Truncated 120-cell Dome
August 7th, 2015



We constructed this dome (upper half of the 3D projection of a truncated 120-cell)
at Kyoto University Museum, with 20 junior high school students and
some (graduate) students of Kyoto university.
After construction, we played entering in it.



We held a series of workshops at the museum, where we assembled models which are based on 120-cell and 600-cell. This time, we decided to try the construction of truncated 120-cell. However, we only have plenty of long struts and truncated 120-cell with long struts will become 3 meters in diameter. It means that the height would be close to the ceiling of the museum hall. Then, it is difficult to assemble the top part and in addition, since the structure is so sparse that it would be difficult to support the weight and we need a lot of support structures in the sculpture but we do not have so many struts.

Therefore, we assembled half of it as a dome. We still have the diffuculty that one cannot reach the top part, which is about 2 meters heigh, from outside. However, because it is so sparse, a person can enter it and assemble the top part. It is designed mainly by Yasuyuki Tsukamoto, who is a Ph.D student of our graduate school.

We assembled the base part in advance. Usually, assembling a whole truncated 120-cell with smaller struts is not a diffucult work, because one can construct it from the center and the symmetry of the structure guides how to construct. However, it was very difficult to construct it from the cross section. The object in the forground is a dome of 120-cell.




This object is composed of tetrahedra with different shapes. The participants of the workshop first made these tetrahedra.



In order to support the weight of the object, it is important to insert support parts at the bottom.



junior highshool students assembled the lower part from inside to outside.



Tsukamoto-kun assembled mainly the higher parts standing at the center of the object. It is almost complete.



Complete! We entered into the object. Not only the regular large decagon, but also there are many decagon holes through which one can enter.



We took a picture inside it.



I can also enter it without breaking it down.







Three-hold symmetry (left) , two-hold symmetry (middle) , five-hold symmetry (right).