WASSCE SHS
A pictorial drawing shows three faces at once. Isometric, oblique and perspective are not the same method.
Isometric drawing uses three axes. One is vertical. The other two are at 30 degrees to the horizontal. The same scale is used on all three axes, so a length along an axis is the true length. A circle on a face becomes an ellipse. There is no vanishing point. Lines that are parallel on the object stay parallel on the drawing. That is how you can tell it from perspective, where parallel edges that recede meet at a vanishing point.
Oblique drawing keeps one face as the true shape, usually the front. The receding edges are commonly drawn at 45 degrees. Cavalier oblique uses the full depth on those edges. Cabinet oblique uses half the depth, so the object looks less stretched. Choose cabinet when the depth would look too long at full scale. Perspective is a different system: edges that go back converge. Do not call an isometric box a perspective drawing because it looks solid. Name the method, the angles, and whether the scale on the depth is full or half.
The Technical Drawing tips guide sets out the objective paper, the geometry paper including vector geometry, and the drawing paper. Start practising on glearn.now with Kevin and Anna. WASSCE Technical Drawing tips
Thirty degrees is the isometric angle to the horizontal, not 45. Forty five degrees is the usual oblique angle. Isometric uses one scale on every axis. Cabinet oblique halves the depth. A vanishing point belongs to perspective. If the question says isometric, a front face in true shape is the wrong method: that is oblique. An ellipse, not a circle, is the isometric view of a circle.
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
3 marks
State the angles of the axes in an isometric drawing, and the scale used on them. (3 marks)
One axis is vertical. The other two are at 30 degrees to the horizontal. The same scale is used on all three axes.
2 marks
Distinguish cavalier oblique from cabinet oblique. (2 marks)
Both keep a true front face. Cavalier draws the depth at full scale. Cabinet draws the depth at half scale.
2 marks
Why is an isometric drawing not a perspective drawing? (2 marks)
In isometric, parallel edges stay parallel and there is no vanishing point. In perspective, receding parallel edges meet at a vanishing point.
More questions on this topic are inside glearn, marked as you answer, with the reason written out. The first ones need no account.
Practise Technical Drawing freeThirty degrees, with one axis vertical. The scale is the same on all three axes. Forty five degrees is the usual angle for an oblique drawing, not for isometric.
An oblique drawing whose front face is the true shape, with the receding depth drawn at half scale. Cavalier oblique uses the full depth. Half scale stops the object looking stretched. All WASSCE Technical Drawing past questions