2.1 Oblique Projection

• Meaning of pictorial drawing and its place beside orthographic views
• Oblique projection: the front face drawn in true shape and true size
• Receding lines drawn at 30, 45 or 60 degrees to the horizontal
• Cavalier and cabinet oblique, and the reason depth is halved
• Choosing the face to put to the front
• Constructing oblique drawings of blocks, stepped blocks and brackets
• Circles and arcs in oblique projection
• Types of line: outlines, hidden detail and centre lines
• Dimensioning an oblique drawing
• Comparing oblique with isometric projection

• explain the principles of oblique projection
• select a suitable front face and receding angle for a given object
• construct oblique drawings of simple objects in cavalier and cabinet oblique
• draw circles and arcs correctly in oblique projection
• dimension an oblique drawing
• appreciate the use of pictorial drawings in communicating design

“How do we show a solid object on a flat sheet of paper?”

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1. Pictorial and orthographic
   40 min · 1 practice tasks · quiz
   Orthographic to make the part. Pictorial to understand it.
2. The two rules
   40 min · 1 practice tasks · quiz
   True shape in front, parallel receding lines behind. That is the whole method.
3. Choosing the receding angle
   40 min · 1 practice tasks · quiz
   Thirty shows the top, sixty shows the side, forty-five shows both.
4. Cavalier and cabinet
   40 min · 1 practice tasks · quiz
   Cabinet halves the drawn depth so the drawing looks like the object.
5. Choosing the front face
   40 min · 1 practice tasks · quiz
   The face with the curves goes to the front. This decision saves more time than any technique.
6. Constructing a cube
   40 min · 1 practice tasks · quiz
   Front face, receding lines, half the depth, join up. Step three goes wrong most.
7. A stepped block
   40 min · 1 practice tasks · quiz
   Draw the enclosing box first, put the profile on the front, then recede every corner.
8. Circles and arcs
   40 min · 1 practice tasks · quiz
   A compass on the front face; twelve plotted points anywhere else.
9. Line types and hidden detail
   40 min · 1 practice tasks · quiz
   Thick for visible, broken for hidden, chain for centres. Hidden detail is not optional.
10. Dimensioning
    40 min · 1 practice tasks · quiz
    Dimension lines run parallel to the edge, and the figure is always the real size.
11. A bracket, worked through
    40 min · 1 practice tasks · quiz
    One plane holds the whole shape, so put that plane in front.
12. Where drawings go wrong
    40 min · 1 practice tasks · quiz
    Six faults, and what each one costs. One bad receding line twists the whole solid.
13. Oblique or isometric?
    40 min · 2 practice tasks · quiz
    Oblique favours one face. Isometric favours none. Choose by where the detail is.
14. The whole method
    40 min · 1 practice tasks · quiz
    Choose, draw, recede, finish. Choose the front face well and the rest is two rules.