CNC Machining vs 3D Printing Complete Comparison of Cost, Accuracy, Lead Time, and Materials

A Complete Comparison of Cost, Accuracy, Lead Time, and Materials

You have a part and aren’t sure whether to use CNC machining or 3D printing?

Procurement needs to control costs, engineers need to ensure tolerances, and designers want shape freedom. This article provides a detailed comparison from five dimensions—cost, accuracy, materials, lead time, and complex geometries—to help you make the right decision.

Five Core Questions – Quick Answers

Before going into details, here are direct answers to the most frequently asked questions.

Single-piece custom: which is cheaper, CNC or 3D printing?

For 1–3 pieces, 3D printing is cheaper (no programming or fixturing costs). For 5–20 pieces, it depends on complexity—simple parts start to favor CNC. Above 50 pieces, CNC is always cheaper.

What accuracy can be achieved? Does the surface need post-processing?

CNC can reach ±0.005mm with a surface roughness of Ra0.8μm (mirror finish). 3D printing typically achieves ±0.1–0.3mm with visible layer lines or a matte texture. If Ra1.6 or better is required, you must use CNC, or machine the 3D-printed part on a CNC afterwards.

Lead time: I need a sample tomorrow – which is faster?

Local CNC with rush service can deliver in 24 hours (simple parts). SLA can ship next day (parts <300mm). SLM metal printing usually takes 5–7 days.

Materials: can you machine PEEK, titanium, or 7075 aluminum?

CNC can handle almost any machinable material, including PEEK, titanium, 7075, brass, and oxygen-free copper. 3D printing is limited to specialized powders or resins—no 7075, and PEEK is extremely expensive and has poor mechanical properties.

How can procurement reduce total cost? Where are the hidden costs?

For 3D printing, hidden costs are mainly support removal and sanding/polishing. For CNC, hidden costs are programming and fixturing. When ordering small batches with 3D printing, always ask about post-processing fees—otherwise the total may double.

Cost Breakdown: From 1 to 1,000 Pieces – How Much Will You Actually Pay?

Cost Components of CNC Machining

Total CNC cost consists of four parts:

• Material cost
  Aluminum 6061: ~30–50 RMB/kg, 304 stainless steel: 60–100 RMB/kg, PEEK: 800–1500 RMB/kg

• Programming fee
  Simple 2.5-axis parts: 100–300 RMB/setup; complex surfaces or 5-axis parts: 800–2000 RMB/setup

• Machine time
  3-axis CNC: 100–300 RMB/hour; 5-axis CNC: 400–800 RMB/hour

• Post-processing
  Deburring: 10–50 RMB/part; sandblasting or brushing: 50–200 RMB/batch; anodizing: ~0.2–0.5 RMB/cm²

Real example:
An 6061 aluminum housing 100×80×50mm, 10 pieces.
Material cost: 20 RMB, programming: 300 RMB, machine time: 600 RMB, post-processing: 150 RMB.
Total ~1070 RMB, ~107 RMB per piece.

Cost Components of 3D Printing

• Printing fee
  SLA resin: 0.5–2 RMB/gram; SLM metal: 5–15 RMB/gram

• Support removal
  Manual work: 0.5–2 RMB/gram of support. For complex parts, support weight can reach 30% of part weight

• Sanding and blasting
  Simple parts: 10–30 RMB/part; complex internal cavities cannot be sanded or incur >100 RMB extra

• Model repair
  If the file has holes or needs support optimization, an extra 50–200 RMB/setup

Example (SLA resin):
Part weight 50g → printing fee 40 RMB; support weight 15g → removal 20 RMB; sanding 15 RMB
Total ~75 RMB per piece

For 10 pieces, still 75 RMB each—more expensive than CNC

Example (SLM metal):
150g × 10 RMB/gram → printing fee 1500 RMB; support removal 300 RMB; heat treatment 200 RMB
Total ~2000 RMB per piece

Quantity Breakpoint – Process Selection

For simple parts, the cost breakpoint is around 5–10 pieces; for complex parts, 20–30 pieces. Above 30 pieces, CNC is almost always cheaper.

Accuracy & Tolerances: Can the Process Meet Your Drawing Requirements?

Accuracy Levels of CNC

Surface roughness: standard milling Ra3.2, fine milling Ra0.8, grinding down to Ra0.2. Sliding and sealing surfaces must be finished by CNC.

