I have a 3” slab that has a crack top and bottom, not separated very much but would like to support it from getting worse. What is a good rule to determine the width and length of the butterfly insert and how thick would you make it. It is walnut and will be a side table. It is from the crotch of the tree. About 23” wide on the twin branch end and 12” on the single branch end. It will have mortised tapered wooden legs 3 1/2” wide by 1 1/2” thick cut to yield a tenon that will be 3 1/8” x 1” Question: The butterfly wedge joint to reinforce the crack on top and bottom.