Method and apparatus for working peripheral wall of hemispherical shell

A method of working the surface of a hemispherical shell having a center of curvature and a central axis of symmetry passing through the center of curvature, with at least one surface projection having a selected configuration and being spaced from said central axis, said surface of said hemispherical shell having rotationally symmetrical portions lying on a side of said projection adjacent said central axis and on a side of said projection spaced away from said central axis, comprising:

• rotating said hemispherical shell about said central axis;
• working said rotationally symmetrical portions of said surface to render said rotationally symmetrical portions spherical;
• said hemispherical shell having an intermediate surface portion lying on said surface of said hemispherical shell at a location spaced from said central axis an equal amount as said at least one surface projection;
• holding said hemisperical shell fixed and, with said hemispherical shell fixed, moving a working tool over the surface configuration of said at least one surface projection for working said surface projection;
• providing a cylindrical model ring which is fixed with respect to said hemispherical shell and which has a proximity switch activating area having a selected configuration which corresponds to an image projection of the selected configuration of said at least one surface projection;
• providing a contactless proximity switch which is operatively connected to a working tool for retracting the working tool away from the surface of the atmospherical shell when the contactless proximity switch passes said proximity switch activating area;
• working said intermediate portion of said hemispherical shell while said hemispherical shell is rotated about its central axis using said working tool in engagement with said intermediate surface portion, said contactless proximity switch moving around said cylindrical model ring with rotation of said hemispherical shell;
• retracting said working tool away from said surface of said hemispherical shell when said at least one surface projection passes as said hemispherical shell rotates;
• by a sufficient amount to avoid contact between said working tool and said surface projection, retracting of said working tool taking place by the passage of said proximity switch over said proximity switch activating area;
• and
• moving said working tool back into engagement with said intermediate surface portion after said at least one surface projection passes, movement of said working tool taking place after said proximity switch passes aid proximity switch activating area.