630,193. Screw-cutting lathes. TAREX SOC. ANON. Jan. 17, 1946, No. 1604. Convention date, June 6, 1945. [Class 83 (iii)] An automatic screwcutting lathe having a tool mounted on a cross-slide, the longitudinal movement of which is controlled by a shoe co-operating with a lead-screw, is characterized in that a quick-action relay is provided under the control of a latch device, the parts of which are disengaged at the end of each working stroke by the movement of a longitudinal slide forming a part of the cross-slide, the relay producing disengagement of the shoe at a speed independent of the speed of rotation of the leadscrew. The machine spindle 1, driven by an electric motor M, carries the workpiece 4 and is connected by gearing 17, 15 and a splined extension 12 to a lead-screw 10. A coupling 18 on the end of a non-rotatable shaft 22 connects the shaft 11 carrying the lead-screw to the longitudinal tool-carrying slide 7 so that on engagement with a slidable part-nut or shoe 25 the lead-screw moves to the right and carries the tool-holding slide with it. The latter slide moves in guides across a transverse slide 6 carried on the bed of the machine. Engagement of the shoe with the lead-screw is effected at the start of an operation by moving a handlever L clockwise into the position shown in the drawings. This engages a clutch 35 to start rotation of a cam 31 which lifts an arm 30 secured to shaft 29 and thus moves the arm 27, also secured to shaft 29, and engaging a recess 28 in the underside of the shoe. At the same time the movement of the lever L rotates a shaft 36 carrying a projection 45 and a toothed segment. The projection is moved ahead of a pair of latches 46, 47 which retain it in position and the toothed segment meshes with a rack 38, moving it inwards to feed the cutting-tool or tools 79 nearly up to the work. Rotation of the shaft 29 by the cam 31 also rotates the gear segments 111, 110, 104, and moves the rack 102 to the right to compress a spring 100, the spring being retained in a loaded position during the cutting stroke by a latch 107 engaging an arm 106 integral with gear segment 104. An arm 103 extending from the rack 102 simultaneously, through linkage and gearing, rotates a member 61 and a crank and slotted lever arrangement 59, 60. The member 61 moves a subsidiary slide 41 on the transverse slide 6, to the left, so that a recess 80 therein is moved out of line with the rack bolt 38 and the tools are thereby moved up to the surface of the work. The crank and slotted lever controls a ratchet mechanism 55, 57 which puts on the necessary cut at the start of each new stroke, including the first, by means of a cam 51, rotating with the ratchet-wheel, a lever 48 rotating about an axis 49 and the latches 46, 47 pivotally carried on a small arm integral with the lever 48. Withdrawal mechanism. At the end of a cutting stroke a stop 81 on the slide 7 pushes a member 82 to release the trigger or latch device 106, 107. The spring 100 then pushes the rack 102 to the left and the segmental gears move to turn the shaft 29 and withdraw the shoe 25 from the lead-screw. Simultaneously, through the arm 103, the member 61 is rotated to move the slide 41 to the right, aligning the recess 80 with the latch 40 and allowing a spring 43 to withdraw the slide and the tools from the work, a spring 8 returning the longitudinal tool slide 7 to its starting position against a stop 9. Completion of cut. The ratchet-wheel 53 and cam 51 are connected by gears 54, 73 to a rack 71 moved against spring tension 72, which contacts a stop set for the end of the cut. This stop moves a trip-lever 70 which withdraws the latch 47 from under the projection 45, thus allowing the slide 6 to be withdrawn by spring 43. On return of this slide a ramp 76 moves lever 77, the end of which operates the trigger and relay gear for withdrawing the shoe 25, and rotates shaft 64 to withdraw the pawls 63 and 55, enabling the ratchet-wheel to return to its initial position. This initial position and thus the starting point used on the cam 51 is determined before a thread-cutting operation by an adjustable stop 75 which controls the position of a stop-rod 74 engaging in a groove in the rack-member 71. Specification 630,194 is referred to.