Sections, Auxiliary Views, and Conventions
Section views
A cutting plane line with arrows and letters marks where the object is cut; the section view is labelled with the same letters. Full sections cut through the whole object; half sections cut to the centreline and are used for symmetric parts; offset sections step the cutting plane to pass through features; aligned sections rotate features into the plane; removed and revolved sections show a cross-section without a full view.
Hatching and conventions
Hatching is thin continuous lines at about 45°, spaced 2–4 mm, and only cut material is hatched. Shafts, pins, bolts, nuts and keys are not hatched when cut longitudinally. Ribs and webs are not hatched when the cutting plane runs along them. Adjacent parts are hatched in opposite directions or at different spacings. Hidden lines are generally omitted from a section because the cut has exposed the interior.
Auxiliary views
An auxiliary view projects perpendicular to an inclined face to show its true shape. Draw a fold line parallel to the inclined edge in the front view, project perpendicular from it, and transfer distances from the adjacent view. A primary auxiliary is perpendicular to one principal plane; a secondary auxiliary is needed for a face inclined to all three.
Worked example
An inclined face appears as a foreshortened rectangle in the front view. Draw a fold line parallel to the inclined edge, project the corner points perpendicular to that fold line, then transfer each corner's distance from the front view's reference line. The resulting view shows the face's true length and true angle; without the fold line parallel to the edge, the projection is not a true shape.
Traps
Hatching a shaft cut along its axis, omitting the cutting-plane letters, drawing hidden lines all through a section, and projecting an auxiliary view from the wrong reference edge.