What Is CNC Machining?
CNC machining explained in plain language: what CNC means, how a CNC machine works, the main processes and machine types, materials, tolerances and costs. Written by the engineers who run CNC machines every day.
What Is CNC Machining?
CNC machining is a manufacturing process in which a computer-controlled machine removes material from a solid piece of metal or plastic until the finished part remains. A rotating cutter (milling) or a rotating workpiece (turning) does the cutting, and every movement is driven by a program instead of by hand.
CNC stands for Computer Numerical Control. “Numerical” refers to the coordinates and numbers in the program that tell the machine where to move, how fast to cut and which tool to use. Because the program is stored, the machine can repeat the same part a thousand times with the same result.
CNC machining is a subtractive process: you start with more material than you need and cut it away. That is the opposite of 3D printing, which adds material layer by layer, and of injection molding, which shapes molten plastic in a mold. The result is a solid part with real material properties, tight tolerances and a clean machined surface.
The cutter follows a programmed path and removes material layer by layer until the part matches the CAD model.
How Does CNC Machining Work?
Every CNC part goes through the same basic chain, from a 3D file on a screen to a measured part on the bench. These are the six steps we follow on every order.
1. Design: the CAD model
An engineer models the part in CAD software such as SolidWorks, Fusion 360 or Creo. The 3D file (STEP is the most common exchange format) defines the geometry. A 2D drawing adds what the model cannot show: tolerances, threads, surface finish and material.
2. Programming: CAM and G-code
In CAM software the programmer chooses tools, cutting speeds and the order of operations, then generates the toolpaths. A post-processor converts them into G-code, the language CNC machines read. A few lines look like this:
G01 Z-2 F150 (feed 2 mm into the material)
G01 X50 Y20 F400 (cut a straight line at 400 mm/min)
M03 S8000 (spindle on at 8,000 rpm)
3. Machine setup
The operator clamps the raw material in a vise, chuck or custom fixture, loads the cutting tools and sets the work zero, the reference point all coordinates start from. Good fixturing is half of the accuracy of a CNC part.
4. Machining
The machine runs the program: roughing removes most of the material quickly, finishing passes bring the surfaces to size. Coolant keeps the tool and part cool and flushes chips away. Complex parts may need several setups, for example to machine the back side.
5. Inspection
The first part is measured completely (first article inspection) with calipers, micrometers, gauges and optical or CMM measurement, and later parts are sampled. At Davantech every order ships with a measurement report.
6. Finishing
Sharp edges are deburred, and the part gets its final surface: bead blasting, anodizing, plating, passivation or powder coating, depending on material and use.
The Main CNC Machining Processes
“CNC machining” covers several processes. Most parts use one or two of them; many use milling and turning together.
- 3-axis: most prismatic parts
- 4-axis: adds a rotary axis for features on several sides
- 5-axis: complex curved parts in fewer setups (through our partner shop)
- Outside and inside diameters
- Threads, grooves and tapers
- Bar-fed production of small round parts
- Metric and imperial threads
- Reamed bores to H7 fits
- Counterbores and countersinks
Other CNC-controlled processes include wire EDM (a charged wire cuts hardened steel and sharp internal corners), grinding for very fine finishes, and CNC routers, laser and plasma cutters, which cut sheet material rather than machine solid blocks. For a side-by-side comparison of the two most used processes, read drilling vs milling and our guide to CNC cutting tools.
Types of CNC Machines
All CNC machines share the same idea: a controller reads the program and drives motors on each axis. What differs is how the tool and the material move, and which parts the machine is built for.
A CNC machine has five main parts: the controller (the computer that reads G-code), the spindle that turns the tool or the part, the axes driven by servo motors and ball screws, the work holding (table, vise, chuck or fixture) and the tool changer that swaps cutters automatically.
| Machine | How it cuts | Typical parts |
|---|---|---|
| Vertical machining center (3-axis) | Rotating tool moves in X, Y, Z over a fixed part | Housings, brackets, plates, enclosures |
| 4-axis machining center | Adds a rotary axis so the part turns between cuts | Parts with features on several sides, cams, manifolds |
| 5-axis machining center | Tool and part tilt and rotate at the same time | Impellers, complex curved and aerospace parts |
| CNC lathe | Part rotates, stationary tool cuts | Shafts, pins, bushings, fittings |
| Swiss-type lathe | Bar slides through a guide bushing near the tool | Long, slender, small-diameter precision parts |
| Wire EDM | Electrically charged wire erodes the material | Hardened tool steel, punches, sharp inside corners |
| CNC router | High-speed spindle on a large gantry | Wood, plastic sheet, aluminum panels |
| CNC laser and plasma cutter | Beam or arc cuts through sheet material | Sheet metal profiles and blanks |
At Davantech parts are milled on 3-axis and 4-axis vertical machining centers and turned on CNC lathes. Parts that need true 5-axis machining are made through a qualified partner shop, with final inspection in our factory.
