run-on
The period when a power saw or other tool continues to run after being powered off.
run-on: blade spin after you kill the motor
A run-on is the interval between the moment you switch off a powered cutting tool and the moment its blade, wheel, or bit actually stops rotating. On a table saw, band saw, or angle grinder, this can last anywhere from a fraction of a second to several seconds depending on the tool's mass, bearing friction, and motor design. The heavier the flywheel or blade assembly, the longer the coast-down.
Run-on matters because a still-spinning blade is a hazard. Your fingers, workpiece, or clothing can catch even as you think the tool is dead. On a 10-inch cabinet saw with a heavy blade, run-on can exceed 8 to 10 seconds. Bench-top models with lighter wheels may stop in 2 to 3 seconds. Hand-held tools like angle grinders typically run-on for 3 to 5 seconds; brushless motor designs sometimes run longer than brush types because they have lower bearing drag.
Control and safety practice
Modern industrial machinery addresses run-on through mechanical brakes. A table saw brake typically engages an aluminum disk or friction pad against a rotating shaft within 5 seconds of power cutoff, meeting safety standards like ANSI B19.42. Consumer and older shop tools often have no brake at all, making run-on a pure waiting game. Some woodworking shops enforce a "hands off" rule for 10 seconds after shutdown, regardless of perceived motion.
Pneumatic tools run-on less than electric ones because air motors have natural drag once supply pressure drops. Wet grinders used in metalworking sometimes have oil-cooled bearings that increase drag and shorten run-on. Conversely, precision spindle bearings in high-speed cutters can extend run-on significantly, which is why spindle brakes are standard on CNC mills.
The term "run-on" comes from the plain English description of what happens: the tool runs on despite your command to stop. It is not a malfunction unless run-on exceeds design specification; it is simply inertia. Understanding your machine's actual run-on time, not the label's claim, is essential for safe work and for timing transitions between cuts or tool changes.