In case there aren’t a million examples out there already, here’s a tiny (2cm diameter) circular cup shape printed with loose belts (left), and then again after everything was tightened up (right). Specifically, it was a loose Y-axis motor belt. Do you know why it was loose? Because the locking nuts on the outside of the cabinet DIG INTO the cabinet plastic over time. How nice. Some washers (flat, not locking) might solve the problem, at least temporarily.
thanks for the heads up 
will make sure to have washers in stock from now on