If you aint breaking em you aint making em
Also if you are not breaking them every now and then you are over-building
The back on second string woods has to be pretty much perfect. Yew, osage, elm in some cases you ca get away with murder. If you are un-sure then back the bow with something, linnen, silk. Some say sinew but that's a whole lot of work for a bow you are not quite sure about.
Crack on! excuse the pun.