A portable grinder incorporates a safety clutch mechanism between the drive motor output and the grinding wheel shaft to prevent the grinding wheel from dislodging due to a malfunction of the motor. In the preferred embodiment, the clutch mechanism comprises a one-way or a free-wheeling clutch and a slip clutch in parallel between the motor rotor and the drive shaft. The one- way clutch transfers power from the motor rotor to the drive shaft and grinding wheel under normal operating conditions. In the event of a motor malfunction which suddenly locks the rotor, the clutch mechanism allows the drive shaft and grinding wheel to slow and stop in a controlled fashion thereby minimizing the possibility of the grinding wheel dislodging from the drive shaft.
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