Engineering Drawing and Computer-Aided Drafting
What the exam tests
Reading and producing orthographic views, applying Indian Standard conventions, interpreting limits, fits and surface finish symbols, and using basic CAD commands and plotting.
Core rules
- India follows first-angle projection (IS 696): the object lies between observer and plane, so the front view sits above the top view and the view from the left appears on the right.
- Hidden edges are drawn as short dashes, and omitted where a solid line of a nearer feature would coincide.
- A dimension is given once, on the view showing the feature in true shape, and never on a hidden line. Lettering is unidirectional as per SP 46.
- Limit dimension 25 +0.021/0 describes a hole of basic size 25 with an IT7 tolerance; written as 25 H7/g6 it is a hole-basis sliding fit.
- Surface roughness Ra in micrometres is placed on the surface line or its extension; a tick with a circle means the process is not specified.
- External threads show thick major diameter and thin minor diameter lines; internal threads are the reverse.
- CAD: absolute (X,Y), relative (@X,Y) and polar (@length<angle) coordinates; ORTHO, OSNAP, layers by object type, blocks for repeated items, and PLOT with the sheet scale set in the layout.
Worked example
A plate 80 × 50 × 10 mm with a central 20 mm hole is drawn at 1:2. On paper the 80 mm edge measures 40 mm and the hole 10 mm, but the dimension text always states the true sizes 80 and 20. Only the drawn geometry is scaled; the numerals never are.
Traps
- Placing the top view above the front view, a third-angle habit.
- Writing the scaled paper measurement as the dimension value.
- Using a centre line where a hidden line belongs.
- Calling 25 H7/g6 an interference fit.