Active learning ideas
The final topic in Class 11 Engineering Graphics covers the isometric projection of frustums and truncated solids. A frustum is what remains when a pyramid or cone is cut by a plane parallel to its base, while a truncated solid is cut by an inclined plane. This requires students to synthesize everything they have learned: scales, sections, and isometric construction.
Activity 01
Students use foam cones and pyramids and a 'cutting guide' to create frustums. They then measure the top and bottom diameters and attempt to create an isometric projection that matches their physical model.
How do you locate the cut surface in an isometric projection?
Activity 02
Groups are given a drawing of a truncated hexagonal prism. They must figure out how to locate the heights of each of the six corners of the cut face and then draw the resulting 'slanted' isometric top.
What is the difference between a frustum and a truncated solid?
Activity 03
Students display their drawings of a frustum of a cone. Peers check if the top and bottom ellipses are perfectly centered along the same vertical axis and if the 'four-center' construction is visible but light.
How do you project the top face of a frustum of a cone?
A few notes on teaching this unit
Watch Out for These Misconceptions
The top face of a frustum of a cone is a circle in isometric.
Like any circular feature in isometric, the top face must be drawn as an ellipse using the four-center method. Because it is smaller than the base, it requires its own smaller isometric square (rhombus) for construction. Peer-checking ensures students don't just 'freehand' the top.
A frustum and a truncated solid are the same.
A frustum is specifically cut by a plane parallel to the base, so the top and bottom faces are similar shapes. A truncated solid is cut by an inclined plane, so the top face is a different, distorted shape. Using physical models helps students see this distinction clearly.
Methods used in this brief
Concept of Isometric Scale and Projection
Introduction to isometric axes, lines, and planes. Students learn to construct and use an isometric scale to draw isometric projections.
8 methodologies
Isometric Projections of Plane Figures
Drawing isometric projections of 2D shapes like triangles, polygons, and circles. Students learn the four-center method for isometric circles.
8 methodologies
Isometric Projections of Simple Solids
Creating 3D isometric projections of prisms, pyramids, cylinders, and cones. The focus is on solids resting on their base on the HP.
8 methodologies