Surface Finishing
Surface finishing covers anodizing, powder coating, plating, polishing, painting, and passivation applied after machining, forming, or molding to protect against corrosion, hide tool marks, match color specs, or improve wear resistance. Coating thickness ranges from 0.25μm (chrome plating) to 100μm (powder coating), and affects every dimension on the part, masking and post-finish machining are part of the design, not afterthoughts. For material compatibility, see our Materials & Properties guide.
Surface Finishing Capabilities
| Feature | Description |
| Maximum Part Size | Anodizing tank: 3000×1500×800mm／Powder coat oven: 4000×2000×1500mm／ Plating tank: 2000×1000×800mm |
| Coating Thickness | Anodizing Type II: 5–25μm／Type III: 25–75μm／Powder coat: 60–100μm／Zinc plating: 5–15μm／Chrome plating: 0.25–2.5μm |
| Surface Roughness | Mirror polish: Ra 0.05–0.1μm／Brushed: Ra 0.4–0.8μm／Bead blast: Ra 1.6–3.2μm |
| Corrosion Resistance | Anodized aluminum: 336+ hours／Zinc-plated steel: 96–240 hours／ Powder coat on phosphated steel: 500+ hours |
| Standard Lead Time | Standard finishes: 3–7 business days／Multi-step finishes: 7–14 days |
| Processes | Anodizing, Powder Coating, Plating, Bead Blasting, Brushing, Polishing, Painting, Passivation |
Materials Supported
Common Metal Materials
Aluminum takes the widest range of surface finishes. Anodizing is the most common: Type II for color and basic corrosion resistance, Type III (hard anodize) for wear surfaces. Powder coating, painting, and polishing also work. 6061 and 6063 anodize evenly; 7075 contains higher zinc and tends to show grain patterns through the anodize layer.
Stainless steel finishes are about surface texture, not corrosion protection, the metal handles corrosion on its own. Brushed (#4 finish), bead blasted, mirror polished (#8 finish), and passivated are the standard options. Electropolishing for medical and food-grade parts where bacterial adhesion matters.
Carbon steel rusts without surface protection. Powder coating (60–100μm thickness) and zinc plating are the defaults for structural parts. Black oxide adds a thin corrosion barrier on tools and fasteners without changing dimensions. E-coating (electrodeposition) covers complex geometries evenly where spray painting can’t reach
Brass surfaces patinate over time without protection. Lacquering preserves the original gold color; antique-style chemical patina darkens it intentionally. Polishing to mirror finish is common on decorative parts. Brass doesn’t accept anodizing or powder coating well, paint and lacquer are the working options
Copper patinates faster than brass. Clear lacquer locks in the bright finish; chemical patina (statuary bronze, verdigris) for decorative applications. Tin plating and silver plating for electrical contacts where the underlying copper would oxidize and lose conductivity. Polishing brings copper to a mirror state but the finish dulls within weeks without protection
Common Plastic Materials
POM has a waxy surface that resists paint adhesion. Surface treatment (flame, plasma, or chemical etch) is needed before painting. Pad printing works after surface activation. POM doesn’t accept most coatings without pre-treatment, design for in-resin color when possible instead of post-paint finishing
Nylon dyes well, heated dye bath penetrates 0.5mm deep, color goes through the surface layer instead of sitting on top. Painting works after primer; sanding before primer improves adhesion. Nylon’s moisture absorption causes dimensional shifts that affect paint thickness consistency,condition parts before finishing
ABS is the easiest plastic for surface finishing. Takes paint, primer, vapor smoothing (acetone), and plating well. Chrome plating on ABS is the standard process for automotive trim and decorative parts. Pad printing, hot stamping, and laser marking all work directly on ABS without pre-treatment
PC scratches easily, protective hard coatings extend service life on optical and display parts. Paint adheres directly without primer in most cases. Avoid solvent-based finishes on stressed areas; PC cracks under solvent attack on bent or molded-in stress zones. Anti-fog and anti-reflective coatings are common on PC lens components
Finish Selection Guidance
Pick the finish based on what the part needs to survive. Anodized aluminum holds up outdoors for 5–10 years. Powder-coated steel handles abrasion better than wet paint but adds 60-100μm to every dimension. Brushed stainless hides fingerprints; mirror-polished stainless shows every fingerprint. Plating adds corrosion resistance plus conductivity for electrical parts. Order matters. Surface finish always comes after machining, forming, and welding, never before. Heat-affected zones from welding burn off most coatings. Threaded holes and bearing surfaces get masked before finishing, or machined again after. Call out which features get protected on the drawing.
