An adjustable mechanical assembly system is disclosed. In some examples, the frame assembly system comprises a plurality of joining pieces having a plurality of openings in each joining piece, each of the plurality of openings having a first cross-sectional shape and framing pieces having a second cross-sectional shape, different from the first cross-sectional shape, wherein the first cross-sectional shape can be formed by an arrangement of two or more of the framing pieces, a first one of the two or more framing pieces positioned approximately perpendicular to at least a second one of the two or more framing pieces in the arrangement. In some examples, four joining pieces form four corners of a rectangular frame, and at least eight framing pieces form four sides of the rectangular frame. In some examples, the joining piece can further comprise a protruding member extending from the joining piece.