I bought a porta spot single sided welder that is older than me, it looks just like the one in the picture . First time using it, I welded 2 scrap pieces of 18ga sheet together, i pryed and twisted the metal and it didn't want to come apart afterwards so it seemed to work pretty good . Since then, I cleaned up the probes a little with a wire brush a bit because they were corroded looking. now I can't get it to stick, I've tried different temperature and timing settings. I'm not sure what I did different the first time but I can't seem to reproduce it. The very first time, I let off the trigger early and didn't let the timer shut it off, so I'm wondering if maybe I have the timer too high now. Is it possible that welding it too long makes it unstick? I'm getting great penetration and a nice glow on the metal but it just doesn't want to stick. I'm open to suggestions.