I had the 90amp harbor freight welder before, and used it to weld up to 1/4". I did prep the metal to do this in multipass though. You just cut the metal at a slight angle and flip one piece so that you have a V to weld into, and tack weld the back out a bit, so that it will remain flat when you fill in the other side of the V. When your done you will have a strong weld. It may take a little time, but you should be able to get the job done, if you know what your doing. This was the way I was taught in school, as the teacher knew that guys will not be able to afford a super nice 220 welder, and may use a 110 to do some repairs, or build something at some point. When I get home from work in a few weeks, I will make a point to do a weld, and I will cut it and polish it and etch it to see what I can do.