Choosing the right material is one of the most significant decisions you will make for any CNC-made part. It affects strength, weight, corrosion resistance, heat performance, surface finish, and the final cost of the job. The good news is you do not need to be a metals expert to make a smart pick. In this guide, I will give you a practical checklist you can use straight away, then walk you through 17 common materials, including when to use each one and what to watch out for.
A simple material pick checklist
Before you lock anything in, run through these points. It will save you time, money, and rework.
- What the part actually does: Is it holding weight, taking impact, or just acting as a cover or spacer.
- Loads and movement: Static loads are different from vibration, shock, or rotating parts. Moving parts often need wear-friendly materials.
- Where it will live: Indoors, outdoors, near salt air, near chemicals, or around water? Corrosion resistance might be non-negotiable.
- Heat conditions: Consider both operating temperature and temperature swings. Some materials expand more than others and that can affect clearances.
- Wear and friction: Sliding contact can cause galling, scoring, or fast wear. Some materials suit bushes and bearing surfaces much better.
- Weight goals: Aluminium, titanium, and plastics can keep assemblies light when that matters.
- Accuracy and stability: If the part needs tight tolerances, you want a material that stays stable and behaves predictably during cutting.
- Finish needs: Will the part be anodised, plated, painted, polished, or left as-machined?
- Budget and lead time: Some materials cost more in raw stock, and some take longer to cut due to hardness or heat build-up.
How the process affects the best material
Material choice is not only about performance after the part is made. It is also about how it behaves during manufacturing. Softer metals may cut quickly but can gum up tools if the settings are off. Harder alloys may hold up better in service, but they can increase tool wear and cycle time. Heat, chip control, and the right tooling matter a lot, especially in tougher jobs like CNC milling machining, where surface finish and dimensional control can change depending on how the material responds under the cutter.
The 17 Materials (grouped for easy scanning)
Aluminium and Lightweight Metals
- Aluminium 6061
Great all-rounder for brackets, plates, frames, and housings. Good strength, light weight, and reliable finishing. - Aluminium 7075
A stronger option when you need higher strength-to-weight. Often used in performance parts, but it can cost more than 6061. - Magnesium
Very light and useful when weight is critical. It needs careful handling during cutting because chips can be a fire risk.
Steels for Strength and Durability
- Stainless steel 304
Solid choice for corrosion resistance in many everyday environments. Good for general-purpose stainless parts. - Stainless steel 316
Better suited to harsh and salty environments. Common for marine-adjacent use and chemical exposure. - Carbon steel 1018/1020
Cost-effective pick for general parts. Good for shafts, plates, and components where corrosion is not a major concern. - Carbon steel 1045
Higher strength than mild steel options. Often chosen for pins, shafts, and stronger mechanical components. - Alloy steel 4140
A step up for strength and toughness. Common in heavy-duty parts and wear-prone components, especially when heat-treated. - Alloy steel 4340
High strength and good toughness for demanding mechanical use. More challenging to cut than mild steel. - Tool steel D2
Hard, wear-resistant, and used for dies and long-wearing surfaces. Expect higher cutting effort and cost. - Tool steel H13
Often used in tooling where heat resistance matters. A good option for hot-work applications. - Tool steel P20
Common in mould tooling. Chosen for a balance of machinability and performance in tooling environments. - Cast iron
Good vibration damping and stability. Often used for bases and housings. It produces fine dust-like chips, so cleanliness matters.
Copper alloys for conductivity and wear
- Copper
Excellent for electrical and thermal transfer parts. It can be sticky to cut, so the right setup helps a lot. - Brass
A favourite for fittings, threaded parts, and neat finishes. It machines cleanly and is great for smaller precision components. - Bronze
Often used for bushes, bearings, and wear pads. Strong performance in sliding contact areas.
High-performance alloys for harsh conditions
- Titanium (Grade 2 and Grade 5)
Strong, corrosion-resistant, and lighter than steel. It needs careful heat control during cutting, but it is hard to beat when weight and strength both matter.
Conclusion
If you feel stuck choosing a material, go back to basics. Start with the environment, then the loads, then the tolerance and finish needs, and finally your budget. In most cases, the right choice is the one that meets the real requirements without over-specifying. That balance is where good parts come from.
If you would like a second opinion on material selection or want parts made to spec, our CNC machining services can help you choose the right option and get moving with confidence.
