Assuming it's a belt drive saw? Remove the belt and see if it still vibrates. If so, it's possible the motor is not tight in the mount. The is the pulley is loose on the shaft? Finally, with the belt back on see if the saw blade wobbles as it shuts down. If so, remove it clean all the mating surfaces and remount it.
If it still vibrates, you may need a new belt. The tool and machine belts are not the same section as automotive V belts, so get the correct one from a tool or hardware store.
If all this fails to eliminate the vibration, you may have some bad arbor bearings or the bearings are about to fail.... :blink:
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