Some other things you should understand welding stainless (since your intro post explained you're new to TIG)-
That structure, whether stainless, carbon or aluminum, needs venting holes in the intersecting tubes when you weld it. For instance, if you weld the stretcher tube to the leg, fully weld the seam on both ends, the heat and gas accumulated inside the tube has no escape. It will blow out the last bit of your weld. Instead, drill a small hole in each intersection so as you close one tube, the gas evacuates into the next tube. Leave the legs open at the top with even a small hole drilled in the top plate to close the leg. Make sense?
Welding stainless will make the pieces move. A LOT. Every bead you weld, will distort the intersecting angle. Keeping things square will be your biggest challenge. You need to be very patient. Weld a bit, let it cool, check/adjust your squares, weld some more. Repeat.
That structure will be very heavy too. Handling it while welding will be a nuisance and you're apt to scratch it up. So extra hands after you get portions assembled to rotate it around are very helpful.
If you order the material from OnlineMetals, it will likely need to be cut by you. Cutting stainless is not fun. Use coolant/cutting fluid, and not WD-40. Cutting oil for drilling holes, and cutting the ends is really necessary. Avoid using a file on the ends. This introduces carbon steel into the stainless and that will rust. Use a flap disc to blend edges.
If your fit is good and tight, you can weld without filler. You need a large cup (#12 is my recommendation) and a gas lens. Sharpen the point. Use pulse on your machine if it is available. Rule of thumb is 80% of the amps for carbon steel when welding stainless. (If you're welding 1/8" carbon, run 125 amps. For stainless, run 100 amps or less). Stainless welds will crack easily if you don't use sufficient gas coverage during post flow. Run gas until the tungsten and weld are silver. Too much color in your welds means too much heat. Welding travel speed is 2x faster than you think you can
Get a puddle, and haul butt!
I would suggest you choose cold rolled steel for that project. Price, ease, and weldability will make your outcome much more successful until you bend the TIG learning curve. And it can look just as beautiful. In fact, I'd use cold rolled and silicon bronze filler for a handmade, industrial look. Easier to weld with SilBr and plenty strong for the application.
Hope this is received as intended, helpful and constructive. Good luck!
