Interlocking calibration clips with curved and straight features for calibrating two filaments to each other. These clips work for calibrating multiple filaments on a single or dual extruder system. They can also be used to calibrate a single filament to itself.
If you are designing a multi-part assembly and need things to fit together these are the clips to use to determine the physical and thermal properties of your filaments.
The clips have a 0.2mm gap between straight parts and a 0.25mm gap on curved features. This allows for the 0.1mm tolerance that most printers and machining operations can hold to and results in a feature fit between parts with about 4 thousands of an inch clearance.
Testing of the clips is accomplished by printing the set found in the single STL file and flipping one of the clips upside down on top of the other to test the fit of the features. If the clips are loose then you are under extruding and need to lower the nominal diameter of the filament or increase the extrusion multiplier. If the clips are too tight then you are over extruding and need to increase the nominal diameter of the filament or decrease the extrusion multiplier. When the clips fit easily together with no wiggle and stay put you have precisely calibrated filament.
Note in the images that one filament calibrated with a nominal filament diameter of 1.66 and a melt temperature of 220 C while the other calibrated at 1.74 and a temperature of 215 C. Both of these are different than the physical measured diameters. Yet both filaments produce matching precision parts while being extruded from identically micro stepped extruders. This is the whole point of calibrating to the thermal properties of a filament.
The last two images show how to find the optimal melting temperature. By extruding out a constant stream of filament you should get a rope like coil with a vertical strand to the nozzle. It will stay this way when you stop the extrusion. I call them cobras because that is what they remind me of. If the filament is too cold it will pig tail and curl under the nozzle. Increase the temp 5 C. If the filament is too hot the vertical part will lean over and spider web as it sags when you stop the extrusion. Drop the temp 5 C. With a good melt temperature you have a +/- 5C range for adjustments to counter oozing (lower the temp) and perimeter gaps (increase the temp).
See the summary for how to determine the optimal melt temperature of your particular filament.
The first layers of the clips need to be opposite and to the outside of each other to avoid calibrating to the bed squish edge that is dependent on the tightness of the bed leveling.