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Roll cage bracket fabrication thoughts


Maverik

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So I'm putting a 2nd hand cage in my 90.

All the brackets apart from the main A frame are bolted in, with the a hoop needing brackets welded to the middle-aft chassis cross member, as per this photos

2577.1316000903.jpg.8e50920c934c3b7bbaef18d27aa79c45.jpg

So I've got the brackets, but I'm a little put out at the thought of having to weld to my galvy chassis.

So i was knocking a few ideas around  and came up with the below (green bracket).

It extends down to the body mounting tube, as it put a bit of a leaver arm on the internal bolts (two M10 bolts fasten the red frame through the floor to the bracket).

So i upgrafe those to a higher tensile bolt and come up with a clamp mechanism.

SnipImage.JPG.e2664d65dbb5912308f6796092809bdb.JPG

Looked at just replacing the plug welds with bolts but I cant get that to work on the chassis. 

I also need to come up with a suitable method for bolting into the green bracket... but anyone got anything I've potentially missed? I reckon i could make it work as the original intended.

Mav

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The body mount tube doesn't look that big compared to the thickness of a roll cage, would it be strong enough? 

Could you make a clamp that goes around the chassis? A 1/2" plate either side with bolts to pinch it to the chassis? It could extend out to touch against the body mount tube at the front and the shock mount or body mount (can't quite make out what's there) behind to ensure it can't slide. I don't think it would crush the chassis but you'd have to keep checking it doesn't come loose with vibration. 

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So assumptions.

Load going onto the bracket will be vertical down through the floor, so the original bracket plug welds are going to be loaded in shear. assuming plug weld size to be about 15mm Diameter x2 you get 352mm2 of shear material.

Assuming the outrigger in 45mm Diamter and 3mm thick you get 205mm2 shear material.

Outrigger tube could be lacking - I do however have rock slide sills installed which have a tube which engages down the middle of the outrigger bulking it up.

The brackets that are supplied from safety devices dont seem to exceed 2.5-3mm much skinnier than I certainly imagine they should be, but you have to keep in mind what they're designed to do.

Also something to take into account, I Installed a 3mm thick rear floor over the standard 2mm.

Clamp idea would work but its pretty industrial and not all that elegant 😋

Need to check the actual outrigger dimensions properly.

The forces the bracket need to cope with I should imagine aren't that huge in relative terms, considering it to be within the realms of survive-ability, I think the most stringent (from googling) loads seat belt anchors need to cope with is 13.5 kN.

 

 

 

 

 

 

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Have a look at some pictures of the bolt in cage from Safety Devices, they have a clamp assembly which goes round that tubular outrigger.

Your bracket solution looks pretty neat to me, just might want something rearward too, maybe to the shock mount holes to stop it trying to rotate backwards?

@discomikey will have some good ideas... but he's quite busy with a new business venture at the moment.

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PITA these galvy chassis :P

I think your solution looks ok. It's a tricky place to bracket.

Not of any use to you at all, but these are my cage mounts. 'Heavy' tube onto 5mm box section at the front (in place of the standard tubular outrigger).

DSC_1700.JPG.de0c84937465c2788631a57668629056.JPGDSC_1701.JPG.557319e61471d20c29bf3cd853117db1.JPG

 

Edited by daveturnbull
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No, I've certainly never been described as elegant :hysterical:

I'm suprised the roll cage company only want a plug weld, it's only really the perimeter of the hole that's doing the sticking, the middle is just a lump of weld and the outer is 2 plates with no connection, must know what they're doing though which is more than can be said for me ;)

A seatbelt has to hold a 100kg person against a dead stop, your cage might have to hold a 2500kg truck depending on exactly what it is. I guess it depends what you do, is the worst your likely to do be put it on its side at 5mph? In which case that hoop will be trying to slide along the tube and pull up from it rather than down? 

Are you planning to do any competitions? If you want a ticket on it then I would check the book or ask someone that does scrutineering? 

Is the body rigidly mounted to the chassis or are there rubber body mounts? 

Edited by Cynic-al
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Its a Safety devices cage, quite an old one too by the serial number.

I actually got a picture of one that was bolted by what looks to be x2 M8 bolts, but as this is a Richards chassis the flanges on the cross-member aren't quite the standard shape so there isn't room to drill and bolt.

 I did some calcs for seatbelt mounts once and worked out you could exert a force close to 5t on a seat belt system  of course dependant on body weight and accelerations (and it being a worse case scenario).

Cage might have to support 2.5t but its also spread over multiple points imho I still think its within similar realms as seat belt stuff - also looking at seatbelt brackets compared to roll cage bracketry there's not a lot in it.

I've not put in on my sketch, but I was planning on retraining the bracket to the outrigger using some U bolts or such like (sorry should have said that at the beginning 🙃)

Regarding competition... I'll say I'm not planning on doing any but... I don't like to shut doors :)

Standard defender rear body mounting, no rubbers.

