Computer-Aided Drawing (CAD) Fundamentals
This domain tests the concepts behind a CAD session: coordinates, drawing and editing commands, layer and linetype organisation, blocks, dimension styles, model space and paper space, and output.
Coordinates
Absolute coordinates give X,Y from the origin; relative coordinates add @ to the last point (@40,25); polar coordinates give a distance and angle (@50<45). Ortho restricts movement to the axes, and object snaps (endpoint, midpoint, centre, intersection, perpendicular, tangent) attach geometry exactly rather than approximately - snapping is the CAD equivalent of the mitre line, and it prevents the tiny gaps that stop a hatch or a trim from working.
Drawing and editing
Draw commands: line, circle, arc, rectangle, polygon, polyline, ellipse, spline, hatch, text. Edit commands: erase, move, copy, rotate, scale, mirror, offset, array, trim, extend, fillet, chamfer, stretch, explode. Fillet and chamfer in CAD set a radius or distance rather than constructing tangent arcs by hand, but the geometry rule is unchanged: the tangent point lies on the line joining centres.
Organisation and output
Draw on layers with assigned colour, linetype and line weight (outlines, hidden, centre, dimensions, text). Define repeated items such as bolts or door symbols as blocks, and use attributes to carry part numbers into a schedule. Set dimension styles to a standard text height and arrow size. Model in full size in model space; use paper space layouts with viewports at 1:1, 1:50 or 1:100 and plot at the correct scale. Common exchange formats are DWG, DXF, PDF and STL.
Worked example
Draw a 100 × 60 mm plate with a Ø20 hole centred. Line: 0,0 then @100,0, @0,60, @-100,0, close. Circle: centre 50,30, diameter 20. Fillet the corners with R10, then hatch the outline on the section layer.
Traps
Typing relative coordinates without the @; leaving object snaps off so lines do not meet; drawing at paper size in model space; putting everything on layer 0; dimming with a style whose text is too small to plot.