Corrie

I am going to be a stay at home mom, and was hoping to supplement the income with making leather dog leashes. I was planning to use kangaroo skin with an eight strand braid using a core. The problem is, I can't even figure out how to round the core. I have a book, "Fine Leather Braiding" by David Morgan, but it is not helping much. I do have until October to perfect this (haha), but am feeling very frustrated. Any pointers, advice?