To weld those acute inside angles you can do as suggested and flatten a nozzle a little and also shorten it. You will still have a longer wire stick out though so to compensate you may need to bump the current a little. It also helps to increase the gas flow. If you start in the middle and weld out then the longest you have to reach is a little over 1/2 an inch. I know that you are welding the wrong way ie. pulling the torch as apposed to pushing it but it is only thin material and you will get away with it. I hope you will forgive me for saying, but some of your welds look a little cold and I would try a little more current with the same wire speed or viciversa a little less wire speed but the same current.
Thanks for the response, Bruce.
All this welding stuff is more complicated that one first suspects, isn't it? I know my welds on this piece do look a little mounded, but I've done a good amount of testing on scrap pieces of 0.75" x 16 Ga. RHS (as in this part) where I can see the underside of the weld on the tubing scraps. The penetration is just about ideal and I can see the metal just beginning to pucker right at the underside of the join with clear discoloration from the arc heat, so it should have fused together. If I up the current, it starts to sag underneath, which I know isn't good. I don't know why the bead isn't flatter. Too much filler wire maybe? Maybe it's something to do with my personal welding style like moving too slow?
My welder has "auto selections" based on the thickness of the material, but I've found it is too hot for my welding style and I see too much sagging on the underside of the welds consistently.
I do use a push, though. That's how I blasted off the corner of one tube when I was trying long stick-out in the acute weld. The low angle of the filler wire just pushed it right off when it got molten rather than fused to it. From my testing on scrap, I do have a "cheat sheet" of settings for various material types and thicknesses that should give good, strong welds even if they're not too pretty.
It would be great if I had the benefit of years of experience welding before taking the chassis on as a project. In that case, I would be anticipating these issues and solving the problems in real time as they arise, or better yet, avoiding them all together. Unfortunately, that's not the case. Every day is a new adventure! That's what it's great to have a resource like LocostUSA.
I tell you, this experience has amplified my already appreciable respect for people who make things, especially race cars. But, I'm like that musician who wants to go to Carnegie Hall, so for me it's practice, practice, practice.