The case is the most visible component of a keyboard and usually the second-largest line item in the bill of materials after the PCB assembly. The choice between CNC-machined aluminium and injection-moulded plastic is therefore not an aesthetic preference — it is a strategic decision about volume, price position and how much design flexibility you need to retain.
CNC Machining: What the Process Actually Involves
CNC keyboard cases are cut from solid aluminium stock. The workflow runs through a predictable sequence, and knowing it helps you read a supplier’s quote critically.
- Design and process planning. The CAD model is converted to a machinable format, tooling is selected, and the processing sequence is defined. Complex geometries may require five-axis machining rather than three-axis, which multiplies both setup count and cost.
- Blanking. Aluminium billet is sawn to size, with the billet diameter typically 5–10 mm larger than the finished outer dimension to leave machining allowance.
- Roughing. Large-diameter tooling removes the bulk of the material quickly, leaving 0.3–0.5 mm of stock for finishing.
- Finishing. The critical tolerances are cut here — typically ±0.05 mm for bores and mounting features. Multi-axis linkage handles curved transitions and non-standard contours.
- Deburring. Manual work on deep pockets and narrow slots, chemical deburring for precision internal features, and vibratory polishing for batch surface preparation.
- Surface treatment. Anodising forms an oxide layer of 5–25 µm, providing corrosion resistance and accepting dye for colour. Sandblasting before anodising produces a uniform matte finish; polishing before anodising produces a reflective one.
Material Grade Selection
Aluminium alloy choice affects machinability, finish quality and cost more than most buyers expect.
| Alloy | Approx. cost/kg | Key properties | Typical use |
|---|---|---|---|
| 6063 | Baseline | Excellent extrusion and finishing characteristics; very good anodising response | The standard for keyboard cases |
| 6061 | Lower | Good strength, excellent machinability, general-purpose | Prototypes, structural parts |
| 7075 | ~3× | Very high strength, significantly harder to machine | Specialty or high-stress applications |
| 2024 | ~2.5× | High strength, good fatigue resistance | Aerospace-derived applications |
6063 is the industry default for a reason: it machines cleanly, anodises uniformly, and holds the surface finish premium buyers judge the product by. Upgrading to 7075 for a standard keyboard case is usually paying for strength the product does not need.
Surface Treatment Economics
| Finish | Added cost (relative) | Result |
|---|---|---|
| As-machined | None | Visible tool marks |
| Sandblasted | Low | Uniform matte texture |
| Clear anodised | Low–medium | Corrosion protection, metallic appearance |
| Colour anodised | Medium | Full colour range, brand differentiation |
| Polished + anodised | High | Mirror-like finish |
A practical cost optimisation that experienced sourcing teams apply: specify sandblasting with clear anodising for internal and non-visible surfaces, reserving full colour anodising for exterior faces. The saving is meaningful per unit and invisible to the end customer.
The Volume Cost Curve
This is where the two processes diverge decisively. CNC machines cut one part at a time — there is no tooling to amortise, so the per-unit price stays relatively flat as volume rises. Injection moulding front-loads a substantial tooling investment but then produces parts at very low marginal cost.
| Quantity | CNC aluminium (per unit) | Injection moulded (per unit, tooling amortised) |
|---|---|---|
| 10 units | High | Very high (tooling dominates) |
| 100 units | Moderate | High |
| 1,000 units | Moderate | Low |
| 10,000 units | Moderate | Very low |
The crossover point depends on case complexity and mould cost, but the shape of the curve is universal. Below roughly a thousand units, CNC is frequently the more economical path — a conclusion that surprises buyers who assume metal is inherently the expensive option.
Capability Comparison Beyond Cost
| Factor | CNC aluminium | Injection moulded plastic |
|---|---|---|
| Tolerance | ±0.05 mm achievable | ±0.1 mm typical |
| Design iteration | Change the program, cut again — no retooling | Requires mould modification or replacement |
| Surface finish | Premium; supports anodising and polishing | May show seam lines and sink marks |
| Weight | Heavy, desk-stable, absorbs vibration | Light, more portable, more resonant |
| Batch consistency | High — same program, same result | Can vary between batches |
| Unit cost at volume | Flat | Drops sharply |
| Best fit | Premium and brand-led builds | Entry-level and high-volume consumer lines |
Rigid metal cases also constrain inner-assembly deflection, which is why CNC aluminium pairs so well with gasket mounting — the case provides the stability while the gasket provides the compliance.
Evaluating a CNC Supplier
If you are sourcing CNC cases, these questions separate capable suppliers from order-takers.
- Is machining in-house or subcontracted? Outsourcing adds a communication layer where tolerance problems get discovered late.
- What equipment is used? Older machines directly affect achievable finish and repeatability.
- Keyboard-specific experience? A supplier who understands switch spacing, stabiliser clearance and plate-to-case relationship will flag interference issues before cutting metal.
- Sample quality. Inspect surface finish, mounting accuracy, threaded holes and edge sharpness — and build a full unit from the sample rather than judging the part in isolation.
- Stated tolerances and QC process. Insist on a defined tolerance range and a documented inspection checklist. A ±0.1 mm alignment error on a switch plate becomes a visible defect once assembled.
Making the Call
The cleanest way to decide is to answer three questions in order. What is your target retail price band? What volume are you committing to for the first production run? Do you expect to revise the industrial design after the first samples?
Premium position, moderate volume, and an evolving design all point toward CNC. Cost-driven position, high volume and a frozen design point toward moulding. Many brand roadmaps use both — a CNC aluminium flagship to establish the brand, and a moulded volume line underneath it to reach the broader market.
Newkra Technology operates both CNC aluminium processing and plastic injection in-house, including tooling, machining, surface treatment and assembly, which allows a single engineering team to quote both approaches against the same brief.
