Build a Cheap Tandem Bicycle with Just a Welder!

Own a welder? Have 2 junk bicycles? Ready to build your first tandem bicycle with just a welder and two bikes? Great! This project was originally inspired by a broomstick tandem I found on the web, built only from broomsticks and duct tape. I had a welder available, but the key is using the seatpost of the front bicycle in the steering tube for the rear bicycle as a pin joint. Check out the pictures below (click for full size).
A couple of critical features:

1. Use a spare derailleur backwards as a chain tensioner for the big chain run, this is actually the hardest part to get aligned, the rest was eyeballed
2. Create the big chain from 2 (or more) lengths of chain, you'll need to find another chain to get this working
3. Use the seatpost of the front bicycle as the fork/steering tube pin for the rear bicycle, it keeps the whole thing stable and stuck together
4. You don't need to build the beefy steel support for the center frame-stay, it really just needs to keep the frame from swaying side-to-side.