Specifications & Standards
Surface finish specifications cover thickness, color, gloss, and durability. Coating thickness affects every dimension, anodizing adds 5–25μm per surface, powder coating adds 60–100μm, plating varies 5–50μm depending on type. Tight-tolerance features need to be masked or machined after coating.
| Coating Thickness | Anodizing Type II: 5–25μm Type III: 25–75μm Powder coat: 60–100μm Zinc plating: 5–15μm Chrome plating: 0.25–2.5μm |
| Color Standards | RAL, Pantone, NCS, or custom color match. Anodizing limited to standard dye colors; powder coat covers full RAL range. Color consistency batch-to-batch held to ΔE ≤ 2 |
| Gloss Levels | Matte (5–10 GU), Satin (20–40 GU), Semi-gloss (50–70 GU), High gloss (85+ GU). Measured at 60° per ASTM D523 |
| Surface Roughness | Mirror polish: Ra 0.05–0.1μm Brushed: Ra 0.4–0.8μm Bead blast: Ra 1.6–3.2μm As-machined: Ra 1.6–3.2μm typical (up to Ra 6.3μm on deep pockets, long-reach features, and turned surfaces) |
| Adhesion Standards | Cross-hatch test per ASTM D3359, minimum 4B rating. Pull-off adhesion per ASTM D4541 for structural coatings |
| Corrosion Resistance | Salt spray test per ASTM B117. Anodized aluminum: 336+ hours / Zinc-plated steel: 96–240 hours / Powder coat on phosphated steel: 500+ hours |
| Maximum Part Size | Anodizing tank: 3000×1500×800mm Powder coat oven: 4000×2000×1500mm Plating tank: 2000×1000×800mm |
| Lead Time | Standard finishes: 3–7 business days. Multi-step finishes (e.g., polish + plate): 7–14 days |
Surface Finishing Options
Anodizing
Electrochemical process for aluminum. Type II builds 5–25μm color layer in dyed bath. Type III hard anodize builds 25–75μm wear-resistant layer. Standard colors: black, clear, red, blue, gold. Type III stays natural gray or black
Powder Coating
Dry powder applied electrostatically, then cured at 180–200°C. Builds 60–100μm thickness. Full RAL color range, matte to high-gloss finish options. Standard finish on steel parts going outdoors or into abrasive environments.
Plating
Zinc plating for low cost corrosion protection on steel parts, often followed by yellow or clear chromate seal. Nickel plating for harder, more decorative surfaces. Chrome plating for wear surfaces and bright cosmetic finishes.
Bead Blasting
Glass bead or aluminum oxide media blasted at the surface under pressure. Creates uniform matte texture, hides machining marks. Standard pre-treatment before painting or anodizing, the rough surface improves coating adhesion.
Brushing
Abrasive belt or wheel drawn across the surface in one direction. Creates linear grain pattern. Common on stainless steel panels, aluminum trim, and decorative parts. Grit 120–240 produces #4 architectural finish
Polishing
Progressive grit sanding (240 → 400 → 800 → 1500 → 3000) followed by polishing compound on a buffing wheel. Mirror finish (#8) reflects clearly. Time-intensive, labor cost scales with surface area and finish target.
Painting
Liquid paint applied by spray gun, air-dried or oven-cured. Lower thickness than powder coat (typically 30–60μm). Covers complex geometries and small batch runs more economically than powder.
Passivation
Chemical process for stainless steel that removes free iron from the surface. Improves corrosion resistance without changing appearance or adding measurable thickness. Required on medical parts.
