GB325764A - Improvements in or relating to screw cutting lathes and like turning engines - Google Patents

Abstract

325,764. Schaerer, O. May 29, 1929. Lathes.-In a screw-cutting lathe of the type wherein the work 2 rotates continuously in one direction while the lead screw 4 is reversed to return the tool between successive cuts, means operated from the work spindle are provided for ensuring that, at the end of the return movement, the lead screw reversal for a fresh cut is effected when the work and the tool are in correct phase relation. The shaft 6, which is connected to the lead screw by the usual change gears 13 .. 15 may be driven from the work spindle 1 either by the gears 8, 11 for the forward movement or by the gears 9, 10, 12 for the return movement. These gear trains are selectively engaged by means of a single-toothed sliding coupling 7 actuated by a fork 28. The fork carries a pivoted lever 17 coacting with a projection 18 on a stop rod 19 which is actuated by a projection on a cam disc 20 carried on the work spindle. Thus the shifting of the coupling 7 to re-engage the wheel 11 and start a fresh cut at the end of the return movement can only be effected at such times as the tool is in the correct position to re-engage the partly formed thread on the work. The movement of the coupling may be effected either manually or automatically. The cam disc 20 may alternatively be mounted on any other suitable shaft driven from the spindle 1, the number of cam projections being then dependent on the relative speeds of the work and cam shaft. In order to avoid shocks on reversal of the shaft 6 the lever 17 carries a cam projection 26 coacting with a similar projection 27 on a brake band 24 acting on a drum 25 secured to the shaft 6. Thus when the coupling 7 is shifted, the brake is momentarily applied to check the shaft 6 before the coupling is reengaged to effect the reversal.