This is a string winder is for making coils of string using a figure 8 pattern sometimes known as a mountaineer's coil.

This is designed for a 6mm square chopstick to fit in the holes. This design is unfortunately not parametric, but I've left enough steps in the blender model for it to be easily modified.

A pair of 5 inch posts easily holds a 100 feet of 3/32" string.

Layer 1 has the final meshed part; layer 2 has the winding posts. Layer 3 has the part with the original bezier curves. There should be enough here to modify it for whatever posts you have.

Update: I've uploaded a larger version for those with big hands.

Winding instructions:

Insert winding posts into the holes; they should fit firmly and not fall out. Put the end of the string in the hand holding the winder. Wind the string over the top of one post and then in the same direction over the other to make a figure 8 pattern. Wind until the posts are nearly full, and then use the string to push the loops down further on each side and wind some more until you run out of string or can't fit anymore on. Then remove one or both posts while carefully holding the coil together. Pull out a few feet of string from the narrow end of the coil near the winder, and wrap it around the coil at least 3-5 times to secure it, and then tuck the end under the windings and tighten.

To use the string, pull the other end (not under the coils). The string should pull out freely with no tangles or twists up to the securing windings.

Rebulding for another size post:

If you want different size holes, draw and align a new post model, duplicate the part in layer 3 and adjust extrusion thickness if necessary. Convert the object to a mesh (alt-C), and then use boolean tools (w) to subtract the posts from the part.