Thank you all for your advise I have attached a photo of the boards pulling apart! so the support peices under the top should not be glued to allow for movement? Is this what you mean?
+1. :yes: I agree.
My husband carefully chooses the boards for the top making sure that they are straight! Is tends to be overally cautious with making his products strong I think it could be to his detriment
How did he assure that the boards were straight. Did he joint the edges to get them straight, and square, or some other way, like just sighting the edge, or laying them to what was thought of as a straight edge or surface?
Properly jointed edges have no gap when placed together. As for gluing them up, jointed edges would require very little clamping pressure to insure a good joint.
But back to the separation problem. Once you have the boards glued up, any cross bracing under them should not be glued. What you can do is pick one board near the middle and you can secure that board with a screw. Then, towards the sides of the top you can make slotted holes in the support piece to insert screws with a washer head, or a pan head, just snug, so that if any one of the boards decides to expand, it can do that from the center one (that's screwed) out to the edges, without being restricted. The rest of the boards will move (or be pushed) in the same direction. Likewise if one or more decides to contract...the action/reaction can happen.
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