I have built a Mendel Prusa i3 Rework. In the final steps of calibration, something wrong was happening that was making my prints too weak, light and fragile.
I’m using slic3r to generate the G-Code. The first time I ran the software I had to configure the parameters for my printer. In my case, what was causing the fragile printing was a wrong parameter.
I had the filament diameter set to 3 mm but my filament is actually 1.75 mm in diameter. That was causing the printer to extrude almost half of what it was supposed to.
After adjusting that value and regenerating the g-code, the problem was solved.