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We strip our clear anodized bars to get them black anodized, but tapped holes go out of tolerance

Hello we are having trouble we stock our extrusions with a clear anodized finish but sometimes people request them to be black anodized and we need to send them out to be stripped and reanodized black. This is causing our tapped holes to open up and we are having troubles holding tolerances. Stocking mill finish profiles when we have over 200 profiles would be a large investment and machining after anodize is not always a great option because some customers need the parts to be completely black.

Ryan Breckenridge
- Huntington, Indiana, USA
November 23, 2011

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Hi, Ryan.

Anodizing is not an additive process like painting or electroplating, where you can strip the coating and be back where you started. The anodized coating is built by converting some of the aluminum to aluminum oxide, so when you strip the aluminum oxide, you have less aluminum than you started with the first time.

I think you will only solve this problem by effectively masking (plugging) the holes, leaving them with the original anodizing.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 23, 2011