used walking foot. drew the center circles with water soluble pen, carefully followed the line with walking foot. on each circle, I lined up the edge of the foot with the previous line. the circles got bigger, and the curve less extreme, basted with safety pins, so maybe this would be the kind of situation where spray-baste would be more appropriate. I switched thread colors every 3 to 5 rounds. I also worked on all the circles at once, adding rings all over until I liked the sizes and overlaps.