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Sorry, this model is no longer printable. Shapeways said it kept breaking because of the small contact points. I tried making the intersections larger, but it doesn't look as cool. If anyone has any ideas on how to fix it I'd love to hear them.
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modified version of George W. Hart's
http://www.georgehart.com/rp/rp.html
No markup because the original model is his and offered for free. I just tweaked it and uploaded it so others can print his design.