britishtrident
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| posted on 26/4/04 at 04:46 PM |
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Surely as long as the diameter is big enough to ressist significant bending and the thickness enough to prevent buckling it dosen't
matter if erw or dom is used --- look at a standard book Locost Escort English axle it is paper thin mild steel and while the banjo stiffens it in
the middle surly beam bending isn't that big a factor.
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NS Dev
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| posted on 26/4/04 at 04:52 PM |
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Yes, you are right, but not as simple as might be thought. ERW is welded, obviously, and so has a heat affected zone (usually visible by the temper
colours). This will affect the fatige life (and probably the ultimate strength but I'm no expert on this) so as long as the tube is sized as a
welded structure and not a full round tube then all is ok, but the weld weakens it significantly, especially if you feed stresses into it right next
to the weld line.
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NS Dev
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| posted on 26/4/04 at 04:57 PM |
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Rob, one of my previous projects was a semi-spaceframed rear wheel drive Peugeot 205, I'll try and find some photos and put them in my archive.
I used normal CFS (CDS) for this, and you may as well because as I said, the main cage elements, if built without a "manufacturers
certificate" must be to the min. sizes in the blue book which are 38x2.5, 45x2.5 or 50x2 irrespective of T45 or CFS (CDS). (ok, you can use
thinner but you have to get it fully stress tested which is not very easy!!)
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britishtrident
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| posted on 26/4/04 at 06:34 PM |
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quote:
Originally posted by Rob Allison
Ah interesting as i have an escort that i'am going to space frame for sprint/hill climb use and T45 had been mentioned, but hard to weld.
Looks like CDS then.
Current specs for rollcages is totally over the top --- impossible to bend in a tube bender without resin filling.
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NS Dev
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| posted on 26/4/04 at 07:31 PM |
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Yes it can be awkward, best to "anneal" the area to be bent first (not strictly annealing! warm area to dull red with blowlamp and allow
to cool before bending, work hardening during bending recovers properties again!) This prevents the kinking!
I have built 2 cages using the spec though, one of which was in a car rolled on at least 5 separate rallies, and although it had to be repannelled a
few times the cage never moved. (we had a jig to check it!)
I would never say the spec is over the top!!!!!!!!!!
I have seen several cages to blue book spec broken clean off at the a-pillars after serious rolls. A lot of the bits for my Pug came from a RWD Fiesta
with mainly 38mm cage, which had folded the cage in two at the a-pillars. I would never use 38x2.5 in a saloon car now, I use 45x2.5 as a minimum. The
forces on the cage during a severe crash can be absolutely massive, on one occasion enough to snap cleanly through 4 pieces of 10mm thick dural plate
holding the seat to the mountings.!!!!
[Edited on 26/4/04 by NS Dev]
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Alan B
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| posted on 26/4/04 at 07:46 PM |
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Guys, while you are reducing wall thickness to save weight while maintaining strength due to an alloy upgrade, you are reducing stiffness. On an item
that sees bending loads like a De Dion tube I would have though this to be quite undesirable, so an increase in outside diameter of the tube will be
needed to maintain stiffness. Also, buckling effects may have to be considered...in other words a significant redesign to take advantage of the new
material.
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MikeR
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| posted on 26/4/04 at 10:59 PM |
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Sorry to jump in and ruin a very interesting thread but .....
quote:
Originally posted by NS Dev
what is the wall thickness of the cold rolled tube that you already have? As long as it is not over 3mm then it is fine, 45mm od 3mm wall is only
3.1kg per m.
So how do you know that then ???? Nout to do with you working it out on my phone a couple of nights ago???? 
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NS Dev
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| posted on 27/4/04 at 07:07 AM |
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Hit the nail on the head!!!!!! Quick formula for anybody else wanting to work out steel tube weight is:
Kg/m = (OD - Wall) x Wall x 0.02466
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Rob Allison
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| posted on 27/4/04 at 03:11 PM |
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Dev, very interested in the photos. (off topic but i started so  ) As i need ideas on doing it. Not sure if i should get rid of the inner wings or
keep them? My basic idea was to fit a locost type chassis where the floor was ??
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NS Dev
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| posted on 27/4/04 at 04:49 PM |
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There is 1 pic of the pug from the back in my photo archive now. If you U2U me your email address then I will send you more photo's and also
more info.
Basically if I did the job again I would remove the complete floor/bulkheads etc and mount everything to the cage. If you go on
www.beardmorebros.co.uk and look at the V8 reliant Kitten project you will see how I would do it now!
[Edited on 27/4/04 by NS Dev]
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Rob Allison
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| posted on 27/4/04 at 10:38 PM |
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Nice job Dev. Looks just like what i'm after doing. u2u sent 
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imull
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| posted on 29/4/04 at 02:32 PM |
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It isnt so much that T45 is stronger, it has more attractive properties.
It has a yield strength of approximately 680N/mm^2 compared to the 350 specified in teh blue book for CDF/CFS
This means that it will not permanently distort, until almost twice the stress (Force/Area) is applied.
Obviously, this means tha tyou can lower the area without it failing the tests.
I am surprised to hear Martin Short doesnt use it, as I spoke to his company at long lengths a year ago when starting my dissertation on this subject.
They never mentioned that he doesnt use it
The MSA will accept calculations for the roll cage testing from what I can figure (no such thing as a straight answer from there ) so it is not
necessary to create a test structure first.
As others said, it is very rarely the first impact that does teh actual damage. It serves to weaken the vehicle in one way or another.
At the end of the day, this is your life we are talking about and if you can afford the extra cost, you would be wise to go with the highest spec
steel that you can afford. That doesnt mean that you have to reduce the thicknesses to suit!
If nothing else, the chassis should withstand the odd bump slightly better...
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NS Dev
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| posted on 29/4/04 at 04:34 PM |
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I hasten to add, Martin Short did not say Rollcentre does not use T45, he said HE does not use T45 on HIS racing cars. (Maybe he does now, this was 2
or 3 years ago)
PS IMull, if you have been in touch with the rollcage manufacturers, did you get the chance to see Safety Devices' facilities!! WOW!! Their CNC
tube cutter/profiler and CNC bender would definitely be on my wishlist!!
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imull
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| posted on 1/5/04 at 11:11 AM |
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misunderstood what you were saying about his cars.
I spoke to Safety Devices quite a lot. Very helpful people in sales. Unfortunately, when I wrote to Tony Fall on more than one occasion regarding
using their coordinate geometry machine, i didnt even get a reply saying no...
Not really felt inclined to spend more time on that avenue. I approched other companies including one world rally team who have been more helpful than
I ever hoped!
Have been told that their set up is awesome though.
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olly_no1
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| posted on 15/5/04 at 10:58 AM |
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On the same topic, does anyone know a decent tubing supplier in the Brighton area???
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James
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| posted on 18/5/04 at 09:21 AM |
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Olly,
Send a u2u to Jasper- he's not far from Brighton and has been driving his car for a year. Should know the best places around you.
Good to see another Southern builder! 
Make sure you come to the Newlands Corner (just outside Guildford) meets 1st Sunday of the month.
Cheers,
James
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olly_no1
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| posted on 19/5/04 at 04:20 PM |
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Cheers for that James will do!
Only partly based in Brighton as i'm currently studying up at Brunel Uni, but the plan is to start building the chasis over the summer months.
Hard life being a student, only 4 months off!! 
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