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Little advise on steel fabrication and weight loading


 
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Fri Jan 13, 2012 5:48 pm Reply with quote

Hi all again, been a while since I have been on here.

Can anyone give me a little advise on what I am going to make will take the weight load?. At the rear of my camper I am going to weld a 4x2" 3mm thick steel box section from one side of the chassis rail to the other, I then want to weld 3 of the same 4x2" box section to make a sort of platform to hold a metal storage box, the picture I have made is not the best but you can see what I mean by that.

I want to know if the size of metal box section and arms where they are welded will take a weight of around 80kg?

Thanks for looking and any replies Ian.
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Alarm

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PostPosted: Fri Jan 13, 2012 6:44 pm Reply with quote

The box section should hold that.
My worries would be the chassis, that might not. And the "frame" will want to twist. You have no supports.
Also "prongs" at the back? Not allowed.
Unless you mean the box would overhang the protrusions. Which puts more pressure on the chassis welds.
I assume your not a welder, this is not really DIY and will need to conform to MOT standard I suspect.

So not really viable in its current shape and form.
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trazor

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PostPosted: Fri Jan 13, 2012 7:34 pm Reply with quote

The tube section you are using is overkill, 50 x 50 x 3 m/m RHS is more than adequate.

What matters most is the strength of ALL your welds, and as Alarm has pointed out, is your chassis strong enough to prevent a downward twist.

You may need to brace underneath, to further back on the chassis, if this is possible, with more brackets

I would also add a cross bar , to act as a bumper.
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Burnerman

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PostPosted: Fri Jan 13, 2012 7:43 pm Reply with quote

Maybe you could buy an appropriate towing bracket for your vehicle (minus the tow hitch) and construct your fabrication onto that?
John icon_smile.gif
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Fri Jan 13, 2012 8:09 pm Reply with quote

Hey guys thanks for all the info, I am glad it is overkill on the size of the box section. i am not a welder by trade but can weld as i am welding all the time, maybe some supports and braces is the way forward.

The chassis is from a caravan and is from memory is 4mm thick.

I have put the below picture on, I am now toying with the idea of welding the box section further back along the chassis and adding a support towards the edge of the chassis arms.

Thanks Ian
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Avocet

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PostPosted: Fri Jan 13, 2012 8:23 pm Reply with quote

I'd be very surprised if the caravan chassis is 4mm thick. I'd be quite surprised if it was half that, in fact!

As has been said, the box sections are fine. In fact, if the 80kg is evenly distributed over all 4 of them, it would still be overkill at half the sizes.

Also, as has been said, the main problem (apart from the legality of sticking sharp pointy things facing backwards!) is stopping the crossmember to which they are welded from twisting. Also, if you're going to well your 4mm wall thickness box sections to the face of the corssmember, the overall strength will only be as good as the rectangle of weld trying to shear a rectangular lump out of the face of the crossmember. (so no matter how thick your box sections are, they'll just pull a square hole out of the crossmember).
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Fri Jan 13, 2012 8:43 pm Reply with quote

Hi avocet, there wont be anything sticking out of the rear, as the box I have made from tread plate and angle iron will sit flush to the ends of the 3 supports. So from a safety point of view I know I will be fine.

As for the mm of the chassis its defo not under 3mm. I think it might be actually 3mm, its from a 1985 van.

here is the pics of the chassis and the camper.

Thanks Ian



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Mursal

from Ireland

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PostPosted: Fri Jan 13, 2012 10:58 pm Reply with quote

Might I suggest you bolt the frame onto the chassis. This will allow for movement without the welds cracking and allow you to take the structure off for modification at a later date.
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
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PostPosted: Sun Jan 15, 2012 10:39 am Reply with quote

After going through your suggestions guys I have came up with a new sketch.

As you can see, the cross-member will have say a 6mm steel plate box welded to it which will let the arms from the box support slide into and bolt so I can detach it for storage. Also I am thinking of welding a plate to the ends of the cross-member so it can be bolted to the chassis as suggested ad I have added a support for the box support arms to try and stop the twisting like mentioned

Does this look any better
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Mursal

from Ireland

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PostPosted: Sun Jan 15, 2012 1:28 pm Reply with quote

That looks the business.

If you do decide to sell the design to the military, you could put another cross-member further up the chassis and have the box sliding into both. This would eliminate all fears of bending downwards.

Edit1: Just noticed the support bar that will do exactly the same thing
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Alarm

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PostPosted: Sun Jan 15, 2012 8:25 pm Reply with quote

Looks much better.
Dinky caravan icon_biggrin.gif
Is that frame steel or Ali?
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Tue Jan 17, 2012 10:16 pm Reply with quote

Hi Alarm, the chassis is galvanised steel, the caravan is called a teardrop trailer. It weighs 630 kg unladen and is soon to be about 700kg after I put my frame and box on the back, the reason I am doing this other than the storage side of it is because the wheel/axle is near the back and it 85kg on the tow hitch and I want to get it up a bit to around 60kg.

Ian
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