Real Accuracy of 3D Printing

Choosing Based on Accuracy

• Appearance only → 3D printing

• Fit testing (>0.2mm clearance) → SLA or CNC

• Interference fit (<0.02mm) → CNC only

• Sliding surfaces → CNC required

• Threads and pins → CNC preferred

Material Selection: Can You Get the Exact Grade You Need?

CNC Materials

• Aluminum: 6061, 7075, 5052, 6082

• Stainless steel: 303, 304, 316, 17-4PH

• Plastics: ABS, PC, POM, PEEK, PTFE, Nylon

• Specialty metals: titanium, brass, copper

Advantages:
Full strength, isotropic properties, supports heat treatment and surface finishing.

3D Printing Materials

Conclusion:
Specific grade or high strength → CNC
Visual validation → 3D printing

Lead Time & Responsiveness

CNC

• Simple: 2–3 days (24h possible)

• Medium: 3–5 days

• Complex: 5–7 days

3D Printing

• SLA: next day (small parts)

• SLM: 3–7 days

• Queue delays possible

Complex Geometries & Special Features: When Is CNC Impossible and 3D Printing Mandatory?

Inherent Limits of CNC

• Internal Closed Channels: Impossible unless made in split pieces and welded.

• Undercuts / Negative Drafts: Require 5-axis and special tools, very expensive, and internal corners cannot be cleaned out.

• Ultra-light Lattice Structures (gyroids, TPMS): Cannot be machined.

• One-piece Moving Assemblies (chains, hinges, clips): Cannot be made in one operation.

• Deep Holes (L/D >10): Prone to wandering and tool breakage.

Unique Advantages of 3D Printing

• Conformal Cooling Channels: Mold cooling efficiency improves by 30-70%, typical in the tooling industry.

• Topology-optimized Brackets: Aerospace parts can achieve 50-70% weight reduction, used in drones and satellites.

• One-piece Assembled Features: Hinges, clips, manifolds without screws, used in consumer electronics and medical devices.

• Multi-material Composites: Different colors or hardness in one part, possible with certain specialized technologies.

Hybrid Process: 3D Printed Blank + CNC Finishing

When a part requires both complex internal channels and high-precision mounting interfaces, no single process works. The hybrid process is the best solution:

1. SLM Metal Prints a Blank: Channels are fully formed, leaving 0.3-0.5mm stock on critical faces.

2. CNC Finishes the Mounting Faces: Drills holes, taps threads, reams bores.

3. Final Heat Treatment: Relieves stress.

• Result: Cost is about 30% lower than all-CNC (saves material and machining time). Accuracy is two grades higher than all 3D printing (from ±0.1mm to ±0.01mm).
  
  

Procurement Decision Checklist: 10 Steps to Choose the Right Process

Use this checklist to make a process decision in just 10 minutes.

1. Check Drawing Tolerances:
   Any dimension < ±0.02mm → Must use CNC.
   All tolerances ≥ ±0.1mm → Both processes are possible.

2. Confirm Material Grade:
   If the material is not a common 3D printing grade (7075, PEEK, brass, etc.) → Must use CNC.

3. Count the Quantity:
   ≤ 5 pieces and complex → 3D printing.
   ≥ 20 pieces → CNC.

4. Evaluate Assembly Requirements:
   Threads, dowel holes, bearing seats → CNC is more reliable (3D printed threads are weak).

5. Consider Surface Finish:
   Anodizing, plating, brushing → CNC only (3D printed parts do not finish well).

6. Urgency of Lead Time:
   Need in 24 hours → CNC rush or FDM.
   Need in 48 hours and plastic → SLA.

7. Calculate Total Cost:
   Get quotes for both processes from a quoting platform and add the hidden costs for each.

8. Check for Undercuts or Internal Channels:
   If present → Consider 3D printing or hybrid process.

9. Validate Mechanical Requirements:
   High load, cyclic stress, high temperature → Prefer CNC or forged + CNC.

10. Request a DFM Report:
    Always ask for a Design for Manufacturability analysis to avoid later changes that scrap the program or tooling.
    
    

Real Customer Examples – How They Saved Money

• Example 1 – Medical Device Company: Surgical Guide

• Requirement: 30 pieces, PEEK, ±0.05mm, 3-day lead time.

• CNC Quote: 800 RMB/piece, 5 days.

• The engineer considered 3D printed PEEK, but that came at 1200 RMB/piece with poor interlayer strength.

