Communicating design ideas: freehand sketching, rendering, isometric and orthographic working drawings, dimensioning, and the use of CAD.

What this dot point is asking

CCEA wants you to know the drawing techniques designers use to communicate ideas: quick freehand sketches, rendering to show material and form, pictorial (isometric) views, accurate orthographic working drawings with dimensions, and the role of CAD. Choosing the right type for the right purpose is the examinable skill.

The answer

Freehand and crating sketches

Early in a project a designer produces many quick freehand sketches to explore ideas. A useful aid is crating: lightly drawing a box (a crate) in proportion first, then building the object inside it so proportions stay correct. Sketches are fast and rough on purpose - they capture ideas before any one is chosen.

Rendering

Rendering turns a flat outline into a convincing picture of the finished product, which helps a client understand the appearance before anything is made.

Pictorial (isometric) views

A pictorial drawing shows the object in three dimensions in one view, giving an immediate impression of its shape.

Orthographic working drawings

When a design is to be made, the designer produces an orthographic working drawing.

Because every view is true to scale and every size is given, a working drawing contains all the information needed to manufacture the product. This is its key advantage over a pictorial sketch, which looks realistic but cannot be measured accurately.

Dimensioning conventions

Dimensions are added so the drawing can be made from. Key conventions:

• Dimension lines have arrowheads; projection (extension) lines run out from the object but do not touch it.
• Sizes are usually given in millimetres, with the number written above the dimension line and read from the bottom or the right.
• Each size is shown once, and overall sizes are given as well as detail sizes.

The role of CAD

Computer-aided design (CAD) lets the designer draw and model on a computer. Drawings can be edited quickly, viewed from any angle as a 3D model, dimensioned automatically, tested by simulation and sent straight to manufacturing machines. CAD is covered in its own dot point; here the point is that it is one of the modern ways to communicate and refine a design.

Worked example: choosing the right drawing for the job

Examples in context

Example 1. A car concept

Stylists begin with hundreds of rendered freehand sketches to explore the look, then produce CAD surface models for the chosen design, and finally detailed working drawings for the parts. Each technique suits its stage.

Example 2. A flat-pack shelf

The assembly instructions use simple pictorial views so the customer can see the 3D shape, while the factory works from dimensioned orthographic drawings to cut every panel to size.

Example 3. A school metalwork part

A pupil sketches the idea, renders it to show the brushed-aluminium finish, then draws a third-angle orthographic drawing with all sizes in millimetres so the part can be marked out and cut.

Matching the drawing type to its purpose, and knowing the conventions for each, lets you answer both "describe the differences" and "explain why" questions precisely.

Try this

Q1. What is added to a sketch when it is rendered? [1 mark]

• Cue. Tone, colour, shadow and texture (to show material and 3D form).

Q2. At what angle to the horizontal are the non-vertical edges drawn in an isometric drawing? [1 mark]

• Cue. 30 degrees.

Q3. Name the three views usually shown in an orthographic working drawing. [3 marks]

• Cue. Front view, plan (top) view and end (side) view.

Q4. Give one reason a working drawing is dimensioned. [1 mark]

• Cue. So the product can be made accurately to size from the drawing.

Q5. State one advantage of using CAD to communicate a design. [1 mark]

• Cue. Drawings can be edited quickly, viewed in 3D, or sent directly to manufacturing machines (any one).