To reduce depth in a wall cabinet the unit must be taken down from its position, disassembled and then certain individual pieces must be cut with a table or radial arm saw. Then reassemble the cabinet and mount it back on the wall.
Calculate how much space you want to remove from the cabinet. If less than 2 inches, then you might want to reconsider the project for it may not be worth the effort to decrease the interior space by so little. For this example, it will be determined that the depth of the cabinet will be reduced by four inches.
Take your reversible screwdriver and undo the screws holding the cabinet against the wall. Be sure to check above and below the actual cabinet for mounting screws.
Mark each piece with a number and letter that explains its position on the cabinet. An example system might include six to ten pieces. It could read front (F), top (T), bottom (B), right side (RS), left side (LS), rear (R), top shelf (TS) and bottom shelf (BS).
Pull the cabinet apart by first using the reversible screwdriver to back out all visible screws. Cut glued joints with a knife and look for screws that might be buried under a putty filling. In the latter case, you must cut away the putty before the screw can be removed.
Measure four inches in from the back side of each piece and make a mark. Then scribe a line that passes through the centre of the mark and runs parallel to the rear end of the board.
Cut four inches from the top, bottom, two side pieces and two shelves. For best results, use a table saw or radial arm saw.
Reassemble the cabinet. This is the most difficult step of the whole process and may involve redrilling new holes and countersinking depressions for every point of attachment. Then cover the head of every flat head screw with wood putty.
Remount the cabinets to the wall with long flat head wood screws. When doing this you must use a four foot level to check both the vertical and horizontal axis for plumbness.
Carefully sand all cut edges after a cut is made with the saw. Cabinet shelves should be removed before cutting the cabinet and they too will have to be cut down to size and reinstalled.
This is not an easy task and should only be undertaken by experienced carpenters. Check your cut area on the cabinet for any pieces of metal that might get in the way of the saw blade.