Anodizing is the most common finish for CNC machined aluminum. It improves corrosion and wear resistance and gives parts their color. Because anodizing changes the surface dimensions, it has to be planned together with the machining.
What anodizing does
Anodizing is an electrochemical process that grows an oxide layer from the aluminum surface itself. Part of the layer grows into the metal and part grows outward, so the part gets slightly larger on every anodized surface. The porous layer can be dyed before it is sealed, which is how colored parts are made.
Decorative (Type II) vs hard anodizing (Type III)
Decorative anodizing, often called Type II, gives a thinner layer and a wide range of colors. Hard anodizing, often called Type III, gives a thicker, harder layer for wear surfaces, with fewer color options and a darker natural tone. Choose by function: appearance and corrosion protection, or wear resistance.
Designing for anodizing
- State whether dimensions apply before or after anodizing.
- Bearing bores, press fits and threads may need machining allowance or masking.
- Sharp edges anodize thinly; a small chamfer or radius gives a more even finish.
- Alloy affects color: 6061 anodizes evenly, while some high-strength alloys come out darker or less uniform.
- Specify color with a physical sample or a reference, and accept that batches can vary slightly.
Machining and anodizing from one supplier
Ordering machining and finishing from one supplier gives you one point of contact for both, and allowances and masking can be planned together with the machining.
Chi Xin Technology is a CNC machine shop in Nantun District, Taichung, Taiwan, founded in 2022. We run 5+ CNC machines — 4.5-axis CNC machining centers and CNC lathes — and mainly machine aluminum alloys and alloy steel, with a metal tolerance of 0.02 mm. We also offer wire EDM and surface finishing including anodizing, and we export to customers in Europe and North America.
Frequently asked questions
Does anodizing change part dimensions?
Yes. The oxide layer grows partly outward, so anodized surfaces get slightly larger. Plan allowances or masking for precise fits.
Can you machine and anodize the same parts?
Yes. We offer surface finishing including anodizing together with CNC machining. Tell us the color and which surfaces must stay bare.
