These buckles were designed to match as closely as possible the original design of those originally clamped on my backpack. Also, they were designed with 3D printing in mind, hence i had to make changes to the primary functional design in the aim to print it better.

Here is the original CAD file location :
https://github.com/bebenlebricolo/3D-printing/tree/master/Backpack%20Buckles%2055mm/CAD%20files

At the moment stuff is still a bit messy, however feel free to share, improve and fork this project as you like. Just remember to respect the CERN OHL license terms under which i've licensed the files.

http://www.ohwr.org/attachments/2388/cern_ohl_v_1_2.txt here is a link redirecting to the official hosting website of the license.

You may also find its trace in this video, posted by Thomas Sanladerer where you can see the supports removal. Thanks to him.
https://www.youtube.com/watch?v=OsQpxkLhDLk

---- Specifications ----
50 mm (actual 47 mm wide) x 55 mm Buckle - Replacement part - Decatlhon Forclaz 30 Litres
Both parts (male and female) + improved male part (2 more springs) and virtual assembly for validation purposes (design)

----EN----
I made a replacement part for the broken piece of my backpack. The original one have been overstressed and broke at the attachement area of the backpack strap.
Then i used my CAD software to make a replacement part, keeping as much as I could the original measures of the original part. I finally made a virtual assembly design to correct the little measurement mistakes, and make some improvements of the design.

---- Fr ----
J'ai conçu cette pièce en suivant les cotes de la pièce d'origine (qui provient d'un sac de randonnée de marque Décathlon, de la gamme Forclaz 30 L) pour remplacer la pièce d'origine (boucle femelle). Les deux boucles se veulent aussi proches que possible des pièces originales, en termes de design. J'ai également effectué un assemblage virtuel "à blanc" pour tester la conception, corriger les erreurs de mesures et effectuer quelques améliorations.

Prusa i3 Rework

Yes

Yes

0.3 (best) or 0.2 mm

100% (max rigidity)

----EN----
These parts might by printed laying flat on the 3D printer bed (biggest side of the part). This will help the buckle to withstand mechanical stress thanks to the lining of the filament fibers (they should be aligned with the X axe of the part, then the mechanical load could be easily handled by the fibers).

---- Fr -----
Ces deux pièces doivent être imprimées à plat, selon leur plus grand côté. La répartition de la charge mécanique sera bien meilleure si les couches sont dans le même plan que le plan de la charge principale (plan xy, avec une composante majorante sur l'axe X).

Male buckle part :

Nothing too hard for this part. I ended with many functionnal parts using Cura and Sli3r. Just make sure to enable supports (and brim / raft for ABS because of the small footprint of the part).
I recommend using pillar structure with Slic3r as they are really easy to remove, and make sure to correctly tweak the gap distance between the support structure and the actual piece.

Support settings (Slic3r):
0.2 mm Z spacing and 2.5 mm pattern spacing.
3 interface layers.
ABS 220 deg Hot end / 70 deg bed

This part is much more tricky than the male one.
Be sure to use supports, but with a big spacing pattern (15 mm for me) to make it easy to remove (the inside of the buckle is quite inaccessible ). I also used Honeycomb structure instead of pillars, and made the Z spacing and interface layers higher than the default values.

Support settings :
0.35 mm Z spacing
15 mm spacing
Honeycomb pattern
3 to 5 interface layers

Overhang threshold : 0 (set Slic3r to automatic mode, it saved my print! )