Design Guidelines
A part can be coated technically and still come back with runs, masking errors, or color mismatch. Design for finishing means knowing how the coating builds on edges, how masking lines fall, and how the finish thickness affects mating features before the part goes to the finishing line
| Core DFM Principles | Better design for finishing means: – masking specified on the drawing for critical features – mounting points identified for hanging in plating/coating tanks – dimensions account for coating buildup on tight tolerances – edges broken to prevent thin coating on sharp corners – material and finish compatible (e.g., not specifying powder coat on heat-sensitive substrates) |
| Edge Treatment | Sharp edges hold less coating than flat surfaces, 80% buildup on sharp corners vs 100% on flat faces. Specify edge break (0.3–0.5mm chamfer) for parts going through corrosive environments |
| Masking Areas | Threaded holes, bearing surfaces, electrical contacts, and grounding points need to be masked. Call out masking on the drawing with notes or separate detail views. Plug masking on threads adds cost per part |
| Coating Buildup | Anodizing adds 5–25μm per surface (10–50μm on enclosed features). Powder coat adds 60–100μm. Plating varies. Mating features with H7/g6 fits need post-finish reaming or pre-undersizing |
| Color and Batch Consistency | Anodizing color varies batch-to-batch,parts from different runs may not match exactly. Critical color-matched assemblies run together in one batch. Specify ΔE tolerance on the drawing if matching matters |
| Avoid Unnecessary Finish | Internal surfaces, hidden faces, and non-functional areas don’t need full cosmetic finishing. Specify which surfaces need full finish, which need basic protection, and which can stay bare to control cost. |
Typical Applications
Concept Models
A CNC machined concept model helps teams review part geometry against engineering drawings. Use it during prototype development to check form, accessible features, and design changes before production.
Functional Prototypes
CNC prototyping produces functional aluminum housing parts for checking mounting features and component interfaces. Prototype manufacturing in the intended material helps engineers identify changes before a production run.
Engineering Validation
Dimensional inspection compares CNC machined features with the drawing. These measurements support design verification of critical dimensions before assembly or further production.
Fit & Assembly Testing
Fit testing checks how a mating pin enters a machined bore. A trial mechanical assembly can reveal alignment, insertion, or clearance issues before parts are ordered in larger quantities.
Market Testing Samples
Small batches of near-final CNC machined product samples give customers physical parts for product evaluation, fit checks, and feedback before broader product testing or launch decisions.
Bridge Production
Low volume manufacturing keeps CNC machined parts available while production plans and bridge tooling are finalized. Repeatable small batches help teams move from prototype to production.
Equipment & Capacity
Our surface finishing services cover aluminum anodizing, powder coating, metal plating, polishing, brushing, and spray painting. Part size alone does not determine whether a job fits the line. Racking space, material, coating thickness, masking, and inspection requirements also affect the setup. Send the drawing and finish specification so we can check the processing route.
Anodizing Line
Type II anodizing is offered for decorative and corrosion-resistant aluminum finishes. Type III hard anodizing is available for specified wear applications. The listed tank dimensions are 3000 × 1500 × 800 mm. Black, clear, and selected dyed colors are available. Actual part capacity and color appearance depend on racking, alloy, and pretreatment.
Powder Coating Line
Our powder coating services cover suitable steel and aluminum parts. The listed curing oven dimensions are 4000 × 2000 × 1500 mm. Steel parts can receive cleaning and phosphate pretreatment before coating. Specify the RAL color, gloss, thickness range, and surfaces that must remain uncoated.
Plating Tanks
Zinc, nickel, chrome, tin, and copper plating are listed among our metal plating services. Tank dimensions are listed as 2000 × 1000 × 800 mm. Barrel plating can serve small, durable parts that tolerate part-to-part contact. Rack plating supports individual positioning and defined contact locations. Coverage in recesses needs review.
Polishing and Brushing Station
Metal polishing services cover brushed, satin, and mirror appearance targets using manual and automated equipment. A directional brushed grain should be marked on the drawing. Deep pockets, internal corners, and existing tool marks can limit the achievable finish. Use an approved sample for critical cosmetic surfaces.
Painting Booth
The painting booth supports liquid coatings using conventional spray and HVLP application. Wet painting may suit selected plastics, temperature-sensitive parts, and small batches with specified colors. Coating selection must account for substrate compatibility, cleaning, film thickness, and cure conditions.
Quality Inspection
Inspection can cover coating thickness, gloss, appearance, adhesion, and agreed corrosion testing. Eddy-current instruments are used for suitable nonconductive coatings on nonmagnetic substrates; magnetic gauges serve appropriate coated ferrous substrates. Specify test locations and acceptance limits in the purchase requirements.
