Me and my buddies are really wanting to find some older steel frames and weld them up to create a bicycle for 4 riders. Its really just for fun .... I have descent welding skills. But how should I even begin this process. I've never built a frame? Any diagrams out there for this? I've seen bikes for up to 6 people before ... are they stiff/strong enough?? or do they just flex like crazy. Obviously this contraption will be more for laughs .... 1 or 2 club rides a year. But i obviously want it to be strong and safe .... while not breaking my bank account.

Hop over to atomiczombie.com, they do this kind of stuff all the time.

I'm not a designer or framebuilder, but if you look at four position tandems in older cycling books, it's all about trusses and designing the frame structure - both geometry and materials - to take the weight of four adults and the dynamic loads imposed by competitive cycling. I've noticed a lot of multi-position tandem frames are made of oversized 4130 chrome-moly, and because of the strange angles between tubes, most are fillet brazed or TIG welded rather than lugged. The wheels of a four position tandem have to be super strong since each of the two axles will be supporting rider weights of 400 pounds or so (four riders @ 200 pounds/2 wheels).

These are pretty typical of the types of trusses used. The top figure reflects more recent designs, while the middle figure is typical of designs around 1900. The bottom figure shows a truss geometry typical of the 1930s and 1940s.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/FourSeatTandems.jpg

Here is a quick, easy and inexpensive way to do it. You can read about it
on my blog here. (http://davesbikeblog.blogspot.com/2005/11/27-years-ago-national-enquirer.html)

wow they have some pretty crazy contraptions over at atomiczombie.com thanks for the help guys. Since i'm totally new to this ... i need all the help i can get