Having a problem with sharpening my straight edge knives. I've used the paper wheels, oiled sand paper, different grits of paper from coarse to fine and can't get the knives sharp enough to cut used thread. I also, have tried using wet and dry stones. My head knife I can get sharp but these straight edge knives have me baffled. The handles on them are green wood and they come from leather suppliers. I wonder if the steel they use is inferior and that's the reason I can't get them sharp???