Reply To: When to use tongue and groove?
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I have only used tongue in groove a few times so I could get this wrong. I am not mistaken, tongue in groove joints are not generally used for table tops. Tongue in groove is most common in wooden floors, but is also common for the backs of cabinets. It can, of course, be used elsewhere as well. Unless I am mistaken, its main function is to is to hold boards together mechanically and without edge gluing them together in a way that allows for expansion and contraction. A wooden floor, for example, can be very wide and hence have a lot of expansion and contraction, maybe enough to break your walls! The tongue in groove joint allows each expanding and contracting board to change size easily without the entire floor expanding and contracting. Of course, tongue and groove can also be decorative and you can even highlight the joint to make it more visible, which is common when you use it for the backs of cabinets. (Obviously, expansion and contraction for the backs of cabinets can be controlled by other methods as well. For example, you can make them using ship lapped joints. You can also use frame and panel. Today, plywood, which does not expand and contract much, is widely used for the backs of cabinets.)
Table tops can generally be allowed to expand and contract as they want. With a table top, the main issue is keeping the top from breaking away from the table apron as the top expands and contracts. This is generally controlled by using turnbuttons to hold the top to the apron rather than by using tongue in groove. I suppose you could make a table top with with a tongue and groove joint, but it might have some unpleasant results. For example, since tongue in groove joints are not glued together, and are left to expand and contract freely, food particles could find their way in there.
I wonder if you are thinking about using splines to help align table top boards to help with gluing. That is fairly common.