Trick is to get both limbs in the same plane. To do this you need to have the same plane on the back of the handle the same as the limb just outside the fade. Best to rough shape your bow limb and leave about a 5" handle section (both billets).
You can either eyeball your work if you have the eye for it or do like me and use a level.
I first work the belly down to where it's in the same plane as the back of the limb, level close to the fade, and adjust the plane of the handle using said level. Once both handle and limb show level you know you're right. Do both the same way, and once spliced or joined for a takedown, both limbs will be in the same plane.
For a takedown, get your handle section very dry. Last thing you want to happen is your wood to shrink later as it season/age out.........Art