CBSE Class 11 Engineering Graphics

Chapters: 3

1. Plane Geometry

Introduction to drawing · Lines, angles and rectilinear figures · Circles, inscribing and circumscribing

Technical Drawing: Communicating Design Ideas – Technical drawing is a shared visual language for showing the exact shape and size of an object. Designers start with freehand sketches, then use pictorial views (isometric, oblique) to show the object in 3D, and orthographic projection (front, top and side views) with standard lines, dimensions in millimetres and a scale so that anyone can make it. Today most drawings are made with CAD software.
Geometric Constructions: Drawing Exactly with Compass and Straightedge – A geometric construction draws a figure exactly using only a compass and a straightedge (a ruler used for straight lines). Key constructions: the perpendicular bisector of a segment, the bisector of an angle, a perpendicular from a point to a line, angles of 60°, 30°, 90° and 45°, a triangle from three sides (SSS), two sides and the included angle (SAS) or two angles and a side (ASA), and regular polygons such as the hexagon. Each works because equal compass arcs make equal lengths, which give congruent triangles.

Orthographic projection of points and lines · Projection of regular plane figures · Projection of right regular solids · Sections of solids

Orthographic Views of Solids – An orthographic view shows a solid as seen straight on from one direction, with no perspective. The three main views are the front view (front elevation), the top view (plan) and the side view (side or end elevation). Each view loses one dimension, so we usually need all three to fix the shape. Views are arranged in a standard layout: first-angle projection (plan below the front view; used in India, Europe and ISO standards) or third-angle projection (plan above; used in the USA). Visible edges are thick continuous lines, hidden edges are dashed, and centre lines are chain lines. A net is the flat pattern that folds into a solid, and a cross-section is the shape you see when you cut through it.
Sections of Solids – A section (cross-section) is the flat shape you get when a plane cuts a solid. Its number of sides equals the number of faces the plane passes through. A cube can give a triangle, a quadrilateral (square, rectangle), a pentagon or a hexagon. A plane parallel to a pyramid’s base gives a smaller copy of the base. In technical drawing, a section shows only the cut face; a cut (sectional view) also shows what lies behind it.

Orthographic projection of simple machine blocks · Isometric projection of laminae

Machine Drawing: Making and Reading Detail Drawings – A machine drawing is an exact picture of one part, made so a factory can build it without asking any questions. A detail (working) drawing shows the views of the part, section views for hidden insides, every size (dimension), how much each size may vary (tolerance), the surface finish, the material and a title block.
Isometric Projection and Axonometric Drawing – An axonometric drawing shows a solid in one picture with three axes: width, depth and height. In isometric projection the three axes are 120° apart and every axis is shortened equally (scale ≈ 0.82). An isometric drawing uses full lengths instead. Dimetric shortens two axes the same, trimetric all three differently. Oblique (cavalier, cabinet) keeps the front face true size and draws depth at 45°, full length (cavalier) or half (cabinet). Circles on faces become ellipses.