A dustproof grinder including: a main body; a rotary shaft vertically mounted in the main body and drivable by the driving unit, a bottom end of the rotary shaft having a plane face facing downward; a bottom cover formed with a central through hole, the bottom cover being disposed at the bottom end of the main body; the plane face of the rotary shaft being larger than the through hole and positioned above top face of the bottom cover; and a sealing member disposed between the plane face and the top face of the bottom cover. A grinding disc is mounted at a bottom end of the rotary shaft for grinding or buffing an object. The bottom cover is sealed with the bottom end of the main body, also, the bottom cover is sealed with the plane face so that the dirt, dusts and chips are prevented from entering the interior of the grinder.
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