Joining sheet steel?

[wortgames]

Hi all, I'm replacing the rusted out parts of a trailer floor (~2-3mm checkerplate).

I need some advice on the best way to engineer the joins. If I run into a lack of skill on my part I'll be taking the half-finished job to a pro, so I don't want to commit to a really fiddly (ie costly) approach!

Options are:

1. Simply overlap the existing plate by a few mm all round.

Pros: Sounds easy. Not too much 'permanent' welding of the new sheet to the trailer chassis. Existing sheet supports the new sheet. Minimal added weight. No critical alignment required. Can be tacked in place and then just siliconed/bogged and painted over if it comes to it.

Cons: Is it as easy as it sounds? I guess the checkerplate texture would need to be ground off the join margin of the underlying piece for a close fit.

2. Unsupported butt welds (starting at the chassis members, then tacking along the unsupported sections (~400mm) in between.

Pros: Seems the 'neatest' way to graft in the replacement sheet.
Cons: Potential for horror. My sheet welding skill is untested. Considerable accuracy required in the cutting stage.

3. Supported butt welds (welding in extra SHS between chassis members, then welding the new and old sheet edges to that).

Pros: Seems strong and tolerant of average skills
Cons: Extra work and weight. Significant welding of sheet to chassis structure will make it a nightmare to remove in the future.


Any recommendations?!

 

[steveo3002]

overlap and seal the seams afterwards is what id go for

 

[Bill Edwards]

Rather than worry about whether you are capable of the welding, why don't you have a play on the same thickness metal first so you know your capability?

 

[wortgames]

Thanks for the quick replies!

why don't you have a play on the same thickness metal first

I've done a bit of that, but I'm amazed at my own ability to do two identical welds and get two entirely different results!

I thought I should start by seeing if there's already a recommended approach to this kind of task.

I'm leaning towards the overlap solution, but a bit worried about sealing all the little rust access points underneath.

 

[rikrobson]

what size is the trailer? and what size sheets are you going to use?

 

[Bill Edwards]

Well if you overlap it's essential to seal it all from underneath - though to be honest, I'm not sure it's actually possible to do this effectively. I can't think of many jobs where overlapping, rather than cutting and butting, is considered anything other than a quick job - e.g to get a car through an MOT or two before it's scrapped.

 

[wortgames]

It's a tandem trailer that's 3750 x 2000. The front 750 is now gone to a mower compartment, leaving about 3000 x 2000 of floor, and 3000 x 300 side walls (x2). I got some new sides folded up that are 3000 x 300 high and 300 wide, and I've cut out the corresponding parts of the original sheet. So long story short there remains a 3000 x 1400 strip of good original floor and I have 6 metres of seam to weld.

It turns out that the steel supplier cut my new sections about 5mm oversize, so right now they overlap the old steel slightly anyway. It was done at mate's rates so I don't want to ask him to redo them (I don't know if they will still fit in his guillotine).

 

[T0rnado69]

what about butting the sheets together and putting a strip over the joint underneath.
that will keep the sheets flush ontop,
and the strip underneath can be used to join the sheets together better then just a butt weld.

 

[wortgames]

what about butting the sheets together and putting a strip over the joint underneath

This could work! I could use a bottle jack and a length of SHS to prop it up during the weld to lift out any sag in the old steel and give me a firm backing to weld to.

However, it does mean removing 6000mm x 5mm of oversize checkerplate...

 

[T0rnado69]

ouch make sure you have your weetabix

 

[mechman]

what about butting the sheets together and putting a strip over the joint underneath.
that will keep the sheets flush ontop,
and the strip underneath can be used to join the sheets together better then just a butt weld.

Good idea tornado, think the method is called a Butt Strap.

 

[wortgames]

I think I may have devised a technique that won't require jacking and fiddling underneath. Ever assemble an old Scalextric track?!

Basically I'm thinking of laying the new section in place over the existing sheet, and tucking the pieces of strap between the two. Then I go along and tack all the straps onto the new sheet, forming a series of tabs that miss the chassis rails. Then I can lift the new section and 'hook' the tabs under the old sheet.

What do you think?! Still means an awful lot of grinding though...

 

[Kent]

2-3 mm? You know it's going to distort if you don't take proper measures if you continuous butt or lap weld it
The rest depends on your skill level impossible to say as suggested already you need to run a test or two