CNC Machining Materials Guide

By CHX Metal Engineering Team · Published 2026-10-09

A guide to CNC machining materials - aluminium, stainless steel, carbon steel, copper, titanium and engineering plastics, with grades, machinability and uses. The factory covers 5,000 m2 and produces up to 5 million precision parts per month.

Material choice sets the floor on what a part can do - strength, weight, corrosion resistance, conductivity - and the ceiling on how easily it machines. This guide covers the grades we see most often, why they behave differently, and how to pick between them.

Aluminium

Aluminium dominates machined parts because it is light, machines quickly and takes finish well.

• 6061-T6 - the default all-round grade. Good strength, excellent machinability and anodizing response, predictable cost. Used for housings, brackets and general structural parts.
• 7075-T6 - higher strength (near steel in some directions) but harder to machine and less corrosion-resistant bare. Used for high-stress aerospace and robot structural parts.
• 2024-T3 - good fatigue resistance for industrial and structural use; it anodizes less uniformly than 6061.
• 5052-H32 - excellent corrosion resistance and formability, commonly used for enclosures and marine or outdoor parts.

Note that 6061 and 7075 have very different machining characters. A part designed in 6061 may need feed and speed changes - and sometimes a different tool - to run in 7075.

Stainless steel

• 303 - free-machining stainless, the easiest of the family to turn. Used for shafts, fittings and parts that need corrosion resistance without a food or medical requirement.
• 304 / 304L - general-purpose corrosion-resistant stainless with good weldability; tougher to machine than 303.
• 316 / 316L - molybdenum-bearing, with better resistance to chlorides and marine environments. Common in medical, food and optical parts.

Stainless work-hardens, so a light pass that rubs rather than cuts will harden the surface and blunt the next tool. It is a material where the shop's feeds and speeds matter as much as the grade.

Carbon and alloy steel

Steel appears in wear parts, fasteners, and structural components. 1045 and 1215 are common machining grades (1215 is free-cutting and machines close to brass), while 4140 offers higher strength for shafts and tool components. Steel parts often ship in a plated, black-oxided or hardened condition, and the heat-treat step should be planned into the process sequence.

Copper and brass

Copper alloys are chosen for conductivity. C360 brass is free-cutting and holds tight tolerances easily, making it a natural for connector pins and small fittings. Beryllium copper (C17200) combines high strength and conductivity and is used in high-reliability connectors and medical contacts. Pure copper machines with a tendency to be gummy, so it needs sharp tools and generous chip clearance.

Titanium

Titanium (grade 5, Ti-6Al-4V, often called TC4) offers a high strength-to-weight ratio and excellent corrosion resistance, at the cost of being slow to machine and hard on tooling. Its low thermal conductivity means heat stays in the cut, so feeds and speeds are conservative and coolant matters. It is justified where weight and corrosion drive the design - high-load links, aerospace and some medical parts.

Engineering plastics

• POM / Delrin - dimensionally stable, low friction, easy to machine. Common for wear pads, insulators and bushings.
• PEEK - high temperature and chemical resistance, with good mechanical strength; used in medical and demanding industrial parts. It is expensive and benefits from careful support during machining.
• PTFE, nylon and PC - selected for chemical resistance, toughness or optical clarity respectively.

Plastics move with temperature and moisture and are more sensitive to clamping force, so a tight tolerance on a plastic part should be qualified with the shop rather than assumed.

How to choose

• Start from function: what load, what environment, what conductivity, what weight.
• Then from manufacturing: how easily does it machine, and how much does it cost per kilogram.
• Only then from finish: does it anodize, passivate or plate the way you need.

If you are between two grades, send both options on the drawing and ask for a comparison. At CHX Metal we quote the material as specified and flag when a different grade would change cost or manufacturability, as part of the DFM feedback.

Frequently asked questions

Which aluminium grade should I pick for CNC machining?

6061-T6 is the usual first choice for machinability, finish and cost. Choose 7075-T6 for higher strength, 2024-T3 for fatigue resistance, and 5052-H32 for corrosion resistance and forming.

Why is 316 stainless harder to machine than 303?

303 is a free-machining grade with additives that break up chips. 316 is tougher, work-hardens, and has better corrosion resistance, so it needs more conservative feeds and speeds.

Do you machine titanium and plastics?

Yes. We machine titanium (grade 5 / TC4) and engineering plastics including POM/Delrin and PEEK, alongside aluminium, stainless, carbon steel and copper alloys.

Can you help me choose a material?

Yes. Tell us the function - load, environment, conductivity, weight - and we will recommend grades and flag how each affects cost and manufacturability, as part of the quotation.

Shenzhen Changhexin Precision Hardware Co., Ltd. (CHX Metal) · Shajing Street, Bao'an District, Shenzhen, Guangdong, China · ISO 9001:2015 (NOA198428) · ISO 14001:2015 (NOA2100184)