Advice Needed To Prevent Warping

[bigyellowplane]

I am in the middle of building a workbench and I'm having a problem with the legs warping slightly as I weld in a crossmember. I attached a photo of the legs that I'm building so you have an idea of what I'm talking about. The lower crossmember is 9'' above the bottom of the legs so when I go to weld it in it gets hot enough that the leg begins to bend in 1/16''-1/8''. I've tried to point the gun towards the crossmember more than the leg to try and direct the heat more towards it. I also only weld one side at a time and let it stand for 10 minutes before welding another just to let it cool off.

Are there other techniques that I should be aware of to help with this problem? Any advice is greatly appreciated.

[OscarJr]

Are you tacking in all 4 corners of the cross-member? How thick is the steel? How many amps are you using? How do you know you are using a correct arc length?

[bigyellowplane]

I have it tacked in 2 of the 4 corners and the metal is 2'' x 2'' square tubing and it's 1/8'' thick. I have my miller welder set to weld 1/8'' metal but I can turn it down, something I have not thought about. And I'm not sure if I'm using the correct arc length... Can you clarify?

[OscarJr]

Hmm I thought you were using TIG since the pic doesn't show the welds close-up, but it looks like you're using MIG. Personally, when doing 2x2" sq tubing 1/8" thick, I tack all 4 corners. Make sure the fit-up is zero-gap if you can for the next piece. It will minimize warping/pulling. Nevermind the arc-length if you're not using TIG. Just keep the stick-out to 1/2" or just a smidge less.

[ryanjones2150]

Clamp that stuff down if you can. The warpage is a product of total heat input which has more to do with travel speed that amperage. <br />
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Good tacks. When that weld solidifies, those stresses can be extreme and the piece will move. <br />
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The sequencing of your welds can also help, but I don't think it will be much help with your joint types in the picture. Anytime you weld something things are going to expand and twist and make you crazy, so clamp that sucker down solid anyway you can, that will help minimize that movement.

[Olivero]

Like Ryanjones said, clamp it down as much as you can and tack it really well, every side on every seam. I have had tacks split when you start welding and then it warps, but if you tack it well and clamp it, you should be fine.

Also just weld a bit at a time, don't do all the seams on the square at the same time, do one seam on the right leg, then do one seam on the left leg, etc. That way your heat input is limited. I have had 3/8" flat bar warp from me doing too many welds on it in one go. Keep the heat input limited, tack well and clamp like ****, that should do it.

[gnforge]

Warping or pulling of metal comes from the cooling i.e. Metal contracts as it cools. It expands as it is heated then it contracts as it cools. The problem is it expands in the easiest direction it can but contracts more even so you get distortion or simply warping. <br />
Try this take 2" piece of 1" round stock place longways in vice & tighten. Heat red hot let cool. It will drop out as it cools, why? as it expands the vice won't let it expand long ways so it expands sideways or swells but as it cools it contracts in all directions i.e. Now becomes shorter & drops out of vice. Now take 1/4"x2"X 12" long bar stock or round stock, put in vice so sticking up in air, no restrictions. Quickly heat 1" area in center red hot from side only. Watch bar bend away from heat then return as cools but will return or contract farther as completely cools, now bent a little toward the side you applied heat to. Why? The metal acts as the vice did and restricts expansion longways so it expands more sideways than long way but again contracts more even so pulls metal back longways More than it expanded, now warped or bent toward side you heated. As you learn and more understand this you can learn how to straighten metal by heating. Getting to a lost art or craft. <br />
Now as for welding same applies but now you are adding very hot metal and it has to contract as it cools so it will pull the metal. <br />
As you weld and the longer you weld you will learn how to control or actually pre guess the contraction and adjust your welding to get the finale result you want. <br />
Like others said lots of tacks and good hold down but you will learn you can't always hold it so learn how to control it. <br />
Even a tack will pull, so pre plan your tacks then measure & check square, plan and weld as needed to keep square i.e. Use contraction to get the result you want. <br />
With that said, the type of weld, the direction of weld, metal thickness, metal temp. number of passes, fit of joint, pre heat, inter pass heat, etc etc etc. all affect the contraction of metal as it cools. So it is a life time of learning. That's why some become masters of there craft i.e. Master welders, fabricators etc and some are just welders. There is something to learn each day if we're willing. Hope it helps & God Bless <br />
Greg

[aametalmaster]

I learned 30+ years ago how to correct things that were welded. Welding is only a fraction of the fix. Making it perfect after welding is the hardest part...Bob

[ryanjones2150]

See all the great info here? As I've said before, anyone can learn the big things in a job, it's all the little things you learn as you go that make you good at it.

[MMW]

If the legs are pulling in towards each other then cut a pc. that is a tight fit at the open end & tack it in before welding. After welded & cooled, remove it.

Straightening after the fact you can heat the tube on the opposite side of the weld to pull it back. This is somewhat of an art as to how much heat to use.

Clamping it down to your table may also work.

You can also use a jack to bend it back straight.

[bigyellowplane]

Thank you for all the great info and tips! I've got some things to try out now...

[wagin]

All the information offered is creditable.....But the bottom line is , if you weld tubing at right angles to the face of tubing it will warp, pull the tubing in. Fit up your cross members and weld the side joints only, do not weld across the face. This is the only way to prevent warping in said joint.

[Oldgrandad]

You can minimize the warp by welding from the bottom (open end) to the top, front and back (butt welds) then do the filet weld on the top only. By doing this all your shrinkage will be at the top of the cross member and pull the bottom in very little. If you also clamp it tight and let cool before unclamping you should be good. tacking a spacer at the bottom is another good way to hold your part straight.

[digr]

No need to weld the bottom, problem solved