Engineering Drawing and CAD Fundamentals
Engineering Drawing and CAD Fundamentals tests whether you can read and produce a technically correct drawing, and whether you can set up a CAD file with the same discipline. Expect orthographic projection, isometric views, sectioning, dimensioning to BIS/SP:46 conventions, limits and fits, and basic CAD commands and coordinate entry.
Core rules
- First-angle projection is the Indian default: the object lies between the observer and the plane, so the top view is placed below the front view and the left side view appears on the right. Third-angle reverses this. Always show the projection symbol.
- Line work: continuous thick for visible edges, dashed for hidden edges, chain (dash-dot) for centre lines, thin continuous for dimension and extension lines.
- Dimensions are in millimetres; do not write mm on each dimension. Numerals sit above the dimension line and are read from the bottom or right edge of the sheet.
- Tolerance = upper deviation − lower deviation. In the hole-basis system the hole's lower deviation is zero, and clearance = hole size − shaft size (a negative value means interference).
Worked example
A shaft is Ø40 +0.025/−0.010 and its mating hole is Ø40 +0.050/0.000. Largest shaft = 40.025, smallest = 39.990; largest hole = 40.050, smallest = 40.000. Maximum clearance = 40.050 − 39.990 = 0.060 mm. Minimum clearance = 40.000 − 40.025 = −0.025 mm, i.e. 0.025 mm interference. Since the result can be either clearance or interference, the fit is a transition fit.
Traps that cost marks
Drawing hidden edges as continuous lines; dimensioning to a hidden line instead of a visible one; omitting the projection symbol; writing units on every dimension; in CAD, leaving units at the default (inches) instead of millimetres, and mixing absolute, relative (@) and polar (@length<angle) coordinate entry.