GB308874A - Improvements in or relating to grinding or abrading machines - Google Patents

Abstract

308,874. Hughes, V. A. B., (Cincinnati Grinders, Inc.). Feb. 25, 1928, Centreless grinding; gauges; guides and rests. - In a. centreless grinding machine, the work is controlled so that it is ground in relation to a predetermined final axis as distinguished from finding and establishing its own axis. The machine comprises grinding and regulating wheels with a work-receiving throat between them, two centring spindles in alignment with the throat and engaging the work therein, and a vertically movable work rest projecting between the wheels and supporting the work held by the spindles, at least one of the spindles being movable in a direction towards the grinding wheel within the limits imposed by a receding stop mechanism. The grinding-wheel B rotates on a stationary axis and the regulating- wheel C rotates in the same direction on a carriage D, Fig. 13, for movement to and from the grinding-wheel. A central bracket 16, Fig. 2, supports the work rest 10 having an inclined top surface and also supports a floating spindle 11 mounted by means of a ball joint 12 in a block 14 which is adjustable axially by means of a screw 19. Rotation of the block is prevented by a screw 17 engaging a slot therein and rotation of the spindle by a pin 20 whose ends lie in slots 20<1> in the block 14. The universal movement of the spindle is limited by a bracket 21 containing a spring plunger 23 which prevents the work from being lifted by the regulating-wheel when out of contact with the grinding-wheel. A second spindle 25, movable in and out of a tailstock 24, is also supported on the bracket 16. In grinding a two-diameter work piece 27, 28, whereof the portion 27 has been ground concentric with the centres in a previous centred or centreless method, a support 29 is provided for the portion 27, the work resting on this support and the rest 10 until it is engaged by the tailstock spindle 25. The latter assists in supporting the work without removing it from the rest 10. One side of the floating spindle 11 is flattened as at 30, Fig. 4, and is adapted to contact during the grinding operation with a screw stop 31 having a graduated collar 32 coacting with a pointer 33. In operation, if a work piece M, Fig. 5, is concentric with an axis N and is required to be ground concentric with an axis 0, the centres are set in alignment with the latter axis and the regulating-wheel is advanced so that the work is reduced in size by the grinding-wheel according to a uniform spiral R. On approaching the final size the spindle 11 engages the stop 31 and limits the advance of the work towards the grinding-wheel and in consequence the removal of material is according to an irregular spiral S and the centre of rotation of the work changes progressively from N to O. The flat face 30 is preferably arranged parallel to the common tangent of the finished work-piece and the regulating- wheel, thus producing the effect of a receding stop from the first movement of contact with the stop 31 and allowing the removal of a slight amount of material from the side having the shorter radius in order to prevent the formation of facets. The same result may be achieved by arranging the face 30 in a vertical plane and providing a stop 31 on a lever connected by linkage to the regulating wheel slide so that the stop may recede as the slide advances. In an alternative construction the grinding-wheel is mounted on a slide movable towards the regulating-wheel, the slide being connected to the stop through linkage. In a further modification, both spindles are capable of universal movement in ball-joints, one being arranged on a slide to allow axial movement for insertion of the work. In operating on the middle portion of a three diameter workpiece, the stop may contact with one of the previously formed cylindrical surfaces and for operating on work which is longer that the width of the wheels, the spindles are mounted on a slide capable of back and forth axial movement in the throat. In the form of machine shown in Fig. 2, the work rest 10 is vertically adjustable to suit different sizes of work by means of a wedge 45 and a screw 46 and in a modified form of machine the work rest 48, Fig. 13, is carried by a bracket 47 adjustable by means of a screw 50 along a, guide which is parallel to the line 49, this line being a radius in the work to the point of contact with the rest and making an angle of about 50‹ with the horizontal. In this machine the grinding-wheel B and regulating-wheel C are each mounted on adjustable slides S, D respectively. The floating motion of the spindle 11 may be wholly or partially restrained by providing a pointed screw at the end of a bracket enclosing a rearward elongation of the spindle and adapted, on adjustment, to engage more or less with a conical recess in its end.