Step 1: Material
This is the piece of black walnut I used. Someone was discarding it. It is 9/16 inch thick, about 6 inches wide, and about 18 inches long, more or less. It has some nice grain figuring in it, but there is also a knot in that part of the board near the far end. The part directly around the knot is not useful.
Step 2: Exploded diagram
Step 3: Begin cutting
The first step was to take physical dimensions of the two books I want to keep in this slipcase. I do not want the books to fit either too loosely, nor too tightly in the slipcase. I held them together and lightly very squeezed them while I measured their thickness.
I figured I would use 1/4 inch rabbets on the top, bottom, and back. That meant allowing 1/2 inch extra in the length of the side pieces. Allow a little more extra just to avoid getting yourself into a corner. You can always cut off a little excess, but it is almost impossible to add something back if you cut too much away.
I wanted the side pieces to be about 1/4 inch thick. I also wanted to glue the sides up from several pieces so I could alternate the circular pattern of the tree rings up and down to reduce the effect of any cupping. Wood will always move with changes in humidity.
I cut pieces from my board about 1 1/2 inches wide. Then I re-sawed those pieces on my bandsaw. I first tried clamping a guide fence to the bandsaw table, but the blade wandered and I wasted a piece of wood. I got much better results by drawing a line and following it.
Step 4: Smoothing
The sanding drum is on my radial arm saw. I feed the wood into the rotation of the sanding drum. I take very light cuts and keep the wood moving to avoid any burning. If you look closely you can see blade marks from the bandsaw on the piece in the foreground.
Some blade marks were deeper than I expected. I did not want to make all of the pieces so thin as would have been necessary to eliminate all blade marks. I decided to make one side good on those pieces and let the side with the blade marks be inside the slipcase where no one will see them.
I am using a small raised table to bring the work up to the sanding drum.
Step 5: Truing the edges
I also needed to true the edges as if run through a planer, but I do not have a planer. I used this setup with my sanding drum. Again, feed the work into the rotation of the sanding drum. I used a framing square for a fence. After a piece has been sanded this way, loosen the clamps on the framing square just a little. Move one end only a few thousandths of an inch closer to the sanding drum and tighten the clamps. Pass the wood between the sanding drum and the fence again, turning the wood over to sand both edges. When prepared this way, the glue joint fits very tightly and is difficult to see. (The piece shown here actually became the top and bottom of the slipcase.)
Step 7: Glued
Here the strips have been glued and clamped to make one larger piece from which the two sides will be cut. Clamp well until the glue is dry.
Step 8: Smoothing the glued up assembly
I used a sharp chisel as a scraper to remove excess glue and to smooth any edges that were high.
Step 9: Some sanding
More sanding will be needed later, but I used a belt sander to remove any hills and valleys in the surface of the side pieces. Use a fairly light grit sandpaper and keep the sander moving so it does not cut too much in any one area.
Step 10: Cut the sides to width
Look carefully at the grain figure and choose where you will cut to make two sides. I did some planning when I was laying up the strips for gluing and decided to cut from each end of the larger piece.
Step 11: Square the side pieces for length
I cut both side pieces for square and to length at the same time. One is on top of the other in the exact orientation planned for their use in the slipcase. Even if something is not quite right, the pieces will be identical and will fit.
Step 12: The top, bottom, and back
The grain on the sides is vertical. That means most of the shrinkage or expansion with changes in humidity will be side to side. I decided I wanted the grain in the top and bottom to match the sides in its direction. If you have ever seen a crack in a tabletop, etc.; the pieces were assembled so they could not move without grain running in another direction opposing that movement, and the wood eventually split. This is a small project and there might not be much movement, especially in black walnut.
The piece you see was cut into short pieces equal in length to the width of the top and bottom. Again, leave a little extra to cover any mistakes, etc. later. See the next step for a photo.
Step 13: Gluing up the top and bottom pieces
Step 14: Check the fit
Step 15: Check settings with a scrap of wood
Step 16: When finished routing rabbets
Step 18: Final assembly with glue and clamps
Here you see the slipcase glued and clamped. Do what you can to check that the assembly is square. Scrape off excess glue as soon as is practical.
When dry enough, remove the clamps and sand with successive grades of sandpaper for a really nice finish. I used Danish oil for my finish.