GB671252A - Improvements in machines for cutting screw threads - Google Patents

Abstract

671,252. Lathes. CHRISTEN, A. March 7, 1950 [March 8, 1949], No. 5798/50. Class 83 (iii). In a screw-cutting lathe for cutting crossed screwthreade 34 in a cylindrical bar 4, comprising at least two tools 1, 2 arranged for cutting threads in opposite directions and mounted on a carriage 3 reciprocable parallel to the bar, the tools being brought alternately into cutting contact with the bar for opposed directions of movement, the bar-holding means 4a is rotatable always in the same sense and the carriage 3 is reciprocated by means of a drum 7 coupled with the bar-holding means through gears 11, 12 and provided with helical ridges 8, 9 engaged by a roller 10 carried by the carriage. The tools are mounted on a carriage 6 reciprocable transversely on the carriage 3 by means of a finger 15 co-operating with a notch 16 in the carriage, movement being transmitted to the finger by a grooved shaft 17 which is moved angularly about its axis by a cam 18 and intermediate levers 19 ... 21. The depth of cut is increased for successive cutting operations by a roller 23 interposed between the levers 19, 20, the roller being displaced by a cam 24 co-operating with a finger 25 of a lever 26 acting on the roller. The cam 24 is driven by a pawl 27 co-operating with a ratchet 28, the pawl being displaced by means of a lever 29 rigidly connected to the lever 19. When the depth of cut has reached a predetermined value, the lathe is stopped automatically, e.g. by an abutment 33 on the cam 24 engaging a member 32 controlling a switch 31. By arranging that each tool is brought into cutting contact with the bar when the latter is in an angular position different from that which it occupied at the beginning of the preceding cut by the same tool, a multiple thread can be obtained.