How would people go about limiting distortion whilst welding this?

[Trevorleach]

Hgv rigid body, approx 8.5mtrs long, I need to weld each cross member to the body chassis rails and also to the side raves (galved!) then it has it come off for shot blasting and painting and refit it, hence why I would like to keep it as straight as possible.
Loads of other stuff to go an as well, lashing rings, moffet pockets, headboard, side guards etc.
All full length cross members are just sitting there, hence why they are all wiggly.

 

[DAPPH]

I'd jack from underneath using a girder as a straight edge on both sides to get them all in line , then do series of quick short tack welds along the top, two on each side wall so you don't get heat distortions .
Then invert and weld the undersides in on go and then reweld up the remainder of the cross members .

London Brick Company mechanics used to set the vehicle chassis on premade strong height stands on a thick floated flat reinforced concrete slab and then load big concrete blocks on the bed to remove twists and bows , using a taught thin high tensile wire to check all were in alignment . Sometimes a twist of four inches was removed and six or more inches of bow .

 

[Trevorleach]

I'd jack from underneath using a girder as a straight edge on both sides to get them all in line , then do series of quick short tack welds along the top, two on each side wall so you don't get heat distortions .
Then invert and weld the undersides in on go and then reweld up the remainder of the cross members .

London Brick Company mechanics used to set the vehicle chassis on premade strong height stands on a thick floated flat reinforced concrete slab and then load big concrete blocks on the bed to remove twists and bows , using a taught thin high tensile wire to check all were in alignment . Sometimes a twist of four inches was removed and six or more inches of bow .

Thank you that is excellent info

 

[Shedendman]

I'd bolt the body rails to the chassis also,i know one thing,there a lot of walking around to do

 

[hotponyshoes]

I'd bolt the body rails to the chassis also,i know one thing,there a lot of walking around to do

That's how I've done horseboxes.
Weld angle brackets to the ends of the outriggers then they can be galvanised.

Drill holes oversize and avdel into place with a wire line attached to either end of the chassis.
When you put the line on the chassis you'll find they are not actually ever stright anyway!

 

[hotponyshoes]

Actually, looking at the photo properly,
Looks like the crossmembers have already been pushed through holes cut into the riser rail.
I'd still make up brackets and avdel both sides of the bracket on after painting alm the sections separate. Seam sealer behind the brackets.

If it was going to weld it you could just weld the inner sides and sealer the outer which would prevent most of the distortion where it mattered.

Or, tack it as-is, flip it, weld all the undersides. Filp back, weld the rest.
Line and a sledge hammer with a block of wood to get them back into place.
Probably quicker to weld them all then 'adjust' after than spend hours walking around a sequence as they will still need some 'adjustment' after welding anyway.

 

[hotponyshoes]

You can buy the bolt-on brackets, about £3 each in smaller quantities I think.

Or, get a length of angle and drill all the holes at once with a stepping template then run it through the saw afterwards.

Edit: Although, if those cross members are a nice snug fit in the holes all you really need to do is stop them moving side to side.
I'd think 4 good tacks on each inside corner (between the rails) would be enough for that, very little distortion, then sealer up around both sides of the holes.

 

[Trevorleach]

You can buy the bolt-on brackets, about £3 each in smaller quantities I think.

Or, get a length of angle and drill all the holes at once with a stepping template then run it through the saw afterwards.

Edit: Although, if those cross members are a nice snug fit in the holes all you really need to do is stop them moving side to side.
I'd think 4 good tacks on each inside corner (between the rails) would be enough for that, very little distortion, then sealer up around both sides of the holes.

Plan is to weld everything, cross members will be welded on vertical sides only to the body chassis, top and bottom left as it, cross members to side raves will be welded both sides, bolted/avdel ones simply are not strong enough in our line of work, as trucks run at max weight most of the time.
We are only going to weld the cross rave sides as that is what all the trailer makers have been doing for years, and I have to assume their stuff is CAD designed, rather than winging it designed which is waht we do!

Last body was bolted/rivets and kind of fell apart, we also have another two bolted riveted ones and they are not faring to well, though in one of theirs defence it is 30 years old!
The 66 plate has the cross raves riveted through angle iron brackets to the body chassis, bloody thing likes to flex and the rivets come loose, had to lift 8 feet of the floor to do an axle A frame bush and whilst in there replaced the rivets.

All the pre fabbed body mounts we have gotten from CBF, used to use them 20 years ago, seem good and very fairly priced.

 

[Hitch]

The holes look pretty central to the PFC,
So as long as you put heat into it evenly you won't have an issue.

It's when things are welded all biased to one side/face it becomes a pain.

I'd have it on trestles.
Weld top and bottom of the same piece straight after each other.
I'd alternate top and bottom first, then it's opposite side.

Move along 5 or 6 then the same again, rather than working along all from one end.

Before you tack it all up, I'd be inclined to stick a packer between the chassis mounting plates and chassis to give some tolerance for paint and to get it on and off without a fight.

Edit, just noticed you're not planning on welding much of it.
Still, spread the heat a bit.
Clamping a spare bit of box along the ends will help keep them level.

 

[Trevorleach]

The holes look pretty central to the PFC,
So as long as you put heat into it evenly you won't have an issue.

It's when things are welded all biased to one side/face it becomes a pain.

I'd have it on trestles.
Weld top and bottom of the same piece straight after each other.
I'd alternate top and bottom first, then it's opposite side.

Move along 5 or 6 then the same again, rather than working along all from one end.

Before you tack it all up, I'd be inclined to stick a packer between the chassis mounting plates and chassis to give some tolerance for paint and to get it on and off without a fight.

Edit, just noticed you're not planning on welding much of it.
Still, spread the heat a bit.
Clamping a spare bit of box along the ends will help keep them level.

I like the idea of welding every 6th one then working my way back the other way, not looking forward to all that kneeling on that steel!

 

[Hitch]

Just spreading the heat out evenly really.
Made a fair few truck bodies over the years.
Get a little wheely stool to sit on perhaps

 

[Trevorleach]

Just spreading the heat out evenly really.
Made a fair few truck bodies over the years.
Get a little wheely stool to sit on perhaps

I have a little wheely stool, best 26 quid I have spent in an age.

 

[Trevorleach]

Slowly taking shape, they keep stopping me to fix the other trucks, which of course needs the pit, which is where I am building the body!

 

[Trevorleach]

Some more done today, getting bored of welding pdq!
Fitted two of the wings, two more to go, then some 6mm plate over the wheel arches, and that will be most of the deck done bare the flooring, then its weld the headboard time, apparently new toolboxes and side guards on their way, guess that means more welding, oh and some sort of fancy detachable winch mount, which would have been handy to have at the start of the job!

 

[Trevorleach]

Bit more done this week, cut side raves to suit wings and the wings are on, that was fun!
4mm steel plate over the wings as there is a 600mm gap between x members over the normal 400mm., these will then be covered by 28mm hard floor boards.
Bit of grinding and flapping, only a bit of flapping as we ran out of flap discs.
So wired up the new leccy mirrors, then sorted out some front light wiring.
Then a nice lady came to audit some paperwork, my did she have a nice bum!

 

[hotponyshoes]

Then a nice lady came to audit some paperwork, my did she have a nice bum!

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Seems like not all of the photos are loading correctly?
Please fix this!!!

 

[Trevorleach]

One of the last jobs before the body went off to the blasters.
Cut out for access to the fuel filler cap, turned out rather neat I thought.