Assembling the Carcass
Let’s get this cart project rolling by cutting the base and sides to size (pieces 1 and 2). Notice in the Drawings that the bottom edges of the side panels are rabbeted to fit over the long edges of the base. To set up for cutting those rabbets, install a wide dado blade in your saw, and clamp a sacrificial fence to the rip fence so you can bury part of the blade in it. Raise the blade for a 3/8″-deep cut, and adjust the fence so the blade’s cutting width matches the thickness of your project plywood. Make a test cut to check your settings, then mill each rabbet on the side panels. I also used a pair of featherboards clamped to my rip fence to press these workpieces down flat against the saw table — even expensive Baltic birch ply can have bows or twists in it that could make your rabbet cuts inconsistently deep.
Switch from your dadoing setup back to the standard blade so you can cut the three ends, shelf supports and crosspiece (pieces 3 through 5) next. Leave the supports and crosspiece overly long at the moment, but go ahead and crosscut the end pieces to final length. Make sure that their length exactly matches the distance between the sides and base when you hold those three parts in position — there’s no place to hide sloppy butt joinery with gaps here.
Before you can get down to some assembly, load the dado blade back in the saw and set its width carefully for cutting dadoes across the shelf supports to house the crosspiece. Plow them 3/8″ deep and centered on the part lengths.
Tote all of your carcass parts over to the workbench for a thorough sanding up to 150- or 180-grit. It’s much easier to smooth these surfaces now while everything still lies flat and open. Once the dust clears, you can fasten the side panels to the base with glue and countersunk wood screws. I first tacked the sides into place with a few brads, then followed behind with screws. Slip two ends into position on the base, and locate the third end piece at the top rear corner of the sides to help the carcass resist racking. Secure these parts with more screws.
The shelf supports come next. Check their length against the actual distance between the installed ends, and trim as needed. Glue and nail them to the side panels. Now install the crosspiece in its dadoes in the shelf supports, cutting it to final length for a snug fit. I brushed a little glue into the dadoes first, slid the crosspiece home and drove brads at an angle and into the supports to pin the crosspiece permanently. Complete the carcass by easing its sharp edges with a 1/8″ roundover bit in your trim router, or use a file or sanding block. Skip the top edges of the sides and the top edges of the end pieces — the top panel and bottom shelf will cover them. Cut and position the top panel (piece 6) so its edges overhang the side panels evenly. Drive countersunk screws down into the cart sides to secure it.