Start a run of wall cabinets with a full-height unit or a corner unit if you have one. Otherwise, start at whichever end will not require a filler piece. The first cabinet is the most critical – it must be perfectly level, plumb, and square, or the entire run will be out of alignment.
Measure where the studs line up behind the first cabinet and transfer these measurements to the inside of the cabinet at the top and bottom hanger rails. Countersunk and drill holes through the back of the cabinet at these marks; make the holes just large enough for the 3-inch screws.
If the cabinets are frameless, they may require a metal support rail, provided by the manufacturer. Install this rail next. It must be attached to the wall behind the cabinets, which will be hung from it. Cut the rail to each stud at the height recommended by the manufacturer.
There are several methods for holding the cabinets in place while you attach them to the wall. One is to build a T-brace slightly longer than the distance between the floor and the bottom of the cabinet. Another method, used when the base cabinets are installed first, is to build a simple rectangular frame out of 2 by 4s; this frame should be just high enough to support the wall cabinets when it sits on a makeshift countertop. A third method can be used if the walls have not yet been finished. Simply screw a 1-by cleat to the wall to support the bottom of the cabinets. A specialty jack is useful here, if you know a professional who might lend you one.
To begin, lift the first cabinet into place and slide the brace up under it. You will need a helper to stabilize the cabinet while you do this. Attach the cabinet to the studs with 3-inch screws, tightening only one of the top screws and leaving the others slightly loose. Place a shim behind the cabinet, next to a screw, at any point where the wall bows inward. Use a level to check that the cabinet is plumb and horizontal in all directions.
Now, transfer the stud dimensions to the inside of the second cabinet and countersink and drill the screw holes. Drill two more screw holes through the vertical stile on the side that will be attached to the first cabinet. Drill where the hinges will cover up the screw heads.
For frameless cabinets, the side holes are already partially drilled, about 3 inches back and 2 to 3 inches up from the bottom or down from the top. Simply complete the drilling. Special fasteners go into these holes; they screw into each other, leaving a smooth head on each side that is covered with a plastic cap.
Lift the second cabinet into place and support it, but do not screw it into the back wall. Instead, clamp the two cabinets together so that the joint between them is tight and flush. Use wood shims to protect the cabinet finish from the clamps. Choose a drill bit slightly smaller than the shank of a 1 ½-inch screw and center it in the first side hole of the second cabinet. Drill about two thirds of the way into the adjoining stile of the first cabinet.
Do the same for the second side hole. Now lubricate two 1 ½-inch screws with car soap and drive them firmly into the holes that you have just drilled. If the cabinets are tall or if the face frames do not align perfectly, pre-drill more holes and add more screws. Then attach the cabinet to the back wall, in the same way as you did the first cabinet.
Repeat this process for all the wall cabinets in the same run. If a vent hood will be mounted to a wall cabinet, cut holes in the cabinet for the duct before you install the cabinet.
If the final cabinet will end next to a sidewall, there may be a gap that needs a filler piece. These come in 3-inch and 6-inch widths and must be cut to fit snugly. Before you install that cabinet, attach the filler piece to the stile in the same way as you would attach two cabinets together. Then take a series of measurements between the wall and the last cabinet installed. Transfer these measurements to the face of the final cabinet, marking them on the filler piece. Now, connect the marks with a line. Cut along the line with a fine-tooothed keyhole saw, angling the back of the cut toward the cabinet. The cut will follow any deviations in the wall so that the filler piece will fit perfectly. Filler pieces for corners are installed in the same way, but they need not be scribed and cut. Some manufacturers provide cabinets with wide stiles, called ears, already attached. These ears function as filler pieces and are trimmed in the same way.
When the full run of wall cabinets is in place, check for level, plumb, and square (measure diagonals). Use shims to make any necessary adjustments, loosening the back screws to slip the shims into place. After all the screws are tightened, make a final check. Be especially careful with frameless cabinets. The slightest warp will make the doors hang crooked.