I adapted this design from a design I found at freetattoos.org. If you'd like to try using the same template I've posted a PDF here. Note that this is my working template, not tidied up at all! The original design wasn't an exact circle so I traced around a zendala tile, extended some lines, and eliminated a wee section. More info is on the template I've posted. (Interesting how the original design uses something akin to Shattuck in the background.)
You can see previous work using this same template here and here.