Bookcase top and wood movement

[Gary Herrmann]

The bookcase I'm working on will have a solid mahogany top - 7/8 x 12.5 x 42. I haven't decided if I'm going to use biscuits to attach the top or those little right angle table top attachment things.

My question is, do I need to be worried about movement if the top is only 12.5" wide? It's glued up from 4 3 1/8" wide boards. I'd rather not have this thing crack a few years down the line.

[Steve Cox]

What are the sides made of? If they are solid also, probably not. If they are plywood, probably.

[Roger Myers]

Yes,
You need to worry about wood movement, even for 12 1/2" . But the question is also based upon what the top is attached to.. if the top is attached to sides (mitred, dovetailed, biscuited...you name it) and the grain direction is the same, and the material is the same, then no..you do not need to account for wood movement. If however it is also attached to front rail, or to the back, then you do. Or if the sides are a frame and panel construction, that would also put the grain orientation different from the top. So if any of the joined surfaces are cros grain, then even for 12 1/2", allow for the wood to move...sooner or later it will!
Roger

[Gary Herrmann]

Thanks guys. It is cross-grain. So I think I'll use the angle brackets or maybe figure 8s.

[Roger Myers]

Gary,
another method I have used is to make small wooden brackets....think of a small rectangle of wood that is L shaped...the block is screwed to the underside of the top and the thin L leg goes into the slot.... I've cut the slots with a biscuit joiner, but you can use a router, or chisel a small mortise for them...using the wood block can be a nice touch.
Roger