David Smith Einstein Hat 28

28 pieces, all equal.
They fit together without gaps, but form a surprisingly irregular structure. It is an aperiodic tiling of the plane.
Roger Penrose made such tilings famous with two or more pieces.
David Smith found a tiling with only one piece, hence the name Einstein.

This puzzle is moderately difficult, when the frame is presented. Fitting pieces into the frame, and working along the outside is a helpful strategy. But eventually the last 3 pieces will not fit. Then you have to rethink your placement, and find variations of the placement.

Included are:
* one svg file, suitable for lasercutting. Green lines for marking the text, red lines to cut pieces and frame.
* freecad file, where the svg was imported and extruded into 3D. These are created with 0.4mm gap between between the pieces, so that a bit of elephant foot or over extrusion is allowed.
* STL files for both Frame and one Hat
* 3MF files created with prusaslicer for Frame + 14 hats, and 14 hats without