There’s nothing glamorous about a wheel dresser, but if you own a tool with a grinding wheel, you need one. A wheel dresser removes the buildup of crud on the grinding surface, exposing new grains for better cutting performance. You can also use it to square the face of the wheel when it isn’t running true.
Grizzly makes their version of this tool (pictured) heavy on purpose. The cast iron handle offers more stabilizing mass for better control.
This #0 wheel dresser from Grizzly can be found for as low as $8 — a lot cheaper than throwing away that errant wheel. And many other companies offer similar products for about the same price.