Sections, cutouts and cross-sections in technical drawing

Many items have an internal structure that cannot be seen from the outside. If you only drew them with broken hidden lines, the drawing would quickly become impossible to read. The solution is the section: imagine the item is cut through, remove the front part and draw the exposed surface. This makes the internal geometry clear and measurable.

§Cutting line and section direction

Where the section is taken is shown with a section line on another view. Arrows on the section line indicate which way you are looking into the item, and the section is named with letters so you can see which section view belongs to which section line. That way the reader can always find back to where the section is taken.

§Hatching of the cut surface

The flat surface where the 'knife' has cut through material is marked with shading — typically slanted, evenly distributed lines. The shading shows what is solid material, as opposed to cavities and openings. If multiple parts are together in the same section, they are shaded in different directions or spacing so you can see where one part ends and the next begins.

§Section types

• 01Full cut: the item is cut completely through on one continuous line.
• 02Half-section: symmetrical parts are shown as half section and half external view on the same drawing.
• 03Partial section (broken section): only a local area is sectioned, bounded by a freehand break line.
• 04Offset section: the section line breaks so several interesting points can be shown in one section.
• 05Rotated section: a cross-section is rotated into the drawing plane to show the cross-section's shape.

§When do you choose a cut?

A section should make the drawing easier to understand — not fill it with more views than necessary. Use a section when the internal geometry is important to manufacture or assemble the item and stick to the simplest section type that solves the problem. A well-chosen half section or partial section is often clearer than a full section that shows more than the reader needs.

§Cut in connection with objective setting

The section is not just for looking at — that is often where the interior dimensions are placed. Make sure that the dimensions that belong to the interior geometry are placed on the section view where they can actually be read, not on an exterior view where the geometry is hidden.