Patent GB-759028-A (GB)
Title: Improvements in screw thread-cutting machines
IPC: B23G1/04
Filed: 1953-07-17
Abstract: 759,028. Screw-cutting lathes. CRI-DAN. July 17, 1953 [Aug. 7, 1952], No. 19946/53. Class 83 (3). In a screw thread-cutting machine of the kind disclosed in Specification 640,142, means are provided for taking a first series of cuts with a first cutting-tool, for stopping the machine or movement of the tool after the first series of cuts has been effected, and for making a second series of cuts with a second cutting-tool. In one arrangement, a cam 5, Fig. 2, engages a pusher 6 for the tool and is mounted on a shaft 4 having a toothed quadrant 3 meshing with a pinion 2 on a shaft 1 carrying a ratchet wheel 7 engaged by a catch 8, Fig. 1, and pawl 11. The catch is reciprocated between cuts by a bar 10 actuated by a feed-cam driven together with the pitch cam which moves the tool slide longitudinally of the work, the catch 8 turning wheel 7 by one tooth and thus advancing the tool. Discs 15, 16 are adjustably mounted on shaft 1 and have projections 17, 18 respectively for contacting levers 26, 35, projection 18 being wide enough to engage both levers simultaneously. Disc 16 has a scale 21 which is positioned relatively to a mark 22 on shaft 1 to determine the total number of cuts to be taken, and is then clamped by knob 23. Disc 15 has a scale 19 which is positioned relatively to a mark 20 on disc 16 to determine the number of finishing cuts in the second series, and is then locked by bolts 24. Levers 26, 30, 35 are pivoted to bolt 27, movement of lever 26 being transmitted to lever 30 by a peg 29. Projections 31, 36, Fig. 4, on levers 26, 35 engage projections 32, 37 on bosses 33, 38 to hold the bosses against rotation in the direction of the arrow F, such rotation when permitted causing boss 33 which is fixed to shaft 34 to stop the machine, and boss 38, which rotates on shaft 34 under the action of spring 41, to engage pawl 11 with an adjustable screw 40 and move the pawl away from wheel 7, the pawl also shifting the catch 8. Shaft 1 is thus released and quadrant 3 returns the cam 5 and discs 15, 16 to their starting position under the action of a spring. Operation. A roughing tool is inserted in the tool carrier and shaft 34 is turned in the opposite direction to arrow F, carrying therewith the bosses 33, 38 which have interengaging projections 48, 49, respectively, until the projections 31, 32 and 36, 37 are engaged. The machine then makes the first series of cuts until projection 17 pivots lever 26 which carries with it lever 30. Projection 32 is disengaged and boss 33 and shaft 34 rotate to stop the machine, whereupon the roughing tool is replaced by a finishing tool. Shaft 34 is then turned back until a projection 47 on the boss 33 engages a projection 45 on the lever 35 and the machine makes the second series of cuts until projection 18 moves both levers 35, 26 to disengage projections 45, 47 and 36, 37. Both bosses 33, 38 rotate in the direction of the arrow F to stop the machine and reset cam 5 and discs 15, 16 in their starting positions. In another arrangement in which the machine is modified so that the advance of the tool between cuts is effected hydraulically, the pitchcam acts on a valve controlling the supply of liquid to opposite ends of a cylinder containing a piston connected to bar 10. This valve is over-ridden by a shut-off valve actuated by boss 33 to stop the advance at the end of said first and second series of cuts. The pawl 11 is urged to engage wheel 7 by hydraulic fluid acting on a piston and controlled by a valve actuated by boss 38 to release the pawl at the end of the second series.