Tongue and groove joints aren't recommended for MDF. Much of that materials strength is in the surface, which is the most dense part of it. If you put a continuous groove across the material you have weakened it quite a bit. The strongest way to use it is to have the top sit on the sides, with glue and screws being an adequate way to hold them together. The best screws have a large pitch, not a fine pitch. The back sheet of MDF is primarily for racking resistance, so doesn't have to be 3/4 inch thick. And, the narrow strip across the front, under the top should be adequate to keep the top flat. I have made a lot of cabinets with this material, using both biscuit joints and screw together joints and brad nailer joints. All any of those do is hold the parts until the glue cures. I gave up any form of grooves in using the material because it did noticably weaken the structure of it. |