GB425311A - Improvements in metal grinding operations - Google Patents

Abstract

425,311. Grinding eccentric workpieces &c. HARLEY, S. J., Long Bend, Old Leamington Road, Stivichall, Coventry. Sept. 7, 1933, No. 24852. [Class 60] [See also Group XXXVII] In grinding metal work-pieces the rotational speed of the work is varied during revolution so that a constant grinding speed may be maintained while grinding eccentric work-pieces or, in grinding a fluted tap, the work may be speeded up while the wheel is passing over the flutes. In Fig. 1 the rotary contact a of a switch b is driven at the same speed as a tap being ground. The driving motor d has a speed regulating resistance e which is shortcircuited each time the arm a engages one of the fixed contacts c----c<3> corresponding in number to the flutes of the tap. In this way the motor is speeded up each time the wheel passes over a flute. In a modification the switch may have a single contact and the arm a make one revolution for each flute in the work. In another modification, Fig. 2, the resistance e is shorted by a switch f actuated by a cam g driven in unison with the work, the double cam shown corresponding to the grinding of a twoflute tap. In another modification a threephase motor is employed and a switch is operated by a cam to make and break the circuits of exciting coils of triple-pole contactors serving high and low speed windings of the motor. In another modification, Fig. 4, the field windings of a generator G and work driving D.C. motor d are both supplied with current from an exciter C which with the generator may be coupled to a main motor M. In this case a cam g<2> operates switches f<2>, f<3> adapted to short-circuit resistances e<1>, e<2> in the field circuits of the generator and motor. In a further modification a cam such as g<2> controls a resistance in the field circuit of the generator only and the field circuits of generator and motor are supplied from mains instead of from an exciter. In a similar form, Fig. 6, the regulating resistances e<1>, e<2> are each connected in series with the field windings of generator G and motor d respectively. In a machine embodiment the cam g operating the switch f through a plunger l is mounted on a spindle driven from a loose wheel n through a splined clutch k. In order to vary the times of acceleration of the work the shoulders of the cam g are formed with helical faces and the cam is axially adjustable relatively to the plunger l. In the case of grinding eccentric cams the speed controlling cam may be a replica of the work to be ground and may move a contact along a suitable regulating resistance. In another modification a constant speed motor may be employed and a control cam may operate variable speed gearing of known type to effect the required speed changes. In another form the speed changer may consist of a hydraulic pump and motor system of known type.