What surface finishes are available for CNC machining?
Selecting the wrong surface finish for your CNC machined parts can lead to premature failure, costly rework, and missed project deadlines. With dozens of finishing options available across different materials, choosing the optimal treatment requires understanding how each finish affects performance, cost, and manufacturing constraints.
Common surface finishes for CNC machined parts include anodizing, hard anodizing, powder coating, bead blasting, black oxide, plating (zinc, nickel, chrome), painting, passivation, electropolishing, and vapor polishing. The best choice depends on your part material and application requirements.
Find the best surface finish for your material, when to use treatments like hard anodizing, and how finishing impacts tolerances and project costs.
Table of Contents
What surface finishes are available for CNC machining?
CNC machining supports numerous surface finishes including anodizing, powder coating, bead blasting, and chemical film for aluminum; black oxide, plating (zinc, nickel, chrome), and painting for steel; passivation and electropolishing for stainless steel; and vapor polishing or painting for plastics. Each finish serves different functional and aesthetic requirements.
Surface finish selection directly impacts your part’s performance, cost, and manufacturing timeline. The wrong choice can add weeks to your project and thousands to your budget through redesigns and rework.
Quick Decision Matrix: Choose Your Surface Finish
Need corrosion protection?
- Aluminum: Type II anodizing or chemical film
- Steel: Zinc plating or painting
- Stainless: Passivation (standard choice)
Need extreme wear resistance?
- Aluminum: Type III hard anodizing
- Steel: Chrome plating or black oxide
- Stainless: Electropolishing
Need aesthetic finish?
- Any material: Powder coating or painting
- Aluminum: Colored anodizing
- All materials: Bead blasting for matte look
Working with tight tolerances? Choose finishes with minimal thickness:
- Black oxide (<0.0001″)
- Passivation (removes material)
- Chemical film (0.00001-0.0001″)
Complete Surface Finish Specifications
Material Surface Finish Thickness Added Primary Benefits Cost Impact Lead Time
Aluminum Type II Anodizing 0.0002 – 0.0012″ Corrosion resistance, can be dyed Low 3-5 days
Aluminum Type III Hard Anodizing 0.001 – 0.005″ Extreme wear resistance, hardness Medium 5-7 days
Aluminum Powder Coating 0.0007 – 0.003″ Color options, durability Low 3-5 days
Aluminum Bead Blasting None (removes material) Uniform matte finish, paint prep Very Low 1-2 days
Aluminum Chemical Film (Alodine) 0.00001 – 0.0001″ Corrosion resistance, conductivity Low 2-3 days
Steel Black Oxide <0.0001" Appearance, mild corrosion resistance Very Low 1-3 days
Steel Zinc Plating 0.0002 – 0.001″ Corrosion resistance Low 3-5 days
Steel Nickel Plating 0.0002 – 0.001″ Corrosion, wear resistance Medium 5-7 days
Steel Chrome Plating 0.00005 – 0.0005″ Hardness, corrosion resistance High 7-10 days
Steel Painting 0.001 – 0.003″ Color, basic protection Low 3-5 days
Stainless Steel Passivation None (removes material) Enhanced corrosion resistance Very Low 1-2 days
Stainless Steel Electropolishing Removes 0.0002 – 0.001″ Smooth finish, corrosion resistance Medium 3-5 days
Stainless Steel Bead Blasting None (removes material) Uniform matte appearance Very Low 1-2 days
Plastics Vapor Polishing None Optical clarity, smooth finish Medium 3-5 days
Plastics Painting 0.001 – 0.002″ Color, UV protection Low 3-5 days
Plastics Texture (machined) Varies Grip, aesthetics None (during machining) –
Expert Recommendation System
For aerospace/medical applications: Passivation (stainless), Type II anodizing (aluminum), or chrome plating (steel) – these meet stringent industry standards.
For outdoor/marine environments: Type III hard anodizing (aluminum), zinc plating with chromate (steel), or powder coating (any material).
For high-volume production: Black oxide (steel), bead blasting (any material), or standard anodizing – fastest, most economical options.
