Hanshi, I lay out evenly spaced hash marks at bottom, middle, and top, then pencil a line that will make one full turn, or sometimes two. Then I fill in the rest of the lines trying to stay equally apart. When it looks right, I spray it with satin clear laquer to preserve the lines while I file. I first cut them with a tri-corn file to make a guide cut for the round file, then round file them in. It isn't rocket surgery, but it takes time.