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CNC Machining Knowledge Hub
CNC Machining Guide: Processes, Materials, Tolerances & Cost Factors
A practical engineering guide covering CNC machining processes, materials, tolerances, finishes and design considerations for OEM parts.
CAD ReviewMachined PartsTolerance CheckOEM Production
Direct Answer
What is CNC Machining?
CNC machining is a subtractive manufacturing process using computer-controlled machine tools to remove material from metal or plastic blocks and create precision OEM components. It is widely used when parts require tight tolerances, functional features, production-grade materials and repeatable dimensional accuracy. CNC machining can support prototypes, low-volume production and end-use components across industries such as automation, medical devices, aerospace, electronics and industrial equipment.
Process Selection Guide
Which CNC Process Should You Choose?
Use project geometry, feature access and tolerance requirements to select the most practical CNC manufacturing route.
Need round parts?
CNC Turning
For shafts, bushings, collars, pins, fittings and cylindrical parts.
Need complex angles?
5-Axis Machining
For multi-sided features, complex surfaces and reduced setups.
Need tight tolerance?
Precision CNC Machining
For critical features requiring drawing-based inspection planning.
Need help choosing the right CNC process? Request Engineering RFQ Review →
Process Details Guide
CNC Machining Processes Explained
Different CNC methods solve different OEM part geometry, access and production requirements.
CNC Milling
Best for machined structures and prismatic features.
- Housings
- Brackets
- Fixtures
CNC Turning
Best for rotational components and concentric features.
- Shafts
- Bushings
- Cylinders
5-Axis CNC Machining
Best for difficult access and multi-sided machining.
- Complex Geometry
- Multi-sided Parts
Drilling & Tapping
Best for functional holes and threaded assembly features.
- Holes
- Threads
Precision CNC Machining
Best for tight tolerance production and inspection control.
- Critical Components
- Tight Tolerance Parts
Milling vs Turning
CNC Milling vs CNC Turning: Which Process Should You Choose?
Choose milling or turning based on part geometry, feature orientation and tolerance requirements.
| Dimension | CNC Milling | CNC Turning |
|---|---|---|
| Part Shape | Complex geometry | Round / cylindrical parts |
| Machine Motion | Cutting tool rotates | Workpiece rotates |
| Best For | Housings, brackets and fixtures | Shafts, bushings and collars |
| Setup | Multiple orientations | Rotational setup |
| Tolerance | Precision features | Concentric features |
Need help selecting the right CNC process? Request Engineering RFQ Review →
Material Selection
CNC Machining Materials Guide
Select CNC materials based on machinability, strength, corrosion resistance, weight, cost and finish requirements.
Aluminum 6061 / 7075
Learn More →PropertiesLightweight, easy machining, strong strength-to-weight ratio.
ApplicationsHousings, heat sinks, brackets and automation parts.
Recommended Surface FinishAnodizing, Powder Coating
Stainless Steel 304 / 316
Learn More →PropertiesStrength, corrosion resistance and clean surface performance.
ApplicationsMedical, fluid handling and industrial components.
Recommended Surface FinishElectropolishing, passivation
Carbon Steel
Learn More →PropertiesHigh strength, good machinability and cost efficiency.
ApplicationsShafts, structural parts, fixtures and mechanical components.
Recommended Surface FinishBlack oxide, zinc plating
Engineering plastic components machined for precision OEM applications.
Engineering Plastics
Learn More →MaterialPOM, PEEK, nylon, PTFE, ABS and PC.
PropertiesLightweight, wear resistance, electrical insulation and chemical resistance.
ApplicationsWear parts, guides, insulators, prototype housings and precision plastic components.
Recommended Surface FinishAs machined, deburring and application-specific preparation.
Related ResourcesCNC Machining ServiceInjection MoldingMaterial Selection Guide
Tolerance Control
CNC Machining Tolerances Explained
CNC tolerance capability depends on material, geometry, feature size, workholding, process stability and inspection method.
| Tolerance Level | Typical Range | Use Case | Engineering Note |
|---|---|---|---|
| Standard CNC | ±0.05 mm | General machined parts | Suitable for most non-critical dimensions. |
| Precision CNC | ±0.01 mm | Critical mating features | Requires drawing control and inspection planning. |
| Critical Features | Drawing Based | Holes, bores, sealing faces and assemblies | Reviewed by GD&T, function and measurement method. |
PositionControls the true location of holes, bores and assembly features.FlatnessControls surface variation for sealing, mounting and datum faces.ParallelismControls opposite faces or axes that must remain aligned.PerpendicularityControls 90-degree relationships between features and datums.
Surface Finishes
CNC Machined Surface Finishes
Surface finish selection affects corrosion resistance, appearance, wear behavior, electrical performance and final assembly requirements.
As Machined
Tool marks remain visible, suitable for functional internal surfaces.
Surface Finishing →Anodizing
Aluminum oxide finish for corrosion resistance and surface hardness.
Anodizing →Powder Coating
Durable organic coating for color, protection and consistent batches.
Powder Coating →Plating
Nickel, zinc and chrome coatings for functional surface performance.
Plating →Polishing
Controlled roughness, burr removal and mirror finish options.
Polishing →Design Guidelines
CNC Machining Design Guidelines
Good CNC design reduces tool access problems, tolerance risk, machining time and unnecessary production cost.
