Yup, those things are a hassle to shim. It just takes alot of patience.

I was shimming the inside first (That will set the mesh) Don't set it up so tight that there is no backlash, there should be a slight amount of play with holding pressure on the bearings. Then shim the outside to take up the slack. When you put the top cover on, the shim pack should just fit into the grooves.