Choosing the Right Material for Your CNC Machined Parts
Material selection is one of the most consequential decisions in any CNC machining project. The wrong material doesn’t just underperform — it can double your machining costs, fail in service, or make your part impossible to manufacture at the tolerances you need.
This guide covers the most commonly machined metals, what they’re good at, and when to use each one. If you’re specifying parts for a quote or designing components for production, this is the practical reference you need.
Aluminum Alloys
Aluminum is the workhorse of CNC machining. It machines fast, holds tight tolerances, and costs less to cut than steel. If your application allows it, aluminum should be your default choice.
6061-T6
The most common general-purpose aluminum alloy. Good strength (40 ksi yield), excellent machinability, welds well, and anodizes cleanly. Use it for brackets, housings, fixtures, frames, and anything that doesn’t need extreme strength or hardness.
- Best for: General structural parts, prototypes, enclosures
- Avoid when: You need high wear resistance or hardness above 95 Brinell
7075-T6
The strongest common aluminum alloy (73 ksi yield). Used in aerospace, high-performance automotive, and any application where strength-to-weight ratio is critical. More expensive than 6061 and harder to weld, but machines well.
- Best for: Aerospace components, high-stress parts, gears, shafts
- Avoid when: Welding is required or corrosion resistance is critical (use 6061 or 5052 instead)
2024-T3
High fatigue resistance makes this the choice for aircraft structural components. Poor corrosion resistance — usually clad (Alclad) or painted. Not commonly stocked at local suppliers, so lead times can be longer.
Carbon and Alloy Steels
When you need hardness, wear resistance, or sheer strength that aluminum can’t deliver, steel is the answer. It costs more to machine (slower speeds, more tool wear), but for the right application, nothing else will do.
1018 Mild Steel
Low-carbon, easy to machine, easy to weld. Use it for pins, shafts, spacers, and structural parts that don’t need heat treatment. Can be case-hardened for surface wear resistance while keeping a tough core.
4140 Alloy Steel
The go-to for parts that need to be hard and strong — gears, axles, tooling, and hydraulic components. Heat-treatable to 50+ HRC. Machines reasonably well in the pre-hardened condition (28-32 HRC). If your part sees high loads, cyclic stress, or wear, 4140 is probably the answer.
12L14 Free-Machining Steel
Contains lead for exceptional machinability — the fastest-cutting steel available. Perfect for high-volume screw machine parts, bushings, and fittings. Not weldable and not recommended for structural applications, but for turned parts on a lathe, nothing beats it for speed and finish.
Stainless Steels
When corrosion resistance is a requirement — food processing, medical devices, marine applications, outdoor exposure — stainless steel is the standard. It’s harder to machine than carbon steel (more tool wear, more heat), so expect higher machining costs.
303 Stainless
The most machinable stainless steel. Contains sulfur for improved chip breaking. Use it for fittings, shafts, valves, and any part where you need corrosion resistance and high-volume machining. Not ideal for welding.
304 Stainless
The most common stainless steel overall — the “18-8” alloy. Excellent corrosion resistance, welds well, and is food-safe. Harder to machine than 303 but more versatile. Use it for food equipment, architectural hardware, chemical processing, and general-purpose corrosion-resistant parts.
316 Stainless
Superior corrosion resistance to 304, especially against chlorides and marine environments. The standard for medical implants, marine hardware, and chemical processing. Most expensive of the common stainless grades.
Brass and Copper
360 Brass (Free-Cutting Brass)
Arguably the most machinable metal in existence. Excellent for fittings, connectors, valve bodies, decorative hardware, and electrical components. Produces beautiful mirror finishes with minimal effort.
110 Copper
Pure copper — excellent electrical and thermal conductivity. Used for bus bars, heat sinks, and electrical contacts. Soft and gummy to machine, so it requires sharp tooling and specific cutting strategies.
Titanium
Ti-6Al-4V (Grade 5)
The most common titanium alloy — used in aerospace, medical implants, and high-performance applications. Exceptional strength-to-weight ratio and corrosion resistance. Expensive to buy and expensive to machine (slow feeds, rigid setups, specialized tooling required). Only specify titanium when the application truly demands it.
How to Choose: A Decision Framework
When selecting a material for CNC machining, work through these questions in order:
- What environment will the part operate in? Corrosive environments push you toward stainless steel, marine grades, or titanium. Clean, dry, indoor applications open up carbon steel and aluminum.
- What loads will the part carry? High static loads favor steel. High cyclic loads favor 4140 or 7075. Light loads mean aluminum saves you money.
- What tolerances do you need? Tighter tolerances are easier (cheaper) to hold in aluminum than in steel. If you need ±0.001″ across a large feature, aluminum is your friend.
- How many parts? High volumes reward free-machining alloys (303 SS, 12L14, 360 brass). Low volumes make material cost less important than machining time.
- Is weight a concern? Aluminum is roughly 1/3 the weight of steel. Titanium gives steel-like strength at 60% of the weight, but at 10x the machining cost.
- What surface finish do you need? Brass and aluminum achieve excellent surface finishes easily. Stainless steel and titanium require more work (and cost) for the same finish.
Get Expert Material Guidance
Not sure which material fits your application? That’s exactly what our quoting process is designed to help with. When you request a quote from DFW Machine, include your application details and we’ll recommend the best material for your performance requirements and budget.
We machine all of the materials listed above — and many more — in our DFW-area shop. Whether you need one prototype or a production run of thousands, we’ll help you get the material selection right from the start.
Browse our knowledge base for more machining guides and technical resources.