To tuck the leather, the edge needs to be cut. Otherwise, you will get a double thickness at the bend point. This process is called sinking or descending the edges. For sherfing, a knife or a special tool is used - a scraper or a plane. The tool must be sharp otherwise you will get married. The knife for work with the leather should be sharpened only on one side. Do not put the side on the leather, the angle is as small as possible. The cut must be along the leather and not in the depth. You can wet the area to be cut a little to make it easier.