If the stands had been positioned so as to prestress a little arch into the trailer that would have been better. You can still move them while you weld on the rest of the deck. The welds across the trailer were minimal contributers to this problem. The welds along the 2X5 long members are the problem. As the weld cools it shrinks, that arches the member toward the weld. A similar sized weld along the bottom of the member should balance things out. I would put in a foot skip a foot on the first pass then check how its going and fill in the spaces as necessary. Vigorous hammering of the top welds with an air chisel with a blunt tool could help a little.

As a last resort you can muscle it out on a frame machine.

Good luck

Bill

yeah...the only time you can weld a long straight bead on something is if you've taken all the steps to minimize distortion: preheat, strongbacks, backstepping the welds, etc. in your case, you don't even need long welds. a 3" weld every 6-12" should be plenty for the decking. and yes, skip around. weld for 3" on the left side, then 3" on the right, then 3" toward the back, etc. the farther away you skip from the joint you just welded, the better. the same thing underneath the decking. kinda like when you tighten the lug nuts on a wheel.

and don't think that just because a piece of steel is thick that it can't be warped by welding...we just welded some 1/2" thick H beams to some half inch plate but we forgot to clamp some pieces down and weld some other joints first and it warped about 1/4" out of square, which was bad news for us. hehehehe shrinking steel is a powerful thing!

and all is not lost...if it comes down to it and you can't get the frame straightened out by bending it, the grinder is your answer. get some 5" diameter 1/16" thick cut-off wheels and cut the long welds from the tubing. or just use a regular grinder w/ a thick wheel...you just have to be more careful that you don't grind too much out of the wrong spots. that should relieve the stress and allow you to start over. then get some thicker grinding wheels and grind down the old welds so everything is nice and flat. you might have to grind the welds off of the bottom too, but i'd just take care of those long welds first to see if that'll solve the problem. that'll only take you a few hrs to do w/ a bunch of grinding wheels, but it'll save you a lot of money on steel.

Goose, I believe you have all the answers you need spread out in several posts. I have had things like this happen in my shop, if you stay at this business long enough it will happen to just about everyone. First, you should not have needed to weld this solid, I believe that and not moving around or using strongbacks caused the warpage. Second, you may very well need to cut the plate free before the frame can be straightened. I would use a rosebud on the underside of the frame, heat the tube until it is red and move steadily down the entire frame and then leave it sit until it cools. If it does not come back enough with the plate on, cut it loose and then use the rosebud again. The mecahanical frame straightener idea would work also, but like was mentioned, these are often best fixed in the privacy of our own shops. Please follow up and let us know of your progress.

Respectfully,
Mike Sherman
Shermans Welding

I may be hardheaded, but I would try to fix the problem before cutting apart the work I've already put into the project. It seems to me that grinding out the welds would not be enough to fix the problem, which would try to re-occur when you replaced the weld.
I used to work for a man who wrote the book on heat shrinking. He could make an I beam walk across the shop floor with a rosebud and a spray bottle.
Anyway, the procedure he taught me was basically this:
First put a pre-bow in the weldment using whatever means are most practical given your situation. (come-along, beam and wedge, turnbuckle, etc...) As you have already begun welding, but have not finished, you should still put in a pre-bow and then finish welding (if at all possible).
After the weldment has cooled remove the pre-bow apparatus and assess the situation.
Heat shrink the longitudinal members in which welding caused the warpage. Use a rosebud torch to create a triangular shaped red hot area on the side walls of the tubing and the bottom, with the bottom side of the triangle about 4" wide. Put as little heat as possible on the welded side. Don't over heat the metal. Your looking for a dull red in color, not yellow. It's important that each side of the tube is heated evenly, otherwise one side will shrink more than the other and cause more problems.
When both sidewalls and the bottom of the tube are an even dull red in color, shut off the torch and immediatly cool the metal with a pump spray bottle, by spraying a mist of water first around the outside of the triangle and move in toward the center as it cools. Continue spraying until the metal is cool enough to touch. This will force the metal to shrink in the opposite direction of the bow.
Start off with the first tringle/hot spot in the center of the bow, on both of your longitudinal members. If you have a buddy to help you, it would be best to do both members simutaneously. If not, then skip from one member to the next. After completing the center spot, move about three feet toward the end and do another spot. Then move about three feet on the other side of the center spot and do another. Keep working toward the each end like so.
If by the time you reach the ends and there is still some bow left, you can shrink more spaces as needed in between the ones already done.
Do both longitudinal members evenly, or you'll wind up with a twist.
It will help if you turn the trailer upside down and support it on the ends only, so the middle is free to sag in the direction you want it to move. You can even put some weight in the center to help it out.
Anyway, ther are many different methods of fixing your problem. The solution I mentioned is what has worked best, many times, for me.
Good Luck and let us know what worked best for you.
Tim

Goose,
Heat makes metal move. So does cold. Welding on metal magnifies the amount of movement because the bead itself shrinks more than the base metal and makes it bow like a banana, if you weld only on one side. These are facts of life that are unavoidable, to a certain extent. Smart engineering and preventative or counter-affecting technique will minimize detrimental warpage, but sometimes you gotta do what you gotta do. In these cases you finish all welding and or heat input to the point where you know no more warpage will result, then you complete the job by straightening it out. Just like washing a shirt. Washing and drying make it clean but leave it wrinkled, so to complete the job you iron it out. Nothing to get worried about or afraid of, just part of the job.
Of course straightening out your trailer is more difficult than ironing a shirt, but it needs to be done, so just do it. The fact that you are worried about messing it up is good. That wiil keep you concentrated on doing it right instead of going haywire without planning it out first.
Consider trying this first.
Measure the amount of warpage you have and write it down.
Then turn the trailer upside down and support it on the ends so the middle is free to sag. Put something heavy in the middle of the bow if you can.
Then just take your torch and run down the entire length of the bottom side of the bowed tubes, slowly, so that you are dragging along a red hot spot, like Mr. Sherman suggested.
After it's had a chance to cool off completely, turn it back over and measure the amount of warpage now.
If that did not solve the problem, then you know you'll have to force it to straighten out like I mentioned in my last post, or with a mechanical straightener, or even by cutting slots in the tubing and welding them up, or a hundred different ways of going about it.
The fact is that you have put a lot of time, money, and effort into this project. Don't quit now, just jump in there and finish the job.
If you would like to learn more about Flame Straightening, I have a copy of a book called "Flame Straightening Technology For Welders" that I could mail to you. Just post you mailing address.
Good Luck!
Tim