Well let me say this about that. He does not call it a stress crack. He is making a point that I made about butt weld gaps. Whether he intended to or not.
His point is that coats of filler, primer or paint will get cracked by this "unwelded" crack. The weld has been ground away.
So when I spoke of the battle of the gap as: some say zero, some say 1T or larger, this illustrates why a gap is necessary. The weld needs to "fill" a gap instead of piling on top. Penetration. If you leave a gap, when you grind, it will not leave a crack. In my experience, it's better to fill the gap and "penetrate" each edge than to try and "melt" the edges together in thin sheet metal. That's what TIG does. You don't even need a filler material in some cases with TIG.
Not to mention that a tight gap can cause deformation. Like I said, there are experts on both sides. Both have good results. The DIY builders can find their preferred way. There is not just one way.
Penetration in this sheet metal case really points out the fact that you are trying to get the filler material to join the base material. There is a fine line, in thin material, between good penetration and burn thru and distortion. That's why you have to zap-dot weld as Robert says. Contrary to the poster saying his case is 16 ga (.060 thick) material, many cases are 18 ga. (.048 thick). That is 20% less thick. 19 ga is hard to find, most suppliers sell even number gauge.
Thick plate is easier to do. No zap welding, lay into it with all you got. Burn thru is not an issue, heating the base enough is, undercutting is, penetration enough to meld thick metal to think metal is.
The aforementioned tool:
If someone credible reviews the tool, I might agree it's a break thru. That will take time. I would like to see the back side of that trench weld. It does have some merit. It is copying the chamfered edge used on thick plate. It will, however, be a different weld than a zap dot, I think?
NOW! The fishy part. They only show what type of weld they did for 6 seconds. The welds look like a spot weld of sorts or tacks, BUT the height shown is not tall enough to level grind as shown in the video. SO......what did they do? What kind of weld was it? Big spots? A bead? A stringer and weave? Don't know. That was not left out by accident. It's the oil part of snake oil....or in this case "Fishy Oil". That's going to have way more fill and way more heat than any other "butt weld" method.
