Home /
Guide / CNC Machining Guide: Processes, Benefits and Applications
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
→ Related: CNC 3-Axis vs 5-Axis — Which Do You Need?
→ Related: CNC Material Selection Guide
→ Related: CNC Surface Finish Guide