Newer better crossbow here: https://www.thingiverse.com/thing:2876091
This is a crossbow that uses the elasticity of the 3D-printed limbs to fire to bolts.
A mini crossbow with fitting arrow. Using 3D printed parts and some screws, one spring from pens (diameter < 5.0 mm) and nylon fishing line.
Screws required were showed in the picture.
Short 3mm screws at the tip of the bow.
Long 3mm screws hold the spring clip, handle and body together.
2mm screws used as the axis of the trigger.
Spring places in the errrr... you see it you know it.
.skp file for SketchUp is available. All versions and designing processes lined up in the file.
The trigger is ugly and a little uncomfortable. Wish someone can improve it.
Crossbow firing video:
Bow limbs should be printed one at a time, to ensure they are symmetric. Printing 2 limbs together will generate asymmetric infill, result in asymmetric draw when loaded.
Resolution 0.2 mm is enough.