The frame is a simple design consisting of the three arches and four spanner blocks held together by a bungee cord passed through.
Here I've assembled the frame. I glued an extra short piece in each arch to accomodate the end of the spanning blocks. The bungee cord holds everything together.
Here I collapsed the frame. I did this simply by pushing down on the spanner blocks to double them up. Then I pushed the arches together. It will stay collapsed under its own weight until I pull it back open. As we shall soon see this is highly convenient.