If the table top is thick enough, you can cut any size opening you want. The drawin below shows how to use four pieces of straight wood to cut the opening and a half inch rabbet for the plate to sit in. The rabbet depth should be a bit more than the thickness of the plate. You adjust height with screws through the bottom in each corner, or go the easy way by purchasing the Kreg leverers in the other picture.
If the top isn't thick enough for a substantial edge for the plate to sit on, consider gluing on a half inch piece of ply with an opening the same size as the inside edge of the rabbet. You can glue this in and then cut it, but it's probably better to clamp the ply to the botton, mark the opening, cut it, then glue it in place. You can add fine finish nails to align the ply correctly as slippery glue sets.
The leveling screws allow you to adjust until the plate is exactly flush with the top surface. If you can feel an edge with your finger nail, it is not flush. I find it helpful to use a 18 inch straight edge for aligning the top. If there is any error, one end will raise a little bit
The more I do, the less I accomplish.
Last edited by DesertRatTom; 12-05-2019 at 03:20 PM.