This frame is made from grey steel shelving. I cut the steel corner angle posts with a hacksaw and put the pieces together with nuts and bolts and washers. The shelving supports are L shaped so I just cut one side of the L and bent it to the rectangular shape. To attach the bike wheels I cut to one of the holes in the shelf supports to make a slot and slid in and bolted the wheel with the original bike bolts. I had to make sure the hole and slot that I cut lined up on the 2 pieces of frame so the wheels would line up straight. The wheels are garbage picks. They come from a kid's bike. In the spring people seem to throw out old rusty bikes that the kids have grown out of.
The curved handle is 3/4 inch conduit pipe. It's not hard to bend if you fill the conduit with sand or if you have the special bender you can buy. The single thickness turned out to be too springy so I doubled it up and this worked better. It is still a bit springy when I am carrying a big load. I guess I should add a third layer of conduit or use a thicker pipe. I attached an eye bolt at the front of the frame and at the back to have a spot for bungees to clip on.
The frame was easy to work with but quite heavy. Commercial trailers usually have aluminium frames.
Box is made from 1/2 inch rough plywood I had taken apart from some old paneling. Its quite rough but I didn't care. Worse though is the weight. If I had to re-do this I would use thinner material and double up where I needed to attach stuff. Everything is glued and screwed. I don't like nails for this because if it flips it will hold together. Nails are always iffy. The box overhangs the frame a bit to allow for 2 rubbermaid containers to fit.
Lulu the cat supervises the painting. I wanted to put some orange too but when I mixed red and yellow it just turned yukky grey/muddy brown. I guess Red and Yellow don't always add up to orange. I glued a bunch of reflectors on the back along with reflector tape I had.
Here is the trailer in use. I had made a nice little hitch but it broke due to metal fatigue. I just bundle up a bungee around the end of the conduit now. I have an eye bolted in the end and wrap the bungee through it and around the bike frame. It works very well and allows for motion of the bike.
The trailer can handle about 100 pounds but it's not all that comfortable to pull that much. The load also has to be balanced. I have since modified the handle to double up the conduit tube so that it is not as springy. It would set up a bounce that just built and built and would sort of pull the bike back. Boing-boing-boing. I had to slow right down. With the thicker handle this is not so likely to happen.It's good to balance the weight in the trailer, this makes riding easier.
A few months later I garbage picked a kid's trailer and took out the seats. It does not carry any more weight but is much lighter. I gave my yellow trailer away on Craigslist. The kid's trailer is wider and that makes it harder to ride with. I think the ideal trailer would be longer but narrower.
Trailer hitch is always a problem. It has to allow the bike and trailer to move independently and still be solidly attached. In the new kid's trailer there is a big rubber piece that allows the connection to move. In the end I attached a clamp on the bike just to have a solid spot to attach to. This was left over from a handlebar bell. I then attached a bunch of bungees. the trailer pipe has an eye bolted at the end to attach. The bungee worked well and allowed the bike to move while well connected to the bike. Not very elegant but it works. If you can scrounge a proper bike trailer hitch from an old kid's trailer that works too and is easier to hook on and off.
When loading the trailer, it's best to keep the centre of balance just a bit in front of the trailer wheels. It seems to ride better that way.
This web site reflects my personal ideas and doesn't represent anyone else's point of view.