I took a week off, for my sanity, and spent a lot of the time printing objects from Thingiverse.  This Klein Bottle is fun

 

 

Here is a working differential:

 

 

This rook has been printed by thousands of people (but few of them as large as this one).  Notice the spiral stair case inside:

 

 

 

 

 

This abstract object is fun because at first it looks like two objects, not one.

 

 

This box has a twist-on top with printed threads

 

 

And, finally, a sphere covered with gears, all of which turn in unison.  The “stand” actually is a gear with a knurled knob, to give you a way to make all of the gears move