It starts with a few tack welds.

After hacking up the bicycle frames to distill them into just the parts that we’re going to use, it was time to start welding the basics of the frame together.  I purchased 120′ of 1 1/2″ x 1/16″ wall chromoly tubing.  Alloy 4130 for those keeping score at home.  I’ve also got some 3/4″ tube on the way, but it hasn’t arrived yet.  Chromoly is more expensive than 1020, but it’s got a high strength to weight ratio.  It’s used in high quality bicycles, so I’m not going out on a limb here.  It’s easy to weld to, and plenty strong.  The 1/16″ wall is thick enough that I won’t blow through it too much with my bad welding.  There are times to cut corners, but the frame of the vehicle is not one of them.

The first of 8

The first thing I put together was a square frame.  This thing will ultimately carry the weight of all 8 passengers.  It’ll be the lowest frame element on the sculpture and it will sit 6″ off of the ground.  I hope that will be high enough to clear speed bumps.  My Spitfireis lower than that, so I’m not too worried.  I mitered the steel tubing and first tacked everything together.  If I was going to change anything, I wanted it to be easy to grind it off.

Fishmouth notching made easy.

Then I welded the first bicycle triangle onto the frame.  We held everything in place with a wooden jig to make sure the pedals would clear the ground and our square frame.  I had the help of two other sets of eyes to make sure everything was aligned before we welded it into place.

The nice fit of notched tubing.

Now we had the process down, it was a simple matter to churn out the other 7 tubes and use the jig to align everything.  We used a tube notcher to cut the round parts out of the tube and cleaned up the edges with a grinder.  We had to grind a few of the tubes for clearance of the bicycle frame tubing, but it was an easy step of trial and error till everything was close enough.

You can almost see it coming together.

At the end of the day we were able to finish welding our 8 bicycle frames onto the sub frame.  It really helped us get a picture of how big everything was going to be.  Suddenly it’s easy to imagine the drivetrain, the wheels, the suspension, etc.  There will be a lot more steel welded in to keep the frame rigid with 8 people (~1200lbs!) riding around.  But, so far things are starting to come together.  For the first time I’m having to deal with storing this monstrosity and keeping it out of the way while I’m not working on it.