Specialist Techniques & Processes
GCSE — 2.1.2 In-depth Knowledge: Product Design
Wastage and addition
Wastage — cutting and removing material from stock forms (e.g. from a sheet). Material is lost in the process.
Additive processes — like 3D printing, build up the desired shape from an additional source without waste.
Marking out and cutting
Marking out is a process where the required shape is marked onto stock material using tools such as:
- Try square, tape measure, steel rule
Materials must be held or clamped (using a vice or clamp) before cutting.
Cutting tools include:
- Hand tools — coping saw, tenon saw, hacksaw
- Machinery — bandsaw, laser cutter
Drilling
Drilling is used when a hole is required in a material. Can be done using a hand drill or pillar drill. Jigs and formers ensure holes are drilled in correct positions.
| Hole type | Description |
|---|---|
| Pilot hole | Small diameter hole to guide a screw, preventing splitting |
| Clearance hole | Large enough for a screw to pass through without the thread engaging |
| Countersunk hole | Top surface flared to receive the screwhead flush with the surface |
| Counterbore hole | Flat-bottomed hole that enlarges another hole |
Screws
Screws come with different head types:
- Flat or round headed
- Slots, crosses (Phillips) or square holes for different screwdriver fittings
- Woodscrew threads are wider than self-tapping screws
- Machine threads: M3, M4, M5 etc (fine standard threads)
Joining and reforming metals
Permanent joining:
- Welding — melting metals together
- Brazing — joining using a filler metal at high temperature
- Soldering — joining using a lower temperature filler metal
- Epoxy resin adhesives
Temporary joining:
- Nuts and bolts, hinges, screws, rivets
Machines:
- Lathe — turns a piece of metal to create differently shaped round pieces
- Milling machine — cuts slots in blocks of metal and faces off edges
Wood joining
Temporary methods: screws, nuts and bolts
Permanent methods: wood joints and adhesives (PVA, epoxy resin, contact adhesives)
Box/carcass joints
| Joint | Description |
|---|---|
| Butt | Simple but weak — edges of two pieces glued together |
| Housing | One edge slots into a groove or slot cut in the other |
| Lap | Stronger — one piece fits into an L-shaped shoulder cut in the other |
| Dovetail | Very strong — a flared ‘finger’ fits into the same shape cut from the other piece |
| Comb (finger) | Straight lengths on one piece slot into gaps on the other piece |
Frame joints
| Joint | Description |
|---|---|
| Dowel | Short length of round timber inserted into holes in both pieces to reinforce |
| Mortise and tenon | A square ‘lug’ slots into a square channel and is glued — very strong |
| Mitre | Two 45-degree cuts form a 90-degree corner |
| Bridle | Like a mortise and tenon but cut into the full width of the timber |
Joining polymers
Plastics can be joined using:
- Mechanical fixings — nuts and bolts, screws, rivets, hinges
- Adhesives — bond polymers together
- Solvent cements — fuse surfaces together chemically
Computer aided manufacture (CAM)
- All cuts are accurate and exact
- Laser cutters cut plastic sheets and certain types of MDF (correct settings essential to avoid burning)
- CAM machines can engrave materials and mark out where holes, joins and fixings are to go
- Can produce features that allow parts to be joined to another part