What Can You Cut With a CNC Machine?

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  Key takeaways
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  What can you cut with a CNC machine: the real constraint
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  Aluminum, steel and stainless: the everyday metals
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  Titanium and superalloys: slow, hot and expensive
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  Plastics and composites: low force, high movement
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  Ceramics and glass: diamond and ultrasonic territory
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  Tooling board and pattern materials
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  Material families and what to expect at the machine

A CNC machine removes material with a rotating or stationary cutting edge. If a tool can be harder than the workpiece, the stock can be cut. That is the whole rule. Everything else — spindle power, rigidity, coolant, tool coating — decides how fast and how accurately the cut happens.

So the honest answer to what can you cut with a CNC machine is: any solid that is softer than the tool. Aluminum, stainless steel, tool steel, brass, titanium, POM, PEEK, carbon fibre, ceramics and glass all get machined every day. What changes is the tool material, the cutting speed and the number of setups.

The list of materials that cannot be cut is short. Soft rubber tears instead of shearing. Thin foils deflect. Wet wood and some composites fray. Custom 3D printing or vacuum casting handles those cases better.

The rest of this page sorts materials by how they behave at the cutting edge, because that is what actually affects your part.

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  Rule of thumbWorkpiece hardness must stay below tool hardness.
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  What variesSpeed, feed, tool coating, coolant and number of setups.
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  What does not workSoft rubber, thin foils, fraying composites.

Aluminum is the most machined metal in our shop. Grades 6061 and 6061-T6 cut freely at high spindle speeds, hold ±0.005 mm, and take anodizing well. 7075 is stronger but gummier and needs sharper tools. 2024 machines cleanly but corrodes without a coating. ADC12 is a cast grade, common in die-cast housings that need secondary machining.

Carbon steel grades 1018, 1045 and 4140 are straightforward. 4130 and 4340 are alloy steels for higher strength. A36 is structural and cheap but gummy. Tool steel is hard and abrasive — expect slower speeds and more tool wear. All of these cut best with carbide tooling and flood coolant.

Stainless steel is where feeds and speeds get serious. 303 is the free-machining grade and behaves well. 304 and 316 work-harden if the tool rubs, so the cut must stay aggressive. 17-4PH (SUS630) is a precipitation-hardening stainless used for shafts and valves. It machines well in the annealed state and gets harder after heat treatment.

Copper and brass cut easily but conduct heat into the tool. C36000 brass is the free-cutting grade. Beryllium copper machines cleanly but the dust is toxic, so it needs containment.

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  Easiest metals6061 aluminum, C36000 brass, 303 stainless.
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  Watch work hardening304, 316 and 17-4PH — keep the tool moving.
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  High strength, higher cost7075, 4340, tool steel.

Titanium grades TA1 and TA2 are commercially pure and cut reasonably well. TC4 (Ti-6Al-4V) is the aerospace workhorse. It has low thermal conductivity, so heat stays in the cutting zone instead of leaving with the chip. Tool life drops fast if you push too hard, and the surface can smolder if coolant is thin.

Inconel and similar nickel alloys are harder still. They hold strength at high temperature, which is exactly what makes them hard to cut. Expect slower spindle speeds, heavier tool wear and longer cycle times. These materials are chosen for turbine and exhaust parts, not for cost-sensitive work.

Magnesium AZ31B and AZ91D cut very fast and very light. The catch is fire risk. Fine chips ignite, so chip control and a dedicated extinguishing plan are non-negotiable. We do not run magnesium without a documented procedure.

For any of these, the geometry of the part decides whether a 3-axis or 5-axis setup makes sense. Complex contours usually justify the extra axis.

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  TitaniumLow conductivity keeps heat in the cut. Sharp tools, high coolant flow.
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  Nickel alloysSlow speeds, heavy tool wear, long cycles.
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  MagnesiumFast cutting, real fire risk. Chip control is the whole job.

Plastics are soft and cut with low cutting forces, so spindle power is rarely the limit. The problem is heat and movement. POM and ABS machine cleanly and hold tight tolerances. PC is tougher and more notch-sensitive. PMMA chips easily and can craze around the cut if the tool is dull.

PA and PEEK are engineering plastics used for gears, bushings and medical parts. PEEK is expensive and abrasive, so tool wear matters more than speed. PP and HDPE are cheap and chemically resistant but soft, and they tend to burr instead of shearing cleanly.

Carbon fibre reinforced plastic is abrasive. The fibres grind away a cutting edge in minutes, so diamond-coated tooling and strong dust extraction are standard. Delamination at the exit face is the common defect. A backing plate solves most of it.

For plastics, the finishing pass does the work. Take a light radial cut at the end and the wall finish is clean. Skip it and you get chatter marks and burrs.

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  Clean cuttersPOM, ABS, PC, PEEK.
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  Burr-pronePP, HDPE — expect a deburring step.
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  AbrasiveCarbon fibre — diamond coating and dust extraction.

Ceramics and glass sit at the edge of normal CNC work. They are hard, brittle and electrically insulating, so they behave nothing like metal. Diamond grinding tools handle most of them. Ultrasonic-assisted machining helps where the geometry is complex or the wall is thin.

The failure mode is fracture, not chip formation. A tool that rubs instead of cutting will crack the part. So the process runs at low feed per tooth with rigid setups and no vibration. Even then, edge chipping is common at sharp corners. Rounded internal corners reduce it.

Applications tend to be small and high-value: insulators, sensor windows, optical components and wear plates. You do not cut these parts to save money. You cut them because nothing else survives the service conditions.

If your design can tolerate a metal or engineering-plastic substitute, take it. The cost difference is large, and the lead time is longer because setups are slower.

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  ToolingDiamond grinding, sometimes ultrasonic assist.
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  Main defectEdge chipping and cracking.
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  Design fixRound internal corners, avoid thin walls.

Tooling board is a dense polyurethane or epoxy board made for patterns and molds. It cuts like hard plastic with almost no tool wear, so you can run long finishing passes and get a smooth surface straight off the machine. That surface becomes the mold face.

The trade-off is strength. Tooling board will not survive production clamping, so it is used for prototypes and low-volume tooling. Once the design is locked, the pattern moves to aluminum or steel.

We machine tooling board on the same 3-axis and 5-axis centers used for metal. The difference is in the toolpath: smaller stepovers, higher spindle speeds, and a vacuum table instead of a vise.

It is a good fit when you need a mold quickly and the part count is low.

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  Best usePatterns, molds, prototype tooling.
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  Low tool wearLong finishing passes are practical.
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  LimitNot for production clamping loads.