f0 to f5 must be normalized before averaging them to get v0Normal.
Even if the points are aligned on x and z axes, the triangles have generally differents areas, so the norms of f0 to f5 are generally not the same.
( according to the cross product properties, the norm of f0 is 2x the area of the triangle (v0,v1,v2) )
f0=normalize(crossProduct(v1-v0,v2-v0)) . . . v0Normal=(f0+f1+f2+f3+f4+f5)/6
should work better
I noticed a confusion between your formulas and your scheme, for example according to your scheme f0 should be the normal of the triangle (v0,v1,v6), not (v0,v1,v2). Hoping this is just wrong typo ?