Hey I've got some tig welding under my belt and I'm planning on doing a catch can. What gauge aluminium should I use for it?

It's going to be a cuboid shape approx battery sized. I might put it where the battery is and relocate that to the trunk.

I was going to order some 0.125" thick sheet but maybe 1/8 is thicker than necessary?

 

.065 or even thinner if you can weld it. The lighter the better. It will be fine as it doesn't see enough pressure to balloon.

 

i work w/ alot of .100 and i really like working w/ it... its stiff enough for building odd projects, but thin enough to cut w/ my stomp shear and bend w/ a hand brake...

 

I built my catch can out of .125 because I didn't know any better at the time, but yeah it's way overkill. .065 should be plenty, just needs to be stiff enough to retain its shape on its own.

 

like draggbody said .100 is really nice to work with and is still very weldable and easy to bend.

 

the question is how thin are you comfortable welding? there is really no serious pressure to worry about, so I would go as thin as possible that will still be easily worked. the thinner the less costly and lighter.