Concealed cabinet door hinges have two advantages. They're hidden inside the cabinet and adjust in three directions to make alignment of cabinet doors easy. Different styles install on different cabinet and cabinet door types, but all of the styles support the cabinet door with a cup, which fits into a hole bored in the door. Drilling this flat bottomed hole in the correct location and without going through the door requires a little care and special tools.
Read the instruction sheet that came with the concealed hinges to find the distance from the edge of the door to the centre of the hinge cup. The distance will be either 22.5 or 20.5 mm (8.86 or 8.07 inches).
Measure up 5 cm (2 inches) from the bottom edge of the cabinet door along the side the hinges will be installed on and make a mark. Measure down from the top edge 5 cm (2 inches) and make a second mark. These marks are the template alignment marks.
Place the concealed hinge template lip against the edge of the door the hinges will installed on. Align the marks on the door with the template centre line. Mark the cup hole location in the 20.5 mm or 22.5 mm (8.86 or 8.07 inches) position according to the hinge instruction sheet.
Place the nail point on the cup hole mark and give the nail a light tap with the hammer. Do the same to the other cup hole mark. These indentations will help centre the Forstner bit properly.
Drill a hole in piece of scrap wood with the 1.2 cm (1/2 inch) spade bit. The hole only needs to be 3 mm (1/8 inch) deep. Set the point of the Forstner bit in the hole and hold the steel rule vertically against the Forstner bit. Mark the bit at 1.2 cm (1/2 inch) with the marker in two places opposite each other on the side of the bit.
Clamp the cabinet door to a sturdy work table. Install the Forstner bit in the drill and tighten the drill chuck securely. Place the point of the bit against the nail indentations made earlier and start the drill turning slowly. The point of the bit will be drawn quickly into the door. Stop the drill when the cutting edges of the bit contact the door. Reverse the drill and back it up about one turn.
Hold the drill firmly with both hands. The drill will exert considerable torque when the bit begins to cut into the wood. Squeeze the drill trigger and allow the bit to be drawn into the wood. Keep the bit turning as the shavings are ejected. Stop the drill to clear the shavings and check the hole depth on the side of the bit.
Check the hole depth with the steel rule at four points along the sides of the hole. The hole must be 1.2 cm (1/2 inch) deep all the way around.
Practice cutting the hole on several pieces of scrap before you work on the actual door. Using a Forstner bit can take a little practice. Some doors are thinner than 1.8 cm (3/4 inch) and the hinges will require shallower holes. Once the cup hole is bored, use the hinge as a template for the hinge's screw holes.
Wear safety glasses while drilling holes. Drill a few test holes to get the feel for the Fortsner bit.