Quality Control Flow
View our ISO 9001:2015 Certificate →
Incoming Inspection
Incoming quality control starts with the purchase order and material certificate. We check the specified alloy, temper, stock dimensions and material identification before machining. Any mismatch needs review before the material is released to production.
In-Process Inspection
First article inspection checks the initial part against the drawing before a production run continues. In process inspection then focuses on critical dimensions, workholding and changes that could affect part consistency. Tool wear or a setup change may call for another check.
Final Inspection
Finished parts are checked against the drawing for specified dimensions, hole locations and mating features. CMM inspection and suitable hand gauges support dimensional checks. Inspectors also look for burrs, damaged edges and surface defects before release.
Documentation and Traceability
Material certificates, job records and inspection results connect the finished part to its production lot. This supports material traceability when dimensions or material identity need to be checked later. Request a first article inspection report with your RFQ if the project requires one.
Surface Finishing: Common Questions
Which surface finishing services are available for metal parts?
EPOC CRAFTER lists anodizing, powder coating, metal plating, polishing, brushing, painting, and stainless steel passivation. The finish must suit the base material and the part’s corrosion, wear, and appearance requirements. Send the alloy or steel grade, drawing, and finish specification with the RFQ.
How do I choose between anodizing and powder coating?
Anodizing creates an oxide layer on aluminum. Type II is often selected for color and corrosion protection, while Type III is used where a harder surface is specified. Powder coating deposits a polymer film on a suitable prepared substrate, including steel or aluminum. Start with the base material, exposure conditions, required appearance, and finished-part tolerances.
Does anodizing or powder coating change part dimensions?
Yes. Powder coating builds a film on the surface. Anodizing converts part of the aluminum surface into oxide, so its full coating thickness is not the same as outward dimensional growth. Pretreatment can also remove material. Identify precision bores, threads, mating faces, and finished dimensions on the drawing before coating.
What is the difference between powder coating and painting?
Powder coating applies dry powder followed by heat curing. Liquid painting sprays a coating that dries or cures under its specified conditions. Powder coating requires a compatible substrate and curing schedule. Liquid painting may be a better fit for some heat-sensitive parts or assemblies. Surface preparation and the complete coating specification drive adhesion and durability.
Which areas should be masked before surface finishing?
Common candidates are threaded holes, bearing seats, precision bores, sealing faces, electrical contacts, and grounding points. Mark each area and its allowed masking boundary on the drawing. A coating on one mating feature can change fit, while an uncoated contact area may be needed for electrical continuity. Confirm masking before production.
How is coating thickness measured?
The method follows the coating and substrate. ASTM B244 covers eddy-current thickness measurement for anodic coatings on aluminum and other suitable nonconductive coatings on nonmagnetic metals. Magnetic gauges can be used for appropriate coatings on ferrous substrates. Record the specified thickness range and measurement locations, especially near edges and recesses.
How is coating adhesion tested?
ASTM D3359 provides tape-test methods for applicable coating films on metal substrates. The method has limits related to coating thickness and does not measure absolute bond strength. Put the required method and acceptance rating on the drawing or purchase order. The correct test also depends on the coating system.
What does salt spray testing indicate about corrosion resistance?
ASTM B117 defines the salt spray test environment. It does not set one universal exposure time or pass criterion for every coating. The buyer must specify test duration, specimen condition, and acceptable corrosion or coating damage. A salt spray result alone cannot predict the number of years a finished part will last outdoors.
Ready to Finish Your Parts?
Include your finish spec in the RFQ and get a quote within 12 hours. Standard finishes in 3 to 7 business days.
Related Solutions
Rapid Prototyping
Low Volume Production
Production Tooling
End-to-End Manufacturing
Related Case Studies
Face Mill vs End Mill: Finishing Large Sealing Surfaces
CNC Machining Lead Time: Can This Quote Really Be Met?
Soft Machining for Thin Walls and Soft Materials: Low-Force CNC Strategies
Galvanneal vs Galvanized Steel After Fabrication: What Changes?
Charpy Impact Strength for Plastics: Charpy Impact Test, Specimens & Results
