I use about a 120 or so grit 3" sanding disc to completely flatten the end of the drill bit (I use a letter A for all my plug welds, works good with the heat setting I am at), You end up with what looks somewhat like a figure 8. With all that flat surface, it would be more difficult to remove paint, so on the back side of the leading edge of the cut, using the sanding disc again, and angled "relief" is formed in each side. This now leaves about a 1/16" wide flat straight across, as you can see above, which works much better to remove the paint. The EP I'm using is KP-2CF from House of Kolor.
Thanks Robert. I'll try that.
For the typical repair panel I am fabricating, I will cut it out about 3 times (hopefully all on the same panel). Tool of choice is offset snips, you'll need left and right handed. Initial cut is a rough cut, a good 1/2" or so oversized. Now it will fit against the adjacent panel a little better without all the extra metal in the way. Trace an outline from your hole/opening to make another cut. Here I'll use a sharpie or similar device, and trim again, leaving about 1/8 extra this time. Fit and trace once more, this time marking with a scribe, ice pick, or similar sharp device, and trim just to the outside edge of the scribe. Test fit again, using your 3" sander to touch up any areas that aren't fitting tightly together. Oh yeah, in case you just missed that, NO GAPS. Any weld is going to cause some shrinking. The wider the gap, the more filler, the more heat, the more shrinking, the more your panel just moved from where you intended the edge to be. And as you have seen, hard to fill and weld a gap with about .023 wire. So here's where we work in the welding scenario. I hope no body gets offended, by my personal view is people set gaps (and use backer plates) because they can't get a full penetration weld otherwise, because the machine is not set hot enough and the panels aren't tight together. Think of the weld pass we discussed earlier. The initial part of the weld does not produce a full penetration weld. So to fix that, let's turn up the heat. We want full panel penetration, the first time, every time. But wait, you say. If I keep welding, it will blow a hole in the panel. So true, That is why in welding sheetmetal, the process I use is more heat (I normally set my machine for the next thicker metal....18 ga, set the heat for a 16 ga panel, etc), but only weld one dot at a time. If the panels are tight together, the feed wire can "feel" the joint even if you're blindfolded! Now, one zap and the panel is tacked. I know this may be different for some, others may have tried it and still found themselves blowing holes due to the "excessive heat". Before giving up hope, first try increasing the wire feed speed a bit more. Think of it this way.....there is enough heat to cause the weld, but not enough filler material going in, so somethings gonna give, hence the blowout. So more heat, more feed, single dots only, and no gaps. I'll follow this post with a small patch I did on a quarter panel to hopefully show the process a little better.
