Today I picked up 72 48" 1x1x 1/16" aluminum tubes to make the chassis.
The 132 water jet cut parts should be ready early next week. Between now and then I have to drill 308 holes into the tubing for the rivets that will fasten the tubes to the water jet parts. LeChatNoir had the great idea of using the CNC mill to do this, so that I only have to load the tube into the vice two times to drill four holes. This is more accurate and faster than using a drill press.
I am glad I am riveting this machine and using flat plates to join the tubes. I've been practicing TIG welding for an hour a day, and have learned that my welds in 1/16th tubing are not strong at all. Or maybe 1/16th tubing just isn't very strong to begin with. I can easily break any weld I make in this tubing by slipping a 4' pipe over it and pushing a little. The welds seem to just rip apart like cardboard. With 1/8th thick tubing I can't break the welds with a 4' pipe.
So next week I will be drilling and riveting. And a little welding to make sure the water jet cut plates don't slide along the tubes. The idea behind this weird construction method is lightweight strength. The tubes are held apart and made into 4" square beams that weigh about the same as 2" square tubing but is much stronger. I'll see how it works out, or if it is even necessary to go this high tech.
I need to get better at out of position welding. It was easy with MIG, but with TIG I can only weld when something is horizontal. When I am welding vertical with TIG the torch is a lot more jittery in my hand and I tend to dip the tungsten into the puddle. Or keep jittering my hand slightly, so the arc is wandering around quite a bit and heating up the whole piece instead of making a nice little puddle, so I sometimes burn a hole through the piece from too much heat. I think resting my hand on the work, when welding horizontal, is a bigger crutch for me than I imagined. A painter or calligrapher would have a big advantage here, in having a practiced steady hand. I don't think I'll be able to flip the chassis around so that whatever I am welding is always face up, so I have to get better at this. Maybe I need a big clamp to move around and rest my hand on as I go.
Corner welds are still a problem. I am getting better, but my corner welds are still really bad. The root of the corner is completely cold, so the bead is just sticking on the sides, about 1/16th to 1/8th of an inch away from the corner. If I cut a practice weld with a bandsaw I can see that the bead is not fused to the corner at all and just sitting on top of it, like you'd see a crease inside playdough that's been folded, while it looks well fused a little distance away. By accident I found a technique that is probably bad-- if there's a slight gap in the corner I can melt the two pieces above and below the corner and then stick the filler rod into the gap, to let the surface tension make a new corner that is fused to both pieces of metal. But that's not really a solution. From all of this practice my bottle of argon is almost spent, so I am thinking of trying a helium-argon mix next: I've read that the arc is more focused when there is a little bit of helium in the gas, so maybe that will let me poke the arc into the corner rather than having a wide cone that seems to want to go everywhere except the corner.
Sometimes my weld beads have pin holes, some kind of ugly nub, or a ball where the bead didn't flow onto the base metal and just rolled onto it with that water-on-wax surface tension-- is it bad to run the torch back over a bead to reliquify these defects or the base metal to smooth these things out? I still don't have the 'stack of dimes' look on anything except a piece of flat plate.