How to Choose a Material for CNC Machining (2026)

Material is the first decision on a machined part and the one that echoes through everything after it: strength, weight, corrosion life, finish options, and a large share of the price. Pick 7075 aluminum where 6061 would have done and you overpay; pick aluminum where the part needed steel's hardness and it wears out; reach for 316 stainless on an indoor bracket and you have spent for corrosion resistance nothing will ever test. This guide walks the common CNC materials and gives you a framework to choose without over-specifying.

TL;DR

Start with four questions: how much load the part carries, what environment it lives in, whether weight matters, and your budget. For most parts, 6061 aluminum is the right default: light, cheap, corrosion-resistant, and fast to machine. Move to steel for strength and wear, stainless for corrosion or hygiene, brass for high-volume turned parts, titanium for strength-to-weight where budget allows, and engineering plastics for light weight, insulation, or chemical resistance. Machinability drives cost as much as stock price does: on the standard machinability scale, where AISI B1112 free-cutting steel is the 100 percent benchmark, free-machining brass rates roughly three times that baseline and 6061 aluminum about twice, while stainless and titanium sit below it. Tell us what you need and we match the part to the right material and shop.

The Four Questions That Pick a Material

Before comparing alloys, answer these:

1. Load and strength. Structural and high-stress? Lean steel, titanium, or high-strength stainless. Light-duty? Aluminum or plastic.
2. Environment. Water, salt, chemicals, or wash-down? Stainless or the right plastic. Indoor and dry? Aluminum or steel are fine.
3. Weight. Weight-critical (aerospace, robotics, handhelds)? Aluminum, titanium, or plastic beat steel decisively.
4. Budget and volume. High volume of small turned parts? Free-machining brass or aluminum keeps cost down. One-off prototype? Machinability matters less than availability.

Most material mistakes come from optimizing one of these and ignoring the others.

The Common CNC Materials

Aluminum (6061, 7075). The workhorse. 6061 balances strength, corrosion resistance, and machinability at low cost and covers most work; 7075 is significantly stronger for structural parts, at higher cost and lower corrosion resistance. Light, fast-cutting, and anodizable. See aluminum CNC machining.

Steel (1018, 4140, tool steels). Strong, hard, wear-resistant, and inexpensive as stock. 1018 is a general mild steel; 4140 is a tougher alloy steel for shafts and high-load parts; tool steels harden for cutting and forming. Heavier and slower to machine than aluminum, and it needs a coating or paint to resist corrosion.

Stainless steel (303, 304, 316, 17-4 PH). Corrosion resistance plus strength. 304 is the default, 316 adds chloride and marine resistance, 303 free-machines for turned parts, and 17-4 PH is high-strength. It cuts slower and work-hardens, so it costs more to machine. See stainless steel CNC machining.

Brass and copper (C360, C110). Free-machining brass (C360) is the easiest common metal to cut and dominates high-volume turned parts, fittings, and fasteners. Copper adds electrical and thermal conductivity for bus bars and heat components, though it is gummier to machine than brass.

Titanium (Ti-6Al-4V). Outstanding strength-to-weight and biocompatibility for aerospace, medical, and defense. The trade-off is cost: expensive stock and slow, demanding machining. Specify it when the strength-to-weight or corrosion case is real.

Engineering plastics (Delrin/acetal, nylon, polycarbonate, PEEK). Light, insulating, corrosion-proof, and often cheaper and faster to machine than metal. Acetal machines cleanly for gears and bushings; nylon is tough; polycarbonate is impact-resistant and clear; PEEK handles high heat and chemicals. Less rigid and heat-tolerant than metal, so not a structural drop-in.

Material Comparison at a Glance

Qualitative, to guide a first pick. Confirm specifics against your part's real requirements.

Material	Machinability	Relative strength	Corrosion resistance	Relative cost	Typical use
Aluminum 6061	Excellent	Moderate	Very good	Low	Brackets, housings, prototypes
Aluminum 7075	Good	High	Good	Medium	Structural, aerospace
Steel 1018	Good	Moderate	Poor (needs coating)	Low	General parts, fixtures
Steel 4140	Fair	High	Poor (needs coating)	Low-Medium	Shafts, gears, high-load
Stainless 304	Fair	Moderate	Very good	Medium	Food, general industrial
Stainless 316	Fair	Moderate	Excellent	Medium-High	Marine, chemical, medical
Brass C360	Excellent	Moderate	Good	Medium	Turned parts, fittings
Titanium Ti-6Al-4V	Poor	Very high	Excellent	High	Aerospace, medical
Acetal (Delrin)	Excellent	Low-Moderate	Excellent	Low	Gears, bushings, insulators

Machinability Is Half the Cost Story

Buyers focus on stock price and underrate machinability, which is how fast and cleanly a material cuts. It is measured on a standard scale where AISI B1112 free-cutting steel is the 100 percent benchmark; higher is easier. On that scale, free-machining brass rates roughly three times the steel baseline and 6061 aluminum about twice, while stainless and titanium sit well below it.

