Santa Monica Cradle: Reflections on Craft and Computation

While it does not strictly follow the Sensing-Evaluating-Shaping design methodology I developed in my SMArchS thesis (Integrating Digital Design and Fabrication with Craft Production), the Cradle sculpture by Ball-Nogues Studio in Santa Monica illustrates many of the issues addressed therein.

My thesis examined if methods of manual craft production can be utilised to overcome the indeterminacies of physical materials and processes that hinder Digital Design and Fabrication. The Cradle sculpture consists of a number of stainless steel spheres that are tangent to a complex curved surface as well as to each other.

The Cradle Sculpture Seen as Spheres Tangent to a Complex Curved Surface and to Each Other

I developed a script which is able to place spheres one at a time on a surface in such a manner. However, if one attempts to physically replicate the the results of the script (say, by placing balls in a bowl)  one will quickly encounter a number of discrepancies between the digital and the physical.

Balls in a Bowl

One of these discrepancies is the effect of gravity on the tangent spheres which will alter the positions of all the spheres every time a new tangent sphere is added. However, this can be overcome if each ball that is added is glued in place before the next one is added.

Another discrepancy which is much harder to overcome arises from the ‘imperfections’ of physical materials. The geometric nature of the system of tangencies between the surface and the spheres and between the spheres themselves means that the displacement of any one sphere or any modification of the surface will cause a displacement of all the spheres in the system. This means that the slightest discrepancy in form between the digital model of the surface and its physical counterpart, or any deviation of the balls from perfect sphereicality, will cause a mismatch between the digital model created by the script and a physical model.

One way to overcome this issue would be to build in a tolerance between all the components of the system (the surface and the spheres). However, this would have two drawbacks – firstly, it would mean that no two spheres in the physical model will actually be touching due to the tolerance between them, and it could be argued that this would unacceptably compromise the visual perception of the sculpture. Secondly, it would require a sophisticated joint at each point of tangency to absorb the tolerance built into the system which would increase the cost of the project significantly considering that there are approximately three hundred and fifty balls in the sculpture.

Instead, in this project, we chose to allow a deviation between the digital model and the physical artefact. The script was thus used only as a guide in the project to visualise the project through renderings, to estimate material costs and quantities, and to perform structural analysis.  This enabled the surface of the form-work to be constructed cheaply and rapidly without the pressure of having to conform to the digital model to a high level of accuracy and to have a very simple welded joint between spheres. The final configuration of balls in the project was guided by the digital model developed using the sphere packing script and also a result of the incomputable, indeterminable characteristics of the physical materials and processes of fabrication and subjective human design responses to these unique conditions. Proof of this idea lies in the impossibility of duplicating the exact placement of balls if one were to repeat this project once again.

The Surface of the Form-Work Fabricated with Two Layers of Curved Lauan
Welded Joints Between Spheres

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