The Cys-Cys dimer model
Molecular sculptures in wood, stone, etc. are models representing parts or pieces of vital biological macromolecules. Just as in life these molecules play unique, significant roles, so these sculptures have been chosen to depict significant segments of much larger biomolecules.
Starting with an idea, one searches for original, experimentally determined structural information from the Protein Data Bank (PDB), where the author wrote the original programs to store and display the first structures 30+ years ago. Here, this information is viewed graphically to select the desired components, size, orientation, and location. This information is passed on to program SCULPT, a program written in FORTRAN to calculate the position of a computer numerically controlled (CNC) milling machine cutting tool to sculpt out the desired model.
Figure 1 gives a view of a CNC machine in operation. These large machines are precise (to 0.0001 inches), robust, energetic instruments; they act like a drill press (cutting up-down in the z direction) while the table holding the model moves laterally (x-y directions).
Figure 2 shows the machining of a layer of the cysteine dimer model; each layer is a plank of red oak, 8"x12"x3/4" (20 cm x 30 cm x 2 cm) in size. Each plank is first machined "bottom-up", then glued in place, then machined "top-down". This two-step process is necessary because conventional CNC machines are 2 1/2 dimensional and thus are unable to carve interior cavities (for example, the figure "S" when viewed from the top).
Figure 3 shows the start of a top-down milling of a growing piece. Because of individual differences in pieces of wood, and especially because the CNC milling machine is used for student teaching, many things can change from one session to the next, so the precise alignment of each piece is necessary to avoid orientation errors in parts of the assembled model.
Figure 4 shows pieces ready for gluing and figure 5 shows them clamped overnight. Brass rods are used to assure precise alignment between slabs.
The most critical moment comes when the top piece is machined and the last void area removed. The forces of the CNC machine are such that special care and special techniques are required at this step in order to avoid destruction of the weakly frame d model. Slow cutting is not the answer because wood, if cut slowly, is burned by the overheated cutting tool; conversely, a fast-moving tool ejects wood chips and excess heat for a clean cut, but also exerts excessive forces on the fragile model.
Figures 6 and 7 show the outer faces of the model just after this crucial step, which puts considerable pressure on the wood as it is being machined.
Figure 8 shows the successful result after
the last step. The model is supported only at the bottom in a wooden frame that,
of itself, is too weak to be clamped properly in the vice of the CNC machine.
The final product can be viewed below:
©2000 E. Meyer