CNC Material Comparison & Selection Center
Side-by-side reference for the materials used in CNC machining: what each family is good at, which grades are common, what tolerances they typically hold, and how they machine. Cost is quoted per part, not banded here — the same grade prices very differently by geometry, quantity and finish.
At a glance
| Material family | Key properties | Typical tolerances | Service page |
|---|---|---|---|
| Aluminum | Light weight; High strength-to-weight ratio; Natural corrosion resistance (oxide layer); Excellent machinability | ±0.05 mm standard; tighter with finishing passes | Aluminum CNC machining service |
| Stainless Steel | Corrosion resistance; High strength; Heat resistance; Hygienic (food/medical compatible grades) | ±0.05 mm standard; ±0.01 mm achievable with finishing | Stainless steel CNC machining service |
| Carbon Steel | High strength; Heat-treatable; Cost-effective; Requires corrosion protection | ±0.1 mm as-machined; tighter after grinding | Carbon steel CNC machining service |
| Brass | Excellent machinability; Natural corrosion resistance; Attractive appearance; Good electrical conductivity | ±0.05 mm standard; excellent surface finish as-machined | Brass CNC machining service |
| Copper | Excellent electrical conductivity; Excellent thermal conductivity; Antimicrobial surface; Soft and ductile | ±0.1 mm typical; soft material moves during clamping | Copper CNC machining service |
| Titanium | Highest strength-to-weight of common metals; Extreme corrosion resistance; Biocompatible; Heat resistant | ±0.05 mm standard; stress-relief consideration for thin parts | Titanium CNC machining service |
| Engineering Plastics | Light weight; Corrosion-free; Low friction options; Electrical insulation | ±0.1 mm typical; thermal expansion and moisture limit precision | Plastic CNC machining service |
Tolerances above are family-level typical values. Tighter requirements are reviewed per part — state them on the drawing and request a quotation rather than assuming a band.
Material families in detail
Each family below lists its common grades with the governing standard, the applications it is typically machined for, the finishes usually applied, and what to watch when cutting it.
Aluminum
| Grade | Standard | Where it fits |
|---|---|---|
| 6061-T6 | ASTM B209 | General purpose; good strength, corrosion resistance, weldability. Most common machining grade. |
| 7075-T6 | ASTM B211 | High strength (aerospace grade); lower corrosion resistance than 6061; not weld-friendly. |
| 2024-T3 | ASTM B211 | High strength-to-weight; poor corrosion resistance; common in aerospace structures. |
Typical applications: Aerospace fittings, Automotive brackets, Electronics housings, Robotics frames, Consumer product enclosures.
Common finishes: Clear/black anodizing, Chromate conversion (Alodine), Powder coating, Bead blasting.
Machinability: Machines fast at high cutting speeds; sharp tools prevent built-up edge; thin walls need support to avoid chatter.
Stainless Steel
| Grade | Standard | Where it fits |
|---|---|---|
| 304 | ASTM A240 | General purpose austenitic; excellent corrosion resistance; work-hardens. |
| 316/316L | ASTM A240 | Added molybdenum for chloride resistance; marine and medical use. |
| 17-4 PH | ASTM A564 | Precipitation hardening; high strength after heat treatment; aerospace/medical. |
| 303 | ASTM A582 | Sulfur-added free-machining grade; best machinability of austenitic; lower corrosion resistance. |
Typical applications: Medical instruments and implants, Food processing equipment, Marine hardware, Valves and fittings, Aerospace components.
Common finishes: Passivation, Electropolishing, Bead blasting, Vibratory finishing.
Machinability: Work-hardens quickly: maintain consistent feed, sharp tooling, adequate coolant. 303 machines easiest; 316 slowest of the common grades.
Stainless steel CNC machining service · 304 stainless steel · 316 / 316L stainless steel · 17-4 PH stainless steel · Quote this material
Carbon Steel
| Grade | Standard | Where it fits |
|---|---|---|
| 1018 | ASTM A108 | Low-carbon, good weldability, general machined parts. |
| 1045 | ASTM A108 | Medium carbon; heat-treatable; shafts, gears, strong brackets. |
| 4140 | ASTM A29 | Alloy steel, chromoly; high strength and toughness after heat treatment. |
Typical applications: Shafts and axles, Gears and sprockets, Machine frames, Tooling and jigs, Structural brackets.
Common finishes: Zinc plating, Black oxide, Powder coating, Painting.
Machinability: Free-machining at medium speeds; 4140 in hardened state requires carbide tooling and reduced speeds.
Brass
| Grade | Standard | Where it fits |
|---|---|---|
| C36000 (free-cutting) | ASTM B16 | Best machinability of common metals; standard for turned parts. |
| C26000 (cartridge) | ASTM B36 | Good cold workability; used for deep-drawn and formed parts. |
Typical applications: Plumbing fittings and valves, Electrical connectors and terminals, Musical instrument parts, Decorative hardware, Instrument components.
