# How do I fold step 3-4 in Maarten van Gelder's caterpillar model?

I have spent several hours trying to decode steps 3-4 of Maarten van Gelder's caterpillar model. Can anyone shed any more light on how to make that fold and the next one in 5-6? It feels like they left out some steps there...

That portion of the instructions:

## 1 Answer

Diagrams 4 and 6 are very misleading and diagram 2 isn't to the same scale. The end isn't as shown, so don't try to make the end look like the diagram. Also, the diagrams don't use line formats to indicate mountain and valley folds, they just show sequence.

Actually, steps 2 and 4 aren't needed. Make the creases in Diagram 1 then Diagram 3. Diagram 3 will add perpendicular creases to accordion fold the strip, and additional diagonal creases (you can identify exact locations by intersections of prior creases).

Note the 6 small diamonds running across the center of the strip. Those will create the peaks at the top of diagram 6. The outsides of the diamonds are mountain folds; the lines dividing the diamonds in half are valley folds. Focus on getting those diamonds folded and that will force the rest into the general "house" shape of diagram 6.

Basically, the perpendicular folds between the diamonds (the even-numbered creases) are valley folds that swing down and meet in the middle to separate the segments. The odd-numbered creases that divide the diamonds in half are valleys inside the diamond, and mountains outside the diamond, where they form the sides of the house shape. Just fold all the segments the same and don't worry about making the ends look like diagram 6; you just need the outline of the segments in the "house" shape.

Starting with the crease pattern in Figure 3 (just the first four diamonds, I replicated this on a short scrap of paper), this is an overhead view of the shape of the folds that produce the house shape:

There's a bit of an optical illusion; those are valley folds bisecting each diamond. Above and below the diamond, they change to mountain folds.

To get to diagram 7, fold each segment side in half in both directions to get a good score line where diagram 6 shows the dotted lines. Open up the segment a little and you'll see the rectangular crease lines shown in diagram 5 for each segment side. Push the side in to invert the rectangle on the fold you just made. When you're done with all the segment sides, it should accurately look like diagram 7.

That last step added the rectangular creases on the segment sides, shown in Diagram 5. If you compare Diagram 5 to Diagram 3, there are also some dotted diagonal creases between the sides that will be missing on your model. Those are where the legs are reverse-folded in step 7. Since this is a continuous sheet, it will be hard to reverse fold the legs without manually adding those fold lines. Open and flatten the model again, and add those missing creases. It may also help to create the row of reverse folds to train the paper as you add those creases.

• I was able to fold the diamonds like you suggested, but it doesn't seem to produce the model I would need to make the "house". Here are a couple of pics for reference: [link]imgur.com/a/F0O3ebJ and [link]imgur.com/a/KntpoaY Mar 19 '20 at 0:48
• @SteveSheppard, I'm not sure what you did in the first picture, The second picture looks like you accomplished diagram 4, but there doesn't appear to be as many segments as there should be and the segments look thick, like you somehow nested what should be multiple segments inside each other. Try this. Flatten the model back to a strip with crease lines as in diagram 3. Start with the 11 perpendicular creases all as valley folds rather than accordion folds. Make all the diagonal creases mountain folds. (cont'd) Mar 19 '20 at 1:56
• Now focus on the 6 small diamonds across the middle; forming those into shape as the top of the 3D model will force the rest. Ignoring the ends of the strip, the odd-numbered perpendicular creases bisect those diamonds; the even numbered ones are between those diamonds. Start with the end of the strip and fold each half-diamond as you come to it. As you fold the sides of the diamonds down and fold each diamond in half on its bisecting crease, the row of diamonds will sort of accordion into 3D. (cont'd) Mar 19 '20 at 1:57
• The even-numbered perpendicular folds will swing down and meet in the middle between the segments. The odd-numbered perpendicular creases outside the diamond will tuck under the diamond as the diamond folds in half. You'll end up with the general 3D diamond shape shown in figure 4. The odd-numbered creases outside the small diamonds that tucked underneath then get inverted (popped to the outside) to form the "walls of the house shape" shown in figure 6. (cont'd) Mar 19 '20 at 1:57
• @SteveSheppard, looks like you figured it out, except you only folded 5 of the 6 diamonds. So that end isn't starting from the correct geometry. Both ends should look the same. BTW, the diagrams show a shortened version for explanation. The actual caterpillar starts with a strip almost 3 times as long (good that you're practicing on the short version). :-) Looks like you may have drawn the line pattern missing half a diamond at the problem end. Mar 21 '20 at 4:57