A grinding apparatus including a cylindrical grinding wheel assembly mounted on a vertical drive shaft extending from an electric motor through a horizontal work table. The apparatus includes a pressure sensitive electrical switch for activating the motor in response to downward force on the work table. The work table is supported on a housing adapted to contain the motor and can be interchanged with work tables of various sizes and configurations. The grinding wheel assembly includes a core element and a grinding element where the grinding element is secured to the core element by various mechanisms to allow the grinding element to be removed from the core element while the core element is secured to the drive shaft so as to interchange the grinding element in the event that a grinding element has been worn out.