How to weld aluminum tube joints not 90 degree

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I'm pretty new to welding, using small hobart MIG for now. I'm trying to weld some 1" OD x 3/16 thick aluminum tubing together. Instead of welding a normal 90 degree joint together, I'm trying to weld at more like a 120 degree angle. I'm making these to be brackets to hold a pirogue on my aluminum boat. The pirogue will sit on the tubing. I've attached a picture that shows on top what i want the final product to look like, and the bottom two pictures show the two ways i can imagine making the joints. I don't know which would be more stable for welding.thanks Attached Images
Reply:square or round tubing?  if square I like illustration #1
Reply:square tubing
Reply:Either should be okay. The first will be easier to cut, but the second will look nicer when you're done.
Reply:I guess for the second one, I'll actually have to cut both pieces at an angle? Seems like if I just cut the bottom piece at an angle, there would be a bigger opening to the inside of the tube than the one thats stock 90 degree cut. In any event, whats a good way to measure the angles i will need to make these cuts?
Reply:You will want to cut both angles equal to have the same tube end shape and the joint to fit up evenly.  Bisect the angle of the joint.  If it was a 90* joint, you would cut each to 45*.  You want 120* joint, so cut each to 60* (or 30*, depending on how you look at it).Once you have them cut, grind a 45* bevel around each tube end so you have a v-groove joint to fill up.  Otherwise, all your weld will sit on top of the joint and will be a weak joint.Last edited by DesertRider33; 09-19-2009 at 10:38 PM.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op