Which Materials Can Be CNC Machined?
Almost any solid material can be machined, but a few metals and plastics cover most industrial parts. The choice depends on strength, weight, corrosion resistance, temperature and cost. Our materials for CNC machining guide goes into each grade in detail.
- Aluminum 6061, 6082, 7075light, fast to machine, anodizes well
- Stainless steel 303, 304, 316corrosion resistant, food and marine use
- Brass C360free-machining, fittings and contacts
- Carbon and alloy steelstrength and wear resistance
- Copperelectrical and thermal conductivity
Read more: aluminum CNC machining parts, stainless steel components, brass parts.
- POM (Delrin, acetal)stiff, low friction, stable
- PA66 (nylon)tough, wear resistant
- PEEKhigh temperature and chemical resistance
- PVDFchemical resistant, pure
- PC, PMMA, ABShousings, covers, transparent parts
Read more: machining nylon PA66, POM / Delrin machining guide.
CNC Machining Tolerances and Surface Finish
CNC machining is one of the most accurate ways to make a part. When a drawing gives no specific tolerance, the general tolerance standard ISO 2768-m applies. Tighter tolerances are possible but take more time, so they should be reserved for the features that need them. More detail in CNC machining tolerances explained.
| Feature | Standard | Achievable on critical features |
|---|---|---|
| General dimensions | ISO 2768-m | ±0.01 mm |
| Precision features | ±0.02 to ±0.05 mm | ±0.005 mm on selected features |
| Reamed holes | H8 | H7 |
| Surface finish, milled | Ra 3.2 µm | Ra 1.6 to 0.8 µm |
| Surface finish, turned | Ra 1.6 µm | Ra 0.8 to 0.4 µm |
Achievable values depend on part size, material and geometry. Confirm critical tolerances at quotation stage.
CNC Machining vs 3D Printing, Molding and Casting
CNC machining is not always the right process. The table shows where it wins and where another process makes more sense. See also CNC machining vs injection molding and plastic CNC machining vs 3D printing.
| CNC machining | 3D printing | Injection molding | Die casting | |
|---|---|---|---|---|
| Tooling cost | None | None | High (mold) | High (die) |
| Best quantity | 1 to a few thousand | 1 to tens | Thousands and up | Thousands and up |
| Typical tolerance | ±0.01 to ±0.05 mm | ±0.1 to ±0.3 mm | ±0.05 to ±0.1 mm | ±0.1 to ±0.3 mm |
| Materials | Metals and engineering plastics | Mainly plastics, some metals | Thermoplastics | Aluminum, zinc, magnesium |
| Strength | Full material properties | Lower, layer dependent | Good | Good, some porosity |
| First parts | Days | Days | Weeks (mold first) | Weeks (die first) |
| Design changes | Change the file | Change the file | Modify the mold | Modify the die |
Rule of thumb: machine prototypes and low to medium volumes, switch to molding or casting when volumes are high and the design is frozen. Many products use both: a molded housing with machined inserts or brackets.
Advantages and Limitations of CNC Machining
Advantages
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High accuracy and repeatabilityThe same program produces the same part, from the first piece to the thousandth.
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No tooling investmentStart from a CAD file. Ideal for prototypes and parts that still change.
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Real materialsParts have the full strength, temperature and chemical resistance of the solid material.
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FastFirst parts in days, not weeks, because there is no mold to build.
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Excellent surface qualityMachined surfaces are ready for anodizing, plating or sealing without much rework.
Limitations
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Material wasteMaterial is cut away as chips. Most metal chips are recycled, but raw material cost counts.
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Unit cost at very high volumeAbove a few thousand identical plastic parts, injection molding is usually cheaper per piece.
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Tool accessA rotating tool cannot make perfectly sharp internal corners or reach fully enclosed cavities.
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Setup time on complex partsParts machined from many sides need several setups or fixtures, which adds cost.
