My company is building the steel bridge for the NJIT school's yearly civil engineering competition. I got the honors to do the welding/fabrication again. Most of the tubing is 1/2" 3/4" 4130 tubing with wall thickness ranging from .037"-.323" or somewhere's around there. It's a lot easier to weld than the .037 wall 1/4" and 5/16" tubing I did last year. I'm using er80-s2 1/16" wire with a syncrowave 250dx and a 20M watercooled torch. Gold lanthanated tungsten in 1/16" is the choice(by defaultI guess with a small amount of my input). Some of the tubing is cleaed at the copes, other is mill scale. I'm told to weld as is so brake clean is all I can use. The fixture is made of 1" aluminum plate with all the details CNCd into it. Most fittings are single shear while the main trusses use a male/female tubular slide fitting that has a 1/4" bolt to hold tight.The lower truss fittings are cylindrical single shear in design. Here are a couple of pics from the first day of fab. DaveBridge2.jpgBridge.jpg