Patent GB-936857-A (GB)
Title: Device for controlling the depth feed in the metal of workpieces in helical surface grinding machines
IPC: B23F13/04
Filed: 1959-11-18
Abstract: 936,857. Grinding screw-threads. P. DURAND. Nov. 18, 1959 [Nov. 19, 1958], No. 39099/59. Class 60. A device for controlling the axial displacement of the workpiece support in a machine for grinding the flanks of the threads of a multistart screw, the workpiece moving axially whilst rotating about its axis and being ground by a separately-driven cupped wheel, includes means whereby the position of the support relative to the grinding wheel is adjusted, after all the threads have been ground, by a step-bystep telephonic-type counter and a relay actuated by the support during each grinding pass, the counter controlling a hydraulic piston mechanism coupled with the support driving means to effect the required shift of the support to put on feed before a further cycle of flank grinding is begun. Feed is adjusted by a nut 5, Fig. 1, on the lead-screw 4, rotation of the nut relative to the screw effecting a slight advance of the work towards the wheel 1. A toothed piston 6, Fig. 2, meshes with a sector 7 which unidirectionally drives a shaft 10 to which wheels 12, 13 are selectively secured in driving engagement by a clutch 14; meshing gears 15, 16 are rigidly mounted on a countershaft 47 through which the nut 5 is driven by a further shaft 49. An idler pinion 17 is interposed between gears 13 and 16 to enable shafts 47 and 48 to be reversed when the clutch 14 is moved by a shifting mechanism 45, 46 to engage gear 13 for drive by the shaft 10 so that work having an oppositely-handed helix may be ground. During the return or non-cutting stroke of the table 2, a stop a 1  strips a switch a, Fig. 2, to break the circuit of a relay CI<SP>1</SP> of the counting device CI, the relay CI<SP>1</SP> effecting a single step at each de-energization of its winding by the opening of the switch a. The counter CI having been set to respond to the number of thread starts of the work, the relay operates CI after this number of breaks through a time-lag device T 2  to energize an electromagnetic valve E to cause displacement of the piston 6 to apply feed. A micrometerically-adjustable stop 25 enables the depth of feed to be controlled by limiting the piston stroke through a series of stepped stops 23 which are engageable by an extension 24 of the piston. The ratchet wheel 9 drives a graduated plate forming part of a manually adjusting hand wheel 11, an adjustable stop 26 being carried by the periphery of the plate. This stop provides an automatic stop when the total of the successive cuts has reached the desired full depth of cut and is pre-set by the operator. A T-shaped lever having arms 27, 29, 31 is actuated by the stop 26, which contacts the arm 27 after the ratchet wheel 9 has been moved through the pre-set angle. A spring-loaded plunger 30 is engaged by the arm 29 to locate it in a second position in which the arm 31 has moved a sliding stop 32 to engage a hole 33 in the sector 7 as it returns to its initial position, thus immobilising it after the last shift of the nut 5. Manual means are provided for controlling partial feeds. A pivoted lever 34 has a noseportion 37 which engages the sector 7, the extent of movement imparted to the sector being determined by a micrometerically adjustable stop 35; this manual control means may be substituted for the automatic control device, the ratchet pawl 7 then being disengaged from the wheel 9.