anodizing aluminium

I have just bored some 52mm dia holes for bearings in Aluminium . I have been boring these holes on a regular basis and use a template to leave sufficient in for a press fit , I also double check that the bearing does not go in the hole on every component . These components have just returned from Anodizing and the bores are loose the bearings drop in the hole , Is there anything in the Anodizing process that could cause this ? These components can be saved by boring and sleeving but in all the years of doing these parts I cannot accept that this is my fault after being so careful after checking and double checking .

Before anodizing, parts have to be cleaned, this is usually referred as etching and will remove material. When anodizing parts with slight burrs, we have asked parts to be heavy etched. So the plater can remove material with too much etching. Usually sizes remain the same since the anodizing replaces material lost thru etching.

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Originally Posted by JimBoyce

Before anodizing, parts have to be cleaned, this is usually referred as etching and will remove material. When anodizing parts with slight burrs, we have asked parts to be heavy etched. So the plater can remove material with too much etching. Usually sizes remain the same since the anodizing replaces material lost thru etching.

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yeh must be the etching, anodizing converts the surface to oxide that takes up more space the the aluminium it consumed so holes should get smaller

Bored holes out and sleeved them . Will certainly be getting somebody to look at them with me next time before they get sent away .

davedoubleu

I don't think the etching has anything to do with it, they would of needed to be in the etching bath a long time to do this, your parts have had stress in them & when going through the process the heat has relieved the stress & made your parts bigger in the bore, other people have had this happen as well, if it was etching that caused your problem there would be no machining marks left in the bores, post a photo this will show if they have been over etched

Did they have the same appearance as other batches? I have had parts change dimension in the 'wrong' way during anodizing; wrong being that outside dimensions shrunk and bores enlarged. This was because the anodizer had done something wrong with the dyeing so they stripped them and re-anodized. This does change dimensions by a few thousandths of an inch.

Geof
stripped them and re-anodized

Stripping the parts & re-anodizing them, if not done very carefully will do this, but normal anodizing will not

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Originally Posted by mactec54

davedoubleu

I don't think the etching has anything to do with it, they would of needed to be in the etching bath a long time to do this, your parts have had stress in them & when going through the process the heat has relieved the stress & made your parts bigger in the bore, other people have had this happen as well, if it was etching that caused your problem there would be no machining marks left in the bores, post a photo this will show if they have been over etched

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This makes sense - there was two batches of four jobs , the two batches looked different aluminium, tooled differently with different surface finishes. four of the components were good bearing size bores and four were oversize makes me wonder if the two grades of aluminium reacted differently to the anodizing process

Thankyou all for your input on this. much appreciated .

davedoubleu

Were any of these parts using color, if so they may have had trouble with the different material, if you were using a Black color, this is most problematic color, If this was the case,& they had a problem with the color, they would of stripped it & re-anodized them not taking enough care in the stripping process, will remove material

As stated above stripped and re-anodized, also too much current will erode anode (your part). Did your parts come back pitted?