Bird and patterns
This tutorial will illustrate a few of the many common patterns found in a crease pattern (cp).
Here was the first crease pattern:
Recall that since there is one crease going into each corner, the corners are narrowed from 90 degrees to 45 degrees. To make a crane, as most know, we need to narrow the corners more. Here is the crease pattern of the bird base:
We see that now the nodes of the corners are 90 degrees divided by 4 = 22.5 degrees. Also, looking at the smaller square in the center of the bird cp, we see that it is exactly the preliminary base we have already done. We can use this symmetry to help us figure out the crease directions for our bird. Since we know the directions for the preliminary base , we can copy this into our new cp problem obtaining partial crease directions as follows:
We can fill in the rest of the directions with the knowledge that on nodes the crease diretions alternate. Thus for each corner we would expect the creases to look as follows:
From this concept, we can fill in the rest of the crease directions for our bird base as follows:
With all the creases the collapse should come pretty easily as the first photo shows the almost collapsed base, the second shows the finished base, and the third shows the finished crane:
Another thing we can learn is that if we had done our crease pattern with every single crease in an oppisite direction, we would have gotten the same result showing a different side of the paper. The crease pattern we came up with is done white side up. When folding crease patterns white side up, you always start with the creases nearest the edge of the paper as valley folds. This helps you fill in all the creases so that when you finish the model you are showing the color side on the outside. A consequence of this is that you work with crease patterns with the innards of the model facing you. This seems odd at first, but it is worth getting used to. If you like, you can fold this bird with opposite crease directions having the color side up. If you work color side up the creases nearest the edge of the paper needs to be mountain folds.
We did the beginner tutorials in two parts because this illustrates the last point before we move on. The bird base is folded normally starting with the preliminary base, then the corners are narrowed. We see in our bird base that the preliminary base is all the lines that are the longest. The additional narrowing folds are the lines that are the shortest. This shows that when collapsing the bases, the longest lines are most important and the shortest lines are the least important. This means that when collapsing a crease pattern, you often collapse the longest lines first, and do the smaller lines later. The smaller lines correspond to the detail, while the longer lines correspond to more of the macro-structure. On the intermediate tutorial, we will explore this concept further.
Copyright 2002 Ben Ball