Solid Geometry: Isometric and Oblique Drawing — CSEC Technical Drawing
Isometric and oblique drawings are pictorial methods that show a 3D impression of an object in a single view.
Isometric drawing
- The receding lines are drawn at 30° to the horizontal; vertical edges stay vertical.
- The three isometric axes are equally spaced at 120° to each other.
- All measurements along the three axes are drawn to the same scale.
- A circle on an isometric face appears as an ellipse.
Isometric gives a balanced, undistorted 3D view and is widely used in engineering.
Oblique drawing
- The front face is drawn in its true shape (a real advantage), facing the viewer.
- The depth lines recede, usually at 45°.
- Cavalier oblique draws the depth at full scale; cabinet oblique draws it at half scale to look more realistic.
Comparing the methods
| Isometric | Oblique | |
|---|---|---|
| Receding angle | 30° | usually 45° |
| Front face | distorted (no true shape) | true shape |
| Best for | general 3D objects | objects with detail on the front |
Method (isometric box)
- Draw the isometric axes (a vertical and two 30° lines).
- Mark length, width and height along the axes.
- Complete the parallel edges of the box.
- Line in the visible edges.
Exam tips
- Isometric receding lines are at 30°; oblique usually at 45°.
- Only oblique shows the front face in its true shape.
- A circle on an isometric surface becomes an ellipse.
- The three isometric axes are at 120° to each other.