[scorpydude]

Just some questions before i start designing a roll bar...

What diameter should be sufficient for a SWB tintop internal roll bar?

Would 60cm be an appropriate size for the 45degree gusset / brace pieces between the top horizontal piece and the vertical size pieces?

Does a rollbar secure to the chassis or just the body via the floor (at the feet of the bar) and the wheel arches (at the angled pieces feet)?

Do you sandwich the body / wheel arch sheet metal between two big flat pieces of plate to bolt it on? (So you would have a piece of plate inside the wheel arch that bolts would go through, then through the wheel arch, then into the plate attached to the rollbar?

What is the easiest way to cut angled semi-circles at the end of pipe (for another perpendicular pipe to sit into?)

Cheers

[Zook_Fan]

scorpydude wrote:

What diameter should be sufficient for a SWB tintop internal roll bar?

Use 1.75" tube for the main hoop at the b pillar, then 1.5" tube for everything else. Remember, tube not pipe.

scorpydude wrote:

Would 60cm be an appropriate size for the 45degree gusset / brace pieces between the top horizontal piece and the vertical size pieces?

What do you mean by this? Slightly confused where you intend on putting a gusset?

scorpydude wrote:

Does a rollbar secure to the chassis or just the body via the floor (at the feet of the bar) and the wheel arches (at the angled pieces feet)?

Yes. It securse to the body. You can also run the tubes through the floor and connect with the chassis but is not common practice. Alternatively you can link the bottom sandwich plate to the chassis to give extra strength.

scorpydude wrote:

Do you sandwich the body / wheel arch sheet metal between two big flat pieces of plate to bolt it on? (So you would have a piece of plate inside the wheel arch that bolts would go through, then through the wheel arch, then into the plate attached to the rollbar?

Yep. The plates do not need to be all that big either. 100 x 100 x 3mm is all that is needed for vehicles over 1150kg in most standards governing roll cages.

scorpydude wrote:

What is the easiest way to cut angled semi-circles at the end of pipe (for another perpendicular pipe to sit into?)

The easiest way is to get a tube notcher. A cheaper way is to cut a V in the end of the tube with a grinder and the grind it smooth to fit nicely on the other tube. Just remember you don't want to be filling up big voids with weld on a cage.

scorpydude wrote:

Cheers

[tanshi]

i used ccda spec tube for mine, simple google should taqke you to their site for spec.

you can also use steam pipe if you just wana a cheep one. its around 48mm NB from memory.

not sure what you mean by 60cm braces...

in the cars we have put roll bars in we have just sandwich plated the body metal with 5mm plate.

damo has a tube notcher which i recently borrowed for notching tube recesses.

[Bruce]

Is someone going hardcore now

[Gwagensteve]

Beaten whilst I was typing this. Oh well, here's my input.

1.75" OD Gr350 CDS is what I'd recommend for cage construction. It is possible to use 32NB Schedule pipe, it's cheaper, but it's heavier and isn't intended for structural applications.

I assume you mean the diagonal bars running from the top of the main hoop down towards the rear of the car? If so, No, 600mm isn't long enough. The higher up the main hoop they are the better, likewise, the further towards the rear of the car the better.

Foot plates would generally be 100X100mm at the body.

Attaching a roll bar to the chassis makes its construction much harder. It is a much stronger method of construction, but look at your use. A chassis mounted cage would really be used where the car was frequently being rolled, like a hardcore open comp type car. If it's there for the "I hope it never happens" accident (like Jazzors) then the car is going to be totalled regardless - I can't see the point of chassis mounting - it will compromise the car with lots of squeaks and creaks and take twice as long to build.

If you attach only to the body it's best to use sandwich plates, although lots of "roll bars" use washers on the underside only. If you use a sandwich plate to back up the foot plate, make sure it is a significantly different size to the foot plate so it doesn't act like a punch and chop through the body. with a body mounted cage only, I'd also try to mount in two planes so make the cage more secure.

You will also make the cage much, much stronger with a diagonal cross brace across the main hoop.

You can cut fishmouths (that's the term for the contoured cut of tube onto tube) with a grinder or chop saw, but you get the best result with a tube notcher. Speedwerx or JD2
(through OPW) are sources for these.

Here's a pic of a cage I made quite a few years ago. It was chassis mounted and very strong (but was never rolled on!)



Steve.

[madmacca]

scorpydude wrote:

Just some questions before i start designing a roll bar...

What diameter should be sufficient for a SWB tintop internal roll bar? depends are you putting the cage in so you can compete in an event ? if so ccda cage specs are here
http://www.ccda4wd.com.au/images/Rollov ... 060428.pdf

Would 60cm be an appropriate size for the 45degree gusset / brace pieces between the top horizontal piece and the vertical size pieces?

