--- title: "Aluminum Anodizing Services | Type II & Hardcoat | OpenSpindle" description: "Custom aluminum anodizing. Type II color and Type III hardcoat on machined parts, with masking and tolerance allowance handled. Upload a CAD file for pricing." canonical: https://openspindle.com/capabilities/anodizing --- # Custom Aluminum Anodizing Services Machine and anodize your aluminum parts in one place. Upload your CAD files or drawings to get pricing for prototypes, low-volume runs, and production quantities. ## Anodize colors our shops run A machined aluminum bracket in each finish. Anodizing is translucent rather than a painted film, so the tool marks and the aluminum underneath read through the color, which is exactly why it looks different from powder coating. Dyed colors vary between lots; supply a sample if parts must match. - **Clear (natural)** -- Type II · machining visible - **Bead blast + clear** -- Type II · uniform matte - **Black** -- Type II · most common - **Red** -- Type II dye - **Blue** -- Type II dye - **Champagne gold** -- Type II dye - **Green** -- Type II dye - **Burnt orange** -- Type II dye - **Hardcoat (undyed)** -- Type III · thicker, matte ## How to design for Anodizing Anodizing grows the part rather than coating it. Roughly half the layer penetrates the aluminum and half builds up on the surface, so every dimension changes and the rules below are mostly about accounting for that. | Design rule | Typical spec | Why | | --- | --- | --- | | Type II thickness | 0.0002 to 0.001 in total | About half of that builds up per surface. | | Type III (hardcoat) | 0.001 to 0.004 in total | Enough to matter on any close-fitting feature. | | Bore diameter change | roughly 2x the per-surface build-up | The layer grows on both walls, so a hardcoat bore can close up meaningfully. | | Tapped holes | mask, or tap after anodize | Added thickness on both flanks can take a thread out of class. | | Electrical contact | mask any grounding surface | The oxide is an insulator. This surprises people on enclosures and EMI parts. | | Racking marks | unavoidable somewhere | The part must carry current, so say where a small witness mark is acceptable. | | Sharp edges | break edges before anodize | Thin coverage and burn risk on knife edges, especially hardcoat. | Figures are typical ranges rather than a specification. Call out the surfaces that must hold size or stay bare, and see the spec chart for MIL-A-8625 detail. ## Anodizing vs the other finishes Anodizing is not always the right answer, and on steel it is not an option at all. The honest comparison: | Process | Best for | Typical volume | Choose it over anodizing when | | --- | --- | --- | --- | | [Powder coating](https://openspindle.com/capabilities/powder-coating.md) | Any metal, bold color, thick durable film | Prototype to production | The part is steel, or you want a color and gloss anodizing cannot hit. | | Chem film / Alodine | Corrosion resistance that stays conductive | Any | The surface has to conduct, for grounding or EMI, and cannot be insulated. | | Bead blast then anodize | Uniform matte cosmetic finish | Any | You want machining marks gone and a consistent appearance across parts. | | As-machined, no finish | Internal parts, fastest turnaround | Prototype | Nothing is exposed, corrosion is not a concern, and the schedule is the priority. | ## What Makes a Good RFQ | Instead of | Send | | --- | --- | | Anodize black | Type II, black dye, MIL-A-8625 Type II Class 2 | | Hard anodize | Type III hardcoat, 0.002 in, undyed | | Do not coat the holes | Mask the four M4 tapped holes and the bore on face A | | Needs to ground | Mask the 10 mm pad next to the connector, bare for grounding | | Match the last batch | Match to supplied sample, or accept lot-to-lot color variation | Color and masking are where anodizing quotes go wrong. The right column is what a shop can act on without calling you. ## Industries Served - Robotics and automation - Aerospace and defense - Consumer hardware and electronics - Medical devices - Drones and unmanned systems - Automotive and motorsport Anything aluminum that is handled, seen, or has to resist corrosion. ## Frequently Asked Questions ### Can you anodize steel or stainless steel? No. Anodizing converts the surface of the metal into its own oxide, and that process works on aluminum, and to a lesser extent titanium and magnesium. Steel and stainless do not form a protective anodic layer this way. If the part is steel and you want a durable colored finish, powder coating is the equivalent answer. ### How much does anodizing change my part dimensions? Roughly half the coating penetrates the aluminum and half builds up on the surface. Type II is thin enough to ignore on most features, at 0.0002 to 0.001 inches total. Type III hardcoat runs 0.001 to 0.004 inches, which is enough to close a bore or take a thread out of class, and a hole loses about twice the per-surface build-up across its diameter. Tell us which features must hold size and we will mask them or machine to allow for it. ### Will anodized parts still conduct electricity? No, and this is the most common surprise. The anodic layer is an electrical insulator, so any surface that needs to ground, bond or carry EMI contact has to be masked, or you should use chem film instead. Mark those surfaces on the drawing rather than describing them, because they are easy to miss. ### Which aluminum alloys anodize well? 6061 is the workhorse and finishes predictably, which is why most machined parts are specified in it. 7075 anodizes but can come out a different shade. High-copper alloys such as 2024 and high-silicon casting alloys tend to finish darker, blotchier, or less evenly, so cosmetic parts in those alloys carry real risk. Say up front if appearance matters and we will flag the alloy before anything is cut. ### Can you guarantee the color will match my last order? Not exactly, and any shop promising otherwise is overselling. Dyed anodizing varies between lots with bath age, alloy, temperature and time. Parts run together will match each other closely; parts run months apart may not. If parts from different batches will sit next to each other, say so, and either run them together or supply a sample to match against. ### Can you machine and anodize in one order? Yes, and it is the point of ordering this way. Splitting machining from finishing means the tolerance allowance for coating thickness and the masking plan become two separate assumptions held by two vendors, which is where anodized parts usually go wrong. One order keeps one party answerable for the finished dimension. ## Other Capabilities - [CNC Machining](https://openspindle.com/capabilities/cnc-machining.md) - [Powder Coating](https://openspindle.com/capabilities/powder-coating.md) - [Sheet Metal Fabrication](https://openspindle.com/capabilities/sheet-metal-fabrication.md) - [CNC Turning](https://openspindle.com/capabilities/cnc-turning.md) ## Related reference charts - [Anodizing spec chart](https://openspindle.com/reference/anodizing-spec.md) -- MIL-A-8625 types, alloy behavior, and how to call it out on a drawing. - [Surface finishes compared](https://openspindle.com/reference/surface-finishes-compared.md) -- Anodizing against the other finishes, side by side. ## Design Notes That Move Your Price Four things that decide whether an anodized part comes back right. - **Decide Type II or Type III before you quote:** Type II is the everyday finish: thin, dyeable, good corrosion resistance. Type III is a thicker, harder wear surface that is usually dark whether or not it is dyed. They are different prices and different dimensional allowances, so choosing at quote time avoids re-machining. - **Mark the masking on the drawing:** Threads, bearing bores, grounding pads and mating faces are the usual candidates. Written in a paragraph they get missed; marked on a face they do not. - **Say where a racking mark can live:** The part has to carry current, so it is held somewhere and that spot shows. If you do not choose, someone else chooses for you, and it may be the visible face. - **Send the alloy, not just the geometry:** Alloy drives appearance more than process does. 6061 is predictable; 2024, 7075 and cast alloys are not, and that is worth knowing before parts are cut rather than after they are dyed. ## Ready to machine and anodize your parts? Upload a CAD file or a drawing and tell us the type, the color and which surfaces must stay bare. We will come back with one quote covering machining and finishing together.