Thread: Welding rhs without distortion

Being a Sprayer of Chicken 5417 [Numberplate Lingo for the Clean minded and Uneducated] :confused:
I'd say tack each and every corner, then tack between and keep on doing a Divide and Conquer.
MIG it if you can.

If you want to keep the 3x2 straight dont weld across the box, you can weld along the edge without too much distortion, but once you weld the box section all is lost.

It will still distort welding along the edge but nowhere near as much.

Unless you plan to clamp the box, and heat treat, then you can get away with it.

Al

Thanks Al, thats what I thought.

Next question
If I put another 3 x 2 on top of the 2 x 2 crosspieces (straight above the first 3 x 2) can I shorten the crosspieces so they only go halfway across the 3 x 2 then weld the ends of the 2 x 2 crosspieces along both the 3 x 2's ?.

I'm making up the rails for a slabbing mill and I need them to stay nice and straight.

I suppose I could bolt the whole lot together and then weld it up.

Originally Posted by echnidna

I suppose I could bolt the whole lot together and then weld it up.

If you bolt and weld, it will still distort.
Dont forget molten metal in the liquid state ie weld, will shrink, as it shrinks so does everything else in contact with it...

Im amazed. All them years ago at Ballarat School of Mines doing a DLI welding course seems to have stuck.

Al

I suppose a combination of bolts at the ends of the 2 x 2's in the centre of the 3 x 2's plus welds only on the corners of the 3 x 2's.

Are you using a mig or stick welder?

stick, don't do enough welding to justify a mig

It wont matter what you use, mig, tig, manual, 3000 degrees molten metal is 3000 degrees, no matter what method you use.

Al

Tack/stitch weld another 3 x 2 rhs(or bigger)on the back side of your rails, this will stay cold while you weld across the rail and stop it distorting while it cools... make sure the welds between rail and support rail are easily accesable with a angle grinder for removal.

Call me silly, but I reckon if you can get an RHS 3X2 to distort, you're either using too thin a gauge of RHS or you're doing something very strange.

Dan

Dan, yer silly.

I've seen that size (and bigger) distorted on structural stuff that was doing what it was supposed to be doing, ie: holding up a building. Not serious twists, but enough to notice it. Usually a little ripple in the surface, but no bends or anything like that. And always an on site add-on.

Only happens what you start whacking bits on with reckless abandon though. Proper flange plates and things don't do much to it.

Bob, does the 2x2 have to sit on top pf the 3x2? If you can butt it into the sides, might have a better chance of keeping it all straight. That, and a porta-power might help.

Just seems to me that sticking it together the way you have shown is asking for trouble. Might be worthwhile asking somewhere to throw one together, depending on what you need as 'straight'.

Or, rethink the thing until you can get it together without too much trouble nor too much twisting. Maybe flange plates on the ends of the cross pieces, a piece of RSJ as the sides, or vice-versa.

In five years of welding RHS (both MIG and ARC) I never had any distortion.

If you use the right thickness of RHS and weld it in the right sequence, you would have to be pouring the amps into it to get it to distort.

Dan

Diesel powered arc, and on site so it was nothing 'professional'.

Seen it a couple of times, usually some kinda bracket tacked onto something to hold guttering or whatever. Nothing special, just a little out of kilter.

With this mill thing, if it had to be straight and true I know I'd blow it with my level of welding. Lots of practise, but I'm no great shakes at it.

I must admit, when a proper welder type did the job at work, you could tell.