Why one more cable chain?
I decided to add some cable chains to better control the cables position in my 3Drag. I start looking in Thingiverse for a "good" cable chain. My needs:
1) "open" because my 3Drag is now fully built.
2) "large" or parametric, because 3Drag uses flat cables.
I found some interesting designs, e.g. i tested http://www.thingiverse.com/thing:868040. But my printer was making large "spider webbing", calling for a long cleanning time for every element.... One more need:
3) "little work after printing".

The winner was 'Open Cable Chain' (http://www.thingiverse.com/thing:611593), requiring very little work after printing.

But 'Open Cable Chain' is not large enough for my 3Drag flat cables, so I re-make this parametric library, starting from some .stl files by Claghorn.

The "paramchain" library builds open cable chain elements and chain ends having parametric size, in three options:
A type, rotating 0:45°, standard
B type, rotating -45°:0°, reverse of A
C type, rotating -45°:45° autoreverse

The open chain can be closed using bits of 3mm filament, or alternating normal and reverse elements.

To help the user, the type and size of any element is printed inside the element.

Notes:

Any element is 15 mm long, and rotates
45°: 8 elements make a circonference, diameter 53 mm

Modules:
chain_one(large, type)
chain_four(large, type)
end_one(large, type)

Parameters:
large: size external, 15 mm up. The internal chain space is: (large - 10.5) x 7.5 mm.

type:
= 0 => S, only for end_one (female start)
= 1 => A, 0:45° chain / end_one (male end)
= 2 => B, -45°:0° chain / end_one (male end)
= 3 => C, -45°:45° chain / end_one (male end)

note: this library (paramchain.scad) requires 2 model files by Claghorn: "nobar_one.stl", "end_two.stl".

Use:
1) If you prefere to use bits of 3mm filament to close the cables inside the chain, to get a standard chain you can use a sequence like:
S + A + A...+ A + end(A).
(the bits can be fixed using glue or the soldering iron).
2) If you do not like to use bits, you can alternate normal and revesed elements:
S + B + A + B... + A + B + end(A)
the cable is keep inside from elements structure.
3) To make a chain rotating in both directions, use C elements, autoreverse.
4) More complex designs, e.g. S-shaped chain, can be built using a mix of A, B, C types.

Printing:
I printed this in series of 4 (chain_four), more times to test different configurations and minimize the "spyder webbing" issue.
Using PLA ('esun' from Futura) and standard 3Drag 1.2 and Slic3r, my best results using:

• bed: mirrow, 50°, no brim
• temperature: 200°/175°
• fan: 80%
• layer: 0.2, infill: 100%
• print speed: 30/60 mm/s
• retraction: 3 mm at 60 mm/s, lift-z 0.3, travel speed 250 mm/s