Surface Finishes for Custom Manufactured Parts
Compare 30+ surface finishing options for CNC machined, sheet metal, tube bent, gear and molded parts. Anodizing, powder coating, plating, bead blasting, passivation and heat treatment, with surface roughness, material compatibility and tolerance impact specified for each.
| Get a Quote |
| Talk to an Engineer |
How to Specify a Finish
Call out cosmetic surfaces on your drawing. Most finishing operations leave incidental marks somewhere: rack and hang points for plated and anodized parts, media contact points on blasted parts. Identifying which faces are cosmetically critical lets the finisher orient and fixture the part so those marks land on non-visible surfaces.
Account for coating build-up on toleranced features. Anodizing, plating and powder coating add material. Threads, bores, dowel holes and mating surfaces are masked or plugged when the finish would push them out of tolerance. Note masking requirements on the drawing.
Sequence matters on formed and hardened parts. Two constraints come up repeatedly:
- Tube bending: form first, finish second. Anodic films are hard and brittle, and bending an already-anodized tube crazes the coating into fine surface cracks.
- Gears and hardened parts: heat treat first, then descale, then coat. Heat treatment leaves oxide scale that must be removed before any protective coating will adhere properly, and coatings applied before hardening will not survive the thermal cycle.
Not sure which finish suits your application? Talk to an engineer before you finalize the drawing.
Process key: CNC = CNC machining, milling, turning, EDM · SM = sheet metal fabrication and laser cutting · TB = tube bending · GR = gear manufacturing · IM = injection molding · UC = urethane casting
The Applies To column on each table shows which processes each finish is compatible with.
As-Machined Finishes
The baseline condition of a part straight off the machine, deburred with sharp edges chamfered. No secondary processing, lowest cost, no dimensional change.
| Finish | Roughness (Ra) | Materials | Applies To | Tolerance Impact |
|---|---|---|---|---|
| As Machined Standard | 3.2μm (126μin) | Metals, most plastics | CNC machining, milling, turning, EDM, sheet metal fabrication and laser cutting, tube bending, gear manufacturing | None. True to machined dimensions |
| As Machined Medium | 1.6μm (63μin) | Metals, most plastics | CNC machining, milling, turning, EDM, gear manufacturing | None |
| As Machined Fine | 0.8μm (32μin) | Metals | CNC machining, milling, turning, EDM, gear manufacturing | None |
Visible tool marks are expected at all three grades, lighter as roughness decreases. Minor cosmetic variation is normal.
| As-machined is the default on every CNC machining quote unless a finish is specified. Get a quote → |
Mechanical Prep and Texturing
Abrasive and mechanical processes that even out surface texture, remove burrs, or prepare a surface for coating. All are reductive: they remove a small amount of material.
| Finish | Result | Materials | Applies To | Tolerance Impact |
|---|---|---|---|---|
| Bead Blasting | Uniform matte to satin texture; removes most machining marks | Metals | CNC, SM, TB, GR | Reductive. Not suited to extremely tight tolerances |
| Sand Blasting | Ra 1.6 to 6.3μm depending on media and pressure; matte, coating-ready | Metals, plastics, composites | CNC, SM, TB | Removes roughly 0.01 to 0.05mm (0.0004 to 0.002in) |
| Media Blasting | Uniform texture; strips rust, scale and old coatings | Metals | CNC, SM, TB | Reductive |
| Tumbling | Bulk deburring; matte to semi-gloss depending on media | Metals, plastics | CNC, SM, GR | Negligible, under 5μm (0.0002in) |
| Brushed | Ra 1.2μm (47μin); directional satin grain | Aluminum, steel, stainless, brass, copper, titanium | CNC, SM, TB | Removes roughly 0.05 to 0.1mm (0.002 to 0.004in) |
| Polishing | Ra 0.8μm (32μin); bright reflective surface | Metals | CNC, SM, GR | Reductive. Tolerances met after polishing |
| Hand Polishing | High-gloss cosmetic surface on visible faces | Metals, acrylic | CNC | Reductive, operator-controlled |
| Vapor Polishing | Ra 0.1 to 0.4μm; optical-grade clarity | PC, PMMA, ABS, PETG (amorphous thermoplastics) | CNC (plastics), IM | None. Does not alter dimensions |
| Surface Grinding | Flatness and parallelism correction; fine Ra control | Hardened and unhardened metals | CNC, GR | Reductive. Specify finish dimension |
Not applicable to plastics: bead blasting and media blasting on molded plastic parts risk embedding media and deforming thin walls. Use tumbling or vapor polishing instead.
