GB442941A - Improvements in or relating to grinding machines and methods of grinding - Google Patents

Abstract

442,941. Centreless grinding. HEALD MACHINE CO., 10, New Bond Street, Worcester, Massachusetts, U.S.A.-(Assignees of Blood, H. L.) Aug. 13, 1934, Nos. 23322 and 23323. Convention dates, Aug. 14, 1933 and June 1, 1934. [Class 60] To obtain substantial constancy of internal diameter of workpieces ground, either singly or a number at a time, on a centreless grinder, irrespective of variations in their outside diameters, the workpieces a, Fig. 3, are supported on their outer surface by rotatable rolls 45, 48 and are internally ground by a wheel 5 which contacts with the workpiece at a point d not in the radial lines connecting the centre b of the workpiece to the points at which the rolls support the outer surface ; and the relative feed of wheel and workpiece is in a direction making a sufficiently large angle with the plane f, h in which the axes of workpieces of different outside diameters all lie as to ensure the desired constancy of internal diameter. In Fig. 3, a and a<1> represent workpieces of normal and oversize outside diameters respectively, their centres lying at band b<1> when they are supported on the rolls 45, 48. The direction of feed of the grinding-wheel 5 is at right-angles to the line f, h passing through band b<1>, and the feed ceases automatically when the wheel becomes tangent to a plane e, at which time the workpiece a of standard outer diameter is ground exactly to the desired internal diameter. In the case of the workpiece a<1>, of greater external diameter, the centre of which lies at b<1>, the final point of contact of the grinding wheel will be at d<1>. Since the distance b, b<1> is small the distance between the points d, d<1> is also small, and hence the deviation of the periphery of the wheel at the point d<1> from the tangent plane e through the point d will be negligible ; hence the internal diameter to which the oversize workpiece a<1> is ground will be substantially the same as that of the standard size piece a. Figs. 1 and 2 show a machine operating on this principle. The workpieces a are supported on rolls 45, 48, the former being positively rotated and the latter being adjustable horizontally by a screw 50, the normal adjustment being that in which the workpieces are supported with their axes in the horizontal plane of crossfeed movement of the axis of the wheel 5. Rollers 56 on spring-urged pivoted arms 55 rest on the workpieces to maintain them in contact with the rolls, their axes being inclined to those of the rolls so that they urge the workpieces against a rotating backing-plate 63. The grinding-wheel head 6 is reciprocated hydraulically, dogs 12, 13 on the table 2 which carries the head operating the reversing lever 8 at the ends of the stroke. Crossfeed of the wheel head is effected by a screw 17 carrying a ratchet-wheel 18 engaged by a pawl 25 on a three-armed lever 24, which is rocked by the engagement with it of a roller 28 on a bellcrank lever 30 operated through a link 24 from a bell-crank lever 32 carrying a roller 34 which rides up a cam 35 at each reciprocation of the table 2. The grinding operation ceases when a cam 20 rotatable with the ratchet wheel 18 engages a switch arm 36 to complete an electric circuit which causes the reversing dog 13 to be raised, so that the table makes a long stroke to the rest position. Mechanism, not described, is provided for compensating the cross-feed for the wear of the grinding wheel. The invention may be applied to the grinding of single workpieces in succession, or to a number at a time. Fig. 4 shows two workpieces, of which a<1> is oversize, being simultaneously ground, the termination of the grinding operation being determined by the entry of a plug gauge 68 into the aperture in a when it has reached the standard size. The method of supporting the workpieces and the direction of feed of the grinding wheel being as described in connection with Fig. 3, the apertures in the standard size workpiece a will be the same size as that in the oversize workpiece a<1> when the grinding is terminal. Specifications 254,417 and 290,999, [both in Class 60], are referred to.