Patent GB-274924-A (GB)
Title: Improvements in and relating to screw-cutting die-heads
IPC: B23G5/12
Filed: 1926-02-25
Abstract: 274,924. Marks, E. C. R., (Landis Machine Co.). Feb. 25, 1926. Screwing die-heads.-A screw-cutting die-head comprises a front part including a head body with longitudinal cylindrical bores of uniform diameter to receive the trunnions of the chaserholders, a plate at the rear of the front part of the head having openings for reduced rearward extensions of the trunnions and means for. holding the trunnions in place relatively to the plate; the longitudinally sliding rear part of the head is resiliently held in engagement with the front part, which carries an operating ring and a setting ring, and pins fixed on the rear part pass through holes in the setting ring and engage holes in the operating ring to lock it in position. The front part consists of a body 30, Fig. 10, carrying the trunnions 39 for the chaser-holders and on which are mounted an operating ring 31 for the chasers and a setting ring 33 for determining the size of thread to be cut. The rear part consists of a non-rotary shank 63 for attachment to a machine turret &c. carrying pins 47 which project into the front part to lock the ring 31 in operative position and is yieldingly attached to the front portion by screws 49 which carry springs 66 tending to draw the two parts together. In operation, the two parts move forwards together on the rotating work until the turret &c. is arrested by a stop, when the front portion moves on alone and the pins 47 become liberated from the ring 31 which is then free to rotate under spring pressure to open the head. The pins 47 engage hardened bushes 48 in the ring 31 and the trunnions 39 are secured with the requisite amount of end play by nuts 40 which engage threaded reduced extensions of the trunnions passing through holes in a plate 34 secured at the back of the front part of the head, the nuts 40 being locked by conically ended screws 42. The chaser-holders 43, Fig. 2, are secured to the trunnions by screws 46 and are moved into and out of cutting position by pins 44 on the ring 31 which engage blocks 45 sliding in slots on the holders. Opening of the head is performed by a spring 51, Fig. 5, arranged in a tangential opening in the ring 33 and engaging a bar 50 secured to the ring 31. The positions of the spring and a closing plug 54 may be reversed to reverse the direction of thread cut by the chasers. The ring 33 is rotated relatively to the body 30 to vary the operative diameter of the chasers by means of a worm 57, Fig. 6, engaging annular teeth 56 on the body and locked against endwise movement by a nut 61 and a washer 62 sliding on a squared portion of the worm. Graduations are provided on a collar 60 of the worm to facilitate adjustment, and graduations are also provided on the periphery of the rear portion 64, Fig. 10, of the head which register with zero marks on a ring 34 which rotates with the ring 33. In a modification the pins 47 have concentric reduced ends which engage the bushings 48 when withdrawn and in a further modification the pins have eccentric reduced ends and may be rotated through 180‹ so as to set the ring 31 in two positions for effecting a roughing and a finishing cut. The chasers are re-set for a fresh cut by a radial handle on the ring 31. The resetting may be performed automatically by a cam, and the bushings 48 may be duplicated, each pair 48<1>, Fig. 21. being separated by a reduced face 75 which allows for overtravel of the ring 31<1>. In a modification of the self-opening mechanism. a work-engaging stop is provided in the central bore of the head and is adjustably connected to the shank 63 so that on engagement with the end of the work the forward movement of this part is arrested.