Sections and Sectional Views
Sectioning questions test your ability to cut an object, show the interior clearly and hatch only solid material.
Cutting planes and hatching
A cutting plane is shown by a chain thick line with arrows at the ends; the arrows point in the viewing direction and the plane is labelled A–A. The sectional view shows the cut surface hatched with continuous thin lines at 45°, spaced about 2–4 mm. Hatching shows solid material, not holes or bores. Adjacent parts in an assembly are hatched in opposite directions. Very thin sections may be filled solid.
Types of section
Full section cuts through the whole object; half section cuts a symmetrical object to one side of the centre line; offset section steps to pass through features; revolved section is rotated on the view; removed section is drawn outside; broken-out section exposes a local feature.
Worked example
A bush has an outside diameter 60 mm and a bore 30 mm. A full section on the axis shows hatching between Ø30 and Ø60 on both sides, while the bore remains clear. Reasoning: the cutting plane passes through solid metal on both walls; the bore is empty space and must not be hatched. Omit hidden lines in the section unless they are needed for a feature behind the plane.
Traps
Hatching the bore; drawing hidden lines over hatching; reversing the cutting-plane arrows; forgetting the A–A label; using the same hatch direction for two adjacent parts; hatching too coarsely.