GB479493A - Improvements in thread chasing mechanism for automatic lathes - Google Patents

Abstract

479,493. Automatic thread-cutting. FAIRWEATHER, H. G. C. (National Acme Co.) Aug. 5, 1936, No. 21.589. [Class 83 (iii)] Thread-cutting mechanism for an automatic lathe comprises a vertically and horizontally movable slide arrangement carrying a cutter, a pattern carrying clutch-controlled shaft, means for rotating it, means operated by the slide arrangement for controlling the clutch, an axially movable oscillating shaft, means operated thereby for horizontally shifting the slide arrangement, means carried by the oscillating shaft and co-operating with the pattern of the pattern-carrying shaft for axially moving said oscillating shaft, and means for oscillating said shaft at a predetermined time. The cutter 4, Fig. 1 (elevation) is carried on a vertical slide 2 arranged on a horizontal slide 1 which is mounted on a main vertical slide S moved bv the usual machine cam shaft. An inclined edge 23 on the slide S engages a horizontal rod 24 and serves through the lever 25 to close a friction clutch 6 and thus start the thread cutting motions. The driving shaft 20 rotates at the same speed as the work spindle of the machine, but the gearing 21 is adapted to rotate the shaft 6 at only half this speed so that the pattern or lead screw 7 is provided with a thread pitch twice the value of that to be cut. This lead screw may be replaced by others of a different pitch and the wheels 8, 9, 10 may be changed to vary the driving ratio of a cam 11, adjustably fastened to the wheel 10, when it is desired to cut threads of more than one start. The cam 11 is adapted to engage, in the retracted position of the thread cutting tool, a lever 13 the movement of which is transmitted to the nut-part 15a, Fig. 4, through a cushioning spring 33. A lever 14 is at the same time rotated to bring its spring pressed end 14a into contact with a ledge 14b thus retaining the nut-part in engagement with the leadscrew as the former is moved along. The horizontal movement thus obtained is transmitted through a tie-bar 16 to a rod 18 coupled to the horizontal slide 1. This movement continues until the nut-part falls out of engagement with the screw by the part 14b reaching the end of the ledge 14a or positively by an abutment 15d and roller 15c Fig. 2, the parts being then returned to the initial position by a compression spring 37 surrounding the rod 18. Relief of the cutter prior to the return of the horizontal slide for the start of another cut is obtained through a cam 35, Fig. 1, which engages with the face 34 of the vertically movable tool carrying slide and releases the latter, pressed upwardly by springs 36, a sufficient distance to clear the cut threads when the reduced. part of the cam comes into operation. This slide is positively moved downwards by a lever 42 engaging a cam surface 41 for the start of another threadcutting operation. An' adjustable screw stop 43 limits the downward movement of the main slide S.