The original instructable that I modified is
I hope you find these steps useful - sorry I don't have more detailed photos of the build - next build I will be sure to include more photos.
The wood cost $5 - that was the most expensive item bought - i bought five bike frames for $15 total ($3 a frame) and then some krylon spray paint at $3.75 a bottle. Overall, the whole bike cost about $35 bucks + time and effort.
Step 1: Connecting the front together
The first difference is how I connect the two frames. Instead of fashioning a bracket to go around the steer tube, I connected them through the holes where the brakes attach to the front fork and rear bracket.
At first I was just going to only have a rear brake, but since the front is where most of the weight is, that seemed like a bad idea in hill country.
First - I disassembled the brake (took the nuts off on both sides and replaced the center bolt with a six-inch section 1/4 inch threaded rod. I didn't know what size rod to get, so I just brought some of the pieces with me to the local hardware store. I got the largest size threaded rod that the washers would fit over.
Second - I reassembled the brake minus the part that holds the spring in - I don't have a drill press, so I didn't try to drill out a hole for it to fit in the assembly. So far, the spring has not popped loose - you will find that it fits rather snug once all reassembled.
Third - attach the brake to the fork.
Fourth - rotate the rear half of the bike that the cranks are on up until you can wiggle the rod through the other brake mount hole. You may need to beat, hammer or drill/grind a little larger hole for it to pop through. Since it is coming in at an angle it may be difficult to work it through - with a little patience and/or a dremel tool, you can get it through there.
Fifth - adjust to length and then finish by putting on lock washers, nuts and then some lock-tite.