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Rate My Cage Mounts!


SiWhite

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I'm in the process of designing the cage stays which will connect the external cage to the chassis. I need you guys to rip my ideas to shreds so I can make the design as good as possible.

For anyone who isn't familiar with my truck, the cage is a Full External Safety Devices cage, with the hardtop stays shortened to suit the kingcab. Picture is worth a thousand words.....

DSC00164.jpg

First thing for you to rate is my design for the chassis-to-floor mounts. They're standard ARC spec mounts on top of the A Frame mount. I intend to make them from 6mm steel, with the side plate (closest to the outside of the truck) extending down about 3 inches onto the main chassis rail. It'll form a box on top of the chassis filling the gap between chassis and tub floor.

Like this....

Ext1.jpg

Inside is fairly difficult as there are two cage points that need to converge onto one mount through the floor onto the chassis. I intend to have a length of custom-bent 48mm CDS going from each of the mounts on the side of the tub to the main mounts on the floor of the tub. I then intend to reinforce these with secondary lengths of CDS going directly down from the tub-side mounts to a second plate on top of the wheelbox, which will in turn go down to the end of the tubular outrigger.

Int2.jpg

If you guys could tell me what you think about this idea, then I'll be able to crack on and build the thing!

In the fullness of time I'll have diagonals going from each top corner to one of the plates - either the floor or the wheelbox plate. Which'd be better? I think the floor would be stronger but the wheelbox would give more internal loadspace.

If anyone's feeling really keen here's a blank picture that you can scribble on in Paint and post alternative suggestions.

IntMaster.jpg

Thanks in Advance! And sorry about the sizing issues!

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Si,

You mean like this for the A Frame X member mounts,

gallery_269_31_32033.jpg

gallery_269_31_21940.jpg

These aree available from Dave @ QT ;) ......... the oval cutout in them is to fit over a chassis pressing that is present on some vehicles..... but not on mine ...... I will plug weld it ...... in the fullness of time :lol:

They come as in the first pic ....... you just need to profile them to size to fit snugly over the X member.

Ian

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Si,

No idea, as I bought mine with the cage package ……. but I will be speaking to the man tomorrow, so I’ll find out & send you a PM

Looking at your setup, I would be worried that there is no triangulation in the main hoop, if it went over, the chassis mounts would only have a very limited effect :(

To go from the chassis mounts to the outer edge, why not use a piece of pre-bent CDS, rather than make up a complex structure ?

These may be helpful :)

A closeup of the offside mount

med_gallery_269_31_69418.jpg

And the load bay view

med_gallery_269_31_50777.jpg

Ian

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Don't like the look of your second picture Si :( . You're tubes will bend under vertical load and the foot on the box out will go straight through it.

Obviously the ideal route involves straight lines and triangles, but I presume you cannot "modify" the box out beneath the speaker? I presume it would afect the bass reverb! :lol:

Er, sorry, back to the issue in hand:

Sicage.jpg

On the right is what you'd ideally want to achieve but you can't because of the box out. On the left is a vague attempt at getting around the corner whilst maintaining some vertical stiffness The hatched areas are gussets :blink::o welded between the tubes to try and add some bending strength. With the two hoops so close together you could also gusset between the internal braces to try and avoid front-to-back deflection of the braces.

As we are talking about a primary piece of safety equipment, I would like to stress (no pun intended) that I have not carried out any calcs and the layout shown is only an idea. I would councel speaking to a cage specialist, if only for advice.

Hands up who's confused...... :blink::unsure:

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If it is real rollover protection then why not just fit a stock ARC type roll hoop with single diagonal inside the cab. Then a pair of thru the roof mounts (see Les and Jon's thread on cage building) to the exo cage that is protecting the bodywork to provide some for/aft bracing.

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Great guys, keep the ideas coming!

It will have twin diagonals in the fullness of time for complete rollover protection. Would this improve things in picture two?

Bish, presumably a straight bar between the side-of-the-tub and the floor mounts would be ideal? It's not impossible to chop the boxes about...

The thinking behind the mounts on the wheelboxes was to add some vertical strength, with the plate going straight down to the tubular outrigger (itself reinforced for the rockslider). I appreciate that the floor mounts would be far stronger than the wheelbox mounts.

Am I right in thinking that if I could have a bar going straight between the side-of-tub mount and the floor mount, I wouldn't need any further vertical strength in the form of the wheelbox mounts? My original idea was to not deviate massively from the ARC spec main loop, but incorporating the Safety Devices outer cage.

Thanks in advance again!

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Simon,

I am not 100% sure of the cage you have, but if its like to other SD cages thaey are "Split" between the top + Outside of the LR and the "Inside & Below"

These 2 inners and outer unit "Bolt" together with I think 4 bolts - and IMHO there is your main serious problem.

Whilst both BBC (Ian Gs) cage mounts, mine, and Jon Ws, and others are all being similar in design / nature / sterength with most being made around 6mm plate, welded etc, the real difference is the 'single hoop design from floor to roof, welded to the plates.

