roll cage tube diameter

[gsr341]

hello , im thinking of having northen chris build me a challange spec cage for me , i asked for 50mm (2" cds) and he said to use 45mmCDS

apart from the signifiocan weight differance between them is there any other reason people use the 2" CDS

whats the norm in cage building ?

edited to correct my mistake , sorry

[Astro_Al]

...and he said to use 4hmmCDS ...

Typo for what? 48mm?

Al.

[dirtydiesel]

Normally speaking 48mmx3.8mm is what i'd use, i don't normally bother with cds either, i like to have a bit of wall thickness to stop individual tubes bending when you hit trees and rocks.

[will_warne]

50mm or 52mm CDS is what you want. I've seen 48mm bend

[northernchris]

50mm or 52mm CDS is what you want. I've seen 48mm bend

Will

It depends what you are building a cage for????? I have seen 45mm, 50mm ,52mm all bend in certain circumstances.Was the smaller dia tube anealed which you mention ????? there are many reasons why you would or would,nt use 45mm tube.Cage design is far more important than tube dia alone.

Chris

PS 45mm is what i suggested.

[northernchris]

Everyone has their own opinion.

Chris

[will_warne]

Will

It depends what you are building a cage for????? I have seen 45mm, 50mm ,52mm all bend in certain circumstances.Was the smaller dia tube anealed which you mention ????? there are many reasons why you would or would,nt use 45mm tube.Cage design is far more important than tube dia alone.

Chris

PS 45mm is what i suggested.

I totally agree but I think there are 2 big issues with LR cages. The first is the wieght of the vehicle (making it nice to have a bit more safety factor) and the second is the fact most cages are external to a certain extent. That means you need a little extra strength to stop damage from trees/rocks when tree rubbing or falling over.

My current cage is 48mm CDS and I've seen a few cages of the same type bend on the straight sections due to impacts with obsticles.

[Hybrid_From_Hell]

It is not that simple

There are a large number of variables IMHFO (had some beer tonight)

1. Tube OD.

You can GAIN strength as the more the OD the stronger

2. CDS Vs er..."Non" CDS

CDS = Cold Drawn Seamless, as it says the tube is Formed as 1 unit, no joins no welds and F expensive

"The rest", whatever is has as a 'BS mark' or "quality" Tag..........BUT it is NOT CDS,

it is in some form or other a 'flat plate', in some way 'formed' to a tube shape and then welded the entire length,

it is NOT as strong OD and ID being the same as CDS.....

BS1387 Corrus in regarded as the "Best" of the welded tubes

3. Wall Thickness

Now we get complicated...................

oh, before we get going.................

4. Deformation Vs Tube type vs wall thickness vs speed

Could write an essay here,

but in really simple terms look at the application,

rally car high speed and very high impacts - CDS 4 me ta,

challenge trucjk, very very very very nasty roll maybe but at low MPH so CDS not as key.

CDS and welded whatever deform very differnertly,

also CDS is NOT the same "Simple stuff" to weld as Welded tube, oh no, do not underestimate it at all .....PITFA to weld.

5. Mounts.

150mm 10mm wall is no good if the mounts are 1mm plate, it will just "Punch Through" on a simple roll, just think on a heavy one

6. Design.

The best CDS poorly bent and poorly designed / thought out is a waste of time money and possibly your life - I joke not.......

Ok, some final thoughts......

The thicker the wall the stronger the tube, BUT

CDS OD the same as NON CDS OD with the same wall CDS= stronger

however, (complicated bit coming)

CDS uses a differing OD system to Non CDS,

so CDS is often 45mm, 50mm, where NON cds is 48.3mm.

The walls are very similar 2.5 3.0/3.2 etc.

So CDS 50mm vs 48.3mm OD with 3.0 / 3.2mm wall, which is stronger ? = CDS

BUT CDS is used to save weight often,

so use 50mm CDS but go down a wall size against the 48.3mm welded, and CDS is then prob equal,

possibly even stonger, but the weight saving is HUGE.

the 48.3 BS1387 Corrus is either 3.2mm wall of 4.0+something,

often the arguement goes to get the same strength as CDS 50mm 3.2 you need 48.3mm welded 4.0++ ,.,,

maybe.45mm CDS is a BIG jump down from either 50mm CDS OR welded 48.3 / 3,2mm welded,

if it was my neck I would still go for a quality cage from 48.3mm welded over 45mm CDS,

but 50mm CDS over 48.3mm welded, ...............all with the same wall.

Oh, and CDS is a HORRIBLE price,

not that you'll worry about that ....

or could you say maybe whats the value of your life ?.... ...or is 48.3 3.2mm ok ? ?????

Look at most AWDC MSA and other cages,

loads are out there and there is a mixture of all of the above.

the more your truck weights the more importnat it is,

for a 90 45mm cds is a tad lightweight in my humble if 2.5mm or less.

48.3mm welded 3.2mm wall is fine,

50 CDS 3.0+wall is the "Ballon Du Chien" IMHO,

just have a wallet ready with a cortisone injection on hand....