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1 hour ago, landroversforever said:

Have a look at some pictures of the bolt in cage from Safety Devices, they have a clamp assembly which goes round that tubular outrigger.

Your bracket solution looks pretty neat to me, just might want something rearward too, maybe to the shock mount holes to stop it trying to rotate backwards?

@discomikey will have some good ideas... but he's quite busy with a new business venture at the moment.

Ross - I think thats where I got the idea from, but I couldn't for the life of me find a reference picture of where I'd seen it?

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Hi Mav 

You can buy bolt on brackets, but i looked into this for my safety devices internal hoop, which currently doesn't have any brackets fitted but they were going to work out horrendously expensive IMHO for 2 pieces of metal (£182). So if you are making some I would happily pay you if you wanted to make a second set or get a couple of sets cut. My roll bar is the safety devices LO33a which looks very similar to the internal bar you have.

Wishing I had speced roll cage mounts on my Richards Chassis but wasn't sure if they would line up

Thanks 

 

Jon 

 

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10 hours ago, Maverik said:

So assumptions.

Load going onto the bracket will be vertical down through the floor, so the original bracket plug welds are going to be loaded in shear. assuming plug weld size to be about 15mm Diameter x2 you get 352mm2 of shear material.

Assuming the outrigger in 45mm Diamter and 3mm thick you get 205mm2 shear material.

Outrigger tube could be lacking - I do however have rock slide sills installed which have a tube which engages down the middle of the outrigger bulking it up.

The brackets that are supplied from safety devices dont seem to exceed 2.5-3mm much skinnier than I certainly imagine they should be, but you have to keep in mind what they're designed to do.

Also something to take into account, I Installed a 3mm thick rear floor over the standard 2mm.

Clamp idea would work but its pretty industrial and not all that elegant 😋

Need to check the actual outrigger dimensions properly.

The forces the bracket need to cope with I should imagine aren't that huge in relative terms, considering it to be within the realms of survive-ability, I think the most stringent (from googling) loads seat belt anchors need to cope with is 13.5 kN.

 

 

 

 

 

 

The tubular outrigger may have a fair amount of cross sectional area but the loads won't work in shear, more bending. 

 

It entirely depends on what you intend to use your cage for. 

If you want a bit of protection in case of an on road accident, then in the event of said accident, if the chassis outriggers were to deform a bit but don't break off or bend too much (disclaimer - it still needs thinking about) then they have done their job, you walk away and the car is scrap. 

If you are intending on competition use, then this probably isn't good enough.

You'll also have to factor in the fatigue loads that will transfer through the cage into the outriggers from elsewhere, mainly seen in hard driving conditions. 

I think the idea has mileage though. Bolted joints are often good because you know an 8.8 bolt of X diameter is good for Y load in Z loading condition. Welding is harder to gauge. 

Thinking outside the box though! I like it

 

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10 hours ago, discomikey said:

The tubular outrigger may have a fair amount of cross sectional area but the loads won't work in shear, more bending. 

 

It entirely depends on what you intend to use your cage for. 

If you want a bit of protection in case of an on road accident, then in the event of said accident, if the chassis outriggers were to deform a bit but don't break off or bend too much (disclaimer - it still needs thinking about) then they have done their job, you walk away and the car is scrap. 

If you are intending on competition use, then this probably isn't good enough.

You'll also have to factor in the fatigue loads that will transfer through the cage into the outriggers from elsewhere, mainly seen in hard driving conditions. 

I think the idea has mileage though. Bolted joints are often good because you know an 8.8 bolt of X diameter is good for Y load in Z loading condition. Welding is harder to gauge. 

Thinking outside the box though! I like it

 

Roll cage I'd more class it as "expedition" use - no big competition melark I'm not going to want to trash this one if I can help it. - but I dont want to rule out potentially doing an odd novice offroad competition of some kinda.

Maybe a bit of an over simplification to just say the bracket will just see shear loading - to clarify my assumptions, considering how the other end of the outrigger is fixed (onto the body/sill and rock slide) and the proximity of my green bracket to the outrigger to chassis weld I think bending loading would be minimised.

The way the main hoop is support mostly by the internal tub body I would doubt that any fatigue issue would arise -  you're on the money with your comment about walking away. The bolt in safety devices cages I've seen always look like they've got the "once use" type of lifespan associated with them - like I mentioned before I was really surprised by the lightness of the bracketry for them in general, if its more full on competition use I'd certainly be looking more at for fully welded cages and fittings.

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I have 2 vehicles caged with what I call "use once and replace" and that is what this is what I'd call the one you're working on

They'll do the job most of the time, will increase the chance of survival and then need replacing.

Competition cages need to do their job over and over again so their design and construction is different, as it their intended use..

Very interesting post this

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