The key insight: specify your surface finish requirements during the design phase, not after machining. This allows us to optimize your part geometry, account for thickness changes, and plan manufacturing sequences that deliver the performance you need without costly redesigns.
Which surface finishes are best for aluminum?
Type II anodizing is best for most aluminum applications providing excellent corrosion resistance at 0.0002-0.0012″ thickness. Type III hard anodizing works best for high-wear parts like pistons and gears. Chemical film (Alodine) is ideal when electrical conductivity is required. Powder coating offers the best color options and durability for outdoor applications.
30-Second Decision Tool
Step 1: Need electrical conductivity? → Chemical film (maintains conductivity + corrosion protection)
Step 2: Heavy sliding/wear contact? → Type III hard anodizing (harder than tool steel)
Step 3: Specific color required? → Powder coating (unlimited colors, chip resistant)
Step 4: Everything else → Type II anodizing (handles 80% of aluminum applications)
Critical Design Failures We Prevent
Press Fit Disasters Type III hard anodizing grows 0.001-0.005″ per surface, destroying your interference fit calculations. We machine parts undersize to compensate or mask critical surfaces. Most expensive mistake: not planning for buildup on precision assemblies.
Threading Problems Powder coating clogs threads smaller than 1/4″. Type III requires masking on threads under 1/4″. We plan masking operations during design review, not after parts are machined.
Electrical System Failures All anodizing creates electrical insulation. We’ve seen grounding systems fail because designers didn’t realize this. Solution: chemical film for electrical contact surfaces, masking for ground points.
Aluminum Alloy Compatibility Based on machining thousands of aluminum parts:
- 6061-T6: Excellent for all finishes, consistent color matching
- 7075-T6: Bronze tint limits color options, chemical film works best
- 2024: Blotchy anodizing results, powder coating recommended
- Cast aluminum: Requires additional machining prep for smooth finish
From our production scheduling experience:
- Chemical film: +1-2 days (fastest option)
- Type II anodizing: +3-5 days (standard timing)
- Powder coating: +3-5 days (includes cure time)
- Type III hard anodizing: +7-10 days (requires thick buildup)
Complex masking adds 2-3 days to any process. Plan accordingly for project deadlines.
Aerospace (MIL-A-8625): Chemical film for conductivity, Type II for non-electrical components Medical devices: Type II anodizing (biocompatible), avoid chemical film
Consumer electronics: Type II with color matching, chemical film for RF shielding High-wear mechanical: Type III hard anodizing per manufacturer specifications
When Each Finish Fails
Type II anodizing fails: Never choose for heavy sliding wear or electrical contact surfaces Type III fails: Avoid on thin walls (<0.060″), complex geometries with tight tolerances
Chemical film fails: Don’t use when aesthetics or color matching matters Powder coating fails: Never use on precision assemblies or electrical contacts
Bottom line: We specify finishes during design review to prevent costly rework. Most surface finish problems result from choosing treatments after machining is complete rather than integrating finish requirements into the manufacturing plan.
When should I choose anodizing or hard anodizing?
Choose Type II anodizing for general corrosion resistance, aesthetics, and electrical insulation at 0.0002-0.0012″ thickness. Choose Type III hard anodizing for high-wear applications, sliding surfaces, and maximum durability at 0.001-0.005″ thickness. Hard anodizing creates a surface harder than tool steel but requires careful tolerance planning.
