What size square tubing for building a frame?

[gto406]

For those not familiar with 'back-purging' is there any good sites that discuss the process?

I found the following for TIG welding, but I am not sure this is what you guys are talking about:

http://books.google.com/books?id=RKP...esult&resnum=8

With respect to the first post in this thread...
I would recommend to anyone building a frame (or any structure like a roll-cage, etc.) to examine the rule-book of an auto-racing sanctioning body that runs a class (or type) of vehicle _similar_ to what is planned. For example, if the plan is to do solo events or the odd track-days, the SCCA would be a good place to start (formal rules can be found here - http://cms.scca.com/documents/Club%2...egulations.pdf). These sanctioning bodies will provide (in there rule books) alot of good details on race car construction. I am sure you could also contact one of their stewards to clarify the information (if required). The nice thing about going this route, is that the sanctioning body has the benefit of input from race car constructors, stewards, standards bodies (like SFI - http://www.sfifoundation.com/), all providing input. Also note that these bodies are typically liable (if something happens at an event) so you know the emphasis will be on the safety aspect.

Thanks,
Brian.