"Screwy" Screw

 A Thingiverse user saw my Wrong Way Nut video on YouTube, which showed two nuts traveling in opposite directions on the same screw thread.  He was inspired to create his own version of it, which he named Screwy Screw.  Full marks for that name!

It was interesting to see how he came up with a similar solution, yet made some vastly different aesthetic choices.  Most conspicuously, his Screwy Screw is much larger than my own bolt model.

Here's a quick video comparison of Screwy Screw against samples of Wrong Way Nut built on my SD300 and another sample built by Bradley Rigdon courtesy of http://printo3d.com/

Here's a closeup of the FDM samples of Wrong Way Nut, built by Bradley Rigdon.  Notice the funny patterns on the side walls?  See below.

Below is a closeup comparison of a nut built on the SD300 (red) and one built on a Dimension by Stratasys (blue).  Both build processes produce these wave-like patterns, often referred to as "chatter", as a result of very subtle vibrations that occur as the machine changes direction at the corners.  The marks don't affect the model's tolerances--in fact they're hard to see except by examining the model's sheen under a bright light source as here.

STL files for Wrong Way Nut are downloadable from Thingiverse here.