Best direction to minimize distortion on corners?

[Trip59]

So I have a project coming up this weekend, finally sourced the metal for it as well as a way to get the metal here (what a PITA that was)

Nearly 200 ft of 1/2" and 3/4" 16ga square stock will be welded up into rectangular shapes around 5'x1'. So essentially a TON of right angles.

Trying to figure out the best way to make up these boxes so I don't distort them and all corners stay at 90*. My initial thought was to cut all ends square, weld them up, then weld caps on the open ends (yes, holes drilled and a vent hole at the very bottom). That seemed like it might be a pain, so I was thinking I'd miter as many as I could. Need to either buy a corner clamp or weld up a jig, BUT, here's the question:

If I miter them, would it be better to weld from the inside corner to the outside corner on the faces, then the corners, or weld the corners then the faces, or weld from the outside to the inside? What would leave me with the least stress and best corner angles? The welds will ALL be ground and filed at the end, so appearance is less of a thing than strength and precise corners.

I do not have a table, this will be done with separate corner jigs and welded up on a concrete backer board for a table (no money for a table yet, though I know that would be the best way to lay this out).

Shape is kind of similar to this, with 3/4" square stock on the outside and 1/2" on the inside

[Jason]

You can use tack welds around the outside to hold it square well you weld it solid.

[Trip59]

Even with tacks, once I put a full pass, won't it melt tacks in and allow shrinkage to distort it?

[geezer]

On something like that ,I would mitre & gap the width of an old hacksaw blade, tack outside and inside 2 each and push weld from the outside towards the inside corner, then grind the tacks down and finish the inside and outside corners, but hey evey guy has his own way of doing things

[Trip59]

Thanks Geezer, that's what I was after. picked up the stock this morning, all couple hundred feet of it, so I'm ready to go this weekend (after the clamp/magnet purchase)

So with that direction, it would pull and try to open it more or close it more? My concern is that one leg of the form is 5' long, I don't want to wind up with a bowing in the middle, or want to minimize it as much as possible

[performance]

Trip
Nice avatar, best one I have seen...makes me dumb my brain.

Go spend 100.00 or so and get a bessey corner vise-clamp. I bought one and it has MORE than paid for itself many, many times over. A quick substitute would be one you could by at HF that is not quite so robust and isn't quite so square. Forget the magnets...They will slip and pull as soon as a little BB's get built up.(and they will). Tack it all up before you weld a single seam. Don't do it all on one side of the frame before you proceed. Its sort of like tightening lug nuts. Also tack as many sides as you can before you weld it up fully...Tack on the top and bottom corners of a seam if you can after you make your first tacks. But make your first tacks in the center, inside of the joints so that if there is a little bit that is off, the joint can be pivoted and moved around. If the tack is on the outside or one corner or the other first, it makes repositioning and correcting draw a much more difficult issue.

Don't consider anything less...You will NEVER be sorry you bought it.

http://www.besseytools.com/pdfs/sale...%20-%20Eng.pdf

[Trip59]

Looks like a heck of a value, I wish I could afford it for this project, but unfortunately, my budget has about $50 left in it max. Are the Hobart ones in the same style better than the HF ones? I can get them for $20 http://www.amazon.com/Hobart-770565-...155978&sr=8-12 I'm not one to turn down an opportunity to buy a quality tool, I just can't afford $93 (Amazon's price) but at the same time, if that's the style to go with, and Hobart's would be better than HF, I have no problem spending a little more.

Thanks for the process guidance, Mark, I'll be posting project pics this weekend.

[performance]

Definitely better than HF...Looks like cast aluminum though. Be careful, and take care of it. Not like the HD cast steel of the Bessey. Work towards getting the real thing when you can.

A helpful hint: Don't overtighten them, good and snug is sufficient. You'll see what I mean. But again, its a no mess, no fuss way or doing it, that will cut your labor time way down.

[geezer]

Thanks Geezer, that's what I was after. picked up the stock this morning, all couple hundred feet of it, so I'm ready to go this weekend (after the clamp/magnet purchase)

So with that direction, it would pull and try to open it more or close it more? My concern is that one leg of the form is 5' long, I don't want to wind up with a bowing in the middle, or want to minimize it as much as possible

You are welcome, the key is to get the gap right so the puddle cools as you go side to side, and it has a place to flow making a nice flat bead, try different gap distances on some scrap and see which gap gives you the least pull/heat required etc. most problems occur when the gap is too small or too wide then you get heat build up and humped up welds or too much heat and pull. Experiment and see what does the job on that thin stuff.

[sschefer]

Geezer got it right. Gap it, tack it, push it. Practice it a couple of times use the cursive E method so you don't stick on an edge too long and burn a hole. Square tube will burn through faster than flat stock of the same thickness. At least it does when I weld it... LOL...

[sportbike]

If you are doing full penetration welds all the way around each joint, I'd start thinking of methods for and gathering the items required to straighten the frames once they are welded. You will likley have some distortion in the tubes that should be able to be tweaked back to straight as required.

Assuming you are using Mig, I'd definately start with the gap as Geezer noted. If you put tacks at each corner of each tube, bridging the gap, it shouldn't shrink much more with the full weld, and the shrinkage should be uniform.

Try to keep your welds symmetric, rather than allowing all of teh shrinkage on one side, then trying to deal with it when you flip.

I'd make up a few test joints with the miters to get the technique down. You can cut and recut apart the miters on the test part time and time again to keep practicing and perfecting the technique.

[I_Love_Plasma]

Geezer got it right. Gap it, tack it, push it. Practice it a couple of times use the cursive E method so you don't stick on an edge too long and burn a hole. Square tube will burn through faster than flat stock of the same thickness. At least it does when I weld it... LOL...

Yeah square tubing holds that super heated air inside, in welding flat all that heat escapes I welded a old broom handle on a 3.5hp briggs for a straight pipe, ended up with a big mess. sounds good though

If you are doing full penetration welds all the way around each joint, I'd start thinking of methods for and gathering the items required to straighten the frames once they are welded. You will likley have some distortion in the tubes that should be able to be tweaked back to straight as required.

Assuming you are using Mig, I'd definately start with the gap as Geezer noted. If you put tacks at each corner of each tube, bridging the gap, it shouldn't shrink much more with the full weld, and the shrinkage should be uniform.

Try to keep your welds symmetric, rather than allowing all of teh shrinkage on one side, then trying to deal with it when you flip.

I'd make up a few test joints with the miters to get the technique down. You can cut and recut apart the miters on the test part time and time again to keep practicing and perfecting the technique.

How much do welds tend to shrink in a percentage? 25-30%? Shrinkage occurs when it is cooling from molten to solid correct?