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Aluminum anodizing is typically in the order of 5 to 100 micrometers thick, depending on the process. Anodizing will build up vertically on the surface and won’t “fill in” the machining marks. So under the right lighting, the scratches will always be visible. However, there are a vast number of post-processing finishes that can reduce or even eliminate these marks altogether to give a completely smooth finish for anodizing.

[Ben S]

I’m experimenting with hard anodizing for an aluminum part and trying to understand how the finish affects the surface. Specifically, does the coating fully mask machining marks, or are they still noticeable through the matte layer? If you’ve dealt with this on visible components, I’d love to hear your experience—or even better, see a photo of a similar part

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[Bjorn]

Aluminum anodizing is typically in the order of 5 to 100 micrometers thick, depending on the process. Anodizing will build up vertically on the surface and won’t “fill in” the machining marks. So under the right lighting, the scratches will always be visible. However, there are a vast number of post-processing finishes that can reduce or even eliminate these marks altogether to give a completely smooth finish for anodizing.

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[Ben S]

What kind of post-processing would you recommend?

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[Bjorn]

It really depends on your geometry. If it’s smooth with large flat or smooth surfaces then tumbling or bead blasting can work quite well. If the part has complex features then you might have to look at other processes, possibly electro polishing for example.

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[Joshua]

Before spending money on expensive post-processing I would tell the machinist that your intent is to anodize and that machining marks must be limited as much as possible. Machining marks can be almost completely eliminated depending on the complexity of the part or the skill of the machinist. A word of warning though, improved surface finishes will result in a more expensive part so only request better finishes on areas that will be visible.

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