Chapter 4 - Representation of Elementary Shapes

Abstract

This chapter summarizes, completes, and compares elementary curves, elementary surfaces, offset geometric entities, solid primitives, and form features. The choice of elementary shapes starts with a straight line. Straight lines are applied as edges of flat, ruled, or other surfaces. Arcs are the elements of compound lines, sections for fillets, and serve many other purposes. Types of elementary surfaces for industrial design engineering are flat surface, rotational surface, tabulated surface, ruled surface, fillet surface, lofted surface, swept surface, and free form surface, of which fillet is of utmost importance. Fillet surfaces are created along a common edge of two surfaces or between two surfaces having no common edge. Construction and application of part models often require making copies of curve and surface entities at a predetermined distance from the original one. Each point of the copy is at the same distance from the same point on the original. Referring to the method of creation, copies are called offset curves and surfaces. A solid primitive is prepared for combination with other solid primitives or a more complex solid model under construction. It is created in its final position or repositioned after creation somewhere in the model space. Values of its dimensions are set and the solid primitive is ready for one of the element combination operations. The shapes of primitives are predefined for the modeling system or defined by engineers at the application of the modeling system. The basic concept of modification of a shape by form features is volume adding and removing.