Computer-Aided Drafting and Basic Software Applications
Computer-Aided Drafting tests practical command knowledge of 2D CAD plus basics of spreadsheets and project software. Questions ask what a command does, how to set up layers and dimensions, and how to plot at the correct scale.
Coordinates
- Absolute: X,Y measured from the origin, such as 100,50.
- Relative rectangular: @dx,dy from the last point, such as @100,0.
- Relative polar: @distance<angle, such as @100<30. Angles are measured anticlockwise from the positive X axis.
Core commands
Draw: LINE, PLINE, CIRCLE (centre-radius, 2P, 3P, TTR), ARC, RECTANGLE, POLYGON, ELLIPSE, SPLINE. Modify: MOVE, COPY, ROTATE, SCALE, MIRROR, OFFSET, ARRAY, TRIM, EXTEND, FILLET, CHAMFER, STRETCH, EXPLODE.
Organisation
Layers separate object types such as walls, dimensions and text, each with its own colour, linetype and lineweight. Blocks reduce repetition, and attributes store data such as door numbers. Model space is drawn at full size; paper space holds the title block and viewports at the plotting scale.
Worked example
Draw a 3 m wall at 30 degrees to the horizontal for plotting at 1:50. Draw at full size, so 3 m = 3000 mm: pick the start point and type @3000<30. On plotting at 1:50 the 3000 mm line prints 60 mm on paper. If drawing units are millimetres and the sheet is in millimetres, a 1:50 plot scale shrinks everything fifty times.
Traps
- Omitting the @ sign, so the entry is read as an absolute coordinate.
- Exploding blocks and losing their attribute data.
- Expecting model-space dimensions to resize on paper without setting an overall dimension scale.
- Choosing fit-to-paper at plot time, which destroys the stated scale.
- Forgetting to set drawing units before starting the sheet.