Technical Prestretch a 72" long butt weld? Updated...

Had some rockers made up for my olds, now comes 6 feet of weld per side. Should i prestretch the rocker panel at the seam in my planishing hammer before welding?

 

Nope, just leave yourself a little gap, then skip weld it, then fill in the blanks. Move around a lot.

 

Yep, that is tack it in place and tack between the tacks and gradually fill in between without any long welds.

 

I tack, stretch the tack weld, then weld complete in one motion if possible.

 

No way to stretch the weld after welding, inclosed rocker panel.

 

what are you even talking about? prestretch what and for what possible reason.

 

Welding/heat shrinks metal. Prestretch the metal so to minimize shrinking warpage.
prestretching can be used before Bead rolling as well.

 

No, it will make fit up in possible.

A 6 foot **** weld that you can't access the back is a bad idea. It's gonna need plenty of mud. Wack-n-pack or if you want a better job do cave-n-pave mud.
Either that or take the rockers further all the way into the spot welds

 

The panel starts at the top of the rocker, then wraps all the way down into the pinch weld.

 

Tack the panel every 3". Wait for an hour.
Split the difference on every-other tack pair, tack. Wait an hour.
Go back to the pairs that you did not split the difference on, tack those, and wait an hour.
Split the difference on every-other tack pair, tack. Wait an two hours.
Go back to the pairs that you did not split the difference on, tack those, and wait an two hours.
Split the difference on every-other tack pair, tack. Wait an three hours.
Go back to the pairs that you did not split the difference on, tack those, and wait an three hours.

And so on....

If you notice any distortion, cut the tack. Straighten, allow to cool, and re-do it.

The faster you go, the more you warp.

The more you try to do at once, the more you warp.

 

Whatever you do. After tacking do not, I repeat, do not weld a long bead.
The more time to cool between small welds the better.

 

4 days to weld it.

There's no pics here,
but if the rocker were a full panel and went from bottom pinch, up, under the doors and into the floor pan spot welds it would be a lot better, easier, faster, cleaner, cheaper.

 

Spent a week running long welds on my car, my routine was weld 2 or 3 tacks far apart, smoke a cigarette, then do it again. It's tempting to hurry up and finish, but don't do it. Think I smoked a pack a night while I was doing that.

 

If it takes four days to weld it without screwing it up, then if it takes four days to weld it without screwing it up.

 

I think you will find rockers were only ever spot welded every 3-6 inches then sealant applied to stop water ingress.
The bottom pinch weld was similar. The manufacturers didn't have the time to fully weld these, some goo and paint is all they needed, the car wasn't supposed to last 40 years.

Good advice above, don't rush and s***ch weld every so often and let the weld cool

 

Well that is certainly one way to look at it.

 

***uming nothing to fix, it is 42-hours, with 1/8" tacks, and exactly 72".

 

10 hrs a day - it's now into 5 days.
I guessed pretty close. !

 

Friendly reminder, Daylight Saving Time ends Sunday, 12 March 2017, to include Alberta, so factor that in.

 

Oh ****, it's gonna warp

 

Yup. No hope.

 

"Wait an hour" After tacking? I don't want to be rude, but you must be paid by the hour.
No prestretch needed. Rockers are inherently strong because of the shape and hopefully correct metal thickness. Spend a little time to get a nice fit with slight gap and start tacking,skipping a few inches between tack welds. By the time you get to the other end of rocker, the first tacks should be plenty cool enough to start again this time splitting the gaps in half again with more tacks making sure to get good penetration. Again, check for cooling with your bare hand and keep heat to a minimum. It shouldn't warp much if at all if done correctly, just don't take all week to weld a rocker, get it done and move on.

 

No, I make perfect MIG **** welds in outer body sheet metal, that require no filler of any kind, ever.

I don't sit on my *** while waiting for welds to cool, either.

 

So what happens with the weld during this 1, 2, and 3 hour wait?

 

I want to hang out with you gimpy !

 

Normalization.

 

Come on over.

 

The entire panel is normalizing back to its relaxed state. A cold panel is a specific size, a warm panel is bigger , a hot panel is even bigger. Plus, the weld pulls as it cools. A round tack pulls a little, a football tack pulls more and a 1"weld pulls more yet.

So if you get a hot tack on a hot panel it's going to do a distortion dance when it normalizes.

I understand it, but I don't do it. I can't get them without filler so if it needs filler what the difference if it's a teas**** or 4 teas****s? Apparently about 39 hours welding time and 30 mins of filler work

 

Thanks guys, the panel has some crown and its 18 gauge. I figured now if I just clamp the pinch flange while I weld, I could sneek a tool from the back to work out any distortion after, then weld spot the pinch. I've welded lots successfully , just never a 6 foot stretch.
I managed to add the 2 lowered sections in this hood without catastrophe!

 

If you can lay your hand on it, it's not hot enough to warp. So make your next midpoint tacks when you can lay your hand on the tacks.

I think the bends and forms of a rocker will keep the weld from warping much.