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Anodizing's effect on close tolerance fit

Q. My question concerns anodizing machined aluminum parts. I am trying to find out if I can anodize small steam, hot air and gas engine parts such as piston, cylinders, shafts and threaded holes with out effects the fit of the item. I would also like to know if it is possible to only anodize part of a item like the outside of a cylinder and somehow leave the inner surface unaffected. I use 2024 and 6061 usually.

Jason Croyle
hobby machinist - Glen Burnie, Maryland, USA
2004

2004

A. Sorry, Jason, it will affect the fit. If you anodize to, say, .0006" thickness, about half this thickness of aluminum will be consumed in the process, resulting in a net growth of about .0003". That means the piston will be about .0006" bigger in O.D., the holes will be about .0006" smaller in diameter.

Yes, the part can be masked to prevent anodizing in selected areas. Our search engine should reveal a few interesting letters on that topic if you use a search term like "mask anodizing".

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

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