How's my butt look?, Weld, that is. Options

[bbrock]

I'm trying to elevate my welding/patching skills and chasing that (so far) elusive invisible butt weld. (IMG:style_emoticons/default/welder.gif) I'm working on the front wheel well and would like to get this down before moving on to outer body panels where it will really count. I'm hoping to get some advise/critique from the experts what to do next and when to call it good enough for a little FG filler. And also what to change for the next time. This is all being done with my trusty, 30-year old, original 120v Hobart Handler MIG welder. Also, this will be a rotisserie job so the whole car will be blasted and primered before any fill goes on. So when I ask about being ready for filler, I mean AFTER proper prep.

Here's where things stand. This is the backside of the weld.



And here is a close up of what I'm dealing with. It looks to me like I didn't quite get complete penetration on the weld, possibly combined with shrinkage around the filler, causing the metal to sink a little.



I've read that the way to handle the shrinkage is to hammer the weld on dolly to planish and stretch the metal. I've tried the best I could, but this is a tough area to reach around. More, I'm thinking I need to turn up the heat on the welder a little for future welds but would appreciate thoughts. So now the questions:

1. The deepest parts are 1/32" deep, at best. Is it worth trying to work this to perfection, or would I be ahead by calling it good for a skiff of FG filler? I'm a bit paranoid of overworking the metal and making it brittle.
2. If I keep working, how best to proceed? My inclination is to hit the low spot on the seam with some very quick tacks to add material. Then grind to close to the parent thickness before hammering on dolly. Then sand flush. But will I do more harm than good, and is it worth it?

And here is a pic of the other side - the front of the weld.



Just a few shallow low spots that I think would come out with some additional 80 grit sanding. But I'm thinking maybe it is better to call it good? (IMG:style_emoticons/default/confused24.gif)

I've done a lot of searching and reading on welding forums but it seems that people like to post pics of their perfect, invisible welds that need no filler, or pics after filler. I haven't found examples of what good welds that need a touch of filler look like. I'm not going for "no filler perfection" but I do want to maintain a high quality standard. Not that a no filler perfect patch wouldn't make me happy, but I would like to actually drive this car some day. (IMG:style_emoticons/default/driving.gif)

Thanks in advance for any suggestions.

[McMark]

I weld at high power, so the weld penetrates quickly, and just do tack welds. That looks like how you're doing it as well, but if you're worried about penetration you may need to step up a bit on power. Pictures of unground welds would help as well.

You're well along the way to making invisible welds. One very important thing to keep in mind is that the perfect weld (like most things) happens in the prep phase. Make sure both sides of the metal are ground clean and bare, make sure that the patch piece is well fit before you start. Never try to work the metal into place as you weld.

And finally, be very careful about how much you grind your welds. You can't MAKE a bad weld into a good one by grinding more. You'll end up with paper thing metal that looks good when you're done but will crack or if you have to weld near those grinds again you blow right through. It can help to think of it this way -- you never want to grind the base metal (the sheet metal), you only want to grind the weld material. And then it looks how it looks.

Just throw another few hundred hours at it and you'll get it. (IMG:style_emoticons/default/shades.gif)