### Nanotubes and Nanocups

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Published on November 4, 2011

#### Description

In "Buckyballs" I described a simple openSCAD method for making molecular models and began a search for interesting molecules to print. I've come across a very nice site for generating the atomic coordinates of carbon nanotubes, TubeASP, by R. G. A. Veiga, Universidade Federal de Uberlandia, Brazil, and David Tomanek, MSU, 2007. see k.1asphost.com/tubeasp/tubeasp.asp

Nanotubes are a form of carbon related to Buckyballs. They have interesting properties and are of great interest to material scientists but they are also very decorative objects. A few turns of nanotube models make the pretty bracelets shown at the left. The cups (see picture) are models of nanotubes to which a bottom and rim have been added. They are about the same size as ornamental pin and hairpin holders.

Nanotubes can be though of as rolled up sheets of graphite. Three integers are used to describe them. Two principal ones, n and m, give information about the diameter of the tube and its twist or "chirality". The tubes extend indefinitely in both directions so in many cases n and m are a sufficient definition. While nanotubes extend to infinity they do have a repeating unit. That is the same pattern occurs over and over again as one procedes along the tube. The number of repeating units can be used to pick out a short segment of nanotube. In order to get nanotube-15-15-3, the middle bracelet in the picture, we have to input n=15, m=15, number of units = 3, into TubeASP. The smaller bracelets are from nanotubes 40-0-2 and 36-0-2; they are not complete as a row from each was lost to the raft. You can learn more at the nanotube site - see pa.msu.edu/cmp/csc/nanotube.html

There are a number of things about nanotubes that makes printing easy. TubeASP by default generates nanotubes aligned along the z axis. Tubes where the hexagons point along the z axis can be chosen to make printing more certain although tubes where the hexagon points wrap around z seem to print equally well. Models are sturdy and print quickly as a nanotube is mostly empty space. A twisted model can be cut at right angles to the z axis and printed on a raft.

#### Instructions

Nanotube coordinates are output by TubeASF. The fortran program nanoread.f generates the openSCAD module calls. In the sample program, makenano15-15-3.scad, the calls were inserted into a union statement. Makenano15-15-3.scad outputs nanotube15-15-3.stl, the larger bracelet. A few notes about the fortran program and the TubeASP file are appended to makenano15-15-3.scad.

The bracelet should be sized on the build platform and printed with a raft. Print it with 100% infill to make it sturdy enough to snap off the raft.

The cups can be built directly or with a raft. Nanocup16-4-4 is an example of a nanotube with a twist.
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