CNC Machining Services — Complete Guide
CNC (Computer Numerical Control) machining is a subtractive manufacturing process that removes material from a solid block to create precise parts. It's the go-to process for prototypes, custom parts, tooling, and jigs where dimensional accuracy is critical.
This guide covers CNC machining capabilities, materials, finishes, tolerances, and how to evaluate a CNC machining partner.
CNC Machining Processes
CNC Milling
A rotating cutting tool removes material from a stationary workpiece. The most versatile CNC process.
- 3-axis milling: Tool moves along X, Y, and Z axes. Best for flat surfaces, pockets, and simple geometries.
- 4-axis milling: Adds rotation around the X-axis (A-axis). Allows machining on 3 sides without repositioning.
- 5-axis milling: Adds rotation on two axes. Machines complex geometries in a single setup — fewer setups = tighter tolerances and better surface finish.
| Capability | 3-axis | 4-axis | 5-axis |
|---|---|---|---|
| Setup count | 2-6 | 1-3 | 1-2 |
| Complex surfaces | Limited | Good | Excellent |
| Tolerance | ±0.05mm | ±0.025mm | ±0.01-0.025mm |
| Typical cost/hr | $40-60 | $60-90 | $80-150 |
CNC Turning
The workpiece rotates while a stationary cutting tool removes material. Used for cylindrical parts.
- 2-axis turning: Basic cylindrical shapes
- Live tooling turning: Adds milling capability to turned parts (cross-holes, flats, slots)
- Swiss turning: For very small, long, thin parts (watch components, medical parts)
CNC Drilling & Tapping
- Through holes, blind holes, threaded holes
- Deep hole drilling (up to 100× diameter)
- Gun drilling for precise deep holes
Material Selection
Metals
| Material | Machinability | Common applications | Relative cost |
|---|---|---|---|
| 6061 Aluminum | Excellent | Prototypes, aerospace brackets, enclosures | $ |
| 7075 Aluminum | Good | High-strength parts, structural components | $$ |
| 303 Stainless Steel | Good | Fittings, fasteners, general purpose | $$ |
| 304 Stainless Steel | Fair | Food equipment, medical, marine | $$ |
| 316 Stainless Steel | Fair | Chemical processing, marine, medical implants | $$$ |
| 17-4 PH Stainless | Fair | High-strength, corrosion resistant | $$$ |
| 4140 Alloy Steel | Good | Shafts, gears, structural parts | $$ |
| P20 Tool Steel | Good | Mold bases, plastic molds | $$$ |
| H13 Tool Steel | Fair | Hot work molds, die casting | $$$$ |
| Brass C360 | Excellent | Fittings, valve components, decorative | $$ |
| Copper C110 | Good | Electrical components, heat sinks | $$$ |
| Titanium Grade 5 (Ti-6Al-4V) | Difficult | Medical implants, aerospace, racing | $$$$$ |
Plastics
| Material | Machinability | Common applications | Relative cost |
|---|---|---|---|
| Nylon (PA6/PA66) | Good | Bushings, gears, wear pads | $ |
| Delrin (POM) | Excellent | Precision parts, rollers, bearings | $ |
| PEEK | Fair | High-temp, medical, aerospace | $$$$$ |
| PTFE (Teflon) | Fair | Seals, gaskets, electrical insulation | $$ |
| Polycarbonate | Good | Transparent parts, light covers, shields | $ |
| ABS | Excellent | Prototypes, enclosures, consumer products | $ |
| Ultem (PEI) | Fair | High-temp, medical, aerospace | $$$$ |
Surface Finishes
| Finish | Description | Ra (µm) | Process | Typical use |
|---|---|---|---|---|
| As-machined | Standard mill finish | 1.6-3.2 | End mill + tool path | Functional parts, hidden surfaces |
| Bead blast | Matte, uniform gray | 0.8-1.6 | Glass bead media | Cosmetic parts, removes tool marks |
| Brushed | Linear grain | 0.4-0.8 | Abrasive belt | Decorative, consumer electronics |
| Anodized (Type II) | Aluminum only, various colors | Sealed 0.8-1.6 | Electrochemical | Corrosion resistance, cosmetics |
| Anodized (Type III) | Hard coat, wear resistant | 0.4-0.8 | Electrochemical | Wear surfaces, military/aerospace |
| Passivation | Stainless steel, thin oxide | 1.6-3.2 | Acid bath | Corrosion resistance, medical |
| Black oxide | Steel, mild corrosion resistance | 1.6-3.2 | Chemical bath | Tooling, fasteners, non-cosmetic |
| Electroless nickel | Uniform coating, wear resistant | 0.4-0.8 | Chemical deposition | Chemical processing, food industry |
| Powder coating | Thick, durable, colored | N/A | Electrostatic + cure | Outdoor equipment, heavy machinery |
| Plating (chrome/zinc) | Decorative or functional | 0.2-0.8 | Electroplating | Automotive, hardware, tools |
Tolerance Capabilities
| Tolerance class | Standard (±mm) | Precision (±mm) | High precision (±mm) |
|---|---|---|---|
| Linear dimensions | 0.125 | 0.05 | 0.025 |
| Hole diameters | 0.05 | 0.025 | 0.0125 |
| Angular | ±0.5° | ±0.25° | ±0.1° |
| Flatness | 0.125/300mm | 0.05/300mm | 0.025/300mm |
| Concentricity | 0.1 | 0.05 | 0.025 |
Note: Tighter tolerances increase cost exponentially. A part with ±0.05mm tolerance will cost 30-50% more than ±0.125mm. High precision (±0.0125mm) can cost 2-3x standard.