Quick Decision Checklist
✓ Choose Type II anodizing if:
- Parts cycle fewer than 1,000 times
- Tolerances tighter than ±0.002″
- Color or aesthetics matter
- Budget is priority ($0.50-$2.00 per sq ft)
✓ Choose Type III hard anodizing if:
- Parts cycle more than 1,000 times
- Heavy sliding or wear contact expected
- Wall thickness over 0.060″
- Performance justifies 3x higher cost
✗ Red flags for Type III:
- Thin walls under 0.060″
- Many small threads under 1/4″
- Tight tolerance assemblies
Performance Thresholds from Our Shop Experience
After finishing over 10,000 aluminum parts annually, here’s when each process works:
Type II failure point: Around 1,000 cycles of sliding contact, the thin coating wears through to bare aluminum
Type III advantage: Survives 50,000+ cycles in hydraulic cylinders and high-wear mechanical applications
Cost reality: Type III costs 2-3x more but lasts 20x longer in wear applications – worth it only when cycles matter
Material Compatibility Issues We Prevent
6061-T6 aluminum: Works perfectly with both processes – our go-to recommendation for new designs
7075-T6 aluminum: Anodizes with bronze tint that won’t match bright colors – consider powder coating for appearance-critical parts
2024 aluminum: Creates blotchy anodizing – we steer clients toward powder coating or chemical film
Temperature and Assembly Planning
Powder coating temperature impact: 400°F curing destroys rubber seals and most plastics – anodize assemblies before installing these components
Lead time reality: Type II adds 3-5 days, Type III adds 7-10 days to your project timeline
Common assembly mistake we prevent: Don’t anodize parts with pressed-in bearings or threaded inserts already installed – the chemicals attack these components
Ready to get your parts?
How do bead blasting and powder coating affect aluminum parts?
Bead blasting removes 0.0001-0.0003″ of material creating uniform matte texture, while powder coating adds 0.0007-0.003″ thickness with excellent color options and durability. Bead blasting is often used as preparation before powder coating. Both processes require masking threaded holes and precision surfaces.
Immediate Design Impact Check
Will bead blasting work on your part?
- ✓ Tolerances looser than ±0.01mm? Safe to proceed
- ✓ Wall thickness over 1.5mm? No warping concerns
- ✗ Deep pockets or internal channels? Coverage will be uneven
- ✗ Need surface smoother than 32 µin Ra? Choose different process
Will powder coating work on your part?
- ✓ All components handle 400°F temperature? Safe to proceed
- ✓ Clearances accommodate 0.001-0.003″ buildup? Fits will work
- ✗ Rubber seals or plastic components present? Remove first
- ✗ Threads smaller than 1/4″? Plan expensive masking
Surface Results You Can Expect
Bead blasted finish: Uniform matte texture similar to 400-grit sanded aluminum – smooth to touch but eliminates machining marks and tool patterns
Powder coated finish: Smooth colored surface available in unlimited colors with chip resistance superior to paint
Combined bead blast + powder coat: Maximum durability for outdoor applications – we see 40% better paint adhesion versus smooth surfaces
Process Selection Based on Your Needs
Choose bead blasting only when:
- Want matte texture without color requirements
- Preparing surface for painting later
- Budget requires lowest-cost option
- Parts won’t see precision assembly
Choose powder coating only when:
- Specific colors required for branding
- Outdoor durability critical
- Smooth machined surface acceptable as base
- Can handle 400°F curing temperature
Choose both processes when:
- Maximum performance needed in harsh environments
- Color plus texture requirements
- Marine or outdoor industrial applications
- Can accommodate both material removal and buildup
Critical Masking and Timeline Planning
Always mask these features:
- Threads smaller than 1/4″
- Press-fit bores and diameters
- Electrical contact surfaces
- Bearing mounting areas
Timeline impact: Bead blasting alone adds 1-2 days, powder coating adds 3-5 days, combined processes require 5-7 days total
Cost impact: Masking adds $75-150 setup cost per batch plus 2-3 days timeline
Bottom line: Both processes change part dimensions – plan for material removal with bead blasting and thickness buildup with powder coating during design phase. Most problems occur when dimensional changes aren’t considered upfront rather than from poor process execution.
Which surface finishes are best for steel?
Black oxide is best for precision steel parts requiring minimal thickness buildup (<0.0001″), zinc plating works for general corrosion protection at 0.0002-0.001″ thickness, nickel plating provides superior wear and corrosion resistance, chrome plating offers maximum hardness, and painting delivers color options with basic protection. Each finish serves different functional requirements and affects tolerances differently.
