This invention provides web-cutting mechanism that can be mounted in line at an appropriate location between the web-handling peripheral (printer) and a web roll. The cutting mechanism operates before the available storage in the winder festoon has been exhausted, and decouples the roll's energy from the web. The cutting mechanism can employ a blade that is drawn through the web solely by the movement of the web itself. The blade is mounted at a (e.g.) 45-degree angle to web travel, causing it to be pulled through the web. A negator spring assembly and associated cable drives the blade into the side edge of the web when a slide-mounted blade shuttle assembly is released by a latching pawl of a solenoid assembly. The solenoid is triggered by a signal indicating an emergency stop condition, such as an upstream jam.