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CP Guide
A Beginner's Guide to Crease Patterns
Locating Creases
The first step to doing any CP is to locate where the major creases lie. If
the designer has been nice, this information will be in the CP; if not, you're
just going to have to work it out yourself. For this, you can either print out
a copy of the CP, and draw lines using a pencil and ruler, or open the CP in
your favourite vector graphics program. Most graphic programs have measurement
functions that allow you to quickly determine lengths and angles of creases.
Of course, you can simply enlarge the CP and print it on a big sheet of paper,
then put in the crease lines where they're printed. It's fine if you just
want to be able to do the CP, but you won't really learn anything about the
structure of the CP this way.
Not all creases are equal...
At first glance, most CPs appear horribly complex, primarily due to the sheer
number of creases all over the place. Often however, only a few creases are
really important in determining the structure of the base; the rest are the
creases needed to fill in the details on the model. It is therefore fairly
useful to be able to distinguish between the structural creases and the detail
creases.
In general, the longest creases in a CP are structural ones,
while the shortest creases define the details. Another clue
would be the angles at which a particular crease makes to
adjacent creases - the smaller the angles, the more structurally unimportant
the crease is. This is particularly true of points which have a lot of closely
spaced creases radiating out from; chances are, these radial creases are
involved in narrowing the flap associated with the point.
If a CP becomes too confusing to work out because of a large number of creases,
try sketching and collapsing a reduced CP containing only the
structural creases (ie, cut out the grafts, etc). Once the reduced CP is
solved, solving the full CP is then a matter of progressively adding the parts
left out in the reduced CP.
Common Crease Arrangements and Divisions
Listed below are some common CP divisions and crease group arrangements:
Equal Divisions
Divisions which are a power of two are straightforward to spot and locate.
Other divisions like thirds or fifths are not as simple to spot. When in
doubt, measure out the distances on the crease pattern. There are various
folding methods which you can use to get any fraction you want, but these
tend to leave messy construction creases all over the place.
The Kite Fold Division
Kite fold divisions in models with diagonal symmetry are usually quite easy to
spot (Figure 1,left). The CP will usually have two 22.5 degree lines radiating
from one point of the diagonal. If these lines are extended until they reach
the edges of the square, the points of intersection between the lines and the
square edges usually form two further points in the model. The double kite
fold division is quite common for four-legged animals.
The intersection point divides the edge of the square into the ratio of
2-√2:√2-1 (Figure 1, centre). Sometimes, a kite fold division is
used even when the model does not have diagonal symmetry. Further point
locations based on the kite fold are also possible, for example, the
intersection between a diagonal a line drawn from one vertex of the kite fold
to the corner of the square (Figure 1, right).
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| Figure 1: The Kite Fold Division |
Diagonal Squares
This arrangement is often seen in many CPs (Figure 2). The two squares usually
form the main points of a model, while the two rectangles contain detail folds.
Interestingly enough, it usually doesn't matter what the relative sizes of the
squares are. Changing the square sizes just results in a differently
proportioned model; it does not affect how the square collapses into the base.
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| Figure 2: Diagonal Squares |
Grafts
Strip grafts are typically used to add more detail to the model. They can run
either along the edge of the square or through its interior. The diagonal
squares arrangement described above can also be thought of in terms of two
strip grafts on adjacent edges of the square. Strip grafts are nice because
you can often "edit" them out of the CP when you're trying to figure out the
basic structure of the model. Figure 3 (left) is an example of two strip
grafts on either side of a main diagonal. This can be broken up into the
component parts (Figure 3, centre) and then put back together again (Figure 3,
right). The reduced CP which describes the model's basic structure is enclosed
in the blue box. These strip grafts allow for details along the strips, as
well as at both ends of the main diagonal.
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| Figure 3: Two strip grafts parallel to a main diagonal |
The reverse process is a common way
of inserting details in a designed model - first, come up with the basic
structure, unfold it and look at the CP for places where you can add the
grafts, then finally fold the revised CP with the grafts in place.