This is a very tight tolerance concentric ring fit and calibration test. It was designed around PLA but should be applicable to any material. It is assumed that the printer on which the test is run can hold a tolerance of 0.1 mm. It is highly recommended that the basic filament calibration test found here http://www.thingiverse.com/thing:1037301 be run before you try this one.
This calibration and fit test consists of three rings that match up and fit inside each other to test different parameters. This will test the fit between two walls, the fit inside a single wall, and flushness on the inner walls from one part to the next. If your X or Y axis are not calibrated properly you will print an oval which will not allow the parts to fit properly. This will also test short span 4 mm radial bridges. If you are getting any sag in any direction the middle ring will not fit flush.
Once printed the only post processing that might need to be done is first removing the lip sometimes created around the edges on the first layer from the squish needed to stick it to the bed. Second, removal of the small vertical ridge sometimes created where a the head starts and stops on a ring and retraction is not quite tuned right. There should be no need to touch any of the other surfaces. When assembled the tolerances will be very tight at around 0.10 - 0.15 mm clearance and the three parts will look like one.
The pictures show the sequence for putting the parts together and the final assembly orientation.
It's fun to show this assembled print to people and ask it they can figure out how you printed it without supports.
The STL file includes all three parts as a collection. They are CURA scaled and oriented for printing.
First layer set to 0.20 mm.
Top and bottom thickness between 0.6 mm and 0.8 mm.
Retraction needs to be on.
Cooling fan is recommended for successful bridging of PLA.
Cooling fan should come on at the second layer