Best to start with HSS, especially one that a machinist friend grinds for you. In a pinch, a diamond nail file will put a sharp edge on that brazed carbide lathe tool you have there. Sharpening only, no shaping! If you have ever used a file before, you will feel that telltale cutting feeling. If you don't get it, that isn't a diamond file. Go to Harbor Freight and grab their multi pack for about $10. They have many uses. And, they're much better than a nail file which tends to have very few diamonds. But, if you are really low budget (many are), the diamond nail file will work, even one which has been discarded after being found useless for its original purpose.