Here is a picture of what I am planning to build. Looking at the way the two boards come together to form a corner, and if I wanted to countersink the screws with a special bit, what is the best way to drill through both boards at once?http://i51.tinypic.com/a5ixrs.png
Thanks for everyone's input,
I wanted to mention you are making the weakest possible joints as shown. I'd rabbet join those shelves, and I'd have
the top shelves extending over the vertical supports, not flush to the sides. Glue alone will not hold that together,
or prevent racking motion side to side. I'd still suggest using a biscuit joiner, wood dowels, or if you have to,
long screws. You can buy a counter sink drill bit to recess the heads at any hardware store. Clamp the boards as
they will be assembled, and drill.
I tried gluing and clamping the rabbets on the shelves shown above. The first sharp blow broke all the glue
bonds. I ended up using dowels. And I will be bracing the back before they go into use.