Steel Finish Selection Guide
Finish Best For Thickness Added Expected Performance Cost Lead Time
Black Oxide Precision tooling, indoor parts <0.0001" Indoor only with oil sealing Lowest 1-3 days
Zinc Plating Fasteners, general hardware 0.0002-0.001″ 2-5 years indoor service Low 3-5 days
Nickel Plating Marine, chemical environments 0.0002-0.001″ 10+ years harsh exposure Medium-High 5-7 days
Chrome Plating High-wear, hydraulic parts 0.0001-0.0005″ Maximum wear resistance Highest 7-14 days
Painting Large structures, color needs 0.001-0.003″ 1-20 years (system dependent) Low-Medium 3-5 days
How We Help You Specify Finishes Correctly
Common mistake we see: vague drawing callouts like “zinc plate” that leave suppliers guessing. Here’s how to specify properly:
Zinc plating: “ASTM B633 Type II, SC2” (we help you match service condition to your actual environment)
Black oxide: “MIL-DTL-13924 Class 1, oil sealed” (always specify oil – parts rust immediately without it)
Chrome plating: “ASTM B177, 0.0002″ min thickness” (we help justify when the premium cost makes sense)
Critical drawing note: “Dimensions apply after finishing” – tells us to account for plating buildup during machining
Common Design Mistakes We Prevent
Black oxide misconceptions: Clients often specify this expecting corrosion resistance similar to zinc plating. We clarify it’s mainly for appearance and anti-galling – requires oil sealing for any protection.
Zinc plating tolerance problems: We’ve seen expensive rework when designers don’t account for 0.0005″ buildup on press fits. We machine parts undersize or plan masking to prevent interference.
Chrome plating cost surprises: Clients specify chrome without realizing it costs 3-5x more than zinc with 2x longer lead time. We help determine when the performance justifies the premium.
Assembly sequence errors: We prevent costly mistakes like specifying plating after pressing in bearings – the chemicals attack rubber seals and threaded inserts.
Real-World Performance from Our Client Experience
Environment Finish Recommended Typical Performance Failure Mode/Notes
Indoor/Controlled Black oxide + oil sealing Indefinite life with proper maintenance Flash rusting if oil sealing fails
General Indoor Zinc plating ASTM B633 SC12 5 years before white corrosion onset Humid environments accelerate failure
Outdoor/Weather Zinc plating ASTM B633 SC26 6 months – 2 years depending on climate Rapid failure in coastal areas
Marine/Chemical Nickel plating 10+ years continuous exposure Pitting at coating defects
High Wear Chrome plating Maximum durability available Cracks at high stress points
Assembly Integration from Our Shop Experience
- Press fit calculations: We machine zinc-plated parts 0.0005″ undersize on diameters to account for coating buildup
- Threading considerations: Fine threads often need masking or post-plating thread chasing – we plan this during design review
- Material compatibility: We never chrome plate assemblies with rubber components – the process destroys elastomers
- Process sequence: We always plate individual parts before assembly operations like bearing installation
Application Patterns We See by Industry
- Automotive suppliers: 90% zinc plating on fasteners, black oxide on precision engine components, chrome limited to hydraulic systems
- Aerospace clients: Black oxide on tooling and fixtures, chrome on landing gear, paint systems on structural components
- Medical device companies: Prefer stainless steel, accept black oxide only for non-contact applications
- Construction industry: Hot-dip galvanizing for structural steel, paint systems for architectural applications
Vendor Quality Issues We Help You Avoid
Black oxide failures: We ensure suppliers oil seal parts within hours of processing – delay causes immediate rusting
Zinc plating problems: We verify thickness on first articles – thin or porous coatings fail quickly in service
Chrome plating defects: We check surface prep quality – poor preparation causes expensive pitting and rework
Paint system issues: We specify proper primer systems – single-coat paint on bare steel always fails through poor adhesion
Bottom line: We specify the right ASTM standard and service condition based on your actual operating environment. Black oxide for precision indoor work, zinc plating for 80% of general applications, nickel for harsh conditions, chrome when wear resistance justifies the cost. Most failures we see result from environmental mismatches, not poor processing.
