Kerf-Based Complex Wood Systems

This research projected investigated complex wood systems constructed from steamed, free formed wooded slats and formed through strategic accumulative local weakening and disruption of fiber continuity by kerfing. Thus the project aimed to develop an integrated computational design tool and robotic manufacturing process that allows programming the bending and twisting behavior of tensioned wood elements through specific kerf patterns.

Because of wood’s anisotropic characteristics, material perpendicular to the main grain direction can be removed without overly compromising the overall structural capacity. In boat construction, furniture making and other fields, regular kerfing is a well known technique for fabricating wooden parts bent in one direction. This project explored how the computer controlled variation of kerf depth, length, frequency and orientation allowed for achieving more elaborate bending and warping figures.
Understood as a system of cumulative kerfs, the macro-scale manipulation of the wooden slats prior to steaming modifies their bending behavior. Constant kerf depth results in stress concentration at the end of the kerfed length, leading to the isolated activation of these regions and consequently produces kinks at these points. However, varying kerf depth gradually in relation to the stress distribution allows for calibrating the bending stiffness with material removal. For example, if the depth variation of parallel kerfs follows a sine curve, the resultant figure displays gradual curvature change avoiding stress concentrations or kinks. Robotic sawing provides the required variability and precision to instrumentalize kerfing in this way.

A custom-designed rotary saw tool for a 6-axis robot was constructed and enabled the testing of related process parameters as for example, saw blade revolution, feed rate, climb cutting and conventional cutting, etc. in relation to geometric kerf parameters including kerf depth, length, frequency and orientation. The behavioral characteristics of the resultant test pieces together with the fabrication parameters were integrated in a computational design tool and tested through the construction of a larger scale prototype.

As initial tests had shown that specific kerf patterns allow for achieving a system-geometry with negative Gaussian geometry once an assembly of multiple kerfed elements is pre-stressed, the prototype was developed as an irregular hyperboloid global system consisting of more than 140 elements with unique local kerf patterns. In order to “program” the physical forming behavior of each element, the computational design tool generates the individual kerf patterns, provides the relevant geometric data and outputs this directly in robot control code. This enables the direct fabrication of the individual kerfed pieces, which were subsequently steamed, pre-stressed, assembled into larger components and finally erected as the 5 meter tall hyperboloid prototype.

Performative Wood Studio (Achim Menges)
Brad Crane, Andrew McGee, Marshall Prado, Yang Zhao
Harvard University Graduate School of Design, 2010