Does a rollbar secure to the chassis or just the body via the floor (at the feet of the bar) and the wheel arches (at the angled pieces feet)?Can bolt with a backing plate or weld to body floor see above link for specs

Do you sandwich the body / wheel arch sheet metal between two big flat pieces of plate to bolt it on? (So you would have a piece of plate inside the wheel arch that bolts would go through, then through the wheel arch, then into the plate attached to the rollbar?
yes again specs in link
What is the easiest way to cut angled semi-circles at the end of pipe (for another perpendicular pipe to sit into?)a pipe notcher is best or angle grinder I used a pipe master tool which helped

Cheers

[royce]

Gwagensteve wrote:

1.75" OD Gr350 CDS is what I'd recommend for cage construction. It is possible to use 32NB Schedule pipe, it's cheaper, but it's heavier and isn't intended for structural applications.

I agree with the toob its the right size for comps and dies are available for the decent bender youll need, however plenty of pipe is available in 350mpa Yield as a CDW style of thing, and certified to AS1163 (Structural hollow sections) be careful the the rules for the comp you want to run if it requires this and therefore the amterial you buy (if cold drawn seamless is certified to this)

/nit picking on pipe threads

[Gwagensteve]

Agreed Royce.

Steve.

[scorpydude]

Bruce: Perhaps (Just making sure things are safe before I try the scary {to me} stuff)

Thanks very much guys for the very helpful information !

Reguarding the 60cm braces that I didnt explain very well...



I had initially planned to use larger 45deg braces about 60cm long (red in image) but I can see from the feedback above that I would be better off going a complete cross brace (green in image above) with smaller gussets like in Gwagensteve's picture (10cm) in the corners.

Where is the best place on the bar to cut and add bolt plates so that I can actually get it into the tintop and bolt it up? From what I can tell even with the seats out, there is no way i'll get it in, in one piece and I really don't want to remove the dash. Would it be OK to have bolt plates half way on the diagonal tube and half way on the tube on the roof ?

Edit: How far from the body should the bar be in mm? Or is the idea that the closer I can get the tube to the roof and side walls - the better ?

[Fatzook]

Gwagensteve wrote:

I'd also try to mount in two planes so make the cage more secure.

Steve.

eg.

[tanshi]

are you talking about doing a 4 point or a 6+ point?

[Fatzook]

tanshi wrote:

are you talking about doing a 4 point or a 6+ point?

X2.

If its a 6 piont, it will have to be built in the car.

[scorpydude]

Yes, sorry... i suppose I was talking about a 4 point bar.



The red dots are where I was wondering if you could bolt together the bar to create it in two parts ? If that's not acceptable then I suppose a simple two point bar would be better as it's one solid piece. It would be a lot simpler for me as well so i would prefer something like that...



Would this be sufficient for non competition wheeling ? Laying on your side or back flipping onto your roof?

Fatzook: That's a great example photo, thanks.

[Fatzook]

If you make the bar the right way, you can get a 4 piont into a hard top by removing the seats only.

[Gwagensteve]

No. You need to have something to stop the bar bending forward and back at the top, that's why cages use diagonals from the main hoop back to the rear like your first picture.

I wouldn't break the main hoop with a coupler. Best for it to be one piece.

Steve.

[tanshi]

a four point shouldnt need to be bolted together.

they usually mount down to the wheel arches in the back.

the standard seats dont generally allow you to have the main hoop where you have pictured it.

a two point is going to do almost nothing in a roll over.

[scorpydude]

Okay. Thanks guys.

I know enough to get on with it now.

I'll stay with the 4 point, without breaking it with bolt plates and just work on a design that will fit with the seats out.

Cheers everyone

[Ace]

If you can find someone with a mill and a.... dia cutter (32-38 etc) the radius in the tube can be cut easily by putting said tube in a vice and plunging centrally to get the radius - even within a few mm is fine for welding

[SierraDan]

A steel 350mpa tube version of the factory option sports bar in soft tops with a diagonal would be plenty for what im assuming you want the.bar for.
The stock alloy 50mm x ?mm wall 4pt bar didnt budge on a decent rollover i had a while ago. So a better/stronger design would do wonders for your safety.

[Fatzook]

Ace wrote:

If you can find someone with a mill and a.... dia cutter (32-38 etc) the radius in the tube can be cut easily by putting said tube in a vice and plunging centrally to get the radius - even within a few mm is fine for welding

That is called notching my friend. And the gap should be as small as feasably possible to ensure a nice strong connection once welded.