CNC machining transforms raw material into precision parts through automated cutting and shaping. Whether you need a single prototype or thousands of identical components, understanding how the process works helps you make smarter purchasing decisions and set realistic expectations. This guide walks you through every stage—from design to finished part—so you know exactly what you're paying for and how long it should take.
What Is CNC Machining?
CNC stands for Computer Numerical Control. A CNC machine uses software to automate cutting, drilling, and shaping operations on metal, plastic, or composite materials. Unlike manual machining, a CNC operator inputs a digital design (usually a CAD file), and the machine executes precise movements based on that code. This repeatability is why CNC shops produce consistent, accurate parts at scale.
The most common types you'll encounter are:
- CNC mills – use rotating cutting tools on stationary workpieces
- CNC lathes – spin the material while cutting tools shape it
- Multi-axis machines – combine milling and turning in a single setup (faster, more complex)
The CNC Machining Process: Step by Step
1. Design and File Preparation
You'll need a CAD file (often .STEP, .IGES, or .DXF format) that defines your part's dimensions, tolerances, and features. If you don't have one, most CNC shops can create it for you—expect to pay $100–$500 for simple designs, more for complex geometry. Your designer or engineer should specify material type, surface finish requirements, and any tight tolerances (like ±0.01 inches).
2. Programming and Setup
The CNC programmer converts your CAD file into G-code—the machine-readable instructions that tell the cutting tool where to move and at what speed. This step typically takes 2–5 hours for straightforward parts. Setup includes installing the correct cutting tools, securing the blank material (called a "blank" or "stock"), and running a test cycle. Total prep time is usually 1–3 hours.
3. Material Selection and Blanking
You specify the starting material—aluminum, stainless steel, brass, plastic, etc. The shop cuts a blank (or uses stock) slightly larger than your final part. Material cost varies wildly: aluminum might be $2–$5 per pound, while titanium can exceed $15 per pound. Waste material (called "swarf") is recycled, so ask if that reduces your cost.
4. Machining Operation
The machine runs your program, making cuts, drilling holes, and shaping the part. For a small component, this might take 15 minutes; a complex part could run 2–4 hours per piece. Multi-axis machines reduce setup time but cost more per hour. Most shops charge $50–$150 per machine hour, depending on equipment and location.
5. Finishing and Quality Control
After machining, the part may need deburring (removing sharp edges), anodizing, powder coating, or other surface treatments. The shop inspects dimensions using calipers, micrometers, or CMM (Coordinate Measuring Machine) machines to verify tolerances. Finishing typically adds 1–3 days and $20–$200 per part, depending on complexity.
Typical Timelines and Costs
A simple CNC-machined part (under 5 inches, basic geometry) usually takes 3–5 business days and costs $75–$500 for a one-off prototype. Higher volumes drop the per-unit price: 100 identical parts might cost $15–$50 each. Rush jobs (48-hour turnaround) typically carry a 25–50% premium.
Complex parts with tight tolerances, multiple features, or exotic materials can double or triple these figures. Always ask for a quote and lead time in writing before committing.
What to Look For in a CNC Shop
- Equipment capabilities – verify they have mills, lathes, or multi-axis machines suitable for your geometry
- Material expertise – some shops specialize in metals; others handle plastics or composites
- Quality certifications – look for ISO 9001 or AS9100 (aerospace standard)
- Tolerance experience – ask about their typical tolerance range and whether they've done tighter work before
- Volume capacity – confirm they can handle your quantities without long wait times
If you're comparing multiple shops, Mercoly makes it easy to collect quotes and credentials from trusted CNC machining providers in one place, saving you hours of outreach.
Frequently Asked Questions
Q: How tight can CNC tolerances go? Most CNC shops hold ±0.005 inches routinely; premium shops achieve ±0.001 inches or tighter. Tighter tolerances require more expensive equipment, sharper tools, and longer machining time—expect to pay significantly more.
Q: Can CNC machines handle soft materials like aluminum and hard materials like titanium equally well? No—titanium requires slower feed rates, specialized cooling, and specialized tool geometry, which increases labor and tool costs. Always inform the shop of your material so they can price accurately.
Q: What file format should I send? STEP (.STEP) or IGES (.IGES) files are most universal and preserve 3D geometry perfectly. DXF works for 2D profiles. Avoid sending native CAD files (Solidworks, Fusion 360) unless the shop specifically requests them.
Get quotes from multiple vetted CNC shops on Mercoly to compare pricing, timelines, and expertise for your next project.