Computer-Aided Drafting (CAD) Fundamentals
This domain tests basic CAD concepts: coordinate entry, drawing and modify commands, layers, blocks, dimensioning and plotting. Expect practical questions on relative coordinates and on the difference between model space and paper space.
Coordinates and commands
Absolute: x,y from the origin. Relative rectangular: @x,y from the last point. Relative polar: @distance<angle. Object snaps (endpoint, midpoint, centre, intersection) ensure accuracy. Draw commands: LINE, CIRCLE, ARC, RECTANGLE, POLYGON. Modify commands: MOVE, COPY, ROTATE, MIRROR, OFFSET, TRIM, EXTEND, FILLET, CHAMFER, ARRAY.
Layers and standards
Put outlines, hidden lines, centre lines, dimensions and text on separate layers with distinct colours, line types and line weights. Use blocks for repeated symbols such as bolts or doors. Dimension styles should match the drawing scale.
Worked example
Draw a line from (20,30) to a point 50 mm away at 30° above the horizontal. Use relative polar entry @50<30. The change in x is 50 cos 30° = 43.3, and in y is 50 sin 30° = 25.0. The endpoint is (63.3, 55.0). Check it with the ID or LIST command. The reasoning is that CAD polar angles are measured anticlockwise from the positive X-axis.
Plotting
Model space holds full-size geometry; paper space or a layout holds the title block and viewports. Set the viewport scale, e.g. 1:2 or 2:1, and plot at 1:1 from paper space. Check line weights with the plot preview.
Traps
Typing absolute coordinates when relative ones are needed puts geometry in the wrong place. Drawing everything on layer 0 makes line-weight control impossible. Exploding dimensions breaks associativity. Do not plot from model space at a random scale without setting the plot scale.