Summary for anodizing close tolerance fit Discussion
Anodizing close tolerance fit is the main concern in this thread. Jason Croyle asked whether small engine parts made from 2024 and 6061 aluminum—such as pistons, cylinders, shafts, and threaded holes—could be anodized without changing fit, and whether only part of a component could be anodized while leaving the inner surface unaffected. The answerer replied that anodizing will affect fit: if the coating is about .0006" thick, roughly half is consumed and the part grows about .0003", so an outside diameter can end up about .0006" larger and holes about .0006" smaller in diameter. The answer also said selective anodizing is possible by masking areas that should not be coated, and suggested searching for "mask anodizing" for related discussions.
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
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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