly to move rearwardly and open the dies. To reset the dies a yoke ring on an operating ring 146 is moved forward to return the ring and the chasers to their original position. During this movement a plate 157 engages the latch ring and moves it into a position wherein the latches may be moved radially inwards to their operative position by springs 142. Springs 161 assist in returning the pilot assembly to its original position. The invention may be modified for tapping, the camming means being in this case arranged to produce an inward movement of the tools during the threading operation. Specification 343,834 and U.S.A. Specification 2,054,028 also is referred to.