Guessing that you're looking for a developed length/flat pattern?
I've had good results with an unnamed, superior cad system by modeling the component as sheet metal (not a sweep) whose thickness and width is the diameter of the bar. This will get you the flat length. For appearances sake, apply a full round and there it is.
There is probably an easier way to do this 
but it has worked well for me.
I also tweak the k factor to more like .5, but shop practice will dictate the final value.