octahedron-joint.scad

slot_dim = 15.4;    
thickness = 4;

length = 40;
outer_scale = (slot_dim+2*thickness)/slot_dim;
difference(){

hull() for(a=[0,90,180,270]){
    rotate([45,0,a]) rotate([90,0,0]) 
    scale(outer_scale) translate([-slot_dim/2,-slot_dim/2,10]) cube([slot_dim,slot_dim,length/outer_scale]);
}

    union() for(a=[0,90,180,270]){
        rotate([45,0,a]) rotate([90,0,0])
        translate([-slot_dim/2,-slot_dim/2,22]) cube([slot_dim,slot_dim,length]);    
    }
    

}