Flexi Snake — print-in-place articulated fidget that coils

A print-in-place articulated snake that comes off the bed in one piece — no supports, no brim, no assembly — and coils into a full spiral in your hand.

16 necked vertebrae are joined by captive ball-and-stalk joints. Every segment tapers to a slim neck at each end, leaving a wide V-groove between beads, so each joint folds 50–70° before any surface touches and the whole body wraps well past 360°. The captive joint can't pull apart (a spherical cap wider than its socket mouth), but it yaws and rolls freely. A carved head with eyes, nostrils, a mouth line and a blunt snout finishes the snake, and light scale rings run down the belly.

Print (one piece, lay flat exactly as exported):

• No supports, no brim — every bead rests on the bed along its belly line.

• Single colour, single extruder. A filament swap can string into the sockets and weld the joints solid, so keep it one material.

• PLA at the shipped clearances (0.55 mm radial). For PETG, raise radial_clr to ~0.65 and axial_gap to ~1.2 (PETG strings + bonds across small gaps).

• After printing, flex each joint once to crack any micro-welds — then it articulates freely.

• Size as shipped: ~204 × 18 × 15 mm.

Fully parametric — make it any length you want. The two knobs at the top of the .scad are exactly what you'd reach for:

• n_segs — number of vertebrae / knobs (default 16).

• seg_len — length of each segment (default 10.5 mm).

Change either to make a stubby little worm or a long python. The only rule is seg_len - stalk_root_overlap > cavity_inset + cavity_d/2 so a segment's own joint stalk never roots into its socket (the defaults leave ~1.15 mm of margin; if you shrink seg_len, watch that inequality). You can also tune the fold range per joint (neck_drop, bevel_depth), the head→tail taper (mid_r_head, mid_r_tail, taper_power), the joint clearance for your material, and toggle the belly scale_rings. The full .scad source is included.