Welding,

a good welder can make an average cage great,

a average welder places a good cage at risk, and

a poor welder can make a fabulous cage as waste of time money and a death trap,

do NOT underestimate this sentence,

I have seen horrors in my time,

barrel rolls where welds "Undo" mean you then have a "Spike 48/50mm stake "Looking for a home" - It could be you -

Hope this makes sense, it is a copmplex subject,

and I'll prob get grief from this post,

however 20years+ I think I know what I am on about.

Nige

[daveturnbull]

2 and a half inch heavy is what stunning services use...

Saved Jules' ass when he took his 90 for a flying lesson. Only a very slight bend in the top hoop that he landed on - enough force to bend the chassis in 5 places.

[istruggle2gate11]

Excellent reply Nige.

It is not that simple

The best CDS poorly bent and poorly designed / thought out is a waste of time money and possibly your life - I joke not.......

Cage design is far more important than tube dia alone

The above statements are probably the most important of all in this topic.

[northernchris]

Dave

A cage that is strong enough NOT to deform but bend the chassis is a VERY BAD cage by design....FULL STOP

A cage should absorb the impact to more or lesser degree.

Nige

I would say you are pretty much spot on.

I have always used 3.6mm wall 45mm o/d CDS 2 tube for cages nice to bend and weld.

Chris

[daveturnbull]

Dave

A cage that is strong enough NOT to deform but bend the chassis is a VERY BAD cage by design....FULL STOP

A cage should absorb the impact to more or lesser degree.

The reason it bent was mainly due a bit of rot causing a few weak spots & the angle it landed on the cab / ARB winch bumper. My point being that the cab was not crushed from the weight of a 90 dropped on it's roof after flying upside down through the air for 15 seconds. Read all about it

I'd rather have a cage that saves my life than one that allows me to be squashed and save a rotten chassis.

the air trip was 3seconds checked on the video with the timer on screen THE moderator

[Hybrid_From_Hell]

45mm 3.6mm is definately more on the HD side,

45mm CDS I think is also 2.0mm (not often used)

and 2.6mm which is often used,

and if so then this 2.6mm wall is IMHO inferior even as CDS to 48.3mm 3.2mm wall welded.

45mm 3.6mm and 48.3mm welded 3.2mm is a close call,

my money woukld be on 45mm 3.6mm being stronger and better than the welded 48.3mm 3,2mm wall,

however 45mm can look "Small" purely from a visual point a view if not made sympathetically -

that the tarts catered for too

Nige

[simonr]

Another consideration is the amount of force required to bend the tube. Tube diameter makes a bigger difference than wall thickness.

In an ideal world, everything would be cross-braced / triangulated, but it is virtually impossible to achieve. If you have spars which are simply relying on the resistance to bending of the tube to keep the shape, go for bigger diameter rather than heavier wall.

When you are triangulating, it's worth considering which nodes are likely to be impacted and arrange that if they are, the spar which stops it bending is in tension, not compression as steel is stronger weight for weight in tension. I considered that in a roll, it would more likely land on the passanger side as you tend to feel safer on the high side if the vehicle is leaning. Also, an impact at the front is more likely than the back. The cross bracing spars reflect this.

It follows on from this, and what HFH was saying that if a weld breaks, you end up with a pointy thing looking for somewhere to go. If that spar broke in tension, the pointy end will move away from the other bit rather than towards it, possibly being diverted towards you.

At the end of the day, any cage is a compromise, but one way or another, virtually anything is better than nothing (save for pointy things coming your way).

Si

[northernchris]

yup

[Diff]

The only thing I would like to add to this thread, for anyone considering building, or having a cage built, is to consider what use you will be putting the vehicle to.

If you are intending using the vehicle in competitions, make sure that you find out EXACTLY what the roll cage requirements are for the clubs/ organisations that you are intending on competing with. Different clubs DO have different requirements, some have no specific requirements other than a cage is required.

I have seen people get very upset in the past when they have not been allowed to compete when they have failed scrutineering because their cage doesn't meet the club requirements(AWDC). Sometimes it has not been because the cage has been poorly welded, but because it hasn't met the dimension or material requirements of the club, or the hoop is too close to the drivers head or whatever.

Sometimes a cage will meet the requirements of one club, but not another.

Regards,

Diff

[Astro_Al]

Some great points in this thread.

I think a nice easy way to consider what to use is to go for the max diameter you can (to increase the moment of area, and all it's related parameters while keeping the weight down where possible), but to remember that wall thickness is important in direct impact damage - like banging into rocks and trees, so a REALLY wide tube is no good if it's gonna get banged a lot.

But as Simon said (ha ha, sorry...), increasing diameter is superior to increasing wall thickness.

One small point - if we are talking about cages made at 'home' by non-professional welders, I think it's worth making the point that the weld is likely to fail before the steel does in tension, therefore (although in theory you're absolutely right) it might be better to design the cage so that as many members as possible are put in compression during a typical impact, so that people are less reliant on their (sometimes dodgy) welding. I just put that in for people attempting stuff themselves (public forum and all).