| Bead blasting and brushing are the most commonly specified finishes on custom sheet metal parts and bent tube assemblies. Get a quote → |
Conversion Coatings
Chemical treatments that convert the top layer of the substrate rather than adding a separate coating. Thin, dimensionally stable, and typically the right choice when corrosion protection is needed without tolerance impact.
| Finish | Result | Materials | Applies To | Tolerance Impact |
|---|---|---|---|---|
| Chromate Conversion Coating (chem film, Alodine) | 0.25 to 1.0μm film; clear or gold; electrically conductive; paint-ready base | Aluminum | CNC, SM, TB | No practical effect on tolerances |
| Black Oxide | Under 1μm matte to satin black; low reflectance; mild corrosion resistance | Steel, stainless, tool steel, bearing bronze | CNC, SM, GR | No practical effect on tolerances |
| Passivation | Removes free iron; restores and strengthens the passive chromium oxide layer | 200, 300 series and precipitation-hardened stainless | CNC, SM, TB | None. Colorless, no measurable build-up |
| Electropolishing | Electrochemical smoothing and brightening; deburrs micro-features; improves cleanability | Stainless steel, copper, aluminum | CNC, SM, TB | Reductive. Removes material, specify final dimension |
Note on black oxide and welding: the coating burns off in the heat-affected zone. Weld first, then coat, or plan for local reapplication.
| Coating a welded or hardened assembly? Sequence changes the result. Talk to an engineer → |
Anodizing
Electrochemical oxide growth on aluminum and titanium. The oxide is integral to the substrate, so it does not chip or peel, but it does add thickness and it will not hide underlying machining marks. Bead blast or brush first if you want a uniform matte appearance.
| Finish | Result | Materials | Applies To | Tolerance Impact |
|---|---|---|---|---|
| Anodizing Type II | Corrosion resistance; dyeable across a wide color range; paint and adhesive base | Aluminum | CNC, SM, TB | Coating build-up must be accounted for. Thread masking as needed |
| Anodizing Type III (hardcoat) | Thicker, harder, wear-resistant layer; limited color range, typically clear, gray or black | Aluminum | CNC, SM, TB | Greater build-up than Type II. Thread masking as needed |
| Anodizing Type III with PTFE | Hardcoat with impregnated PTFE for a dry, self-lubricating contact surface | Aluminum, titanium | CNC, GR | As Type III. Color varies light gray to brown |
| Titanium Anodizing | Matte gray oxide; enhanced corrosion and abrasion resistance | Titanium and titanium alloys | CNC | Minimal build-up |
| Type II and Type III anodizing are available on machined, sheet metal and tube bent aluminum parts. Note anodize type and masking on your drawing. Get a quote → |
Plating
Deposited metal layers for corrosion resistance, wear resistance, conductivity or appearance. All plating adds thickness and needs masking on toleranced features.
| Finish | Result | Materials | Applies To | Tolerance Impact |
|---|---|---|---|---|
| Electroless Nickel Plating | Uniform nickel-phosphorus layer that follows complex geometry and internal surfaces evenly | Aluminum, steel, stainless | CNC, SM, GR, IM | Build-up to be accounted for. Thread masking as needed |
| Electroplating | Nickel, zinc, copper, chrome, gold or silver deposits for corrosion resistance, conductivity or appearance | Metals | CNC, SM, TB, GR | Build-up varies by deposit. Uneven on complex geometry due to current density |
| Zinc Plating (galvanizing) | Sacrificial barrier layer; clear or black passivate | Steel, stainless | CNC, SM, TB, GR | Build-up to be accounted for |
Note on electroless vs. electroplating: electroless plating deposits evenly regardless of geometry, which makes it the better choice for internal bores, blind features and gear tooth flanks. Electroplating suffers uneven deposition on recessed features.
