1.1.26 Specialist Techniques & Processes
D&T 2026 — 1.1(c) Product Design Pathway
Wastage and addition
Wastage — shaping a material by removing parts of it, by cutting, drilling, sawing, filing or machining. The removed material is waste.
Addition — shaping or building a product by adding material or joining parts together, e.g. 3D printing, welding, gluing or fixing with screws.
Most products are made through a sequence of stages:
- Marking out — transferring measurements onto the material using a steel rule, try square or engineer’s square, marking gauge, scriber or pencil, measuring from a straight datum edge.
- Holding — securing the work so it cannot move while it is cut: vices, G-clamps, hand vices and machine vices. Holding work securely is both an accuracy and a safety requirement.
- Cutting — removing material with hand saws (tenon saw for wood, hacksaw for metal, coping saw for curves) or machines (scroll saw, bandsaw, laser cutter).
- Shaping — refining the shape with files, planes, chisels, rasps, abrasive papers, sanders and lathes.
- Drilling — making holes with a hand drill, cordless drill or pillar drill (see holes below).
- Forming — changing the shape of a material without removing any, e.g. bending sheet metal in folding bars, line bending acrylic or vacuum forming.
Jigs and formers for accuracy in manufacture
Jig — a device that holds the work and/or guides the tool, so the same operation can be repeated accurately on many parts without marking out each one.
Former — a solid shape that material is bent, laminated or formed around, so every part takes exactly the same shape.
- A drilling jig places holes in exactly the same position on every part — for example, the holes for a hinge.
- A bending jig holds heated acrylic at the correct angle while it cools after line bending.
- A laminating former gives every laminated chair leg the same curve.
- Jigs and formers speed up production, reduce mistakes and waste, and make parts interchangeable — essential for batch production.
A template is a related aid: a shape that is drawn around to mark out the same outline repeatedly.
Pilot, clearance, tapping, countersunk and counterbored holes
| Hole | Purpose |
|---|---|
| Pilot hole | A small hole drilled first to guide a screw or larger drill, and to stop timber splitting |
| Clearance hole | A hole just larger than the screw or bolt, so it passes through the first part without its thread gripping, pulling the two parts tightly together |
| Tapping hole | A hole drilled to the correct size for a thread to be cut inside it with a tap, slightly smaller than the bolt — e.g. a 5 mm hole for an M6 thread |
| Countersunk hole | A cone-shaped recess at the top of a hole so a countersunk screw head sits flush with the surface |
| Counterbored hole | A flat-bottomed, wider recess so a bolt or cap screw head sits below the surface |
Tap and die — a tap cuts an internal thread inside a hole; a die cuts an external thread on a rod. Taps are used in order: taper tap, second tap, then plug tap.
Deforming, reforming and fixing: soldering, nuts and bolts, screws, riveting and lathe turning
Deforming — changing the shape of a material without removing or adding any, e.g. bending, pressing or forging.
Reforming — melting or softening a material and changing it into a new shape, e.g. casting metal or moulding polymer.
- Soldering — a permanent method of joining metals with a filler metal that melts at a lower temperature than the parts. Soft soldering uses a tin-based solder for electronics and plumbing; hard (silver) soldering is stronger and used for jewellery. Flux keeps the joint clean so the solder flows.
- Nuts and bolts — a temporary fixing. A bolt passes through clearance holes and a nut tightens onto its thread, clamping the parts. A washer spreads the load; a lock nut stops it working loose.
- Screws — temporary fixings that cut or grip their own thread. Wood screws have a tapered, coarse thread; self-tapping screws cut a thread in sheet metal or plastic; machine screws fit a tapped hole or nut. Heads may be countersunk, round or pan, with slot, cross or hex drives.
- Riveting — a permanent fixing. The rivet is deformed to clamp the parts together. Pop rivets are fitted from one side with a rivet gun; snap-head rivets are hammered over from both sides.
- Lathe turning — a wastage process where the work spins and a cutting tool removes material to make round parts: cylinders, tapers, grooves and threads. A metal-working centre lathe and a wood lathe both turn work, but in different ways.
