hello , I'm intend to start building a seven look a like . al the drawings a have seen so far are made using square tube and acctualy I want to make one from round tube, has any one experince with it ? and what size tube should I use ?

general concensus is that it would make life much more difficult cos of all the compound angled fishmouths you would need to make.

also, it wouldnt help fitting the floor and sides to curved surfaces....

atb

steve

A good starting point would be to substitute 25mm box ERW for 25mm CDS. The Cold drawn seamless however is a bit more expensive and takes a lot more effort to cut the fishmouth joints accurate without the tooling, which is why most people stick to good old box section. The rewards however on the finished chassis is night and day, especially if u Tig weld it. A less well used method these days is Bronze welding. Common as hell on most of the Formula Ford chassis and other "exotics" well into the 70's and early 80's. As a rough guide a gifted amateur could achieve very good results in twice the time it would take u to do it in Box section with a wee bit of practise.
Gimme a u2u if u get stuck or wanna discuss the pros and cons, We use a combination of CDS and ERW
regards
Shugster.

Substitution of 25mm box ERW for 25mm (round) CDS of same wall thickness will make the chassis lighter but less rigid and not necessarily stronger. If you go for round tubes you can get higher rigidity with the same wight by increasing the diameter of the tube.

Cheers!

[Edited on 04-10-1 by leto]

I normally build with a combination. A square base for easy floor panelling.

Square is definitly easier if you have a chassis which is quite simple as the joints are easy to cut.

However if you have lots of compound angles i actually find round easier to shape.

Another advantage of round is the welds at the joints are more loaded in shear. With box section the welds are often in tension. As a chassis should ideally have every member loaded in tension or compression having butt joints as is often the case with square is not ideal.

Another plus for the round is that higher quality steels ie CDS T45 4130 etc are easier to source in round.


John

My chassis is made in 1" CDS round, apart from the box section bottom which is square - but only because it's easier to add the floor to square than round.

Making a chassis out of 1" CDS round rather than 1" square ERW WONT make it necessarily weaker, CDS is a higher grade steel (1026) than ERW for a start. Again it's back to sweeping statements and design. My chassis has been through FEA and is about 220% stiffer than a "standard" book chassis - and its made of round.

One other point though, CDS is harder to get hold of than ERW and is one hell of a lot more expensive. I was buying 1" 16swg CDS at £25 for 8' last year (£3.12 per foot). In ERW that would have been £15 for 20' (75p per foot). If you start looking at T45 then you may as well just start leaving blank cheques.