Line Types & DIMENSIONS: British Standards for Engineering DrawingS

High school Design and Technology students often have to demonstrate a working knowledge of appropriate British Standards for technical drawings, including the guidelines for adding dimensioning to drawings and using recommended scales. This article helps students learn this material.

What are the British Standards for Engineering Drawings?

The British Standards for Engineering Drawings are a set of rules produced by the British Standards Institution governing the way that technical drawings are presented.

Following these standards encourages clear communication between designers, manufacturers, and clients, and helps to ensure consistency across different projects, companies, and countries. Using common drawing conventions is particularly important for students studying international qualifications (such as Cambridge IGCSE and A Level Design & Technology) because it ensures that both students and examiners speak the same ‘visual language.’

What is the difference between BS 308 and BS 8888?

BS 308 was the original British Standard for technical drawings, which has now been replaced by BS 8888, which aligns with international ISO standards (international, world-wide standards).

What does the British Standard BS 8888 cover?

BS 8888 covers a range of drawing conventions and symbols, such as how to represent different views of an object, line types and their meanings, dimensioning rules, annotation guidelines, scale representations, paper sizes and layouts, and so on.

Key aspects of these standards are outlined below.

Line types for use in technical drawings

Dimensioning standards

• Dimensions lines are slightly lighter than outlines, but darker than construction lines;
• Avoid placing dimensions on the drawing – project lines approximately 10mm from the drawing;
• Dimension a visible face;
• Project lines out on same angle as the face dimensioned;
• Leave small gaps between the object and projection lines;
• Arrowheads should be small and drawn at a ratio of 3:1;
• Measurements should be in m or mm (units can be left out if you state elsewhere that all measurements are in mm, for example);
• Measurements less than 1 should have a leading zero, i.e. 0.35 not .35;
• Number should be placed centrally, above or to the left of the line using small tidy writing.

Dimensioning a series of items

Either of these methods is fine:

Dimensioning small spaces

Any of these methods is fine:

Dimensioning a radius

Dimensioning a diameter

• Precede all dimensions with: Ø
• Example (a) below shows two common ways of dimensioning a circle;
• If the circle is small, the dimension is placed outside the circle (b);
• If it is very small, both the arrow and dimension are placed outside the circle (c). The arrow must point directly toward the centre of the circle.

Scales

• Tells you how big a drawing or model is comparison with the item in reality;
• A scale of 1:50 means that if something is ‘one’ unit on the drawing, it is ‘fifty’ units in reality. In other words, the item is fifty times bigger in real life. A length of 2mm on the drawing will represent 100mm in reality.
• A scale of 5:1 means that the drawing (or model) is five times bigger than the item in reality.
• A scale of 1:1 means that the drawing (or model) is drawn full size.