Standardized drawing: dimensioning, normalization, sketching and CAD
This block is scored on rules, not on drawing skill: a correctly executed figure with wrong dimensioning loses the marks. Expect questions on line types, dimensioning criteria, formats and basic CAD concepts.
Formats and lines
ISO/UNE A-series: A0 is 841 × 1189 mm (1 m²) and each following size halves the larger side (A4 = 210 × 297 mm). Margins and a title block at the bottom right, with the drawing field bounded by a frame. Line types: thick continuous for visible edges, thin continuous for dimension and hatching lines, dashed for hidden edges, thin dash-dot for axes and symmetry. The standard width series is 0.13, 0.18, 0.25, 0.35, 0.5, 0.7, 1.0 mm, with a ratio of about 1:√2.
Dimensioning
Each dimension has a dimension line with arrowheads, extension lines from the object, and the value placed above the centre of the line. Dimensions are in millimetres with no unit symbol. Never repeat a dimension, never dimension hidden edges, and never close a chain twice. Symbols: ⌀ for diameter, R for radius, S⌀ and SR for spheres, □ for square, and a note such as 4×⌀8 for repeated holes; angles in degrees, minutes and seconds; chamfers by their length and angle.
Normalization
Geometric tolerancing, fits (hole-basis H is the common one), surface texture with Ra values in micrometres, and sections: the cutting plane is drawn with a thick dash-dot line ending in arrows and labelled with capital letters, and the cut area is hatched at 45° thin lines. Spain uses first-angle projection, marked by its truncated-cone symbol beside the title block.
Sketching and CAD
Sketches keep proportion with freehand straight lines and block lettering. In CAD, work with layers by line type, model space and paper space with scaled viewports, blocks for repeated symbols, and the coordinate entries: absolute x,y; relative @x,y; polar @distance<angle.
Worked example
A plate with four holes: the outer diameter is written ⌀60, the four holes as 4×⌀10 on a dimension line through their centres, a fillet as R8, and a 2 × 45° chamfer noted on the edge - never as four separate ⌀10 dimensions.
Traps
Writing mm after every number; placing the value below the dimension line or uncentred; dimensioning to a hidden line; forgetting the arrows and letters of a cutting plane; drawing the projection symbol in third-angle orientation.