Bought this black walnut cookie off of Facebook marketplace for a good price. The only catch is it is warped, cracked, cupped, and twisted. It's about 4 in thick and that's plenty of material to make a coffee table, but I need some advice and guidance on making a router planing jig please.
Maybe this is a dumb question, but why not just use a hand plane?
A hand plane removes the same thickness of wood wherever you run it, so getting something flat (that isn't already flat) is a challenge.
A router sled/jig (not sure exactly what to call it, I'm not an expert either) acts as a flat reference.
A hand plane is for both thicknessing and straightening a board. A hand plane does not remove the same amount of material unless the board is already flat. The long flat heel of the plane serves as a reference surface. There is some skill required to not taper the workpiece and you can use winding sticks to check your progress as you flatten the workpiece.
A router sled/CNC router will be able to accomplish the same thing.
Ah, good point.