A grinder can work as a sander if you attach the right type of disc to it. The most common type of disc used for sanding is an abrasive disc, which comes in different grits. The higher the grit, the finer the sandpaper-like material on the disc will be. You can also get special discs that are specifically designed for use with a grinder, such as flap discs. These have abrasive material on them as well, but also have flaps that help to create a more even finish.