Material management, tolerances and tools

Tolerances and quality control

• A tolerance is the acceptable range a size can vary by, such as 50 mm ± 0.5 mm, meaning anything from 49.5 mm to 50.5 mm is acceptable.
• Tolerances make sure parts fit together, especially in mass production.
• Quality control checks parts during and after manufacture, using measuring tools, gauges and visual checks.

Material management

• Plan cutting to reduce waste: arrange parts closely (nesting or tessellating shapes) on a sheet.
• Use a cutting list that sets out every part, its size and material.
• Mark out from a datum (a straight edge or line that all measurements are taken from), so errors don't add up.
• Include an allowance for cutting (the kerf of the saw) and for joints or seams.

Marking-out and specialist tools

• Marking out: steel rules, try squares, marking gauges (timber), scribers and odd-leg callipers (metal), and pencils, pens or tailor's chalk.
• Cutting and shaping: saws, snips, files, planes and scissors; machines such as lathes, milling machines and laser cutters.
• Holding: vices, clamps and jigs keep work steady and safe.
• Safety: wear goggles and aprons, use guards, tie back hair and follow risk assessments.

Key terms

Tolerance

The acceptable range a measurement can vary by.

Datum

A reference edge or line that all measurements are taken from.

Nesting

Arranging shapes closely on a sheet to reduce waste.

Cutting list

A list of all the parts needed, with sizes and materials.

Quality control

Checking products meet the required standard.

Kerf

The width of material removed by a saw cut.

Try square

A tool for marking and checking right angles.