When using painters tape was mentioned for making lines,,,has anyone seen the new painters Frog Tape? I is not straight but one has a gentle snake curve (wavy line or rounded zigzag), one is zigzag and .....I forget that the third is. These would make good "lines" to follow if you don't want just straight lines. The one with the snake or rounded zigzag would give you the gentle meandering lines by just sewing down each side of the tape before moving it over. You could also stagger the curves so instead of lining up the curves shift them for different designs. The zigzags you could make squares or diamonds.