Common finishes: Polishing, Lacquer coating, Nickel plating, Antique/aged finish.
Machinability: Reference standard for 100% machinability rating; very high cutting speeds; watch for lead-free variants (C360 is leaded) in potable-water applications.
Copper
| Grade | Standard | Where it fits |
|---|---|---|
| C11000 (ETP) | ASTM B152 | 99.9% pure; best electrical/thermal conductivity; gummy to machine. |
| C14500 (tellurium) | ASTM B301 | Free-machining copper; near-C110 conductivity; preferred for machined electrical parts. |
Typical applications: Electrical busbars and contacts, Heat sinks and thermal components, RF/microwave components, Plumbing fittings.
Common finishes: Electro/nickel plating, Tin plating, Anti-tarnish coating, Polishing.
Machinability: Gummy chip formation: use sharp tools, high speeds, flood coolant. Prefer C14500 for machined electrical parts.
Titanium
| Grade | Standard | Where it fits |
|---|---|---|
| Grade 2 | ASTM B265 | Commercially pure; best formability/corrosion resistance; chemical and medical. |
| Grade 5 (Ti-6Al-4V) | ASTM B265 | Workhorse aerospace alloy; high strength-to-weight; most common machined titanium. |
Typical applications: Aerospace structural parts and fasteners, Medical implants and surgical instruments, Marine components, High-performance automotive, Sporting goods.
Common finishes: Anodizing (color, type II/III limits), Passivation, Bead blasting.
Machinability: Low thermal conductivity causes heat concentration at tool edge: low cutting speeds, high feed pressure, flood coolant, sharp carbide, never let tool dwell. Fire risk with fine chips — proper chip handling required.
Engineering Plastics
| Grade | Standard | Where it fits |
|---|---|---|
| POM (Delrin/Acetal) | — | Low friction, high stiffness, dimensional stability; gears, bushings, precision parts. |
| Nylon (PA6/PA66) | — | Tough and wear-resistant; absorbs moisture (dimension planning needed). |
| PEEK | — | High-performance: chemical/heat resistance; medical implants, aerospace; expensive. |
| ABS | — | Impact resistant, low cost; prototyping and housings. |
| PTFE (Teflon) | — | Near-zero friction, chemical inertness; seals and insulators; hard to hold tolerance. |
Typical applications: Gears and bushings, Insulators, Seals and wear strips, Medical device components (PEEK), Enclosures and jigs.
Common finishes: As-machined (typical), Vapor polishing (select plastics), Dyeing.
Machinability: Sharp positive-rake tools, moderate speeds, air blast or coolant; watch heat buildup (melting) and clamping pressure (deformation).
Swapping one material for another
Material substitutions are rarely clean one-to-one swaps: a look-alike grade can differ in corrosion behaviour, strength after heat treatment, or how it behaves in service — even when the machined part looks identical off the machine. Two examples from practice: free-cutting brass C36000 is leaded, which matters for potable-water components; and lower-cost stainless substitutes can lose corrosion resistance that the drawing assumed. Treat any proposed substitution as an engineering decision, not a price line.
- → 6061 vs 7075 for CNC machining — Choosing between the two most common aluminum grades.
- → Aluminum temper designations explained — Reading what T6, T651 and other tempers actually mean for a part.
- → 5052 vs 6061 aluminum sheet — Sheet-metal enclosures that need forming or welding.
- → 304 vs 316 stainless sheet — Specifying stainless for corrosive service.
- → 201 vs 304 stainless: cost-driven substitution risks — When a cheaper stainless substitute is offered.
- → C260 brass machining guide — Brass turned parts and connector work.
Head-to-head decisions
For the pairings buyers ask about most often, the comparison pages put the two candidates side by side — values read from the collected evidence, the decision rule, and the boundary cases where the obvious answer is wrong.
- → 304 vs 316L for CNC Machining: Choosing the Stainless Grade
- → 17-4 PH vs 316 Stainless: Strength or Corrosion Resistance
- → CNC Milling vs CNC Turning: Which Process Fits the Part
What decides the final choice
Cost and lead time are quoted per part, not listed as generic bands — the same grade prices very differently by geometry, order quantity, stock form and finish, so a band would mislead more than it helps. Documentation requirements (mill certificates, traceability records, first-article inspection) should be declared in the RFQ so they are quoted in. Compliance-driven material limits — for example lead content in drinking-water components — are part of the drawing and application context, not a property table.
Final material selection must be confirmed against your drawing and service conditions. The tables on this page are family-level references to narrow the candidates — not a substitute for an engineering review of the specific part.
Ready to narrow it down? Send an RFQ with the drawing and the grade you are considering, or browse the full list of machining services.