Engineering Drawing

Orthographic projection represents a 3D object by 2D views (front, top, side) using parallel projectors. India follows first-angle projection, where the object lies between observer and plane, per engineering-drawing texts (IS SP-46).

Isometric projection shows a 3D pictorial with the three axes at 120° apart; isometric lines are foreshortened to 0.816 of true length, though isometric drawings use full length. It conveys shape in one view, per engineering-drawing texts.

Sectional views reveal internal features by imagining the object cut along a cutting plane; the cut surface is hatched at 45°. Full, half, offset, and revolved sections suit different geometries, per engineering-drawing texts.

Dimensioning states sizes and locations with extension and dimension lines and arrowheads; tolerancing gives the permissible variation. Geometric tolerancing (GD&T) controls form, orientation, and position, per engineering-drawing texts (IS/ISO).

Surface development unfolds a 3D surface into a flat pattern; a cone's lateral surface develops into a sector, and its slant height is L = √(r² + h²). It is essential for sheet-metal fabrication, per engineering-drawing texts.