Just a couple of quick question for those with big brains.

I'm just planning out how I'm going to mount my rollcage into my series, I have read the ARC guidelines etc, although they don't need to apply as I don't plan on using it for anything serious.

What I think I am going to do is have a 5mm plate underneath the chassis, and a 5mm plate above the floor, with some box section between the floor and the chassis as a packer. I was then going to have bolts going from the one plate to the other and probably tube between to stop it crushing.

I was thinking M12 bolts would be big enough, what do you think?

What Tensile Strength would be required?

I can buy threaded M12 bar for £1.35/metre, but it doesn't say what tensile strength it is, would that be sufficient.

The rollcage is just going to be the rear hoop and rear stays, I have decided to ditch the front part as I want to be able to put the roof on and off.

The roll cage is there as I do a bit of light non competitive off roading, so it's there to give a little extra protection should I do something stupid (roof will probably always be on for off-roading) and it's also there to give me a proper seat belt mounting point for seatbelts/harnesses which works if the roof is on or off.

not an expert but I think that the sandwich type fixing you suggest used to be an acceptable means of fixing that has been superceded.

As for threaded bar - no no no. I wouldn't use anything but minimum 8.8 rated bolts, I think the ones on mine are M12

I would say that has all the makings of a horrible bodged lash up

Why go this way ?


I have lost count of the number of people who have said their cage won't be used in anger - then something happens and boy they are glad its done right.

Why not just weld the proper or decent mountings for the cage to bolt to ?

Sorry, not what you want to hear but you need to really think this though

Nige

HI

You have one life, live it!! do not waste it with cheapish or wrongish fabrication

Not very encouraging but safety is not to be taken lightly...

There is actually quite a lot off good treads on rollcages here if you use the search function, I used them my self when I started my build The Kitten"


Kind regards

Ole.

Oh...

I didn't think it was the bad a way of mounting having read the ARC guidlines as they suggest something very similar minus the tube to stop it crushing.

What is the problem with it this way?

I thought with the threaded bar not having a tensile strength it might not be up to the job, the bolts I was looking at are 8.8 Tensile strength, so they should be fine.

I've read loads of threads but hadn't seen anything to say there was anything wrong with this method

Its no so much a poor method as having all sorts of problems getting it right.

For instance, think if your top face of the chassis and bottom face of the chassis are not say 100% flat abnd level both sides
you'll be adjusting the spacers accordingly, then say the plate is sitting on welds and not cleanly on the metal inself,
dogging it all up tight will be when these things show, but lets say its all then OK.

You go off road and just gently kiss a tree or something, not hard not a roll, but "Enough" to move the assembly a bit
as it was on a slightly raised weld bit etc, now things are not so tight anymore....etc etc

It can be done (and has been done) but there are MUCH easier in the long run and safer ways IMHO ?

Nige

HFH your thoughts then on how you would see a suitable mount?

My thought would be an inverted, folded, U shape directly under the floor with the roll bar bolted through it from above trapping the floor between.
The side cheeks of the U are then down either side of the chassis and welded in place. If the distance between the top of the chassis and the floor was more than an inch or so then I would weld plates front and back to close the U into a box. The nuts would need to be made captive before the section is closed up.

Steve

There's a HUGE amount in the tech archive for cage construction, if you read through it will:

a) Give you some inspiration.
b) You will know exactly what is needed to make a cage secure.


*CLICKY*

I wouldn't trust threaded bar, unless you know that is is rated... but why go to the hassle when you can buy rated bolts easily?

HTH

This is the way most people recommend, using a "saddle" on the chassis, as it acts as a spreader plate, and is much easier so weld that just a flat plate, and also there is more places to weld, so it is stronger.

I've read a lot, and that's what brought me to the conclusion that the sandwiched bolt idea seemed the best for me, as it was a. good enough for ARC, b. was completely reversible leaving just the holes for the bolts in the floor and c. looked pretty secure.

I wanted to know if threaded bar was suitable as I didn't know if it was rated or not, it would be slightly easier to do threaded bar as I can buy it per meter and at the moment I'm not 100% sure what length bolts I need. Now that, it has been answered though I will be using 8.8 M12 Bolts.

Thanks for the advice, and keep any suggestions coming, it's all helpful, at the moment I'm still probably going to go with the bolt through method as I think it suits my purposes best.

Having seen some peoples (mine?) attempts at welding in 'difficult' places, I'm tempted to say that a bolted sandwich isn't such a bad idea. After-all, you often see the same construction used in buildings, bridges and other steel structures - so done properly, I doubt it's as bad as many of you are suggesting.

Regular 'studding' or threaded rod is useless. It's made from recycled deck chairs & kit-kat wrappers . You can however buy high tensile studding in whatever grade you like. It's actually not much more expensive than the chocolate variety. I've used quite a lot of it over the years - particularly when I've needed extra-long bolts.

My biggest worry would be the top and bottom plates bending as you tighten the bolts. This can be cured by either using heavier plate - say 10mm or folding a lip on the two edges which lie across the chassis to stiffen it in that plane. These could equally be welded on ribs.

If you are going to make a spacer out of box section - make the tube vertical so the plate on top of the chassis and the plate under the floor act as ends for the tube. Welded all the way round that will give you a plenty strong structure. These can of course be welded on the bench - making the welding much easier and probably better.

It also avoids the potentially contentious issue of welding to the chassis possibly requiring the vehicle to be SVA'd.

Si

Thanks for the input, that is exactly what I was wanting to hear!

I thought to solve the issue of the plates bending when the bolts are tightened that a tube between the plates would do this? It might be hard to get the size exact but with a little trial and error it shouldn't be too bad. The top plate has the floor to act as a bit of a spreader plate (my floor is rather thick as well, it looks to have been replaced). I'd be more worried about the bottom plate.


Another option which has been put to me is U bolts round the chassis, a friend was showing me how they use these on lorries to hold the bodies on, initially in my head I was worried about the chassis crushing on the corners but it doesn't seem to with the lorries. They have a catalogue with a whole variety of sizes.

Any thoughts on using a couple of U bolts on each foot, with the same principle on the top?

I don't like the idea of U bolts much. A plate on the bottom, I think, offers greater strength.

Si