Why Material Matters
Your material choice affects everything. It sets the part's strength, weight, cost, and lead time. The wrong material wastes money. The right one saves it.
CNC machines can cut most metals and many plastics. But each material behaves differently. Some cut fast. Others need special tools. Your pick changes how long the job takes and what it costs.
Decision Framework
Ask these five questions before you pick a material:
- What loads will the part see? High stress needs steel or titanium. Low stress works with aluminum or plastic.
- Does weight matter? Aluminum weighs one-third as much as steel. Plastics weigh even less.
- What temperatures will it face? Steel handles heat. Plastics soften above 200–400°F.
- Does it need to resist corrosion? Stainless steel and titanium handle moisture. Carbon steel rusts.
- What is your budget? Aluminum costs the least to machine. Titanium costs the most.
If you are not sure what to use, start with 6061-T6 aluminum. It machines fast, costs less, and works for most parts. Switch to something else only when 6061 does not meet your needs.
Top 7 Metals for CNC
6061-T6 Aluminum
The most popular CNC material. It machines fast and costs less than steel. Tensile strength is 45 ksi. It resists corrosion and anodizes well. Use it for brackets, housings, and enclosures.
7075-T6 Aluminum
Much stronger than 6061. Tensile strength hits 83 ksi. It costs more and does not anodize as evenly. Use it for aerospace parts and high-stress brackets.
304 Stainless Steel
The go-to stainless steel. It resists rust and handles food contact. Tensile strength is 73 ksi. It machines slower than aluminum. Use it for medical, food, and marine parts.
316 Stainless Steel
Better corrosion resistance than 304. It handles salt water and chemicals. Tensile strength is 79 ksi. Costs 20% more than 304. Use it for marine and chemical parts.
4140 Steel
A strong, heat-treatable steel. Tensile strength reaches 95 ksi (up to 150 ksi heat-treated). It rusts without coating. Use it for shafts, gears, and fixtures.
Grade 5 Titanium (Ti-6Al-4V)
The best strength-to-weight ratio. Tensile strength is 130 ksi at 60% of steel's weight. It resists corrosion. But it costs 5–10x more than aluminum. Use it for aerospace and medical implants.
C360 Brass
The easiest metal to machine. It cuts fast with great surface finish. Tensile strength is 58 ksi. Use it for electrical parts, fittings, and decorative hardware.
Top 3 Plastics for CNC
Delrin (Acetal/POM)
A stiff, low-friction plastic. Tensile strength is 10 ksi. It machines cleanly. Use it for gears, bushings, and sliding parts. It does not absorb water.
PEEK
A high-performance plastic. Tensile strength is 14 ksi. It handles temperatures up to 480°F. It costs 10–20x more than Delrin. Use it for aerospace and medical parts that need to be light and strong.
Nylon 6/6
A tough, flexible plastic. Tensile strength is 12 ksi. It absorbs moisture, which can cause swelling. Use it for wear pads, rollers, and light-duty gears.
Material Comparison Table
| Material | Tensile (ksi) | Density (lb/in³) | Machinability | Relative Cost |
|---|---|---|---|---|
| 6061-T6 Aluminum | 45 | 0.098 | Excellent | $ |
| 7075-T6 Aluminum | 83 | 0.101 | Very Good | $$ |
| 304 Stainless | 73 | 0.289 | Fair | $$ |
| 316 Stainless | 79 | 0.289 | Fair | $$$ |
| 4140 Steel | 95 | 0.284 | Good | $$ |
| Ti-6Al-4V | 130 | 0.160 | Poor | $$$$$ |
| C360 Brass | 58 | 0.307 | Excellent | $$ |
| Delrin | 10 | 0.051 | Excellent | $ |
| PEEK | 14 | 0.047 | Good | $$$$ |
| Nylon 6/6 | 12 | 0.041 | Good | $ |
How to Choose
Follow this simple path:
- List your requirements. Write down the loads, temperatures, and environment.
- Rule out materials that fail. Cross off anything too weak or too heavy.
- Compare what is left. Look at cost and machinability.
- Pick the cheapest option that works. Do not over-spec. A stronger material is not always better.
Using titanium when aluminum works wastes money. Material cost and machine time both go up. Pick the simplest material that meets your needs.
Not sure which material to use? Send us your CAD file. Our engineers will suggest the best fit for free.
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Upload CAD for Instant QuoteFrequently Asked Questions
What is the best material for CNC machining?
6061 aluminum is the most popular choice. It machines fast, costs less than steel, and resists corrosion. It works for most general parts. Pick a different material only when you need more strength, heat resistance, or special properties.
When should I use steel instead of aluminum?
Use steel when your part needs high strength, wear resistance, or hardness. Steel is about 3 times stronger than aluminum. It also handles higher temperatures. Choose steel for gears, shafts, fixtures, and load-bearing brackets.
Is titanium worth the cost for CNC parts?
Titanium costs 5 to 10 times more than aluminum. It also machines much slower. But it has the best strength-to-weight ratio of any metal. Use it when you need light weight plus high strength, like in aerospace or medical implants.
Can you CNC machine plastics?
Yes. CNC machines cut plastics like Delrin, PEEK, nylon, UHMW, and polycarbonate. Plastics work well for lightweight parts, electrical insulators, and food-contact parts. They machine faster than metals and often cost less per part.
How does material choice affect CNC cost?
Material affects cost in two ways. First, raw material prices vary a lot. Titanium costs 10 times more than aluminum stock. Second, harder materials machine slower, which means more machine time. A steel part may take twice as long to cut as the same part in aluminum.
