A machine operator holds a chicken carcass to a circular saw, or a casting to an abrasive cut off wheel. Considerable risk to the hands is minimised with a controllable (about 10 ms) wheel stop mechanism, optically triggered when a gloved finger enters a hazardous zone. (An option uses a conductive glove trigger). An electromagnet releases a powerful spring mechanically linked to opposing brake shoes, forcing them against both sides of a brake disc. The brake disc and the cutting wheel share a shaft but are located in separate compartments. Incident reporting over a network is included.