When should I use black oxide, plating, or painting on steel?
Use black oxide for precision parts requiring minimal thickness and mild corrosion resistance, zinc plating for moderate corrosion protection on fasteners and hardware, nickel plating for high-wear or marine applications, chrome plating for maximum hardness and wear resistance, and painting for color, large parts, or basic outdoor protection.
Decision Framework We Use with Clients
Your Primary Need We Recommend Standard We Specify Common Pitfall We Prevent
Dimensional Precision Black oxide + oil MIL-DTL-13924 Class 1 Expecting corrosion resistance
Moderate Corrosion Zinc plating ASTM B633 SC1/SC2 Wrong service condition
Maximum Corrosion Nickel plating ASTM B733 Not justifying 4x higher cost
Extreme Wear Chrome plating ASTM B177 Specifying without wear analysis
Color/Large Areas Paint systems Varies by application Skipping proper surface prep
Environmental Matching from Our Experience
Indoor controlled environments: We recommend black oxide with oil sealing. Common mistake: clients skip the oil sealing requirement and parts rust within days.
General indoor applications: We specify zinc plating ASTM B633 SC1. Provides 2-5 year service life we typically see in office/warehouse environments.
Outdoor weather exposure: We upgrade to zinc plating ASTM B633 SC2 minimum. Coastal clients need to understand 6-month to 2-year realistic service life.
Marine/chemical processing: We specify nickel plating. The 4x cost premium pays off with 10+ year service life we document in harsh environments.
High-wear mechanical applications: We recommend chrome plating only after wear analysis justifies the premium cost and lead time.
Design Integration Checklist We Follow
Before recommending black oxide:
- Confirm indoor use only (we’ve seen outdoor failures in weeks)
- Verify oil sealing maintenance is acceptable
- Ensure anti-galling properties are the primary need
- Check that minimal corrosion resistance meets requirements
Before specifying zinc plating:
- Calculate thickness impact on press fits and threaded assemblies
- Add “dimensions apply after finishing” to drawing
- Plan masking for critical surfaces during design review
- Match service condition to actual environment
Before recommending chrome plating:
- Justify 3-5x cost premium with wear analysis
- Plan 7-14 day lead time impact on project schedule
- Confirm wear resistance requirements exceed base material
- Verify no rubber components in assembly
Drawing Specification Best Practices We Use
Complete zinc plating callout: “Zinc plate per ASTM B633, Type II, SC2”
Complete black oxide callout: “Black oxide per MIL-DTL-13924 Class 1, oil sealed”
Chrome plating callout: “Chrome plate per ASTM B177, 0.0002″ minimum thickness”
Essential drawing note: “Dimensions apply after finishing” plus any masking requirements for critical features
Integration Mistakes We Prevent Daily
- Assembly sequence errors: We never specify plating after press-fitting components – chemicals destroy bearings and seals
- Tolerance stack-up problems: We account for plating thickness variation – complex parts get less uniform coating than simple shapes
- Environmental mismatches: We prevent black oxide specs for any outdoor use and zinc specs for continuous salt exposure
- Post-processing conflicts: We plan finish sequences to avoid damage from welding, forming, or machining after plating
Quality Control Based on Our Supplier Network
First article verification: We check plating thickness meets specification using calibrated magnetic gauges
Performance validation: We ensure salt spray testing happens within 72 hours of processing per ASTM requirements
Visual inspection standards: We verify uniform coverage, proper chromate color, and absence of pitting or voids
Dimensional confirmation: We measure critical dimensions after finishing to confirm drawing compliance
Bottom line: We match your finish selection to actual operating conditions and specify complete ASTM standards on drawings. Our experience prevents the common mistakes: black oxide for indoor precision work, zinc plating with proper service condition for general use, nickel for harsh environments, chrome only when wear analysis justifies the cost. Most problems we see stem from incomplete specifications or environmental mismatches rather than supplier process failures.
Need your parts within 2 days? We've got 2 days lead time
Which surface finishes are best for stainless steel?
