Auxetic Grip Pad — Rotating-Squares Metamaterial (parametric, 4 sizes + coupon)

Auxetic Grip Pad — a rotating-rigid-squares metamaterial sheet.

WHAT IT IS A flat sheet of rigid square tiles, each joined to its four edge-neighbours at ONE corner only, and that corner alternates in a checkerboard so neighbouring tiles are forced to counter-rotate. Pull the sheet in one direction and every tile twists, which also opens the gaps the other way: it expands on BOTH axes at once. That is a negative Poisson ratio (about -1). A normal sheet necks in when you stretch it; this one fattens.

WHY IT GRIPS Because it has a negative Poisson ratio it goes synclastic: drape it over a jar lid, a bottle cap or any dome and it forms a cap that hugs the curve instead of wrinkling, so far more of the pad touches the surface. The open lattice and tile edges bite into a lid's knurling. Pull to conform, release to grip. It also makes a satisfying flexible fidget sheet.

What Is In The Bundle

• auxetic_grip_pad.stl — the default 6 x 5 pad (about 66 x 55 mm)

• auxetic_grip_pad_3x3.stl — small 3 x 3 (about 33 x 33 mm)

• auxetic_grip_pad_8x8.stl — large 8 x 8 (about 88 x 88 mm)

• auxetic_grip_pad_10x10.stl — extra-large 10 x 10 (about 110 x 110 mm)

• coupon.stl — a 3 x 3 test coupon: print this FIRST, stretch it by hand, and confirm your filament's necks flex without snapping before committing to a big pad

• auxetic_grip_pad.scad — the full parametric OpenSCAD source (see below)

Print Settings

• Prints completely FLAT on the bed, one piece, zero supports, zero bridges.

• 0.2 mm layers, 2-3 perimeters. The thin necks must be at least 2 perimeters wide (the default neck width 1.0 mm prints fully solid on a 0.4 mm nozzle).

• MATERIAL MATTERS: the necks are living hinges. Print in PETG or TPU. PLA necks fatigue-crack after a few dozen flex cycles. PETG necks survive; TPU makes it a stretchy, silicone-like pad.

• Print the coupon first and flex-test it in your chosen filament before running a full-size pad.

CUSTOMISE IT YOURSELF (parametric OpenSCAD) The .scad is fully parametric — open auxetic_grip_pad.scad in OpenSCAD (free, openscad.org) and either edit the variables at the top or use the built-in Customizer panel (Window > Customizer). The grouped parameters:

Grid: nx, ny — tiles across / down (footprint = nx*pitch by ny*pitch) pitch — tile-centre spacing in mm (default 11) Tile + hinge: gap — rest gap between neighbouring tiles (the void seed) neck_w — living-hinge neck width (the fatigue-critical dimension; keep >= 0.8 mm) bite — how far each neck sinks into its two tiles (weld overlap) corner — tile corner rounding radius Body: thick — sheet thickness in mm (default 2.4) part — "pad" (the sheet) / "coupon" (a 3x3 corner to test) / "demo" (a preview of the stretched, rotated state)

To make your own size, set nx and ny and export: openscad -o my_pad.stl -D 'nx=12' -D 'ny=4' auxetic_grip_pad.scad or just press F6 (render) then F7 (export STL) in the OpenSCAD GUI. Want a softer, floppier pad? Lower neck_w toward 0.8 and/or thick toward 1.6. Coarser, chunkier tiles? Raise pitch.

The four bundled STLs were all generated from this one file by overriding nx/ny.