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Author: Subject: Frame with 3 or 4 inch tubes?
bigtime

posted on 12/6/13 at 03:23 AM Reply With Quote
Frame with 3 or 4 inch tubes?

Hi guys
This website is great. Now I registered to post.

I need some advice on some 3 or 4 inch square tube frame construction with some triangulation in it.

What would be a nice tube wall thickness: thick enough so it wont buckle and to make it easy to weld, yet thin enough so it won't be too heavy?
Maybe some rectangular tube?

The 1 inch frame just scares me, looks too feeble to me.
While it may be sturdy enough I wouldn't feel comfortable driving it.

Thanks guys.

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iank

posted on 12/6/13 at 05:27 AM Reply With Quote
3 or 4 inch tube is truck/housebuilding technology and I've never seen it in anything sensibly thin. It would be hugely heavy even in 1mm. Hot rods in the US use large size tubes for the frame rails in ladder frame designs as you don't need much triangulation to get a reasonably stiff chassis.

You can buy 2"x2" in 16swg (1.6mm) which looks huge but is over 8x stiffer than 1" for 2x the weight.
40mmx40mm is 2.5 times stiffer than 1".

JC is using it for his chassis.
http://www.mistrale.blogspot.co.uk/

Here's some 1" 16swg and 18swg in action - along with a full cage - it's much stronger than you think (tin tops are down to less than 1mm if you want to compare)







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HowardB

posted on 12/6/13 at 05:47 AM Reply With Quote
Welcome to the forum. It is an amazing place.

Will respect to 1" box section, I can vouch for the crash & survivability of the standard chassis. Mine was a front end right off but the passenger & drivers cell were both fine. weakness in the 7 design is side impact strength. So often an extra side bar is fitted as part of the cage..

If you want to see the damage on my car there are pictures in my photo archive under "oops"

hope that helps







Howard

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snapper

posted on 12/6/13 at 05:55 AM Reply With Quote
If you want a car with much bigger tubing the Robin Hood 2b uses large round tube and the chassis is like a complete roll cage
It's heavy and not the easiest to build but if safety is paramount you won't find a bigger chassis in a 7 replica





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Slimy38

posted on 12/6/13 at 07:01 AM Reply With Quote
Doesn't the locust design use a couple of 3 inch beams to form its ladder chassis? That's about as close as I can think. Although I would actually consider that to be less safe than the 'standard' design, mainly because there's no metalwork on the side of you.

When I was buying my steel, I did notice as the size went up, so did the thickness and more importantly the weight. On the list I saw, anything above 2 inches got exponentially heavier. And I wouldn't like to even consider the price!

If you're really concerned about the chassis, do what I'm doing and look at the 'australian mods'. Their requirements are much more stringent than our IVA, and there is a tested and proven design that still uses 1 inch metal but with additional bracing in key areas. Interestingly, the document I downloaded also contains a few comparisons to production cars, and I was truly amazed to see a well designed seven had a higher resistance to twisting than some pretty major mainstream vehicles.

You can also gain a lot of strength and safety for the passengers by adding a good rollcage with side impact bars.

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Talon Motorsport

posted on 12/6/13 at 07:47 AM Reply With Quote
Oh come on really??? This is my first post and I want to use 3-4" tubing in my chassis.... pass me the can of welding spatter to pour back in to the welder please.
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designer

posted on 12/6/13 at 07:48 AM Reply With Quote
Using 3-4 in. tube means that you will have to make the chassis 6-8 in wider to accomodate it.
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ReMan

posted on 12/6/13 at 09:18 AM Reply With Quote
quote:
Originally posted by Talon Motorsport
Oh come on really??? This is my first post and I want to use 3-4" tubing in my chassis.... pass me the can of welding spatter to pour back in to the welder please.


I thought it you said it





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hughpinder

posted on 12/6/13 at 09:25 AM Reply With Quote
A full FIA spec roll cage for a rally car is only 50mm dia*2mm thick, admitedly of high tensile tube. Do a search on youtube for kit car crash or caterham crash - that sort of thing, and look at some of the horrendous track crashes in cars will a full cage, that have been filmed and people just walk away from, should give some confidence!
Regards
Hugh

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kj

posted on 12/6/13 at 09:28 AM Reply With Quote
That was some crash, makes me want a full cage or a taller roll bar as my head is above it.
Just shows how strong the car is, just imagine a corsa or similar.





Think about it, think about it again and then do it.

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scimjim

posted on 12/6/13 at 09:40 AM Reply With Quote
quote:
Originally posted by kj
......or a taller roll bar as my head is above it.

Is it a rollbar then - or just additional weight?

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kj

posted on 12/6/13 at 09:50 AM Reply With Quote
Roll bar at least, but if a roll bar came up i could handle the extra weight for safety





Think about it, think about it again and then do it.

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scimjim

posted on 12/6/13 at 09:59 AM Reply With Quote
Sorry - I meant your current setup. Sounds like its just additional weight as its not going to do much in a rollover situation?

It's a pet hate of mine after my son rolled his car - I'd lowered the floor, fitted a decent seat with harness and a rollbar just weeks before.