Passivation is best for most stainless steel parts to maximize corrosion resistance by removing free iron and enhancing the natural oxide layer. Electropolishing works best for parts requiring smooth surfaces and superior corrosion resistance. Bead blasting provides uniform matte appearance for aesthetic applications. Most stainless steel parts don’t need additional finishing beyond proper passivation.
Immediate Decision Tool
✓ All machined stainless steel → Passivation per ASTM A967 required (machining embeds iron contamination)
✓ Food/pharmaceutical contact → Electropolishing per ASTM B912 (smooth surfaces resist bacteria)
✓ Medical implants → Electropolishing + passivation combination (maximum biocompatibility)
✓ Decorative appearance only → Bead blasting (purely cosmetic)
Expertise from Processing 25,000+ Stainless Parts Annually
Common mistake we prevent: “Stainless doesn’t need finishing.” ASTM A967 standard requires passivation to remove free iron contamination from machining operations. We see untreated parts develop rust spots within weeks.
Cost reality: Passivation adds 10-15% to part cost. Electropolishing costs 3x passivation but provides 30x better corrosion resistance. Always justified for pharmaceutical and food contact applications.
When electropolishing fails: Poor surface preparation causes uneven results. We ensure proper cleaning per ASTM A380 before electropolishing to prevent process failures.
Drawing Specification Standards
Standard passivation callout: “Passivate per ASTM A967, nitric acid method”
High-performance callout: “Electropolish per ASTM B912″(for pharmaceutical/medical applications)
Critical note: “Passivate after all machining and welding operations”
Industry Requirements We Follow
Medical devices: ASTM A967 passivation minimum, ASTM B912 electropolishing for implants
Food processing: 3-A sanitary standards require passivation, electropolishing for dairy applications
Pharmaceutical: ASTM B912 and ASME BPE specifications standard for process contact surfaces
Bottom line: From our ISO 9001/AS9100 certified facility experience, passivation is mandatory for all machined stainless steel parts to restore corrosion resistance. Electropolishing justified when surface smoothness or maximum corrosion resistance required for critical applications.
How do passivation and electropolishing improve stainless steel?
Passivation removes free iron contamination from machining and enhances the natural oxide layer, restoring maximum corrosion resistance. Electropolishing removes surface material to create a smooth finish while providing superior corrosion resistance beyond passivation alone. Both processes are essential for machined stainless steel parts.
Performance Improvement Data
Passivation results: Removes free iron contamination and promotes formation of protective chromium oxide layer. We measure complete free iron removal using copper sulfate testing per ASTM A967.
Electropolishing benefits: Removes 0.0001″ surface material with precision control, achieving Ra finishes down to 8-16 μin. Provides 30x better corrosion resistance than passivation alone.
When Each Process is Required
Passivation mandatory for: All machined stainless steel parts. Machining operations embed tool steel particles that create corrosion initiation sites.
Electropolishing upgrade when: Pharmaceutical equipment requiring smooth surfaces for cleaning, medical implants needing biocompatibility, or maximum corrosion resistance critical.
Quality Standards We Follow
Passivation verification: Copper sulfate test, salt spray test, and visual inspection per ASTM A967 confirms complete treatment.
Electropolishing confirmation: Surface roughness measurement and passivation testing per ASTM B912 verify results.
Cost vs Performance Analysis
Passivation economics: 10-15% cost increase prevents field failures. Essential for removing free iron that compromises stainless steel corrosion resistance.
Electropolishing premium: 3x passivation cost but eliminates need for additional processes like hand deburring and mechanical polishing.
Process Integration We Manage
Proper sequence: Machine → weld → pre-clean per ASTM A380 → passivate/electropolish
Quality timing: Testing within 48 hours of processing for accurate verification.
Contamination prevention: Stainless-steel-only handling and storage after treatment
What Failure Looks Like
Skipping passivation: Rust spots appear within days on “stainless” parts where machining contamination remains.
Inadequate electropolishing: Residual phosphate films from electropolishing electrolyte require proper post-dip removal.
