Click on the image to enlarge and download and you can use this layout form or template to help layout crowns.
This form will help you lay out prongs when creating new crowns. Use the crossed lines on top when making a 4 or 8 prong crown, and the bottom lines for a 6 prong crown.
This form works equally well for round, oval, pear, and marquise shape stone.
In addition, the graph lines and circles will help you keep your jewelry symmetrical while laying out the design and constructing the peice of jewelry.
This form is very useful for this topic.