My nephew and I were looking at a cool book about building wacky bikes. We decided a tall bike would be a good one for a first project.

This was an educational adventure as well. He learned how to work with metal, create from instructions and expand his comfort zone with some adventure.

Step 1: The Parts

We started with 2 junk BMX bikes from the parts pile. We used the following

2 frames (note: we actually used 3 frames, but that was because I did not have a fork for the top frame and had to improvise.
2 wheels
2 cranks, 1 modified
2 forks, 1 cut down to just the bearings and stub out bottom
1 stem
1 seat and seat post
1 piece of scrap angle iron
1 piece of scrap pipe
2+ bike chains. We pieced together 2 full ones and a partial.
Some scrap 2x4's were used to hold it together while welding.

Step 2: Set Up, Jig, and Welding

We did all of the frame clean up, then used 2x4's screwed together along with some scrap metal as a jig to hold everything in place. We snugged it all up, then moved it around until the head tubes were perfectly lined up. THIS IS A HUGE STEP, do not rush at this point or you will have an ill steering/handling bike.

Once we were satisfied with the alignment, we welded a piece of angle across the head tubes. We took care to notch around the bearing cups. We also added the head tube from another bike to make my parts assortment work (if you start with 2 whole bikes you will not need this step).

After the head tube welding we added a tube from the lower seat post tube to the bottom bracket of the top bike. Finally we welded a cross brace of scrap metal to triangulate the frame area. We also added to down tubes in the back for looks really not strength per say (my nephew had an idea for future paniers/trombone carrier).

The last fabrication step is the steering. Since I thought we may want to cut the top bike off for re-use at a later date, we made the stem removable. That way if we really wanted to, we could cut the welds off and use it as a regular bike later. The fork for the top bike was cut at the welds to the down tube. between there and the top of the fork sticking through the bottom frame we welded in some scrap tube. You will notice in the pictures the bottom end uses the original clamping arrangement from the donor bike. This is an easy way to do it. Plus you can now service the bearings and disassemble at a later date.

Step 3: Final Assembly

Once the frame is all welded up, all you have left to do is final assembly. Pretty much nothing to it accept you will need to splice together 2 and 1/2 chains. Yours will vary on bike size. In my neighborhood, the bike shop keeps all the remnants they take off customer chains. They gave me some lengths of chain for free. Then its ride time.

Step 4: Ride and Enjoy

There is a slight learning curve to riding a tall bike. Below are some tips:

Ride at you own risk. Realize that you cannot just stop and put your feet down. If you make some bad judgement calls injury or death could result.
Stay out of traffic and areas with unpredictable pedestrians.
Practice in a open area where you can easily bail off if need be.
Maybe start next to a wall or something you can hold onto.
Once you get your bearings it becomes quite easy to start at stop at will
Have fun.