What Materials Can Be Used in a CNC Machine?

• 1
  How to Tell Whether a Material Fits a CNC Machine
• 2
  Aluminium, Stainless, Steel, Copper and Titanium
• 3
  Plastics and Their Machining Limits
• 4
  Composites, Hard Alloys and When to Say No
• 5
  How Machinability Affects Cost and Lead Time
• 6
  How We Choose and Verify the Material
• 7
  Machinability Comparison by Material Group

A CNC machine does not care what the material is called. It cares about hardness, how well the material conducts heat away from the cut, and whether the chip breaks cleanly or smears. Those three properties decide tool wear, surface finish and whether your part holds tolerance.

So the practical question is not can it be cut, but can it be cut repeatably. Beryllium copper, Inconel and Ti-6Al-4V are all machinable. They just need slower speeds, more rigid setups and more tool changes than 6061 aluminium.

Three numbers tell you most of what you need. Hardness above roughly 45 HRC pushes you into carbide or ceramic tooling. Thermal conductivity below about 20 W/m·K means heat stays in the cut and goes into the tool edge instead of the chip. On a 4,000 mm gantry part, that heat has nowhere to go and the tool pays for it.

Chip formation is the third signal. Aluminium and brass break chips that clear the flute. Stainless 304 work-hardens the moment the tool rubs instead of cuts, so a light pass is worse than a heavy one. If your drawing needs a 0.2 mm finishing pass on 304, expect to fight it.

Stiffness matters as much as hardness. Thin walls, long reach tools and deep pockets on any material will chatter. When we quote materials used in a cnc machine for a job, we look at the thinnest wall and the deepest pocket before we look at the alloy name.

Aluminium is the default for most machined parts because it cuts fast and holds tight tolerance without drama. We machine 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and the die-casting alloy ADC12. Use 6061 when you need weldability and a clean anodized finish. Switch to 7075 when the part is a stressed bracket or a fixture and strength per gram matters more than cost.

Stainless is where engineers get surprised. Grades 303, 304, 316 and 316L are common, and 303 is the free-machining one. If the part touches salt water or a sterilizer, 316L is usually the right call and the extra cut time is part of the price. Harder stainless such as 17-4PH (SUS630), 420, 430, 431 and 440C machines like tool steel: pre-hardened stock, slower speeds, more finishing passes.

Carbon and alloy steels cover the structural side. We run 1018, 1045, 4130, 4140, 4340, A36 and tool steel. A 4140 shaft at 28–32 HRC is routine. Once you go past about 45 HRC, the part usually needs grinding after milling, so budget a second operation.

Copper and brass conduct heat away from the cut so well that they cut clean and leave a fine finish, but they also grab the tool and pull it into the wall. Grades C101, C103, C110, C27400, C28000, C36000 and beryllium copper all behave differently. Beryllium copper is machinable but the dust needs control, so tell us if the part is beryllium copper before we quote.

Titanium, Inconel and magnesium sit at the hard end. TA1, TA2, TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B or AZ91D are all in our wheelhouse, but each one changes the plan. Titanium needs low surface speed and flood coolant. Inconel work-hardens fast and eats inserts. Magnesium cuts easily but the fines are flammable, so chip control is a safety item, not a preference.

Plastics are not soft metals. They cut differently. ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre all behave differently under the same cutter, and the failure mode is usually melting or cracking rather than tool wear.

POM (acetal) is the best general engineering plastic for machined parts. It holds tolerance, machines to a good finish and does not absorb much water. PA (nylon) is tougher but moves with humidity, so a nylon part that fits today may not fit next month. Design a slip fit rather than a press fit.

PEEK is the high-temperature choice and the expensive one. It holds up in sterilizers and chemical lines, but it is abrasive and needs sharp tooling. PMMA and PC are for optical or impact parts. Both can chip at the edges, so we leave a finishing pass and polish edges when clarity matters.

ABS, PP and HDPE are the low-cost options for covers, jigs and fluid handling. Carbon fibre is its own category: strong, light, and hard on cutters. It delaminates if you push it, and the dust needs extraction. Expect a higher price per part than aluminium, not lower.

One rule applies to every plastic: heat is the enemy. A plastic that looks fine on the machine can warp after a day as internal stress releases. If the part has tight flatness, say so on the drawing.

Composites combine fibre and resin so you get stiffness without the weight. Carbon fibre and glass-filled grades are common in aerospace, robotics and motorsport. Machining them means trimming and drilling cured laminates, not forming them. The main risks are delamination at the exit side and frayed edges on the top ply.

Support the back of the laminate, use sharp diamond or carbide tooling, and keep the feed steady. A backing plate and a climb cut solve most edge problems. If the part is a structural laminate with a specific fibre orientation, tell us the layup direction so we can plan the cut path.

Specialty materials exist for a reason. Inconel for exhaust and turbine parts. Titanium for medical and aerospace hardware. Beryllium copper for moulds that need fast cooling. Magnesium for weight-critical housings. Each one is a deliberate trade of cost and cycle time for a property you cannot get otherwise.

There are cases where we advise against a material. A 0.5 mm wall in 316L will chatter no matter how good the setup is. A 200 mm deep 5 mm slot in titanium will burn tools. A part with a mirror finish requirement in ABS will not hold that finish. In those cases we suggest a design change or a different alloy.

That is the honest answer to what materials can be used in a cnc machine. Most materials can be machined. The question is whether the geometry, tolerance and quantity make that material the sensible choice.

Machinability is not one number. It is a combination of cutting speed, feed, tool life and how much of the cycle is spent changing tools. A material with a good rating still costs more if it needs three setups and a deburring operation.

Aluminium and brass keep cycle times short and finishes fine. Stainless and steel sit in the middle. Titanium, Inconel and hardened tool steel push cycle time up two to four times, and tool cost follows. That gap shows up in the quote long before it shows up on the machine.

Setup count often matters more than the alloy. A part that fits in one 5-axis setup avoids re-fixturing error and saves hours. That is why we run 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. The right machine for the geometry usually beats the cheapest alloy.

Tolerance drives process choice too. We hold ±0.005 mm (±0.0002 in) when the part needs it. As-machined surfaces sit at Ra 1.6–3.2 μm, high-finish parts at Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. Asking for a tighter finish than the function needs adds polishing time with no benefit.

Quantity changes the answer as well. One prototype in 7075 is fine. Ten thousand units in the same alloy may be cheaper as a die casting. We run both paths, so the recommendation follows the volume, not the other way around.

Material selection starts with the drawing, not the stock rack. We read the function, the load path, the environment and the tolerance stack, then propose one or two alloys with the trade-offs written down. If a cheaper material meets the requirement, we say so.

Every job gets a raw material check before the first cut. We verify grade and condition against the certificate, because a 6061 bar and a 6061-T6 bar look identical and machine very differently. In-process monitoring catches drift before the part is finished, and final inspection runs on 100% of parts before shipment.

Reports are available on request. Dimensional reports, material certificates and inspection records can travel with the shipment. If your quality system needs a specific format, send the template with the PO and we will fill it.

GreatLight has run three wholly-owned plants, 7,600 m² of floor space and 150 technicians since 2011. We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. That matters for material traceability, not just for the certificate on the wall.

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