edges can be polished by successively sanding with finer grit sandpaper, or using a buffer and compound,To get a sharp edge with sandpaper, use a sanding block to keep the edge flat. If you want a rounded edge, use hand sanding. Using wet/dry sandpaper with water will give the best results.

Using a buffer can polish your edge very quickly. Either sand until smooth and then buff with blue compound, or buff first with red compound, then blue on a separate buffing wheel. Don’t allow the buffer to catch the edge of the material, it may get thrown.