Design Guidelines
Feature Recommendations
| Feature | Minimum size | Optimal size | Notes |
|---|---|---|---|
| Wall thickness (metal) | 0.5mm | 1.0mm+ | Thin walls reduce vibration |
| Wall thickness (plastic) | 1.0mm | 2.0mm+ | Plastic is less rigid than metal |
| Hole diameter | Ø0.5mm | Ø2.0mm+ | Small drills break easily |
| Thread size | M2 | M3+ | Below M2 requires tapping |
| Internal corner radius | R0.2mm | R1.0mm+ | Square corners need EDM |
| Pocket depth | 4× tool diameter | 2× tool diameter | Deep pockets need long tools |
Cost Factors
| Factor | Cost impact | Why |
|---|---|---|
| Material | 2-10× range | Aluminum vs titanium, or standard vs engineering plastic |
| Complexity | 1.5-5× | More features = more tool changes + longer cycle time |
| Tolerance | 1.3-3× | Tight tolerances require slower feeds, more setups, CMM inspection |
| Quantity | Economy of scale | Setup cost spread across more parts (typically break-even at 50-100 parts vs 3D printing) |
| Surface finish | 1.2-2× | Post-machining finishing adds labor time |
| Part size | Machine hour rate | Larger parts need bigger (more expensive) machines |
CNC vs Alternative Processes
| Factor | CNC Machining | 3D Printing | Injection Molding |
|---|---|---|---|
| Best quantity | 1-1,000 | 1-100 | 5,000+ |
| Tolerance | ±0.025mm | ±0.15-0.5mm | ±0.05-0.1mm |
| Material options | Hundreds | 20-50 polymers | 200+ polymers |
| Lead time | 5-15 days | 1-5 days | 30-60 days |
| Part size limit | Very large (1m+) | Limited by build volume | Limited by machine |
| Surface finish | Excellent | Needs post-processing | Excellent |
| Unit cost (100 qty) | $5-50 | $15-150 | $0.10-2.00 |
Why MFGABC for CNC Machining?
- Machine park: 20+ CNC machines including 3-axis, 4-axis, and 5-axis milling centers
- Precision: Standard tolerance ±0.05mm, precision to ±0.01mm
- Materials: Process 50+ metals and 30+ engineered plastics in-house
- Surface finishing: Full range — as-machined to anodized to electroless nickel
- Quality inspection: CMM measurement + full dimensional report on every order
- Communication: English-speaking project engineers, online portal for order tracking
- Turnaround: Standard 10-15 working days, expedited available in 5-7 days
*Submit your CAD files for a free CNC machining quote. We respond within 24 hours.*
*→ Next: [Sheet Metal Fabrication Guide](/capabilities/sheet-metal/)*
*→ Related: [CNC 3-Axis vs 5-Axis — Which Do You Need?](/blog/cnc-3-axis-vs-5-axis/)*
*→ Related: [CNC Material Selection Guide](/blog/cnc-material-selection-guide/)*
*→ Related: [CNC Surface Finish Guide](/blog/cnc-surface-finish-guide/)*
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