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Mark Allanson

posted on 12/6/13 at 10:10 AM Reply With Quote
If doing it all again, I would make the upper and lower tubes from 50x25mm 16g tube aligned vertically making the chassis 50mm taller to make it easier to fit OHC engines, and make the chassis considerable stiffer





If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation

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kj

posted on 12/6/13 at 10:15 AM Reply With Quote
current set up has a roll bar but its a bit low as i am tallish and head is above the bar, fully built so can't drop the floors, seats are richfield.





Think about it, think about it again and then do it.

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mark chandler

posted on 12/6/13 at 10:58 AM Reply With Quote
I built mine with an integrated roll hoop, if I made another I would integrate a cage to the floor, apart from that 16swg 1" is fine everywhere else.

As the cars have little mass you do not need big heavy structures, just triangulate so they do not deflect easily.

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Not Anumber

posted on 12/6/13 at 12:05 PM Reply With Quote
I'm just trying to imagine what a Locost built entirely with 4" tubing would look like, how it would handle, what type of suspension it would need etc.

It could demand another reboot of the book franchise

"Build Your Own Sportscar -with pipes the size of sewersl" perhaps






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suzcruz

posted on 23/9/14 at 04:28 AM Reply With Quote
Just keeping this thread alive, I am hoping to build a roadster in Australia mindful of these mods, so no need for a new topic.
Our rules state that there are 2 paths to follow;
1/ A rebodied vehicle, as in a ladder platform to id the base vehicle.
2/ An individually constructed vehicle, conforming to all current design laws.
So people in Australia build hotrods on a Mitsubishi Express frame or a 4x2 Hilux utility ladder frame.
These frames are typically 4 x 2 inch tubes with a 1/8 wall section, now you can understand my interest.
Luckily, if the motor is an non turbo 4 cylinder a 3 x 1 1/2 tube will pass so you can imagine some scope for heavily cutting into a standard 4x2 ladder frame.

Has anybody ventured into stiffening a ladder frame aside from those big, heavy cobras?
Could anybody please share a link to such a build please?

By the way, my build is hoping to be inspired by the 'haigh special' from your country, a tough little auto test style of car.
(we call them motorkhanas here).


[img]http://www.btrda.com/pics.php?imageid=580_1976988[/img]

Image is the property of http://www.btrda.com





No brain, no pain!

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Sam_68

posted on 23/9/14 at 06:15 AM Reply With Quote
quote:
Originally posted by suzcruz
Has anybody ventured into stiffening a ladder frame aside from those big, heavy cobras?


Some guy called Chapman used spaceframe bracing superimposed on an Austin Seven ladder chassis back in the early 1950's.

The idea didn't go very far, I don't think.




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suzcruz

posted on 23/9/14 at 06:39 AM Reply With Quote
Thanks Sam, those little Austin 7's look like old mattress frames scraps and I'll bet that Chapmans bracing sure made improvements.





No brain, no pain!

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TheGecko

posted on 23/9/14 at 10:14 AM Reply With Quote
quote:
Originally posted by suzcruz
Just keeping this thread alive, I am hoping to build a roadster in Australia mindful of these mods, so no need for a new topic.
Our rules state that there are 2 paths to follow;
1/ A rebodied vehicle, as in a ladder platform to id the base vehicle.
2/ An individually constructed vehicle, conforming to all current design laws.
So people in Australia build hotrods on a Mitsubishi Express frame or a 4x2 Hilux utility ladder frame.
These frames are typically 4 x 2 inch tubes with a 1/8 wall section, now you can understand my interest.
Luckily, if the motor is an non turbo 4 cylinder a 3 x 1 1/2 tube will pass so you can imagine some scope for heavily cutting into a standard 4x2 ladder frame.

Has anybody ventured into stiffening a ladder frame aside from those big, heavy cobras?
Could anybody please share a link to such a build please?

By the way, my build is hoping to be inspired by the 'haigh special' from your country, a tough little auto test style of car.
(we call them motorkhanas here).


[img]http://www.btrda.com/pics.php?imageid=580_1976988[/img]

Image is the property of http://www.btrda.com

Suzcruz, I suggest you join the Australian equivalent of this forum, OzClubbies - http://www.ozclubbies.com.au. There's all you could need to know about meeting Australian registration requirements. And be aware, there's LOTS of Locosts and the like registered in Oz with their "weedy" 1" tube frames

Dominic

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IanSouthLincs

posted on 28/9/14 at 06:43 PM Reply With Quote
Hi Suzcruz, yes I have pretty much done exactly as you have described. Over here there's an old fashioned style kit that I have called a Hornet, this is a wide bodied version of a Locust. These cars have a ladder chassis with a plywood tub bolted to this which is wrapped in thin aluminium. The car I have was in need of serious tlc as the plywood had rotted away, thoug early on I had decided to rebuild it using 16 gauge 25mm square ERW instead. Here is a picture of it in red oxide primer,




Still building it at the moment, chassis is all painted fuel tank in, new fuel line in, brake lines in, just trying to make sense of the abysmal wiring. Have my 2mm floor cut and ready to go in, hopefully next job is to make my new aluminium body panels.

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