Most limitations can be designed around. Our guidelines to design machining parts show how.
Where Is CNC Machining Used?
CNC machined parts are inside almost every machine and electronic product. These are typical parts we machine for our customers.
- Aluminum housings and front panels
- Heatsinks and cooling plates
- 19-inch rack modules
- Brackets, plates and mounting blocks
- Shafts, bushings and spacers
- Fixtures and machine parts
- EV charging connector parts
- Brass pins and contacts
- Sensor housings
- Device housings and covers
- Precision plastic components
- Mechanical sub-assemblies
- Aluminum shafts and couplings
- Grippers and end-of-arm parts
- Linear motion components
- Hard-anodized enclosures
- Stainless and brass fittings
- Sealed connector bodies
See real examples in our portfolio, such as custom 19-inch rack modules and hard-anodized aluminum enclosures.
How to Get Parts CNC Machined
Ordering CNC machined parts from Davantech in Dongguan follows five steps. You deal directly with the factory and an English-speaking engineering team.
What Does CNC Machining Cost?
The price of a CNC part is mostly machine time: how many minutes the part spends on the machine, multiplied by the hourly rate. Material, setups, finishing and inspection come on top, and the setup cost is spread over the quantity, which is why ten parts cost much less per piece than one.
For hourly rates by region and real part examples, read how much does CNC machining cost. For small series, see small batch CNC machining.
The five main cost drivers
CNC Machining Questions
Short answers to the questions we hear most about CNC machining, from the Davantech engineering team.
What is CNC machining?
CNC machining is a subtractive manufacturing process in which computer-controlled machines remove material from a solid block of metal or plastic with rotating cutting tools until the finished part remains. The machine follows a program generated from a 3D CAD model, so parts are accurate and repeatable.
What does CNC stand for?
CNC stands for Computer Numerical Control. A computer reads a program of coordinates and commands, called G-code, and controls the machine's motors, spindle and tools, instead of an operator turning handwheels by hand.
How does a CNC machine work?
A CNC machine reads G-code that CAM software generates from the part's 3D model. The controller drives servo motors on each axis to move the cutting tool or the workpiece along programmed paths at set speeds, while the spindle rotates the tool (milling) or the part (turning). The operator clamps the material, loads the tools and checks the first part.
What is the difference between CNC milling and CNC turning?
In CNC milling the cutting tool rotates and moves over a stationary workpiece, which suits flat and prismatic parts such as housings and brackets. In CNC turning the workpiece rotates and a stationary tool cuts it, which suits round parts such as shafts, pins and bushings. Many parts combine both processes.
What materials can be CNC machined?
Most metals and engineering plastics can be CNC machined. Common choices are aluminum 6061 and 7075, stainless steel 303, 304 and 316, brass C360, steel and copper, and plastics such as POM, PA66 (nylon), PEEK, PVDF and polycarbonate.
How accurate is CNC machining?
When a drawing gives no specific tolerance, CNC parts are made to the general tolerance standard ISO 2768-m. Critical features can be held to ±0.01 mm, and to ±0.005 mm on selected features, depending on part size, material and geometry.
What is G-code in CNC machining?
G-code is the programming language CNC machines read. Each line tells the machine what to do, for example G00 for a rapid move, G01 for a straight cutting move and M03 to start the spindle. It is normally generated by CAM software rather than written by hand.
How much does CNC machining cost?
The cost of a CNC part depends mainly on machining time, the number of setups, the tolerances, the material and the quantity. Setup cost is spread over the batch, so the price per part drops quickly as quantity rises. Our CNC machining cost guide shows hourly rates by region and real part examples.
When should I choose CNC machining instead of injection molding or 3D printing?
Choose CNC machining for metal parts, tight tolerances, prototypes and low to medium volumes, or when the design may still change. Choose injection molding for high volumes of plastic parts once the design is frozen, and 3D printing for quick, low-cost plastic models where accuracy and strength matter less.
How long does CNC machining take?
At Davantech, samples of 1 to 10 pieces typically ship in about 15 days and standard orders in about 30 days from order, depending on material, finishing and quantity. You receive a quote with DFM comments within 24 to 48 hours, or you can use our instant online CNC quote.
Send us your STEP file and drawing. You get a price, DFM comments and a lead time from engineers who machine parts every day, directly from our ISO 9001:2015 certified factory in Dongguan, China.