David it is hard to give a proper opinion without seeing it but, wood is subject to movement if the moisture content of the air changes, that is unfinished wood, after any item is made then proper polishing/sealing should stop that, the thing about polishing is this, to effectively close of the effects of moisture levels changing then you have to polish all the exposed surfaces, and that means under the top as well, it means inside drawers and under them and their backs as well and inside cabinets and over the drawer runners (if they are wooden that is), any spray sealer should normally be good enough, that is you do not have to polish the inside of an item to the same finish that you have achieved on your seen areas but it has to be closed off and under table tops is as important as the seen areas. So if there are areas of your item that are not properly sealed then the water in the air will keep entering the item through those surfaces and expansion/contraction will keep happening as the ambient local moisture level wanders up and down and it would be worse if you do have very dry to more wet ambient moisture levels, now having said that then your joint should not be opening up, without seeing it I also cannot say what happened so what glue did you use and did you spread it around and glue up the joint completely and what joint support (loose tenon, tongue and groove, dowels, biscuit joints) did you use? Glues are not all the same and you have to use a glue that works, do some test joints, if the glue was not effective then the join can move around but when you do a proper glued joint theN the wood should break before the join does, there are many spectacular glues these days that "do not let go" and when you make widening joints in a top, and I think that this is the jointing that you are referring to, then you have to do the best damn joints and use the best glue that you can, I will say that even if you did not use joint support, like dowels or tenons, then a straight but joint should still be very strong if the join is done to meet properly and if the glue is suitable, and the item is properly sealed up inside and out. I hope that this helps and if you want my professional opinion then strap the coffee table to your back and catch a flight to Sydney Australia, Mascot International Airport has excellent coffee and you can have some as I have a look at it so I will meet you there.
Don't ever forget that working with wood is fun but sometimes it is not that funny. NGM
Last edited by neville9999; 05-04-2013 at 02:23 PM.
Reason: I left out an n, I hate a then that is typed as a the