2.11 Accuracy in Design and Manufacture

Question 1

Marking out

Answer 1

Transfer of designs on to materials or parts to indicate the position of features such as holes and edges

Question 2

Accuracy

Answer 2

The level of conformity of a measurement to the required value

Question 3

Tolerance

Answer 3

Acceptable upper and lower limits of accuracy of a measurement

Question 4

Datum

Answer 4

Reference surface or edge from which measurements are taken to improve accuracy

Question 5

Ensuring accuracy in manufacture examples

Answer 5

• Dials on manual machine controls allow precision movement of tools and workpieces
• Digital test gauges are very accurate, often computer-linked, measuring devices
• Profile projectors measure fine details such as threads to an accuracy of 0.015mm
• CNC machines use computer codes to control movement and ensure accuracy
• Laser micrometers, material thickness sensors, and alignment systems are examples of accurate non-contact measuring devices

Question 6

Jigs

Answer 6

Devices that both hold the workpiece and guide tools accurately for repetitive machining operations without the need for marking out

Make high-quality, fast machining operations able to be carried out by semi-skilled workers as there is a reduced risk of human error

Question 7

Fixtures

Answer 7

Maintain the accurate alignment of parts for processes such as welding by providing a framework into which they are securely clamped during manufacture

Often designed so that parts can only be fitted the right way round - ensuring high-quality assembly

Question 8

Templates

Answer 8

Rigid shape or pattern to transfer a design onto a workpiece to ensure consistency

Ensures consistent repetition of the same outline by providing a consistent profile for marking out the shape of identical pieces

Question 9

Standardisation: geometric dimensioning and tolerancing (GD&T)

Answer 9

A standard system of engineering drawing symbols and figures used for specifying the product component dimensions and tolerances