Improved method of producing a substantially spherical or substantially cylindrical surface of large radius

854,521. Milling; planing. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 9, 1957 [April 16, 1956], No. 11510/56. Class 83 (3). A method of producing a surface of substantially circular cross-section on a member A, comprises supporting the member on spaced abutments a, a , b, b , applying force to the member at a region located symmetrically with respect to the abutments and on the opposite face of the member from that engaged by the abutments, so that the member is deflected into a convex or concave shape, machining the curved face of the member into a plane surface e, and then removing the deflecting force to restore the member to an unstressed condition and allow the machined surface to acquire the desired shape. For producing a substantially cylindrical or spherical convex surface, a single or, as illustrated, a double row of abutments a, a , b, bl is provided which, in the case of a spherical surface, follows a circular path, the deflecting force being applied by bolts f. In the case of a spherical surface, central pressure is applied by one or more bolts, or by an eye-bolt screwed or welded to the underface of the member and stressed by a hook bolted to a bedplate. For producing concave surfaces, abutments in the form of clamps restrain outward movement of the periphery of the member while it is deformed, as by a screw-jack, into convex form. The convex surface is then machined into a plane surface and the deforming force released to allow the machined surface to assume a concave form. Alternatively, the central portion of the member is supported on one or more abutments, and the deforming force applied to the periphery by bolts. Instead of clamping the members to the bed of a machine to produce the deforming force, one member may be clamped to another with interposition between them of the abutments, the members thus being deformed in pairs. If the deforming force stresses the member beyond its elastic limit, so that its initially plane unmachined undersurface does not return to plane form, the member is bolted against the plane surface of a backing to restore the undersurface to plane form.