Abstract: A center machine for producing corrugated fins for heat exchangers has servomotor driven pullout rolls for stretching a compressed corrugated strip to desired fin density and normally driven in phase with corrugation forming rolls. A cutoff knife severs parts from the strip and a sensor measures the length of each part. A control determines part length error, calculates servomotor speed adjustment needed to nearly correct the error and causes such a speed adjustment for a short period to alter the phase of the pullout rolls relative to the forming rolls.