1.1.28 Stock Forms of Materials & Components
D&T 2026 — 1.1(c) Product Design Pathway
Sectional forms and standard sizes of natural timber
Stock form — the standard shape and size in which a material is supplied before it is made into a product, e.g. sheets, planks, rods and granules.
Buying materials in standard sizes keeps them cheaper and easier to obtain, and lets designers plan parts to fit with little waste.
Natural timber is cut at the sawmill into standard sectional forms (the shape of the cross-section):
| Form | Description | Typical uses |
|---|---|---|
| Plank | A wide, thick piece with a rectangular cross-section | Workbenches, table tops, heavy shelving, construction |
| Board | Wide and relatively thin, with a rectangular cross-section | Shelves, cladding, box sides, furniture panels |
| Strip | Narrow and thin | Frames, edging, beading, light structures |
| Square | Equal width and thickness | Legs, frames, posts, turning blanks |
| Dowel | A long, round section, in diameters typically from about 6 mm to 25 mm | Dowel joints, rails, pegs, handles, axles |
Sizes are given as width × thickness, plus a length — for example 95 × 22 mm. Softwood is commonly sold in standard lengths that rise in steps of 300 mm (for example 1.8 m, 2.1 m, 2.4 m, 2.7 m and 3.0 m).
Sawn and planed timber
| Sawn timber | Planed timber | |
|---|---|---|
| Surface | Rough, straight from the saw, with visible saw marks | Smooth on all faces |
| Size | Close to its nominal (stated) size | Smaller than the nominal sawn size, because planing removes a few millimetres from each face |
| Cost | Cheaper | More expensive, because of the extra processing |
| Uses | Hidden structural work: roof timbers, fencing, garden structures, studwork | Furniture, joinery, visible woodwork and products made in school |
PAR (planed all round) — timber planed smooth on all four faces. PSE (planed square edge) is planed on its edges and faces so the edges are square and ready to use.
If you buy “50 × 25 mm” planed timber, it will measure a few millimetres less than that. Always check the actual size when designing joints and working out quantities.
Manufactured boards: sheets, standard sizes and thicknesses
Manufactured boards are supplied as flat sheets. The full standard sheet size is 2440 × 1220 mm (8 ft × 4 ft), and suppliers also sell half sheets (1220 × 610 mm) and smaller cut pieces.
| Board | Common thicknesses (mm) |
|---|---|
| MDF | 3, 6, 9, 12, 15, 18, 25 |
| Plywood | 3, 4, 6, 9, 12, 18, 24 |
| Chipboard | 12, 15, 18, 22, 25 |
| Hardboard | 3.2 |
Boards are also available pre-finished — veneered, melamine-faced or primed — and in special grades such as moisture-resistant MDF, exterior or marine plywood and flexible plywood. School laser cutters typically use 3 mm MDF and plywood cut down to fit the machine bed.
Planning parts on a sheet: designers lay out parts to fit the standard sheet with as little waste as possible (nesting), allowing for the width of each saw cut (the kerf).
Standardised fixtures and fittings, including knock-down fittings
Standard component — a part made in large quantities to an agreed size and specification, so it can be bought ready-made rather than made for each product, e.g. screws, hinges and bolts.
Why use standard components?
- Cheaper — mass production keeps the price low.
- Reliable and consistent — made to standards (such as BSI and ISO sizes) and easy to replace.
- Saves time — the designer does not have to design or make them.
Common standardised fixtures and fittings:
- Screws — wood, self-tapping and machine screws, with countersunk, round or pan heads, sized by length and gauge.
- Nails and pins — round wire nails, oval nails, panel pins.
- Nuts, bolts and washers — metric sizes such as M4, M5, M6 and M8.
- Hinges — butt hinges, piano (continuous) hinges, concealed kitchen-cabinet hinges, flush hinges.
- Catches, handles and knobs — magnetic and ball catches, pull handles.
- Brackets and corner plates.
Knock-down fitting (KDF) — a fixing that lets a product be assembled, and taken apart again, using only simple tools. KDFs are the basis of flat-pack furniture.
| KDF | How it works |
|---|---|
| Cam lock | A metal dowel screwed into one panel locks into a round cam in the other panel when the cam is turned |
| Corner (modesty) block | A plastic block screwed into both panels to hold a corner at 90° |
| Scan fitting (cross dowel and bolt) | A bolt passes through one part and screws into a barrel nut set across the other |
| Threaded insert | A metal insert with an internal thread is fitted into the wood so a bolt can be screwed in and out repeatedly |
Advantages of KDFs: furniture can be flat-packed, which saves space in transport and storage and lowers the cost; it can be assembled by the user and taken apart to move or repair. Disadvantages: joints are usually weaker than glued joints and can work loose; assembly instructions can be hard to follow.
The forms polymers are supplied in: powders and granules
Raw polymers leave the chemical plant as granules (also called pellets or nibs) or powders, so they can be measured, coloured and fed into machines easily.
| Form | Used for |
|---|---|
| Granules / pellets | Fed from a hopper into injection moulding, blow moulding and extrusion machines, where they are melted. Colour can be added as masterbatch granules |
| Powders | Rotational moulding (hollow products such as kayaks and road cones), compression moulding of thermosets, and powder coating and dip coating of metal |
Polymers are also supplied in semi-finished forms for schools and small-scale makers:
- Sheet — e.g. 3 mm acrylic for laser cutting; HIPS sheet for vacuum forming
- Rod and tube — for turning, handles and frames
- Film — for packaging and laminating
- Filament — on spools, such as PLA and ABS for 3D printing
- Foam — such as Styrofoam blocks for modelling