File the bottom of the plate with the emery board. Purchase a thick emery board (for acrylic nails).
File down the plate until it begins to feel smoother.
Purchase a clear or white shellac from your local hardware store. This will help coat the underside of the plate to keep it smooth.
Brush the shellac onto the bottom of the plate very lightly. Let it dry for approximately 30 minutes.
Reapply if necessary. After the shellac is dry, feel the bottom of the plate. If it is still a little rough, add more shellac to the plate.