There are occasions when a drawing cannot provide adequate information to indicate the form of an object or environment. In these circumstances an additional view must be drawn in combination with, or instead of, the normal outside views. The new view is called a sectional view.
Sectional views represent a view that has been sliced along a cutting plane to reveal a product or environment's inner detail.
Whenever a sectional view is drawn, the remaining solid or material components are indicated by hatch lines. Drawn at 45°, hatch lines should be drawn as thin lines and evenly spaced over the entire part.
Spacing of Hatch Lines
Hatching lines should be evenly spaced and as best fits across the object or component of the part or environment being sectioned. If the hatching coincides with one or more sides of the part then an alternative angle can be used.
Types of Sectional Views
Thin sections are used to show the thickness of thin parts without having to draw the material thickness out of scale. To ensure that thickness of each part is communicated clear a minimum gap of 1mm between parts is shown.
Any part or environment that is symmetrical can be drawn half sectioned.
Local sections can used to avoid showing a separate sectional view. The local area being sectioned is indicated by a continuous thin irregular line.
Successive sections can be drawn as removed sections when, through lack of space, the sectional views cannot be shown in normal projection.
Revolved sections are used to the cross section of an arm, rib, spoke, or bar. Revolved sections are shown by drawing the cross sectional view of the part in position with the adjacent detail drawn around the revolved view.
Removed sections are similar to revolved sections but they are drawn outside of the original part. They can be drawn adjacent to the original part or completely away from it. If drawn completely away from the part, both the section and the cutting plane must be clearly indicated to avoid confusion.
Exceptions to Sectioning
As with most rules there are exceptions. When a section plane cuts parts such as bolts, ribs, nuts, rivets, shafts, spokes, or wheels then these parts are not sectioned but shown in an external view.