Case Construction - Dados

[Jim Fox]

Looking at various project in different magazines;

Why is it sometimes the bottom and top pieces are rabbeted and fit into dadoes on the sides?

While other times the tops and bottoms just fit into the dadoes on the sides with no rabbets?

[Tom Veatch]

My call on that is that it's just a design feature depending on whether you want the top/bottom to be flush with the sides or whether you want the sides to extend above/below the top/bottom.

The last set of bookcases I made used dados instead of rabbets. Reason was that I wanted the bottom to be slightly proud of the molding across the bottom front and to have room under the bottom for glide/levelers. Likewise, I wanted the bottom of the top piece to be slightly above the bottom of the molding across the top front.

I don't know that there's any structural reason to go with one technique over the other. Neither one gives a particularly strong joint - all the glue joints in either case involves end grain if you're using solid wood. The dadoed joint does give a little more gluing surface and might be marginally stronger.

[John Thompson]

Agree with Tom... matter of choice or circumstances that might affect a given project.

Sarge..

[Steve Jenkins]

probably not the reason but if you rab all the pieces on a shaper such that the tongue is formed between the cutter and the table, say 1/2", you can cut a 1/2" dado and everythng will fit perfectly even if the ply is slightly different thickness. Makes it simpler than fussing with trying to cut dadoes to fit.

[Bob Johnson2]

I agree with Steve, that's the reason I do it anyway. Plywood varies too much in thickness to get a good fit on a dado without a corresponding rabbit.

[Frank Drew]

The shoulders on the rabbet contribute a bit of strength to the joint, plus hide the dado in case the fit isn't perfect. You have to be sure, though that the shoulders hit the case sides before the shelf bottoms out in the dado.