Bottom line: Based on our NADCAP certification requirements, passivation per ASTM A967 is mandatory for restoring stainless steel corrosion resistance after machining. Electropolishing per ASTM B912 provides additional smoothness and corrosion benefits when justified by critical application requirements.
Which surface finishes are best for plastics?
Vapor polishing works best for clear thermoplastics like polycarbonate, acrylic (PMMA), and ABS requiring optical clarity. Painting provides color and UV protection for most plastic types with proper primer. Machined texture during fabrication offers grip and decorative effects at no additional cost. Most plastic parts work well as-machined without finishing.
Instant Decision Tree
Step 1: Is your part clear plastic needing optical quality? → YES: Vapor polishing (PC, PMMA, ABS only)
Step 2: Need specific color or UV protection? → YES: Paint with plastic-compatible primer
Step 3: Budget priority with texture acceptable? → YES: Machine texture during fabrication
Step 4: Everything else → As-machined (works for 80% of applications)
Common Design Mistakes We Prevent
Wrong material assumptions: Vapor polishing only works on thermoplastics, not thermosets like G10 or phenolic. We screen materials before quoting to prevent process failures.
Temperature damage: Vapor polishing uses heated solvents – we verify each plastic grade can handle process temperatures without warping.
Paint adhesion failures: Standard metal paints don’t bond to plastics. We specify proper surface preparation and compatible primer systems per ASTM standards.
Process Limitations Per ASTM Guidelines
Vapor polishing cannot fix: Deep scratches, sink marks, or design issues – only smooths microscopic surface roughness
Paint system requirements: Proper cleaning, compatible primer, controlled cure temperature – skipping steps causes adhesion failure
Quality standards: We follow ISO surface finish verification procedures including dimensional inspection and visual clarity testing
Bottom line: Based on industry standards, most plastic parts work adequately as-machined. Vapor polishing justified for optical applications, painting for color/UV protection. Always verify process compatibility to prevent part damage.
When should I use vapor polishing or painting on plastics?
Use vapor polishing for clear thermoplastic parts requiring optical clarity by smoothing surface roughness at the microscopic level. Use painting for color requirements, UV protection, or improved appearance. Both processes require temperature compatibility verification .
Application-Based Selection
Your Primary Need Recommended Process Compatible Materials Critical Check
Optical clarity Vapor Polishing PC, PMMA, ABS thermoplastics Temperature compatibility, suitable plastics only
Color matching Paint with primer Most plastics Cure temperature limits
UV protection UV-resistant paint Outdoor applications Thermal expansion compatibility
Cost priority As-machined All plastic types No additional processing needed
Temperature Compatibility Requirements
Vapor polishing process: Uses heated solvents – acetone vapor achieves transparency in seconds for PC parts
Paint curing limits: Most plastic-compatible paints cure at 180-250°F – thin-wall parts may warp during thermal cycle
Material screening: We test compatibility before processing to prevent stress cracking that can occur during the process.
When Each Process Works Best
Choose vapor polishing for:
- Medical instruments requiring smooth surfaces where debris cannot collect
- Clear lenses needing optical quality finish
- Premium appearance justifying 2-3x cost increase
Choose painting for:
- Color matching or branding requirements
- UV protection for outdoor exposure
- Chemical resistance enhancement
Process Failure Modes
Vapor polishing limitations: Cannot erase deeper scratches – only works at molecular level Paint system failures: Wrong primer, incompatible cure temperature, or poor surface prep causes complete adhesion failure
Quality verification: Visual inspection for transparency, cross-hatch adhesion testing for paint, dimensional verification per ISO standards
Cost vs Performance Analysis
Vapor polishing: 2-3x base part cost but eliminates secondary polishing operations
Paint systems: 1.5-2x part cost including primer and controlled curing
Failure costs: Thermal damage requires part replacement, paint failures need complete refinishing
Bottom line: Use vapor polishing when optical clarity justifies premium cost on compatible thermoplastics. Choose painting for color/UV with proper temperature verification. Both require material screening per industry standards.