Internal Corners
Don't
Sharp 90° corners.
Do
Add tool radius for cutter access.
Thin Walls
Don't
Use walls that are too thin for stable machining.
Do
Maintain proper thickness for material and feature size.
Deep Cavities
Don't
Create excessive depth without tool clearance.
Do
Optimize tool access and depth-to-width ratio.
Threads
Don't
Thread to the absolute bottom of blind holes.
Do
Allow proper thread depth and tool runout space.
Cost Factors
What Affects CNC Machining Cost?
CNC cost is driven by engineering choices. Early DFM review helps reduce unnecessary machining time and quality risk.
Material
Issue: Material cost and machinability vary widely.
Solution: Review material alternatives before quoting.
Part Complexity
Issue: Deep pockets, undercuts and tight access increase cycle time.
Solution: Simplify geometry where function allows.
Tolerance
Issue: Over-specified tolerances increase inspection and scrap risk.
Solution: Apply tight tolerances only to critical features.
Quantity
Issue: Setup cost is spread differently across prototype and production volume.
Solution: Choose prototype, pilot or production routing.
Surface Finish
Issue: Finishing adds process steps and handling requirements.
Solution: Define finish and masking needs early.
How Engineers Reduce CNC Machining Cost
Material SelectionGeometry OptimizationTolerance ControlProcess SelectionProduction Planning
Need cost-focused DFM support? Engineering RFQ Review →
Process Comparison
CNC Machining vs Injection Molding vs Die Casting
Choose a manufacturing process based on volume, material, tooling investment and part function.
| Process | Best Application | Material Range | Tooling |
|---|---|---|---|
| CNC Machining | Low-medium volume precision parts | Metals and plastics | No hard tooling required |
| Injection Molding | High volume plastic parts | Thermoplastics | Mold required |
| Die Casting | High volume metal housings | Aluminum and zinc alloys | Die casting tooling required |
CNC Applications
CNC Machining Applications
CNC machining supports OEM programs where precision geometry, production-grade materials and inspection control are required.
Automotive & EV
Applications: housings, brackets and structural components.
Automotive CNC Applications →
Robotics & Automation
Applications: precision brackets, joints and mechanical components.
Robotics CNC Applications →
Semiconductor Equipment
Applications: fixtures, precision frames and equipment parts.
Semiconductor CNC Applications →
Medical Devices
Applications: precision housings and functional components.
Medical CNC Applications →Aerospace Components
Applications: lightweight precision components.
Aerospace CNC Applications →
Industrial Equipment
Applications: machine parts and production equipment.
Industrial CNC Applications →Quality Control
CNC Machining Quality Inspection
Dimensional verification and documentation help OEM buyers approve parts with confidence.
CMM Inspection
Coordinate measurement for critical dimensions and geometric features.
FAI
First Article Inspection before production release.
Material Certificate
Material traceability for production and regulated applications.
Dimensional Report
Documented measurement results based on drawing requirements.
Quality Control →Precision CNC Machining →Project Examples
CNC Machining Project Examples
Typical CNC project routes combine machining, finishing and inspection based on part function.
Aluminum Housing
Process: 5-Axis CNC + Anodizing
Precision Bracket
Process: CNC Milling
Shaft Component
Process: CNC Turning + Finishing
Free Engineering Resource
Free CNC Machining DFM & Tolerance Cheatsheet
Download a practical reference covering CNC design rules, tolerance planning, material selection and surface finish choices for OEM parts.
CNC Design RulesTolerance GuideMaterial SelectionSurface Finish Guide
FAQ
CNC Machining Guide FAQ
What is CNC machining?
CNC machining is a subtractive manufacturing process that uses computer-controlled machine tools to remove material from metal or plastic stock and create precision OEM components.
What materials can be CNC machined?
Common materials include aluminum 6061 and 7075, stainless steel 304 and 316, carbon steel, brass, copper, titanium and engineering plastics such as POM, PEEK and nylon.
What tolerances can CNC machining achieve?
Standard CNC tolerances are commonly around ±0.05 mm. Precision CNC features may reach ±0.01 mm depending on geometry, material, process stability and inspection requirements.
What is CNC milling?
CNC milling uses rotating cutting tools to machine flat surfaces, pockets, slots, holes and complex features for housings, brackets, fixtures and precision structures. Explore CNC Milling capabilities.
What is CNC turning?
CNC turning rotates the workpiece while cutting tools shape cylindrical features. It is commonly used for shafts, bushings, collars, fittings and other rotational components. Explore CNC Turning capabilities.
When should I choose 5-axis machining?
5-axis CNC machining is recommended for complex surfaces, multi-sided parts, tight feature relationships and components that would otherwise require several setups. Explore 5-Axis CNC Machining.
How much does CNC machining cost?
CNC machining cost depends on material, part complexity, tolerance requirements, quantity, setup time, inspection needs and surface finish. Engineering RFQ Review helps reduce unnecessary machining cost.
What files are needed for CNC quotation?
Submit STEP or STP 3D CAD files, 2D drawings with tolerances, material, quantity, finish requirements and inspection expectations. See RFQ Checklist.
CNC RFQ Support
Need CNC Machining Support?
Upload CAD files, drawings, material, quantity and tolerance requirements. FSD engineers review your CNC machining project before quotation.