Shafted grinder and polishing tool

A shafted grinder comprising:

• a shaft having a shank section at a rear end;
• and a grinder having a rotationally symmetrical shape around an axis of the shaft and fixed to a front end of the shaft, the grinder having an outer peripheral end located on an outer peripheral side with respect to the shaft, the shank section being chucked into a hand-held rotary tool to polish a workpiece with the outer peripheral end of the grinder,
• wherein the grinder includes a plurality of grinding element bundles of a plurality of inorganic filaments bundled together and includes a resin bonding the grinding element bundles,
• a natural frequency has a value that does not cause resonance during a polishing process when the following conditional expression is satisfied:
• 0.4≤S≤100
• where S is a stiffness of the shaft, and
• when a region 30 mm from the rear end of the shaft as the shank section is fixed to a jig and a rear end of the outer peripheral end of the grinder is pushed from a direction orthogonal to the axis, the stiffness of the shaft is determined by using the following formula:
• S=F/δ
• where F (N) is a push-in load, and δ (mm) is an amount of displacement of the front end of the shaft.