Just got some parts back from the anodizer

[turbo2ltr]

Two out of the four have some marks on them and I'm curious if anyone would know why.



Was it improper prep? Just wondering if it's something I did. This was the first time I sent parts to an anodizer. They were machined, then put in a tumbler for an hour.

TIA,
Mike

[Caprirs]

Wild speculation is the parts were placed on something before being fully cooled and dried.

[turbo2ltr]

To my surpise, someone from the anodizing company just came here to take a look at the parts. (I'm impressed, heh) He took a look at them and thought it might have been something that could be cleaned up with scotchbrite, but that didnt work. So he took the parts back and said they would re-run them tonight and have them back tomorrow. He really wasn't sure exactly what it was....possibly something in the base metal. Both surfaces that were affected were surfaces that were not machined, just sanded lightly to take out the imperfections of the bar stock. I dunno... I know three of the parts were milled from the same stock and two were fine. Guess we'll see how they come out tomorrow.

Thanks!

[Geof]

That is very good service from your anodizer, let us know how things turn out.

My suggestion is the same as Caprirs', water staining from the aluminum being in contact with something while it was wet. The water marks can be unnoticeable until after anodizing. We have had this happen with individual parts dried on a plastic rack but most commonly it arises from parts being allowed to touch on the drying rack after washing. We have also had it on the unmachined surfaces of bar stock and a frequent cause is bringing cold metal into warm humid shop. Water condenses on and between the bars in a bundle and creates all manner of blotches.