the blue frame could use some diagonal cross bar at the base and back or be strapped to a tree

intuitive i felt that a double Chebyshev would preform good enought even with low precision parts, a double or triple sarrus might do that to but in a Chebyshev all rotational joints are coplanar and i felt that it were simpler to construct at low precision as its function less depends on the joints ability to withstand sideways momentum. A sarrus links linearity is derived from the perpendicular stiffness of rotational joints there for stability and linearity depend directly on sideways joint precision, in a Chebyshev linearity is derived from the relative length of the linkage. sideways stability could be increased with further cross bracing.

the challenge is can a sarrus be made without a drill-press