Working drawings

Drawings which contain all the information needed to make the object you have designed, including dimensions and details of components, materials and assembly instructions, are called working drawings. Although working drawings for simple products may sometimes be done in isometric or planometric projection, the normal drawing technique for working drawings is orthographic projection.

Some products may need a section drawing to give extra structural information, or an assembly drawing to show how parts fit together.

Orthographic projection

Orthographic projection shows complex objects by doing a 2D drawing of each side to show the main features. Orthographic drawings usually consist of a front view, a side view and a plan [plan: scale drawing showing an object as seen in a cutaway view from directly above ], but more views may be shown for complex objects with lots of detail. A drawing board and parallel motion or T-square is used to project one view from another.

Orthographic drawing may be done using first angle projection or third angle projection. The graphic below shows the differences between the two.

Section drawings

Section drawings show the various parts of a product as if it had been sliced in half. (Sometimes they are called cross-sections.) The position of the imaginary cut is called a section plane, sometimes represented by a line consisting of long and short dashes.

The purpose of a section drawing is to make clear how a product is constructed. Parts of the object that are cut through are shaded with lines at 45° and spaced 4mm apart - called cross-hatching. If two parts of a product are touching, then the cross-hatching goes in opposite directions. Parts such as nuts and bolts and axles are not normally sectioned.

Assembly drawings

An assembly drawing shows the various parts of a product drawn to show exactly how they fit together. They are often used for products such as construction and model kits or flat-pack furniture, to show the user how to assemble the parts.

They can be drawn in two ways.

• A fitted assembly drawing shows the parts put together, and can be drawn in 2D or 3D.
• An exploded drawing shows the parts separated, but in the correct relationship for fitting together. Exploded views are usually drawn in 3D, as illustrated.