Since left foot is getting printed, I also made ready a second tension spring to be placed in the Achille's tendon area. Differently from the previous one, this has been salt annealed in order to boost its mechanical properties and therefore be able to have a higher fatigue life @ working max deflection.

Here you can find a short video with the main steps about the annealing process and below its detailed description.

What is salt annealing?
It's a thermal treatment of 3D prints that turns the inner structure of prints from amorphous to crystalline and therefore highly increases its mechanical properties (UTS almost doubles).

How to do it (in this case for PLA+)
- Print your part with 100% infill (the part shall not have inner voids)
- Remove supports and perfectly clean and sand the surface (don't leave strings or other imperfections)
- Completely cover the part in fine salt (sand or talc would work too, the finer the better) and make sure salt goes in all voids. Once covered, slightly press the salt and make it a compact block. This is an important step since the function of the salt is to keep the piece on place avoiding deformations when the piece softens.
- Preheat an electric over at about 100°C (above glass transition temperature but below melting point of your material)
- Leave the piece in over for 1 hour (control the salt temperature is stabilized)
- Remove from over and let cool down to room temperature
- Enjoy your strong piece