Wooden joints
Frame joints: mitre and dowel
| Joint | How it is made | Strengths and weaknesses | Uses |
|---|---|---|---|
| Mitre | Both ends cut at 45° so they meet to form a 90° corner; no end grain shows | Neat and attractive, but weak because it is glued end grain to end grain; often reinforced with dowels, a spline or pins | Picture frames, mirror frames, door trims |
| Dowel | Short round wooden pegs (dowels) glued into matching holes drilled in both parts | Strong and invisible once assembled, but the holes must line up exactly — a dowelling jig helps | Furniture frames, chair joints, flat-pack furniture |
Box and carcass joints: butt and lap
| Joint | How it is made | Strengths and weaknesses | Uses |
|---|---|---|---|
| Butt | One square-cut end glued against the face of the other | Quick and simple, but the weakest joint — small gluing area, often reinforced with nails, screws or blocks | Simple boxes, quick prototypes |
| Lap | A rebate (step) cut in one piece so the other sits into it | Stronger than a butt joint because of the larger gluing area, and partly hides the end grain | Drawer fronts, boxes, cabinets |
CAM machines: laser cutters and 3D printers
CAM — computer aided manufacture: making a product directly from a CAD file using computer-controlled machinery.
Laser cutters cut and engrave flat sheet materials such as acrylic, plywood, MDF and card with a focused beam. They are extremely accurate with very little waste, but need extraction, can scorch some edges, and must never be used on PVC, which gives off toxic fumes. Settings (power, speed and number of passes) are set differently for cutting and engraving each material.
3D printers build a product in layers from a CAD model that has been “sliced”. School printers melt a filament such as PLA or ABS through a heated nozzle (fused deposition modelling). They make complex shapes and one-off prototypes with little waste, but are slow and leave layer lines.
See Computer aided manufacture (CAM) in 1.1.1 for the advantages and disadvantages of CAM.
Joining plastics permanently and temporarily
| Method | Permanent or temporary | How it works |
|---|---|---|
| Solvent cement (e.g. Tensol for acrylic) | Permanent | Dissolves the surfaces so they fuse together as the solvent evaporates |
| Epoxy resin | Permanent | Two-part adhesive that bonds plastics to themselves and to other materials |
| Plastic welding | Permanent | Heat (hot air or ultrasonic vibration) melts the surfaces of thermoforming parts so they fuse |
| Nuts, bolts and machine screws | Temporary | Pass through drilled clearance holes and clamp the parts |
| Self-tapping screws | Temporary | Cut their own thread into a moulded hole (boss) in the plastic |
| Snap fits and clips | Temporary | Flexible moulded features that click together — common on battery covers |
| Hinges and knock-down fittings | Temporary | Allow parts to move or be taken apart |
Adhesives and the materials they suit
| Adhesive | Suits | Notes |
|---|---|---|
| PVA (polyvinyl acetate) | Wood and wood-based boards; paper and card | White glue that dries clear. Joints must be clamped while it sets (about an hour; full strength after 24 hours). Water-resistant grades are available for outdoor use |
| Contact adhesive | Sheet materials such as laminates, veneers, rubber, leather and fabric onto wood or metal | Spread on both surfaces and leave until touch-dry, then press together — it bonds instantly, so it cannot be repositioned. Gives off fumes: use with ventilation |
| Epoxy resin (e.g. Araldite) | Almost anything — metals, plastics, wood, glass, ceramics, and joining different materials | Two parts (resin + hardener) mixed in equal amounts. Very strong, waterproof and gap-filling, but expensive and slow to cure |
Name the adhesive and the materials: “Epoxy resin, because it can bond the aluminium to the acrylic” earns more than just “glue”.
Industrial manufacturing processes for metals, woods and plastics
| Material | Industrial process | What it does |
|---|---|---|
| Metals | Die casting | Molten metal (often aluminium or zinc) is forced into a steel mould under pressure — high-volume, detailed parts |
| Sand casting | Molten metal poured into a sand mould — larger parts, low to medium volumes | |
| Press forming and stamping | Sheet metal pressed between shaped dies — car body panels, drinks cans | |
| Extrusion | Metal pushed through a shaped die to make long, constant cross-sections — aluminium window frames | |
| CNC machining | Computer-controlled lathes and milling machines cut parts precisely | |
| Woods | CNC routing | Computer-controlled router cuts parts from manufactured boards — flat-pack furniture |
| Laminating and steam bending | Thin layers or solid timber bent around formers to make curved parts — chair frames | |
| Veneering | A thin slice of decorative timber glued onto a cheaper board | |
| Wood turning | Round parts such as table legs and handles turned on automated lathes | |
| Plastics | Injection moulding | Molten polymer forced into a closed mould — complex, high-volume products such as casings and bottle caps |
| Blow moulding | A softened tube of polymer inflated inside a mould — bottles and containers | |
| Vacuum forming | A heated sheet pulled over a mould by suction — trays, packaging, bath tubs | |
| Extrusion | Polymer pushed through a die to make continuous lengths — pipes, window frames, cable sheathing |