mike is right,, its very hard to find just the right pc of wood for a 1pc core,,i gave up finding that pc of wood long ago,,but I have made a core with just three pcs,the riser carved in ,the siyahs added later,,
using just one can be done ,takes a lot of looking and culling of material...
p.s. I do have an acient crab bow, that the limbs and siyah are 1 pc then splices at the riser,,,hence proven methods =proven results