Patent GB-509579-A (GB)
Title: Improvements in screw-threading die-heads
IPC: B23G5/12
Filed: 1938-12-08
Abstract: 509,579. Screw-cutting die-heads. FAIRWEATHER, H. G. C. (National Acme Co.). Dec. 8, 1938, No. 35852. [Class 83 (iii)] In a screw-cutting die-head, chasers are radially movable on the body by an axially sliding sleeve thereon and an internal slide has a number of pivotal connections with the sleeve and body so that a difference in movement between the slide and sleeve may be produced for cutting a taper thread on the work. The head body 2 is secured to a machine spindle at 3 and is preferably rotated whilst the non-rotary work x is fed axially. Circular chasers 11 are carried by holders 10 secured to slides 9 radially guided by renewable hardened plate 7 attached to a flange 6 on the body, the slides having bevelled grooves 14 engaged by similar ribs on plungers 12 attached to a flange 35 on an axially sliding sleeve 34. The sleeve is moved by pins 36 on a ring 29 pivoted at 31 to the body and rocked by a pin 28 thereon attached to a lever 25 pivoted at 26 to the body and oscillated by a pin 23 attached to a slide 15 guided axially within the body 2. An extension 17 of the slide 15 carries a removable ring 16 engaging the end of the work so that during screwing the slide 15 will be moved axially relatively to the body 2, thus rocking the lever 25 and therefore the ring 29 and causing the sleeve 34 to slide on the body and produce a tapered thread. The ring 16 is held between a nut 59 and a flange 57 on a sleeve 57<1> so as to have rotation relatively to the sleeve, the sleeve being adjustably screwed on the extension 17 and secured by a key 56 so as to vary the length of thread cut by the head before a trip operates to open it. For producing the longest thread the ring 16 is adjusted in the same plane as the rear faces of the chasers 11 so that a parallel thread will be cut before the ring meets the work to expand the chasers for producing the tapered thread, whilst if the ring 16 is placed level with the front of the chasers the thread will start tapered and will therefore be shorter. Adjustment of the ring 16 further forward, as shown in Fig. 6, causes the chasers to commence expanding before they reach the work and thus produces a still shorter thread. A coarse adjustment for diameter of work is made by engaging the ribs on the plungers 12 with different grooves 14 on the chaser slides 9 and a fine adjustment is made by axial movement of the pivot 31. This is effected by wedges 50 engaging a block 32 carrying the pivot and adjusted by screws 48, 49 whereof the former is graduated. The wedges are enclosed in a block 41 held on the body 2 by a trip lever 37 so that axial movement of the pivot 31 by the wedges 50 will rock the ring 29 and move the sleeve 34 axially through the pins 36. When the desired length of thread has been cut a cam plate 45, Fig. 17, secured in a fixed position on the internal slide 15 engages a tapered surface 46 on the trip lever 37 to rock one end inwardly and release it from a groove 40 in the block 41 thereby releasing the block from the body and allowing springs 42 to push back the block 41, ring 29 and sleeve 24 to open the head. The trip 37 may be relased at any time by depressing a plunger 65, Fig. 17, which acts on a spring- pressed plunger 69 engaging a bevelled depression 71 in the trip. Springs 42' push the slide 15 forwards as soon as the work has been removed, and the die-head may be re-set externally by a lever or yoke &c. engaging the ring 29 to oscillate it forwards until the trip 37 snaps into the groove 40 of the block 41, or re-setting may be effected internally by pushing a rod through the machine spindle against the slide 15 and causing a dog 60 thereon to engage a lug 63 on the block 41 and carry it forwards. Adjustment of taper may be made by removing the pin 23 from the slide 15. and replacing the lever 25 by a longer lever 25', Fig. 6, engaging a pin 24 on the slide to decrease the movement produced at 28 by the slide. Further adjustment may be effected by adjusting the fulcrum pin 26 on the lever radially by means of slots 51<11>, Fig. 15, on a plate 51 carrying the pin, this plate being secured in adjusted position by screws 51<1> and serrations 52 on a block 53 attached to the body 2. An additional adjustment may be made by mounting the pin 26 in another hole 54 of the plate.