Repairing Aluminum

[scocklin]

I’m trying to fill in a large hole (1/8-1/4 inch) in a piece of aluminum and then prep it for anodizing. I have been told that I will have to send it out to a machine shop to be welded and then milled. Are there other ways such as metalic filler compounds that can be anodized over?

[Fibergeek]

Unfortunately, no.

All metal-loaded fillers use epoxy (or a variant) for adhesion which are insulators, even those advertised as "conductive" aren't conductive enough.
Alumium solder contains too much un-anodizable metal to work properly.

Aluminum MIG or TIG (preferred) welding is the best way.

[acidrain]

Even a good tig job may show. Could you tap the hole and then add a threaded aluminum plug of the same alloy, then file it flat? It will show too, but I'm not sure how pretty this has to be for you. Just a thought.

[scocklin]

Thanks for the replies, the piece in question is one of my Son’s expensive paintball markers. He had some electric eyes installed some time ago and now he wants to have the main body custom milled and anodized. He found someone that will do the milling and repair the hole that will be left after the milling is complete. I’m just trying to do the research for him and insure that all of his bases are covered so I don’t have to deal with an expensive problem later. Thanks again.

[Fibergeek]

If you use threading, you will need a REAL TIGHT fit, tighter than a Class 1 thread. I have gotten reasonably good results by deforming the thread using a common Class 3 tap /dye combination. It is essential that no electrolyte seeps in between the hole and the plug. You know that will happen to the anodization of the plug if it does. An interference fit machined plug pressed into a corresponding reamed hole is more sure fire, and straightforward if you have the tools and machining skills. Having the plug the same alloy as the work obviously helps uniform anodizing of the two.