Newbie problem

[bootzey]

Hi. I'm not sure if this is the right place as I'm using a stick welder bit here's my problem...

I'm trying to weld a 5mm x 80mm x 2000mm length of flat into a 2200mm 3mm x 88.9 tube with the intention of opening up the tube with 50mm wide channel. Hoping that the flat will help the tube retain its structure.

I've tried a couple of times but end up with the tube bowing probably as a result of too much heat and the fact each end of the tube is supported on axle stands.

I'm putting the flat in the tube then packing it so it's tight against the inside. Then grind away a slot about 3 inches long to expose the edge of flat and then weld it up.

Then after this is done about 8/9 times either side I open up 6inch sections and further weld inside and then fully open the tube up along its length.

But I'm getting warping and movement. When I cut the opening out the edges aren't straight

Do you think this is the correct way to do it please?

Should cut smaller slots across the edges of the flat?

I'm prototyping something, not at all trained in welding or anything to with metal working/engineering.

Many thanks in advance.

Dave

 

[Kent]

Well from a written description I am fairly clueless - a drawing will be better

Welding such a material continously along its length will distort it - there are ways of mitigating this but I don't understand exactly what you're trying to do without drawings

5 mm flat edge on to 3 mm Round tube with a stick plant is not easy. The angle of dangle makes it a tough job even for well practiced hands. Lacking that practice it's likely a step too far for now with the gear your using

 

[AdrianH]

It sounds a bit like a type of large keyway in round tube using the internal flat bar to help keep the shape, but I would say the only real way to go is to use solid bar and mill.

I can never remember if internal or external but I will assume external 3.5" tube 10's gauge.

Instead of flat bar how about drilling a batch of holes through the diagonal and countersinking them, say you use 5mm holes and some 5mm round bar, then weld in round bar, space the holes at say 100mm ( 4") and then use a flap disc or grinder to hide weld. That would put a lot less heat into it then trying to do a continuous weld.

It all depends on what you are trying to do as an end result, how rigid you need the thing. But I would suggest that using tube as soon as you open up a face it will always deform as the tension is then off the tube and it will bow away from the open face.



Adrian

The above are just my interpretation of what he is trying to do?

 

[pedrobedro]

It sounds very complicated. Could you find a piece of round bar that will fit inside it and plug weld it through holes then do the shaping.
edit:- Just read Adrians post and same idea.

 

[bootzey]

Whoa...a drawing! Brilliant! Cheers Adrian. Thanks for taking the trouble.

Drawing is spot on for what I'm aiming to do with 2.2 metre lengths of 88.9mm x 3mm wall tube and 80mm x 5mm flat.

I've had success with 1 metre lengths and the opening opposite the one in the drawing. With no distortion. But the longer lengths are proving difficult.

Both spaces either side of the flat are to be used so have to be kept clear.

I've been told today that I had it set up wrong. Lifting it up off the floor with axle stands at either end meant there was a hell of a lot of unsupported weight in the middle...Guess where the first welds were...yep, in the middle. I also made the welds too long at 2 inches and probably did too many welds at a time so latent heat built up.

New tube and flat arriving tomorrow. So I'm going to try with much smaller slots to expose the edge of the flat and build each weld with 3 passes rather than one long pass. And it'll be on the floor.

The local scrappy loves me at the moment lol

Thanks again and to petrobedro and Kent.