Question 1

Can you anodize steel or stainless steel?

Accepted Answer

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.

Question 2

How much does anodizing change my part dimensions?

Accepted Answer

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.

Question 3

Will anodized parts still conduct electricity?

Accepted Answer

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.

Question 4

Which aluminum alloys anodize well?

Accepted Answer

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.

Question 5

Can you guarantee the color will match my last order?

Accepted Answer

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.

Question 6

Can you machine and anodize in one order?

Accepted Answer

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.

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.

Process	Best for	Typical volume	Choose it over anodizing when
Powder coating	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.

Instead of	Send this
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

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