Materials & manufacture · Higher
Joining, assembly & finishing
10 cards · 7 quiz · 2 exam
Design & Manufacture · Higher · mrkellydt.co.uk
What you're learning in this topic
Learning intention WALT
We are learning about joining, assembly & finishing, specifically to understand:
- commercial assembly methods: adhesives, joints, knock-down fittings, fixings, snap and press fit, riveting, spot and arc welding, thermal bonding
- methods to identify assembly methods and the issues that influence them
- chrome plating, galvanising and plastic dip coating
Success criteria WILF
- I can describe commercial assembly methods: adhesives, joints, knock-down fittings, fixings, snap and press fit, riveting, spot and arc welding, thermal bonding
- I can describe methods to identify assembly methods and the issues that influence them
- I can describe chrome plating, galvanising and plastic dip coating
Wood joints
- Frame joints: mortise and tenon (strong; tables, chairs, frames), bridle (strong corner joint for frames), halving (simple frames), dowel (replaces traditional joints in factory furniture), lap.
- Rub joint: two planed edges glued together side by side to make a wide board (table tops, panels).
- Carcase joints: housing (bookshelves, cabinets; stopped housing looks neater), rebate (fitting back panels), butt (quick but weak), dovetail (drawers, decorative), mitre (hides end grain).
Fixings and adhesives
- Screws: countersunk (flush), round head (head can stand proud), chipboard screws. Drill a pilot hole, then a clearance hole in the top piece, then countersink.
- Nails and pins: panel pins hold glued joints while they set; oval brads less likely to split wood; punch below surface with a nail punch.
- Nuts and bolts: strong and removable.
- Pop rivets: join thin sheet from one side.
- Welding: permanent, strong joint in metal.
- PVA: general woodworking, non-toxic, about an hour to set. Epoxy resin: two parts, joins different materials (metal, plastic, wood).
- Knock-down fittings: non-permanent, for flat-pack furniture (cam locks, corner blocks, cross dowels). Allow self-assembly, easy storage and transport, avoid complex joints.
Commercial assembly methods (Higher) HIGHER
| Method | Notes |
|---|---|
| Adhesives | Hidden joints, joins dissimilar materials; permanent, harder to recycle |
| Carcass and frame joints | Strong wood joints, often machined by CNC in furniture production |
| Knock-down fittings | Flat-pack; low transport and storage cost; customer assembles |
| Nuts, bolts, screws | Removable for maintenance and recycling; extra parts and time |
| Snap and press fit | Moulded clips or interference fit; very fast, no extra parts; may be hard to dismantle |
| Riveting | Permanent; joins sheet metal from one side (pop) quickly |
| Spot welding | Fast, automated joining of overlapping sheet steel (car bodies) |
| Arc welding | Strong permanent joints in thicker steel (frames, gates) |
| Thermal bonding | Heat fuses thermoplastic parts together; no extra materials |
Features that aid assembly: bosses, location pins, ribs, symmetrical parts, labelling. Issues: volume, materials, function, safety, aesthetics, life expectancy, environment.
Identifying assembly methods: take the product apart and reassemble it; look for visible screws, rivet heads, weld beads, glue lines, moulded clips and snap-fit features.
Surface finishing
- Wood: sand with the grain through finer grades, then varnish (hard, protective), oil (natural look, food safe on some), stain (changes colour), wax (sheen), paint.
- Metal: file (cross then draw filing), emery cloth, wet and dry paper, polish; then lacquer, paint or dip-coat to stop corrosion.
- Plastic (acrylic edges): file, draw file, wet and dry, then polish.
- Dip coating: heat metal in an oven, dip into fluidised plastic powder; gives a smooth, coloured, protective, comfortable finish.
- Poor finishes come from dust, runs, brush marks, skipping grades, or not removing oil and dirt.
Commercial coatings (Higher) HIGHER
- Chrome plating: electroplated chromium layer. Mirror finish, corrosion resistant, hard, easy to clean (taps, car trim).
- Galvanising: steel dipped in molten zinc. Corrosion resistant. Identified by a "spangled" mottled finish (fences, railings, nails).
- Plastic dip coating: smooth coloured plastic coat. Protects, adds grip and comfort (tool handles, dish racks).
Key terms
| Mortise and tenon | Strong frame joint for tables, chairs and doors. |
|---|---|
| Housing joint | Carcase joint for shelves in bookcases and cabinets. |
| Knock-down fitting | Non-permanent fitting for flat-pack furniture. |
| Epoxy resin | Two-part adhesive that joins different materials. |
| Pop rivet | Joins thin sheet from one side only. |
| Dip coating | Hot metal dipped in plastic powder: protective, coloured, grippy finish. |
| Snap fit | Moulded clips that click together; fast assembly, no extra parts. |
| Spot welding | Fast automated welding of overlapping sheet steel (car bodies). |
| Galvanising | Dipping steel in molten zinc; spangled finish; prevents rust. |
| Chrome plating | Electroplated chromium: mirror finish, hard, corrosion resistant. |
Quick check
1. Which joint is best for fixing shelves into the sides of a bookcase?
- Housing
- Halving
- Mortise and tenon
- Lap
Show answer
A: Housing. Housings support the shelf along its width.
2. Why are knock-down fittings used in flat-pack furniture?
- They are permanent, so the product can't be taken apart
- Product can be packed flat and assembled at home
- They are stronger than any traditional wood joint
- They hide every screw, so the product looks seamless
Show answer
B: Product can be packed flat and assembled at home. Easy storage, transport and self-assembly.
3. Which adhesive would join aluminium to acrylic?
- PVA
- Wood glue
- Epoxy resin
- Glue stick
Show answer
C: Epoxy resin. Epoxy bonds dissimilar non-porous materials.
4. Before varnishing wood you should…
- Sand across the grain with a coarse paper first
- Wet the surface and varnish while it is still damp
- Apply a coat of oil to seal the grain beforehand
- Sand with the grain through finer grades and remove dust
Show answer
D: Sand with the grain through finer grades and remove dust. Preparation gives a quality finish.
5. What is the purpose of a pilot hole for a screw?
- To guide the screw and stop the wood splitting
- To let the screw head sit below the surface
- To make the screw easy to remove later
- To hold extra glue around the screw
Show answer
A: To guide the screw and stop the wood splitting. A clearance hole lets the top piece pull tight; countersinking sets the head flush.
6. A galvanised fence post can be identified by…
- A mirror finish
- A spangled, mottled surface
- A smooth coloured plastic coat
- Visible layer lines
Show answer
B: A spangled, mottled surface. Zinc crystals form spangles.
7. Which method joins car body panels quickly on an automated line?
- Arc welding by hand
- Dovetail joints
- Spot welding
- Thermal bonding
Show answer
C: Spot welding. Robots spot weld overlapping sheet steel.
Exam-style questions
1. Describe how a mild steel part would be prepared and finished by dip coating. (3 marks)
Show marking guidance
- Clean/degrease and remove burrs (1)
- Heat the part in the oven (1)
- Dip into the fluidiser of plastic powder, which melts onto the hot metal (1)
- Allow to cool / reheat to smooth (1)
2. Describe the benefits and drawbacks of using snap fits to assemble a product. (3 marks)
Show marking guidance
- Benefit: fast assembly with no extra parts or tools, lower cost (1)
- Benefit: features moulded in during injection moulding (1)
- Drawback: may be difficult to dismantle for repair/recycling; clips can break (1)
Printable worksheet
An I do, we do, you do worksheet for this topic, with a separate answer sheet.