InMoov Calibrator

I have decided to start the journey of building the famous InMoov robot. I have started with the basic Finger Starter and the very first thing to do is calibrate the printer to ensure that the parts will fit together properly.

I am using an Ender 3 printer, Cura and PETG filament. Upon my first attempt the pieces were so tight that once I was able to forcefully put them together I could not pull them apart.

Calibrator with 0.0mm horizontal expansion

After a bit of searching, I found that others with the same issue had been able to fixing by changing the Horizontal Expansion setting in Cura. They suggested different values, so I had to try for myself. That setting affects the "holes" in the print, negative values means the holes are more "loose". I tried -0.2, -0.4, -0.1, -0.05 and -0.08 mm in that order. Here's some pictures with the results.

Calibrator with -0.2mm horizontal expansion

Printing with -0.2mm left the pieces fit but a little too loose. Then I still went on to try -0.4mm to see how much different it was and the result was as follows.

Calibrator with -0.4mm horizontal expansion

This time the holes were even bigger, by too much. So I moved the other way and tried -0.1mm.

Calibrator with -0.1mm horizontal expansion

That one fit almost perfectly but I still ha dto try to get better results, so I went for -0.05mm.

Calibrator with -0.05mm horizontal expansion

This time the sides fit tight but not too much, the problem was the center rectangle that I could not take apart after trying for a few minutes. So I finally tried -0.08mm...

Calibrator with -0.08mm horizontal expansion

And here I stopped trying! It fit slightly better than -0.1mm and I could remove the pieces easily.

Conclusion: If you are having trouble with the calibrator pieces not fitting, I'd try the Horizontal Expansion setting on your slicer first, your perfect number will be most likely different than mine but somewhere between -0.1mm and -0.2mm is a good place to start.