roll cages

[katanaman]

as kiwicar said plus depends on what the cage is made of. If its molly they you cant just mig weld onto that as the bit of the cage you weld to could go brittle. If its just CDS then its fine to mig.

[bones]

its cds, im just trying to find a supplier of seamless tubing, dont suppose anyone knows of a company that supplies small amounts ,i would need about 20m of 38mm o/d, so im going with the round stuff, just would like it cheaper than £16 a metre, rich.

[bones]

another question,i want to put bars from the rollcage to the front chassi rails and to the back to strengthen it up , should they go right to the front and the back or can a gap be left ,say 6" back, the front bars will be going through the bulkhead and to the bar under the dashbaord, the rear ones will be attached to the x-bar, does that seem ok rich.

[kiwicar]

Hi Rich
I have used this company for steel and ally and they do CDS and various other stuff (if they don't have what you want call them and they will normally get it in). Not quite as cheep as some but they do do sensable quantities (no minimum order) and are quick to deliver.
http://stores.ebay.co.uk/Ringwood-Precision-Engineering
for the tubes to the chassis, it is a question of judging where the load paths are going to be.... you are trying to make triangles in three planes from where the load enters the chassis (this includes your new roll cage)i.e the suspension points, engine mountings diff mounting points. you want the tubes from the chassis and roll cage in tention or compression with the loads acting in ilne with the tubes so there is no bending load is bending a tube at an angle, stopping a tube short of a suspension point will means it acts in shear or bending. yhis can cause a stress raiser and weaken the chassis locally as the generally stiffer chassis increases the load locally. you can get around this for short runs by adding stiffening plates on the chassis and into the roll cage joint but a straight tube will be stiffer and lighter. There are some good books on the subject and quite alot on t'internet but it is either go by what looks right when you understand the principles or get some very expensive chassis modeling software . If you have a good look at a seven chassis and try and follow what is happening (the haynes seven build bookis good) there and a NASCAR chassis (and try and wiork out what is happening there with safty bars and chassis stiffening) you should be able to get somewhere.
This is a good book on the subject Chassis engineering for HP cars,

good luck
Mike

[bones]

thanks Mike, it looks confusing, think i better ask websters on monday, ive found a company that can get the tubing at a very good price just want to check the tube wall is thick enough,what ever i do is never easy, thanks for the help and advice, rich.