What Can a CNC Machine Make?

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  Key takeaways
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  What a CNC machine can make, by part type
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  Which materials can be cut, and how they behave
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  How part geometry decides the machine and the setup
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  Tolerance, size, and where the process stops
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  Choosing the axis count for a part

CNC machining covers a wide band of part families because the tool moves in programmed paths rather than a fixed die shape. Prismatic parts dominate: housings, brackets, plates, manifolds, heat sinks, impellers, valve bodies, and connector shells. Turned parts cover anything round and concentric: shafts, bushings, spacers, pins, threaded studs, and hydraulic fittings. Mill-turn centers handle parts that need both, which is common in automotive and fluid power work.

The list gets longer when you add surface work. A CNC machine can also produce engraving, laser marking, chamfers, counterbores, tapped holes, keyways, dovetails, and O-ring grooves in the same setup as the structural cuts. That matters for assembly, because a part that arrives with the seal groove already cut saves a second operation downstream.

What ties these together is that the geometry is defined by tool paths, so design changes cost little. A revised pocket depth or a shifted bolt pattern is a program edit, not a new mold. That is why CNC is the default for prototypes and bridge production, and why it stays in the picture even after a part moves to casting or molding for the volume phase.

The one hard rule is tool access. Every internal feature needs a path for the cutter to reach it and for chips to leave. Blind pockets with sharp internal corners, deep narrow slots, and fully enclosed cavities are the usual reasons a design cannot be cut as drawn. Redesigning a corner radius or opening a side wall is often cheaper than adding an EDM step.

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  Prismatic partsHousings, brackets, plates, manifolds, impellers, valve bodies
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  Rotational partsShafts, bushings, spacers, fittings, threaded studs
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  Surface featuresEngraving, marking, chamfers, counterbores, tapped holes, grooves
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  Fixtures and toolingJigs, soft jaws, end-effector plates, inspection gauges

Material choice drives tooling, speed, and finish more than any other single factor. Aluminum is the easy case: 6061-T6 machines fast, holds tight tolerances, and takes anodizing well. 7075 is stronger but less forgiving of poor chip evacuation, so deep pockets need air blast or through-coolant. Brass and copper cut cleanly, though copper tends to grab the tool and needs sharper geometry and lighter depths of cut.

Stainless steel is where process discipline shows. Grades 303 and 304 are common; 316L and 17-4PH appear in medical and marine work. Stainless work-hardens if the tool rubs instead of cutting, so feed rates stay aggressive enough to stay under the hardened layer. Tool steel and the 4130/4140/4340 family cut fine but eat inserts, which shows up in cost rather than feasibility.

Titanium and nickel alloys sit at the difficult end. TC4 (Ti-6Al-4V) and Inconel generate heat at the cutting edge and conduct it poorly, so coolant delivery and tool life dominate the process plan. These are still routine parts for us, but cycle times are longer and the finishing strategy is planned before the first cut.

Plastics behave differently again. POM and PEEK hold dimensions well; ABS and PMMA are softer and prone to burrs and melting if the spindle runs too slow. Carbon fiber cuts cleanly with diamond-coated tooling but wears edges fast. In every case the material list is a starting point, not a guarantee, so we confirm stock and machinability at quoting.

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  Aluminum6061, 2024, 5052, 5083, 6082, 7075, ADC12
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  Stainless303, 304, 316L, 420, 440C, 17-4PH
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  Steel and titanium1018, 1045, 4130, 4140, 4340, TC4, Inconel
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  PlasticsPOM, PEEK, PC, PMMA, ABS, PP, carbon fiber

Three-axis machining cuts from one direction at a time, with the part repositioned between setups. It suits flat plates, shallow pockets, and parts with features on two or three faces. Cost per part is lowest here because setup is simple and the program is short. If a design can be reached in three axes, there is rarely a reason to pay for more.

Four-axis work adds rotation around one axis, usually A or B. That lets a single setup cut features on four sides of a prismatic part, or wrap a pattern around a cylinder. It removes a re-fixturing step, and each re-fixture is a chance to lose position. For parts with bolt patterns on multiple faces, four-axis is often the cheapest way to hold a tight true position callout.

Five-axis machining moves the tool or the table in two additional rotary axes, so the cutter can approach a surface at an angle rather than straight down. This matters for contoured surfaces, deep cavities with tapered walls, impeller blades, and any part where a long tool would otherwise chatter. It also allows shorter, stiffer tools, which improves both finish and tool life on deep features.

Undercuts are the classic dividing line. If a feature cannot be seen from any single direction, it needs either a rotary axis or a second setup. Where a part has a compound angle and a tight tolerance between two such features, five-axis is usually cheaper than the fixturing needed to do it in multiple three-axis setups.

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  3-axisFlat plates, shallow pockets, features on two or three faces
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  4-axisFour-sided parts, wrapped patterns, multi-face bolt patterns
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  5-axisContoured surfaces, impellers, deep tapered cavities, compound angles

Tolerance is a negotiation between cost and function, not a blanket number. We hold ±0.005 mm (±0.0002 in) on features that need it, and we will tell you when a callout is tighter than the geometry can support. A 0.005 mm true position on a deep hole in stainless is a different problem from the same callout on a shallow aluminum bore. Standards should be realistic per feature.

Surface finish follows the same logic. As-machined finishes land around Ra 1.6–3.2 μm. A high-quality finish of Ra 0.8–1.6 μm is common for sealing faces and bearing bores. Fine finishes down to Ra 0.2–0.8 μm are possible, but they add passes and inspection time, so they belong on the surfaces that actually seal, slide, or mate.

Size limits are set by machine travel. Our largest envelope is 4,000 × 400 × 150 mm. Mid-range machines cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm, and compact cells handle 500 × 500 × 450 mm and 500 × 310 × 200 mm. A Ø400 mm rotary table supports round parts that need indexing. If a part exceeds these, it usually gets split and assembled.

The process also stops where another one starts. Thin walls below roughly 0.5 mm deflect under cutting force. Sharp internal corners require a tool radius, so EDM or a redesign is the answer. Very high volumes of a simple part are usually cheaper cast or molded, with CNC reserved for the critical faces.

Cost per part stays low at every volume because there is no tooling charge. Setup dominates the first piece, then drops away. A prototype and a 10,000-part run use the same program; only the fixturing changes. That is why CNC stays in the supply chain long after a part moves to a casting or molding process for the body.

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  Feasible±0.005 mm on functional features, Ra 0.8–1.6 μm on mating faces
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  Needs careWalls under 0.5 mm, deep narrow slots, thin floor sections
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  Wrong processSharp internal corners, fully enclosed cavities, very high volumes