Interpretation of technical drawings, diagrams, and work instructions
This domain tests whether you can extract the right dimensions, views, symbols, and revision status from a drawing and turn them into a correct assembly or maintenance action. Questions often mix orthographic views, schematic symbols, title blocks, and work-instruction steps.
Core rules
- Orthographic projection: first-angle places the view on the far side of the object; third-angle places it on the near side. The projection symbol beside the title block settles the convention.
- Read the title block, drawing number, revision, scale, units, material, and general tolerances before dimensions.
- Line conventions: visible outlines are continuous, hidden features dashed, centre lines chain-dotted, and section hatching identifies cut material.
- Dimensions give nominal size plus tolerance; fits such as H7/h6 describe hole and shaft limits, not a single size. Schematic diagrams show function; wiring diagrams show physical terminals.
- Work instructions may add torque, sequence, and inspection points not shown on the drawing; the latest revision governs.
Worked example
A bore is dimensioned Ø20 H7. For the 18–30 mm size range, IT7 is 21 µm and the fundamental deviation for H is zero, so the hole limits are 20.000 mm minimum and 20.021 mm maximum. A mating shaft marked 20 h6 has an upper limit of 20.000 mm and a lower limit of 19.987 mm. The fit can therefore range from zero clearance to 0.034 mm clearance. The reasoning: always convert tolerance class to upper and lower limits before judging assembly.
Traps
Mixing first- and third-angle views; using a scaled print instead of the stated dimension; ignoring a revision cloud; reading a hidden line as visible; treating a schematic wire number as a physical terminal; and assuming a general tolerance overrides a specific note. These errors cause wrong parts and lost marks.