For a heavily machined part, that difference often outweighs the raw stock cost: an easy-cutting material comes off the machine in less time, with less tool wear and less scrap. It is why the same geometry can cost meaningfully more in stainless or titanium than in aluminum or brass, driven by machining time rather than the metal itself. Tolerances compound this, as covered in CNC machining tolerances and GD&T.

A Simple Decision Framework

• Default to 6061 aluminum unless a requirement pushes you off it.
• Need strength or wear? Go to 4140 steel, 7075 aluminum, 17-4 PH stainless, or titanium, in rough order of cost.
• Need corrosion resistance? Stainless (316 for chlorides) or the right plastic.
• Need minimum weight? Aluminum, titanium, or plastic.
• High volume of small turned parts? Free-machining brass or aluminum. See turning vs milling.
• Need insulation, chemical resistance, or transparency? Engineering plastics.

Common Mistakes Buyers Make

Mistake 1: Over-specifying strength. Titanium or 7075 on a part that a 6061 bracket would carry is money spent on capability nothing uses.

Mistake 2: Defaulting to stainless "to be safe." It costs more and machines no easier than 304. Use it when corrosion or hygiene demands it.

Mistake 3: Writing "steel" or "metal" on the drawing. The grade drives the process, the finish, and the price. Specify 6061-T6, 4140, 316, and so on.

Mistake 4: Ignoring finishing. Aluminum anodizes, stainless passivates, steel needs a coating to resist rust. Factor the finish into the material choice, not after it.

Finishing Follows the Material

Each material has a finishing path worth planning up front: aluminum anodizes for hardness and color, stainless is passivated or electropolished for corrosion resistance, and steel needs plating, black oxide, or paint to survive. The finish is part of the material decision, since it affects both performance and cost. The stainless guide covers passivation and electropolish in detail.

Sourcing in Canada

Every material here is machined across Canada's $931.2 billion manufacturing sector, and some are made from domestic feedstock: Canada is the world's fourth-largest nickel producer, the input that makes austenitic stainless corrosion-resistant. Sourcing domestically keeps freight and lead times short and IP in the country. Compare local capacity in Toronto, Vancouver, and Montreal, or start with how to choose a CNC machine shop.

How FrankWorks Handles Material Selection

Not sure which material fits? Describe the part, its load, and its environment, and FrankWorks helps match it to the right material and grade, then routes it to a Canadian shop set up for that material and returns pricing and a lead time. Send a STEP file and drawing with the grade specified, or tell us the application and we help you choose.

Frequently Asked Questions

What is the best material for CNC machining? There is no single best; it depends on load, environment, weight, and budget. 6061 aluminum is the common default. Steel for strength, stainless for corrosion, brass for high-volume turned parts, plastics for light weight or insulation.

Is aluminum or steel better for CNC parts? Aluminum is lighter, cheaper to machine, and corrosion-resistant, and it suits most brackets and housings. Steel is stronger and more wear-resistant for shafts and high-load parts. Default to aluminum unless you need steel's strength or hardness.

When should I choose stainless steel over aluminum? When the part must resist corrosion (water, chemicals, salt), be cleaned aggressively (food, medical), or exceed aluminum's strength and temperature tolerance. Stainless costs more and machines slower, so use it when the environment demands it.

What is the easiest metal to CNC machine? Free-machining brass (C360), rating roughly three times the free-cutting-steel baseline (AISI B1112) on the standard machinability scale. Aluminum 6061 follows at about twice the baseline. Easier machining means faster, cheaper parts.

What is the strongest CNC machining material? Among common options, titanium (Ti-6Al-4V) and alloy or hardened steels like 4140, with 17-4 PH stainless strong and corrosion-resistant. Titanium adds strength-to-weight but is costly and slow to cut. Match strength to the real load.

When should I use plastic instead of metal? When you need light weight, insulation, chemical resistance, low friction, or transparency at moderate loads. Plastics machine cheaply and fast but are less rigid and heat-tolerant, so they are not a structural drop-in for metal.

Does material choice affect CNC machining cost? Significantly, via stock price and machinability. Free-machining brass and 6061 aluminum are cheaper to make than stainless or titanium, which cut slower and wear tooling faster. On heavily machined parts, machinability often outweighs stock cost.

What is 6061 aluminum used for? The general-purpose aluminum alloy: a strong balance of strength, corrosion resistance, weldability, and machinability at low cost. Brackets, housings, plates, enclosures, prototypes. 7075 is the higher-strength step up.

What file should I send to get a material quote? A STEP file for geometry plus a drawing or notes specifying material and grade, tolerances, and finish. "6061-T6 aluminum" or "316 stainless" quotes accurately; "metal" does not.