How to specify surface finish for painting aluminum?

Hello,

We design sheet aluminum parts that are often welded to form closed corners. The fabricator sands the outside corners of the welds to nominally make them flat. Oftentimes the entire surface of the part is then sanded with either a "jitterbug" or a "timesaver" which leaves a grain which is visible through a smooth paint finish. We can prime and sand the parts prior to topcoating, but is there an appropriate specification for the fabricator such that the parts are suitable for painting without priming or sanding?

Thanks

Not sure how big your parts are, but you might want to consider having him mass finishing these parts. I'm not sure if there is a formal specification for mass finishing, but if you give him an RMS to adhere too, say around 22-28 RMS, I'm sure that would cover it a good finish for painting.