How do surface finishes affect cost, tolerances, and fit?
Surface finishes add 10-200% to part cost depending on complexity. Anodizing costs $0.44-1.00 per part with $75-125 minimum charges. Coatings add 0.0001-0.005″ thickness affecting fits while processes like passivation remove material. Planning finish requirements during design prevents costly rework.
Verified Cost Impact
Finish Cost Increase Thickness Change Typical Application
Black oxide +10-20% <0.0001" Precision tooling
Passivation +10-15% Removes material All stainless steel
Zinc plating +30-50% 0.0002-0.001″ General hardware
Anodizing +20-40% ($1-15/unit) 0.0002-0.0012″ Aluminum parts
Powder coating +40-70% 0.0007-0.003″ Large surfaces
Chrome plating +150-300% 0.0001-0.0005″ High-wear applications
Tolerance Planning Strategy
Material removal processes: Passivation, electropolishing – we machine parts 0.0005-0.002″ oversize to compensate
Material addition processes: Plating, anodizing – we machine critical dimensions undersize or plan selective masking
Press fit impact: Anodizing adds 0.0005″ typical buildup – destroys 0.0002″ interference fits without compensation
Real Cost Examples from Industry Data
Small parts: 5.2 sq inch aluminum parts cost $0.25 each for Type II anodizing
Batch processing: UK shops charge £35-45 per jig (5 sq ft coverage), US shops $0.44 per part for colored finish
Minimum charges: $75-125 typical minimum regardless of quantity
Hidden Cost Factors
Masking requirements: Simple masking $50-100, complex geometry $200-500 per setup
Quality verification: Surface finish inspection $200-500 but prevents batch rejection
Rework scenarios: Paint adhesion failure costs 3-4x original finishing plus schedule delays
Fit and Assembly Impact
Threading problems: Hard anodizing and powder coating clog threads under 1/4″ – masking prevents assembly failures
Bearing clearances: Chrome plating builds up 0.0003″ average – affects running fits in precision assemblies
Sealing surfaces: Bead blasting roughens O-ring grooves – selective masking maintains seal integrity
Budget Planning Guidelines
Conservative estimates: Budget +20-30% for standard finishes, +100-200% for premium treatments
Lead time impact: Standard processes add 3-5 days, premium finishes add 7-14 days
Volume benefits: Batch processing reduces per-piece cost 30-50% through shared setup
Bottom line: Plan finish requirements during design phase. Anodizing typically costs $1-15 per unit with significant tolerance impacts. Most failures result from inadequate planning rather than poor processing – early specification prevents expensive rework.
Conclusion
Surface finish selection directly impacts part performance, cost, and manufacturing timeline. From passivation and anodizing to vapor polishing and plating, choosing the right treatment during the design phase prevents costly rework and ensures optimal results. Contact us to explore manufacturing solutions tailored to your surface finishing requirements.
Frequently Asked Questions
Depends on the finish and thread size. Threads 1/4″ and larger usually work with zinc plating and Type II anodizing. Powder coating and hard anodizing typically require masking threads under 1/4″ or post-finishing thread chasing operations.
Some can, others can’t. Paint and powder coating can often be touched up locally. Anodizing and plating usually require complete stripping and refinishing. Chrome plating damage typically means part replacement. Design for the expected service environment.
You’ll see rust spots within weeks, especially on machined surfaces. Machining embeds iron particles that corrode first, then spread to the base material. Passivation is mandatory for machined stainless steel – it’s not optional.
Absolutely. Coatings add thickness, removal processes take material away. We machine parts oversize or undersize depending on the finish. Always plan finishing during design – retrofitting causes tolerance problems.
We test a sample first. PC handles the process well, PMMA works with proper solvent selection, but ABS has limited effectiveness. Thermosets like G10 won’t work at all. Always verify compatibility before committing to vapor polishing.
Yes, but it’s expensive. Adding coatings like anodizing or plating after final machining often requires dimensional adjustments or remachining. We’ve seen 50-100% cost increases when finish requirements change late. Always specify finishing during design phase.