Now for my Q:

Is there a list or table or anything of which types of tubes are available in which sizes - you know, I.D. (or O.D.) wall thickness, cost per metre etc... CDS / Blue band etc.

It'd be pretty useful to have this info as I'm about to do a cage using several diamaters of tube (necessary, unfortunately) - anyone???

Dave - I don't want to nit pick as I agree with you about larger diameter tube, but 'flying through the air for 15 seconds'? That's a LONG time...

My fag packet tells me that with an initial velocity of zero, after 15 seconds of free-fall ('flying through the air') he'd be doing 350 mph and have covered a distance of 1.1km (downwards).

Cheers, Al.

[bishbosh]

Corus do one or two sizes HERE

[Renny]

Great input on this topic. Just remember as Diff says check the regulations for the clubs that you compete with.

As a Scrutineer, I hate having to reject a motor for anything, but a non-compliant roll cage is something I'd be quite tough on and is something you cannot often sort out in the field.

[ltwt1981]

Extract from the Blue Book Q1.3 spec for steel.

1.2.8. Guidance on Welding. All welding

should be of the highest possible quality with

full penetration and preferably using a gas

shielded arc. Although good external

appearance of a weld does not necessarily

guarantee its quality, poor looking welds are

never a sign of good workmanship. When

using heat-treated steel the instructions of the

manufacturer must be followed (special

electrodes, gas protected welding). It must

be emphasised that the use of heat-treated

or medium carbon steels may cause

problems and that bad fabrication may

result in a decrease in strength (caused by

brittle heat-affected zones) or inadequate

ductility.

1.3. Material Specifications

Specifications of the tubes used:

Minimum Material

Cold Drawn Seamless Carbon Steel

Minimum Yield Strength

350 N/mm2

Minimum Dimensions (Ø in mm)

45x2.5 or 50x2.0

38x2.5 or 40x2.0 (For roll cages/bars approved

prior to 1.1.95)

In selecting the steel, attention must be paid

to obtaining good elongation properties and

adequate weldability.

The tubing must be bent by a cold working

process and the centreline bend radius

must be at least three times the tube diameter.

If the tubing is ovalised during bending, the

ratio of minor to major diameter must be 0.9

or greater.

1.4. Exceptions

The only exceptions to the foregoing

requirements for Saloon, single seater and

Sports Cars are as follows:

1.4.1. Safety Cage manufacturers may make

application to the MSA for a Roll Over

Protection System (ROPS) Certificate to be

issued.

Note: ROPS manufacturers wishing to make

application for such a certificate should contact

the MSA Technical Department in order to

obtain details of the requirements to be met and

the fees payable. Subject to these requirements

being met a ROPS Certificate will be raised and

SAFETY CRITERIA

Q 232

This may help, basically to comply with MSA rules you must use CDS, I think ARC allow Corus tube to relevant BS.

[dirtydiesel]

This may help, basically to comply with MSA rules you must use CDS, I think ARC allow Corus tube to relevant BS.

Not strictly true there are a few exeptions within section H of the blue book that allow you use blue band (bs 1387) for roll cages.

The awdc's sr's used to state blue band as a minimum requirement, But havn't been a member for a while so i don't know if they still do.

The arc's rules still state blue band as a min requirement.

[LR90]

All welding should be of the highest possible quality

Seems a very tall order and making a better weld would imply other welds are no longer of the highest quality?

[white90]

Some great points in this thread.

I think a nice easy way to consider what to use is to go for the max diameter you can (to increase the moment of area, and all it's related parameters while keeping the weight down where possible), but to remember that wall thickness is important in direct impact damage - like banging into rocks and trees, so a REALLY wide tube is no good if it's gonna get banged a lot.

But as Simon said (ha ha, sorry...), increasing diameter is superior to increasing wall thickness.

One small point - if we are talking about cages made at 'home' by non-professional welders, I think it's worth making the point that the weld is likely to fail before the steel does in tension, therefore (although in theory you're absolutely right) it might be better to design the cage so that as many members as possible are put in compression during a typical impact, so that people are less reliant on their (sometimes dodgy) welding. I just put that in for people attempting stuff themselves (public forum and all).

Now for my Q:

Is there a list or table or anything of which types of tubes are available in which sizes - you know, I.D. (or O.D.) wall thickness, cost per metre etc... CDS / Blue band etc.

It'd be pretty useful to have this info as I'm about to do a cage using several diamaters of tube (necessary, unfortunately) - anyone???

Dave - I don't want to nit pick as I agree with you about larger diameter tube, but 'flying through the air for 15 seconds'? That's a LONG time...

My fag packet tells me that with an initial velocity of zero, after 15 seconds of free-fall ('flying through the air') he'd be doing 350 mph and have covered a distance of 1.1km (downwards).

Cheers, Al.

Al wouldn't terminal velocity be around the 120mph mark? the free fall was infact 3seconds from flip to landing BTW