I am making a coffee table and have the same problem i always do when glueing boards together, they never come out perfectly flat. I bought the boards pre planned so they should all be the same thickness. When I glued the 4 boards for the top together they are all just slightly higher or lower than one another. How do I improve this to save time sanding and planning? I used some scraps as cauls but still didn't achieve a perfectly flat top.