Bookshelf design, support and movement

[Shawn Christ]

I'm considering a bookshelf design similar to this except mine would be wider and shorter, roughly 3'H x 5'W, with a third vertical frame added for center support. I would like to use solid ash for the shelves and either cherry or walnut for the vertical frames. Here are my thoughts and questions:

1. Back support. I think I would need to add a horizontal top and bottom rail to prevent racking. I'm not sure which wood species would look better.
2. Shelf attachment and wood movement. I don't have much need for adjustable shelves, so they will likely be fixed. I have a few attachment ideas and am not opposed to mechanical fasteners. I'm thinking hidden wood dowels or resting the shelves on threaded rods in bottom dados. Would a 1/8" gap between shelves and frames be adequate for expansion?
3. Shelf span and frame support. This will likely be 7/8 or 3/4 material. Will three frames adequately support the weight of the shelves, and what should be the maximum span of the shelf without a face frame? This shelf will be for my son and used mostly for legos, toys, and trophies (for now). In the future probably some books, binders, and maybe eventually electronics.

I would be interested to hear your thoughts.

[Jamie Buxton]

My big concern would be racking. If you must have the back open like the example, it'd be really good if every fixed shelf is firmly joined to the uprights. For instance, if you put a dado across each vertical member everyplace a shelf crosses it, and if the dado is a good fit to the shelf, that would add a lot of anti-rack bracing.

With the shelves firmly fastened to the uprights as you propose, there's no need for the horizontal crossbars which the example has. In fact, they get you in a little bit of a problem with expansion/contraction of the shelves. The shelves will change dimension in the direction of the crossbars, but the crossbars will not, so you get possible stress. If you eliminate the crossbars, there's no stress. (The crossbars are included in the example because the shelves are adjustable, so there's nothing holding the uprights together except the crossbars.)

Your shelves are going to span 30", and will be solid 4/4 hardwood, right? They'll support your proposed loads.

[Shawn Christ]

Jamie, thanks for the insight. I agree the crossbars are problematic. Although I think they are a large part of the appeal, perhaps eliminating them would be the best approach.

[Kenneth Speed]

I made a very similar set of shelving with glass shelves as a display case for a camera store a long time ago and while it turned out nicely and was a good vehicle to display cameras it wouldn't be a design I would recommend as a bookcase.

[Jamie Buxton]

Jamie, thanks for the insight. I agree the crossbars are problematic. Although I think they are a large part of the appeal, perhaps eliminating them would be the best approach.

Well, you could make them visual but not structural. For instance, join them to the uprights with box joints, but glue only one end. They'd stay firmly fixed at the glued end, but slide a bit at the unglued end.