Three Puzzles - Tiling a 3x3x3 Cube

A tiling of a cube (3x3x3) made of 27 sub cubes. Restrictions placed on the tiling procedure can make the process a simple one with few answers. Here the tiling is limited to 4 pieces: 3 identical pieces composed of 7 sub cubes and a single piece of six sub cubes. A search found seven sets of 3 identical pieces made of 7 sub cubes that together with a six sub cube piece tiled the 3x3x3 cube. More than one six sub cube piece can be used with some of the 7 subcube sets so there are a total of 23 sets of pieces that tile the 3x3x3 cube with these restrictions.

Five files are included. The first is "seven_set.stl" one of the unique sets of three identical pieces of 7 sub cubes.

The second file - "six_set.stl" - contains 7 pieces, each of 6 sub cubes, each of which can be used together with the set of three identical seven sub cube pieces to tile a 3x3x3 cube. Not difficult but interesting to see how this is done. The seven six pieces consist of
different ways sets of two sub c