With the SD cage, it is almost irrelevent the mounts to the chassis as the weak point will alwys be the 'join' on the outside of inner and outer, plus the tube on many SD cages I have seen is 44mm cds and thin wall too.............

Think of any cage, ..................then imagine the LR (or what ever vehicle) .............is "Picked up" say 15 -20 ft, .............turned upside down ................................and then dropped.....

When it lands the impact, weight, and forces 'travel' through the cage and body, .............and those 4 bolt mounts innner / outer are IMHO the "Shear" point ..............and weak spot..............

The base mounts whilst important cannot overcome this problem.....

I may be wrong as I said................. I am uncertain of your cage and dewign and have gone from memory of the many I have seen and modified, .................maybe either shout me down......... or post some more pics ?

Nige

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Nige - correct, it's a SD bolt together cage. I like the design and appearance of the cage but appreciate there are weaknesses in the bolt together-ness.

I appreciate what you are thinking about with the bolts shearing, but the top of the cage is held on by 28 8.8 7/16 bolts. They'll not all recieve the same shear strain in a roll but I'd imagine the forces to be pretty massive.

Seems to me that a better idea (as proposed by you guys) may be to have an internal hoop (like an ARC-spec loop) made from CDS and have that inside the body with diagonals and rear stays as normal, and then braced to the SD cage through the body. The SD cage would then act mainly as body protection and tree sliders, with the internal hoop doing all the rollover protection. I could then brace the SD cage all I liked to prevent it being deformed in a roll, but the internal hoop would do the vast majority of the rollover protection.

The more I think about it the more I like this idea. Thanks guys, keep any further suggestions coming!

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I'm in partial agreement with nigel, however, a flexible structure (flexible joints connected by rigid bars) can achieve higher strength than a rigid one as a rigid one concentrates forces at fewer intersections than a flexible one. The flexi structure can distribute the forces to more than one vertex. It is also more likely to put the individual bars in straight tension or compression rather than torsion or shear.

I would guess at the bolt together joints being more flexible than a welded joint. Thus the calculation of the deformation of the cage in an impact may not be as simple as the shear strength of the bolts in one plate if it takes the brunt of the impact.

I would be inclined to change the design of the B post mounts to a single (straight) diagonal from each down to the top or side of the chassis. This is a lot simpler than what you have drawn (although you will have to drill a big hole through the seat box through which to pass the tube). It will also be stronger than what you have drawn. You can increase the strength by adding a tie bar across the width of the vehicle between the top of the diagonals. Under most if not all circumstances this will be in tension and need not be at all heavy.

Probably only worth putting such a tie-bar on one of the two B post hoops as they are pretty close together.

This is how my C post hoop works, but without the tie bar. Not too bothered if that bit gets a bit squashed!

Best bet for trying such things is to build a model from flexi-straws held together with hot glue. You can quickly see where the weak points are by pressing on different intersections.

I'll see if I can draw it tomorrow when I'm more awake.

Si

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I would be inclined to change the design of the B post mounts to a single (straight) diagonal from each down to the top or side of the chassis. This is a lot simpler than what you have drawn (although you will have to drill a big hole through the seat box through which to pass the tube). It will also be stronger than what you have drawn. You can increase the strength by adding a tie bar across the width of the vehicle between the top of the diagonals. Under most if not all circumstances this will be in tension and need not be at all heavy.

This is what I was trying to present (I think :blink: ) in the right hand side of my sketch. However, I think the best suggestion so far is to put in a standard hoop with double cross bracing. I somehow managed to miss that post on my first read through... :o

It is proven and should be relatively easy if you are happy to chop the box out about. You'd just have to sort out mounting brackets to connect it through the side of the vehicle to the external cage.

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lose that ally box, the rest is cake! B)

you need triangulation though, not only in the main hoop, but also to the crossmember.

You might think it aint that bad, and I wont need that cage really, Which is what I thought untill.....

Anyway, show us the endresult.

Daan

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Si, I think the easiest approck is probably the internal hoop which is connected to the outside SD bars (proably the neatest way is to link them where they bolt through the body and, later, somewhere towards the top of the vehicle).

The only other issue I see with your cage is the rear stays. At the moment they only go the the top of the rear of the tub. This means that the cage may well just fold backwards in a roll. If I were you I'd get some stays going from the top of the SD cage going down to the top of the rear x member either side of the tailgate at the same time. The spare tyre should still go in OK I guess..... The worst case scenario is you'd have to lower some of the 'floor' ;) of the tub but I guess that isn't a massive issue.

Nige, interestingly, when I do the cage for the trayback I'm going to have all the chassis mounts welded on and then a complete external cage bolted onto the mounts through the body. That way if I want to remove the cage there's no body work to come off and just bolts to undo. With either 9 or 10 bolt ponts each with 4 bolts I don't think it will shear in a hurry.

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one horizontal bar between the two stays where they join the body (inside),

two diagnols inside from top down to the proposed floor/chassis mounts.

two rear stays from the top of the external cage to the rear of the load tray,

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