Butt Weld 1/4"x1" aluminum bar. How big should bevel or gap be?

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I am using 1" wide 1/4" thick aluminum bar 6061 t6 . I have four pieces of it, about 16" long and I'm making a simple square out of them with each corner having a butt weld. I will weld the front and then back so if i get penetration half way 1/8" on each side I will be fine. structural requirements are very low, it will basically be part of a portable shelf.My question is what is the easiest way to get good penetration, bevel or gap? If I gap the butt weld, is there a rule of thumb about how much of a gap to give for a given thickness of metal.I already treid butt welding it without a gap and the penetration wasn't that good. Cranking up the amps to 300 helped, but the arc is hard to control when it is making huge ripples that need to be ground down latter.  thanks for any helpful tips. this is the first time I'm trying out thick aluminum. Most of my experience is with thin aluminum tube.
Reply:You don't really get 'penetration' with aluminum (this is why fusing with a tig never works well like it does on steel). The heat isn't really concentrated in one spot like it is on steel, it sinks out sideways. Bevel both sides, 45 degrees on all pieces, weld up one side nice and slow using like 3/32" filler, then weld up the other side. Score the root of the first weld with a cutoff wheel if you need to to and you'll get full pen.With aluminum almost always build up the material with filler and bevel everything, dont rely on penetration, use minimal heat and just fill it in.Last edited by MikeGyver; 06-15-2014 at 03:01 AM.Welding/Fab Pics: www.UtahWeld.com