| Plating on gear tooth flanks, blind bores or internal features needs process selection before quoting. Talk to an engineer → |
Painted and Powder Finishes
Applied coatings that fully cover the substrate. All three mask minor surface imperfections and machining marks, and all three add meaningful thickness.
| Finish | Result | Materials | Applies To | Tolerance Impact |
|---|---|---|---|---|
| Powder Coating | Heat-cured thermoset film; durable, impact and UV resistant; broad RAL and Pantone color range; smooth, gloss or textured | Metals | CNC, SM, TB, GR | Significant build-up. Threads masked. Tolerances met before coating |
| Wet Painting | Sprayed liquid coating; matched to RAL or Pantone; suits parts too large or heat-sensitive for oven curing | Metals, plastics | CNC, SM, TB, IM, UC | Build-up to be accounted for |
| Electrophoretic Coating (e-coat) | Immersion-deposited uniform film; excellent coverage on complex geometry and internal surfaces | Metals | CNC, SM, TB | Thin, uniform build-up |
Heat Treatment and Surface Hardening
Applied primarily to gears, shafts, cams and wear components. These alter the metallurgy of the part rather than coating it, and they are specified for mechanical performance, not appearance.
| Process | Result | Materials | Applies To | Notes |
|---|---|---|---|---|
| Case Hardening (carburizing) | Hard, wear-resistant surface case over a tough, ductile core; raises fatigue strength on loaded gear teeth | Low-carbon and alloy steels | GR, CNC | Case depth to be specified. Distortion control required on precision geometry |
| Nitriding | Hard nitrided layer at low process temperature; high wear and fatigue resistance with strong dimensional stability | Alloy steels, tool steels | GR, CNC | Minimal distortion. Not suited to stainless where corrosion resistance must be retained |
| Induction Hardening | Localized surface hardening of selected features via electromagnetic heating and quench | Medium-carbon and alloy steels | GR, CNC | Hardened zone can be targeted to tooth flanks or journals only |
| Through Hardening (quench and temper) | Uniform hardness and strength through the full section | Alloy and tool steels | GR, CNC | Full-section property change. Expect some distortion |
| Tempering | Controlled hardness reduction after hardening; restores toughness and relieves stress | Hardened steels | GR, CNC | Specified as a temper temperature or target hardness |
| Annealing | Softens material and relieves internal stress; improves machinability | Metals | CNC, GR, SM | Usually an intermediate step, not a final finish |
Specify hardness targets, not just the process. A stated surface hardness (HRC or HV) and case depth gives the partner facility a measurable acceptance criterion. Our inspection process verifies against that callout.
| Case hardening and nitriding are specified alongside custom gear manufacturing and precision CNC machined parts. Get a quote → |
Molded and Cast Part Finishes
For injection molded and urethane cast parts, surface texture is defined by the tool, not applied afterward. Specify the finish standard on the drawing so it can be cut into the mold.
| Finish | Result | Applies To |
|---|---|---|
| SPI Finish Grades (A1 to D3) | Standard mold finish scale from high-gloss diamond-polished through fine and coarse matte | IM |
| VDI Texture Grades (VDI 12 to VDI 45) | EDM-textured matte mold surfaces, fine to coarse grain | IM |
| Matte | Smooth, low-reflectance surface, sometimes called eggshell | UC |
| Glossy | Smooth, reflective surface; suits clear parts and sealing faces | UC |
| Light, Medium and Heavy Texture | Graded surface graining for grip and to disguise handling marks on housings and enclosures | UC |
| Mold texture is cut into the tool, so specify it before tooling starts. Injection molding · Urethane casting · Get a quote → |
Part Marking
| Process | Result | Materials | Applies To |
|---|---|---|---|
| Laser Engraving and Marking | Permanent, ink-free marking for serial numbers, logos, barcodes and traceability data | Metals, most plastics | CNC, SM, TB, GR, IM |
Laser marking is the standard route for part-level traceability where serialization is required.
Get Your Parts FinishedUpload your CAD file with finish callouts and masking requirements noted. A mechanical engineer reviews every upload and prices the job directly, with quotes returned within 12 hours median and 24 hours worst case. Your quote includes shipping, and where duties apply they are stated upfront before you order.
|