Active learning ideas
Sections of solids are used to reveal the internal details of an object that would otherwise be hidden. By 'cutting' a solid with an imaginary plane, students can see the internal cross-section. This topic covers drawing the sectional views and determining the 'True Shape' of the section, which is the actual shape of the cut surface when viewed perpendicularly.
Activity 01
Students create solids (cones, prisms) out of modeling clay. They use a wire to cut the solid at an angle. They then press the cut face onto paper to 'stamp' the true shape and compare it to their theoretical drawings.
Why do we use sectional views in engineering drawing?
Activity 02
Students draw sectional views of different solids. They display their work to check for consistent hatching: lines must be equally spaced, thin, and usually at 45 degrees. Peers provide feedback on the 'neatness' and 'correctness' of the cut area.
How do you determine the true shape of a section?
Activity 03
The teacher shows a sectional top view that is foreshortened. Students must discuss with a partner why this is not the 'True Shape' and what steps are needed (auxiliary plane) to find the actual dimensions of the cut.
What are the hatching conventions for cut surfaces?
A few notes on teaching this unit
Watch Out for These Misconceptions
The hatching lines should be thick and dark like the object lines.
Hatching lines (section lines) must be thin and light (using a 2H pencil) to distinguish them from the solid outlines of the object. If they are too dark, the drawing becomes cluttered and hard to read. Hands-on practice with pencil pressure is key here.
Any view showing the cut surface is the 'True Shape'.
A view only shows the True Shape if the line of sight is perpendicular to the cutting plane. If the cutting plane is inclined to the HP, the sectional top view will be a foreshortened version. Students must draw an auxiliary view to see the True Shape.
Methods used in this brief
Orthographic Projections of Points and Lines
Understanding the four quadrants and projecting points and lines inclined to one or both reference planes. This forms the basis of 3D spatial visualization.
8 methodologies
Projections of Plane Figures
Drawing projections of 2D planes (triangles, squares, pentagons, hexagons, circles) inclined to reference planes. Students learn to visualize surface orientations.
8 methodologies
Projections of Right Regular Solids
Projecting 3D objects like prisms, pyramids, cylinders, and cones in various positions. Emphasis is placed on solids with axes inclined to one reference plane.
8 methodologies