I just had to flatten several glued up panels to be used as solid wood drawer bottoms. They are aromatic cedar and are 24″ across the grain. How do you clamp up a large panel that flexes in order to flatten it? I find the panel flattens back to my flat bench top and my planing does nothing to flatten it. I guess this is kind of like planing with our jointing first; just thinning the wood and not really flattening. Do I need to shim it like I would if I tried to plane it with my planer?