An interactive computer simulation of the steady-state melt spinning of poly(ethylene terephthalate) was developed based upon a combination of physical laws and empirical relationships. The simulation incorporates crystallization effects which makes it valid for a wide range of take-up speeds. Modifications to the conventional threadline that allow judicious control over the threadline dynamics were modeled and included in the simulation for exploration of the effects of these perturbations. The modifications include quenching and on-line zone heating. The simulation was verified using experimental measurements of threadline diameter, velocity, and temperature at 3000, 4000, 5000, and 6000 m/min take-up. Off-line measurements of crystallinity and birefringence were also compared with the values calculated by the simulation at these speeds.