• After optimizing the CNC toolpath (smaller tools, high-speed milling), the price dropped to 550 RMB/piece, lead time 4 days.
  Conclusion: PEEK 3D printing is extremely expensive and has poor performance – don’t blindly assume 3D printing is better.

• Example 2 – Drone Bracket: Topology-optimized Structure

• Requirement: 5 pieces, aluminum, lightweight, no fine surface finish needed.

• CNC milling could not machine the internal lattice – not feasible.

• SLM 3D printing was used, weight reduced by 55%, unit price 1800 RMB/piece. Expensive, but performance was achieved and no other process could make it.
  Conclusion: Topology optimization is a killer application for 3D printing.

• Example 3 – Automation Equipment: Small-batch Gearbox Housing

• Requirement: 80 pieces, 6061 aluminum, bearing bore tolerance H7, sandblasted appearance.

• 3D printing quote: 600 RMB/piece, but roundness failed (measured 0.08mm vs. requirement 0.02mm).

• Switched to CNC: 180 RMB/piece, roundness 0.01mm, one-week lead time.
  Conclusion: Above 30 pieces and with tight accuracy, 3D printing is completely unsuitable – CNC is required.

• Example 4 – Injection Mold: Conformal Cooling

• Requirement: One mold insert with internal cooling channels that follow the part contour.

• Traditional drilled channels gave low cooling efficiency and long cycle time.

• SLM printed insert with conformal cooling: Cooling time reduced by 40%, throughput increased by 30%. The insert itself was more expensive (3000 RMB vs. 800 RMB), but the investment paid back in 3 months.
  Conclusion: Conformal cooling is a high-return application of 3D printing.
  
  

Frequently Asked Questions

• Which is cheaper – CNC machining or 3D printing?
  There is no absolute answer. As a rule of thumb:
  1–3 pieces → 3D printing is cheaper.
  30+ pieces → CNC is cheaper.
  You need a quote based on your drawing and quantity.

• How strong are metal 3D printed parts?
  After printing and heat treatment, tensile strength can reach 90-95% of forged material, but fatigue life is about 20% lower, and there is anisotropy (weakest in the Z direction).

• Is there any part that must be 3D printed?
  Yes: Internal conformal cooling channels, periodic lattice structures, one-piece moving hinges, and certain implants (porous structures for bone ingrowth).

• Can CNC be used to machine a 3D printed part?
  Yes – that is the hybrid process: 3D print a blank, then CNC finish the critical surfaces. It is ideal for parts with complex internal cavities and high-precision interfaces.

• How can a buyer quickly get quotes for both processes?
  Upload a STEP file to a quoting platform that offers both processes (e.g., Xometry, Protolabs, JLCPCB), or find a supplier that has both CNC and 3D printing capabilities.

• What is the typical price for a small-batch CNC part?
  For a 50×50×30mm aluminum block, 10 pieces: About 80–150 RMB per piece (including deburring). Complex geometry will double that.

• How much does 3D printing post-processing cost?
  Support removal is charged by the hour – typically 80–150 RMB/hour. A simple part may take 10 minutes, a complex part 2 hours. Always ask for support removal costs in advance – they can exceed the printing cost.

• Which process can make PEEK parts?
  Both can, but CNC machining is more mature and gives better properties (no interlayer weakness). CNC price: ~800–1500 RMB/kg. PEEK 3D printing requires a high-temperature nozzle (>400°C), few machines exist, price is 3000–5000 RMB/kg, and interlayer bonding is weak.

• Why is 5-axis CNC expensive?
  High programming fees (800–2000 RMB/setup), high machine time (400–800 RMB/hour), and expensive tooling. It is used for complex surfaces, undercuts, deep cavities, turbine blades, etc.
  
  

A Simple Selection Formula

• If (tolerance < 0.02mm OR material is non-standard OR quantity > 50 pieces OR anodizing required) → Choose CNC.

• If (internal channels OR lattice structures OR one-piece moving assembly) → Choose 3D printing or hybrid process.
  
  

Get Your Personalized Comparison Quote

Upload your 3D drawing (STEP, IGES, STL, X_T) and we will send you within 2 hours:

• CNC quote (material, programming, machine time, post-processing details)

• 3D printing quote (printing, support removal, sanding)

• DFM analysis (which process might fail and how to modify the design)

• Process recommendation (based on your quantity, lead time, and budget)

Contact Brightstar
Email: amy@brightstarprototype.com
Phone: +86 13750105351

Or email us your drawing directly, and get 24/7 support.