To make a sheath pattern, you start by tracing the blade and as far up the haft as you want to go. In general, there's a one-piece style that dates from at least medieval times where the seam is to the back and the sheath is molded to fit the blade tightly; a fold-over style that uses a welt on the sharpened side so that it won't cut the stitching and is then molded to fit the blade;, and the type I hope to make with two pieces of leather, one on the front and the back, with a welt that goes on both sides of the blade and the tip. With the last design, the welt gives the room for the blade, but I may have to stack the welt toward the haft to make it thick enough, then skive it down so that there's a smooth transition to the thinner part. Intend to either use my micrometer to measure the thickness of the blade to get an idea of what I need to do, or to cut out the welt and try it with the blade before gluing and sewing. Probably both.
Tonight I learned that I don't have to use a groover, but can make a crease instead for the thread. That should save on tools.