Odd that an individual one of these polygons by itself will render and even
print from the resulting GCODE. But when added to this cylinder, they
preview fin. But they disappear when rendering and are not visible when
attempting to print GCODE.

module fin (size=100, $fn=100){
polyhedron(points=[[0,-50,0],[5,0,0],[0,50,0],[-5,0,0],[0,-25,50],[0,0,50],[0,25,50],[0,0,50]],
faces=[[0,1,5,4],[1,2,6,5],[2,3,7,6],[3,0,4,7],[0,1,3],[1,2,3],[4,5,7],[5,6,7]]);
}
cylinder(d=32.1, h=100);
translate([0, 15.2, 50]) rotate([-90, 0, 0])fin(100);
translate([0, -15.2, 50]) rotate([90, 0, 0])fin(100);
translate([15.2, 0, 50]) rotate([90, 0, 90])fin(100);
translate([-15.2, 0, 50]) rotate([-90, 0, 90])fin(100);
http://forum.openscad.org/file/n19270/Capture.jpg

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Nice!

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I saw this, had a few minutes, and played around with it. I came up with:

module fin (size=100, $fn=100){
polyhedron(points=[[0,-50,0],[5,0,0],[0,50,0],[-5,0,0],[0,-25,50],[0,25,50]],
faces=[[0,4,5,2,1],[0,3,2,5,4],[0,1,2,3]]);
}
fin();

Face descriptions can have any number of points, using versions of OpenSCAD
later than 2014.03 (See:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#Alternate_Face_Descriptions
). However, it says there that the points should be "all in the same plane".
However, the above example works (I'm using 2015.3-2 on Mac), but the points
for the two sides are not in the same plane. Is this allowed now?

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