Why material matters
The material you choose affects three things: cost per unit, machining time, and tool wear. A CNC shop quotes based on material because they know what spindle speed, feed rate, and tool life to expect. Choose the wrong material and you either overpay or face delays when tooling breaks.
Material also affects tolerances, surface finish, and durability in service. A prototype in aluminium might look good but fail in production if the final part needs stainless steel's corrosion resistance or tool steel's hardness.
Aluminium
Aluminium is the fastest and cheapest to machine. It cuts at high speeds with minimal tool wear, so setup times are short and per-unit cost drops fast. It finishes well—you get good surface quality without extra work. The downside: it's soft, corrosion-prone unless anodised, and not suitable for high-load applications.
6061: The workhorse. Good strength-to-weight, easy to machine, and takes anodising well. Use this for brackets, enclosures, heatsinks, and prototypes. Most affordable choice when you need corrosion resistance (anodised).
7075: Stronger and harder than 6061, but slower to machine. Tool wear increases, so cost per unit rises. Reserve this for aerospace, high-stress tooling, or applications where light weight and hardness matter more than cost. Anodises well but costs 15–20% more than 6061.
Cost range: €20–50 per kg raw stock. Anodising adds €2–5 per part depending on finish (Type II / Type III).
Steel
Mild steel (low-carbon) machines slower than aluminium but faster than stainless. It's stronger, harder to work with, and tougher in service. Tool cost is higher because steel requires lower speeds and more frequent tool changes. Surface finish isn't as automatic—you may need an extra pass for tight tolerances.
Mild steel (S235 / EN3B): Affordable, widely available, and serviceable. Good for structural brackets, shafts, gears, and any part that needs real strength. No corrosion protection without paint or plating, so specify if the part will be outdoors.
Tool steel (H13 / O1): Hard, heat-treatable, and much slower to machine. Used for dies, punches, gauges, and any part requiring high hardness. Cost is 2–3x mild steel. Machining time doubles. Reserve for prototypes of injection-mould cavities or specialised tooling.
Cost range: Mild steel €15–35 per kg; tool steel €40–80 per kg before heat-treat.
Stainless steel
Stainless is corrosion-resistant but notoriously slow to machine. Work-hardening is the culprit—the material hardens as the tool cuts, dulling the tool faster than the material is removed. Spindle speeds must be lower, feeds slower, and tool changes frequent. A part that would take 2 hours in aluminium can take 6 in stainless.
304: The most common food-grade stainless. Good general-purpose choice if corrosion resistance matters. Widely available, well-understood by shops. Slower than 316 to machine.
316: Better corrosion resistance (marine environments, salt spray) but slightly harder and slower to machine than 304. Often specified for medical or coastal applications. Cost premium is 10–15% over 304.
Cost range: €30–60 per kg raw stock. Expect 40–50% longer machining time than mild steel, which usually translates to 30–40% higher labour cost per part.
Engineering plastics
Plastics machine extremely fast with minimal tool wear. Speeds are high, feeds aggressive, and tool life measured in hours rather than minutes. However, you're limited to non-load-bearing prototypes and small runs—injection mould tooling or production volume doesn't justify CNC plastic work.
Acetal (Delrin): Stiff, low-friction, and machines beautifully. Used for bushings, spools, non-critical gears, and quick prototypes. White or black. Cost is low; lead times are short because machining is fast.
PEEK: High-performance thermoplastic. Retains strength to 250°C, used in aerospace and medical. Machines well but material cost is 10–15x Acetal. Justify only when thermal resistance is critical.
PTFE (Teflon): Low-friction, non-sticking. Machines easily but is brittle—requires slow feeds and careful tooling to avoid chipping. Used for seals, bushings, and non-stick fixtures.
Cost range: Acetal €8–20 per kg; PEEK €80–150 per kg; PTFE €40–100 per kg. Labour cost is lowest of all materials because cutting time is short.
Cost and machinability comparison
| Material | Relative Cost | Machinability | Corrosion Resistance | Best for |
|---|---|---|---|---|
| Aluminium 6061 | €€ | Fast | Anodised only | Prototypes, light parts, brackets |
| Aluminium 7075 | €€€ | Slower | Anodised only | Aerospace, high-stress |
| Mild steel | €€ | Medium | None (paint/plate) | Shafts, gears, brackets |
| Tool steel | €€€ | Slow | None | Dies, gauges, moulds |
| Stainless 304 | €€€ | Slow | Excellent | Food contact, general corrosion |
| Stainless 316 | €€€+ | Very slow | Excellent | Marine, salt spray, medical |
| Acetal | € | Very fast | N/A | Prototype bushings, spools |
| PEEK | €€€€ | Fast | N/A | Aerospace, high-temperature |
What to specify when you quote
When you contact a shop, say this: "I need the part in [material name and grade]. If you have a preference or alternative, let me know." Most shops carry common stock—6061, mild steel, 304 stainless—so delivery is fast. Exotic materials like 7075 or PEEK may need ordering, which adds a week or two to lead time.
If you're unsure which material is right, describe what the part must do. Does it need to survive outdoors? Must it withstand heat? Is weight critical? The shop will recommend the cheapest option that meets your requirements.
Lead times by material
Aluminium parts are usually fastest—stock is common, machining is quick. Expect 5–10 days for a prototype run. Mild steel is similar. Stainless takes longer because machining is slow; add 3–5 days. Tool steel and plastics depend on shop queue, but if stock is on hand, lead time can be short (the actual cutting is fast for plastics; slow for tool steel).
Next steps
Once you've decided on material, the next decision is geometry. Read the milling vs turning guide to pick the right machine type for your part shape. Then prepare your CAD file and send a quote request to Irish shops with your material choice included.