Here's how I make the best sraping tools for ring chasing or tillering that I have ever found. Use an old pocket knife or similar knife with about a 3-4" blade on it. Sharpen it good til it's nice and sharp, and then continue to sharpen but only on one side. If you're right handed, continue to sharpen the knife on the right side, applying pressure as you stroke. Left handed, sharpen on left side. Do this for a few strokes and then feel the edge on your knife. It will not hardly scrape at all if you rub your finger across it one way, but going the other way it will feel like it really grabs your skin. Try that. It's all I ever use.
Note: Once you have sharpened the knife, and then sharpened on one side to make it a scraper, you don't have to sharpen it again, except on the one side. A scraper should never be truly "sharp" as in good for cutting something, in my opinion. My scraper that I use makes wood fly when I want it to, but I honestly think I would have trouble cutting an eighth inch twine string.
CP