Engineering Drawing - Lecture 10 - Projection of Solids - Solids

Oct 28, 2026

Lecture 10 on Projection of Solids explains 3-D objects by defining solids as bodies bounded by plane or curved surfaces and classifying them into polyhedra and solids of revolution. It details regular polyhedra including tetrahedron, cube/hexahedron, octahedron, dodecahedron, and icosahedron, then outlines other polyhedra such as prisms and pyramids with types like right and oblique. The lecture also covers generation of solids via revolution and introduces visibility rules for orthographic views using full and dashed lines to represent visible and hidden edges.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages221

Reading Time9 h 17 min

AccessFree to download

Engineering Drawing

Lecture 10

Projection of Solids

Solids

Polyhedra

Solids of Revolution

Visibility and Orthographic Views

Engineering Drawing Lecture 10 Projection of Solids 1 Solids A 3-D object having length, breadth and thickness and bounded by surfaces which may be either plane or curved, or combination of the two. ▪ Classified under two main headings ▪ Polyhedron ▪ Solids of revolution ▪ Regular polyhedron – solid bounded only by plane surfaces (faces) . Its faces are formed by regular polygons of same size and all dihedral angles are equal to one another. ▪ Other polyhedra – when faces of a polyhedron are not formed by equal identical faces, they may be classified into prisms and pyramids. Five regular polyhedra Tetrahedron – four equal equilateral triangular faces Cube/hexahedron – six equal square faces Octahedron– eight equal equilateral triangular faces Dodecahedron – twelve equal regular pentagonal faces Icosahedron– twenty equal equilateral triangular faces Prism – a polyhedron formed by two equal parallel regular polygon, end faces connected by side faces which are either rectangles or parallelograms. Different types of prisms Pyramids – a polyhedron formed by a plane surface as its base and a number of triangles as its side faces , all meeting at a point, called vertex or apex. Axis – the imaginary line connecting the apex and the center of the base. Inclined/slant faces – inclined triangular side faces. the apex and the base corners. Right pyramid – when the axis of the pyramid is perpendicular to its base. Oblique pyramid – when the axis of the pyramid is inclined to its base. Triangular pyramid Pentagonal pyramid Square pyramid Hexagonal pyramid Rectangular pyramid Oblique pyramid Solids of revolution – when some of the plane figures are revolved about one of their sides – solids of revolution is generated. Cylinder – when a rectangle is revolved about one of its sides, the other parallel side generates a cylinder. Cone – revolved about one of its sides, the hypotenuse of the right triangle generates a cone. Sphere –when a semi-circle is revolved about one of its diameter, a sphere is generated.. Oblique cylinder – when a parallelogram is revolved about one of its sides, the other parallel side generates a cylinder. Oblique cone Truncated and frustums of solids – when prisms, pyramids, cylinders are cut by cutting planes, the lower portion of the solids (without their top portions) are called, either truncated or frustum of these solids. Visibility – when drawing the orthographic views of an object, it will be required to show some of the hidden details as invisible and are shown on the orthographic views by dashed lines Rules of visibility All outlines of every view are visible – the outlines of all the views are shown by full lines. In the top view, the highest portions of the object are visible. Frustum of a pentagonal pyramid – the top face ABCDE is the highest, it is completely visible in the top view. In the top view, edges ab, bc, cd, de an d ea are shown as full lines. The bottom pentagonal faces A1 B 1 C 1 D 1 E 1 is smaller than the top face, hence invisible. The slant edges AA1 , BB 1 , CC 1 , DD 1 and EE 1 are invisible in the top view, hence they are shown as lines of dashes. The line connecting a visible point and an invisible point is shown as an invisible line of dashes unless they are outlines.

FAQs

How are solids classified in this lecture?

Solids are classified under two main headings: polyhedron and solids of revolution.

What makes a regular polyhedron different from other polyhedra?

A regular polyhedron is bounded only by plane faces formed by regular polygons of the same size, with equal dihedral angles. Other polyhedra have faces that are not formed by equal identical faces and may be classified into prisms and pyramids.

What visibility rules are used in orthographic views?

All outlines are shown by full lines. Hidden details are represented using dashed lines, and the highest portions are visible in the top view while lower or slant edges may be treated as invisible and drawn with dashes.

Oct 28, 2026

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