(program has a hard-coded path to input file in the first few lines of code - set it to your computer file structure to run)
Change in handedness (chirality): Both ends of this helix are right handed with the middle 50% of the helix left handed. This is our first CAD drawing of a work piece that we have not yet actually made. The switch in handness is a trivial operation on the lathe that is usually set right or left at the beginning of a run. We plan to make this sculpture with two kinds of finish texture. In the middle, left handed segment, we plan to cut shallow steps that will be finished to a smooth texture. The right handed ends will show actual lathe steps that are very sharp but only a blade-width thick. Note that it is topologically impossible to make this piece double stranded by simply screwing two pieces together - as we did with Watson's double helix. Also note that each sculpture has custom computer code behind it because the algorithms used in design are too unique as to be anticipated by a common graphical user interface. In other words, if you can visualize a design, you have to be able to modify our computer code to see it in the manner shown in this figure.
The Overlap of Circles and our Sculpture
When we place a cylindar in orbit as our template, one might expect that the helical tube that is cut will have a circular cross-section. It does not, for the same reason you see in the figure (above) for overlapping circles (from Wolfram MathWorld). As the pitch of the helix increases or as the distance between the linear axis (z) of the helix and the helical tube increases, this effect is magnified. While this figure is exagerrated for the effects we see, it is still significant. You might have noticed that we use a linear stylus and a circular blade. In fact, the stylus should be the same shape as the blade, and that is how we did replications on our earliest lathe. However, this circle overlap effect overwhelms effects observed by using a linear stylus. Experiments are in progress (both on the lathe and in simulations) to create rounder helical tubes. Fortunately, the long axis of the lens is always oriented perpendicular to the z-axis of the helix, so we anticipate that a lens-shaped template (in a single, compensatory orientation) will compensate for this circle-circle overlap.