Choosing the right material for your machined part
Material selection is one of the most important decisions in any machining project. The right choice balances mechanical properties, machinability, cost, and end-use requirements. This guide covers the materials we machine most often and when to use each one.
How common CNC materials stack up against each other
The most commonly machined material — lightweight, strong, and cost-effective
Aluminum is the go-to material for CNC machining. It cuts fast, holds tight tolerances, and produces excellent surface finishes. It's also significantly lighter than steel — roughly one-third the weight — making it ideal for aerospace, automotive, and any application where weight matters.
6061 is the workhorse of the aluminum world. It's affordable, widely available, machines beautifully, and anodizes well. If you're unsure which aluminum to choose, 6061-T6 is almost always a safe bet.
7075 is nearly twice as strong as 6061 while staying lightweight. The trade-off: it's more expensive, harder to weld, and slightly less corrosion-resistant. Choose 7075 when strength is the priority.
2024 is the classic aircraft aluminum — excellent fatigue resistance but poor corrosion resistance. It's typically clad or coated for protection. Choose 2024 when fatigue life is the driving requirement.
If your part is structural but doesn't carry extreme loads, go with 6061 — it's cheaper, easier to work with, and welds well. If your part must handle high stress, impact, or vibration and weight is critical, choose 7075. When in doubt, call us at (805) 686-1071 and we'll help you decide.
When you need strength, hardness, and wear resistance
1018 is affordable and easy to machine. It can't be through-hardened but can be case-hardened for surface wear resistance. A great default when the drawing just says "steel."
4140 is the most versatile alloy steel. It machines well in the annealed condition, responds well to heat treatment, and offers a great balance of strength, toughness, and wear resistance.
4340 is a step up from 4140 in strength and toughness. It's commonly specified for aerospace and high-performance applications where failure is not an option.
Corrosion resistance for medical, food, marine, and chemical environments
Stainless steel is harder to machine than aluminum or mild steel, but it's essential when corrosion resistance matters. The key is choosing the right grade — some stainless alloys machine easily while others will eat tooling if you're not careful.
303 contains sulfur for improved machinability. It's the easiest stainless to machine by far. The trade-off is slightly lower corrosion resistance than 304 and it doesn't weld well. If your stainless part doesn't need welding, 303 saves time and money.
304 is the most widely used stainless grade. It work-hardens during machining, so sharp tools and consistent feed rates are critical. Slower to machine than 303 but more versatile.
316 adds molybdenum for superior resistance to chlorides and acids. If your part will be exposed to saltwater, chemicals, or harsh cleaning agents, 316 is the right choice.
17-4 PH is the best of both worlds — it can be heat treated to very high strength while maintaining stainless corrosion resistance. Machine it in the annealed (Condition A) state, then age-harden to final specs. We can do the aging in-house in our furnaces.
For tooling, dies, and extreme wear resistance
The best all-around tool steel. Air-hardening means minimal distortion during heat treat — critical for precision tooling. Our most-used tool steel grade.
D2's high chromium content (12%) gives it semi-stainless properties and outstanding wear life. The trade-off is lower toughness — it can chip under heavy impact.
O1 is the easiest tool steel to machine and the most forgiving to heat treat. Oil-quenching gives more distortion than A2's air-hardening, so it's better for simpler geometries.
When your tool will take a beating, S7 is the answer. Highest toughness of the common tool steels, so it absorbs impact without cracking. Also air-hardening for minimal distortion.
M2 maintains its hardness at elevated temperatures where other steels would soften. Essential for cutting tools that generate heat during use.
H13 resists thermal fatigue from repeated heating and cooling cycles. The standard choice for any tooling that contacts molten or hot metal.
We machine tool steels in the annealed (soft) condition and heat treat in-house using our Lindberg/Blue M and Cress furnaces. Hardness is verified on our Rockwell HR-150A tester before shipping. See our equipment →
Titanium demands respect — low thermal conductivity means heat stays in the cut. We use rigid setups, sharp carbide tooling, lower speeds, and heavy coolant on our Haas and DMG Mori machines. Expensive material but nothing else matches its strength-to-weight ratio.
C360 is the benchmark for machinability — all other metals are rated against it. Produces beautiful chips, excellent surface finishes, and minimal tool wear. If your design allows brass, it's the fastest and cheapest to machine.
Pure copper has the highest electrical and thermal conductivity of any common engineering metal. It's soft and gummy — sharp tooling with positive rake angles and high speeds prevent built-up edge.
BeCu is the strongest copper alloy — it can be precipitation hardened like 17-4 stainless. Excellent for parts that need both conductivity and spring properties. Requires dust collection during machining (beryllium dust hazard).
Phosphor bronze has excellent fatigue resistance and low friction against steel — the classic bearing material. It's also highly resistant to saltwater corrosion.
Inconel work-hardens aggressively and generates extreme heat during cutting. We use ceramic inserts, rigid setups, and aggressive coolant. Budget for 3-5x the machining time of steel. 718 is age-hardenable; 625 is used in the solution-annealed condition.
Monel resists both acids and alkalis where stainless steel would fail. It's tough to machine — similar to Inconel but slightly more forgiving. Common in offshore oil & gas and chemical plants.
When nothing else can survive the chemistry, Hastelloy C-276 is the last resort. It resists oxidizing and reducing acids, chlorides, and virtually everything else. Extremely expensive to buy and machine — specify only when the environment truly demands it.
Lightweight, corrosion-proof, and non-conductive
The go-to machinable plastic. Delrin holds tight tolerances, machines like butter, and has excellent dimensional stability because it barely absorbs moisture. If your part needs to be plastic, start here.
Nylon is tougher and more impact-resistant than Delrin, but absorbs moisture which causes dimensional growth (up to 0.015"/inch). Machine dry parts oversize if they'll operate in humid environments. Oil-filled grades reduce friction and moisture absorption.
PEEK is the king of engineering plastics — it can replace metal in many applications while saving 70% of the weight. It survives autoclaving, radiation, and aggressive chemicals. Stock is expensive ($50-100+/lb), so minimize waste with good nesting.
UHMW is the slipperiest common plastic — things slide across it with almost no friction. It's also extremely abrasion-resistant and FDA-compliant for food contact. Not suited for tight tolerances due to its flexibility.
PTFE resists virtually every chemical and has the lowest friction of any solid material. It's soft and tends to cold-flow under load, so it's not suited for structural applications. Glass-filled grades improve stiffness and wear resistance.
Polycarbonate is virtually unbreakable — 250 times the impact resistance of glass. It can be machined to create clear viewing windows, guards, and housings. It scratches easier than glass, so handle finished surfaces carefully.
G-10 is fiberglass-reinforced epoxy laminate — incredibly strong for a non-metal. The glass fibers are highly abrasive to tooling, so carbide or diamond tools are required. Dust requires collection (fiberglass hazard).
Ultem sits between standard plastics and PEEK in performance and cost. Inherently flame-retardant and low smoke — it meets aerospace flammability requirements. A good PEEK alternative when 340°F is enough temperature resistance.
Material selection depends on your specific application — loads, environment, temperature, weight constraints, and budget. We're happy to discuss your requirements and recommend the best material for your part. Send us your drawings and we'll include material recommendations with your quote.