Gluing Table Aprons to Plywood Table Top

Question

I'm building a tall, large standing desk and removable legs are required for this to fit through doors. I'm using pocket screws to attach the aprons (hardwood maple) the table top (birch veneer hardwood plywood). Screws are 6" apart

Would adding glue between the aprons and tabletop be beneficial for structure? Or would the glue not have a benefit because of the thin birch veneer that it's being glued to? Or would glue cause problems if the wood warps (I live in dry, Colorado climate and warping may not be an issue).

Answer 1

Glue is rarely a bad thing to add to a (permanent) joint. Pocket hole screws are plenty strong on their own for most typical applications, but adding glue only makes the joint stronger. Plywood is very strong and very stable (two big reasons for using it), so there's no concern related to that.

One potential problem that may develop as a result of using glue is getting the joint to line up nicely, especially while screwing in the pocket screws. Glue acts as a lubricant here, allowing the two pieces to slide around quite a bit during clamping. If the two pieces are not clamped very securely, they will move when driving in the screws. If you can come up with some kind of registration / alignment system it will make the whole process much easier. Use biscuits, dominoes, rabbets (UK: rebates) (even a 1/16" deep rabbet would aid alignment), whatever to keep the apron aligned on the tabletop.

Answer 2

One way to make a strong joint for apron boards like this is to add in glue blocks made of hardwood. They are glued along the face toward the apron and the side that attaches to the table top. Then they are alternately screwed into the apron and the table top. Positioned under the top and inside the apron they are thus not seen. Here is an example although in practice they may be long enough for two screws in each direction.

Overall these can be stronger than just the pocket screws and will work fine as long as the joined materials are dimensionally stable with respect to one another with humidity and temperature changes.

If your materials are not going to be stable and have different rates of expansion and contraction then another approach is needed. In this case the apron frame needs to be built as a self sufficient unit unto it own amnd then the table top is attached using clips, brackets or finger blocks to hold the top secure to notches in the inside edge of the apron. Here is an example of finger blocks screwed to the table top and fitting into routed grooves in the apron.