When you replace your exterior door threshold with a new one, you may find you have another problem: The new threshold sits higher and now the front door will not close. The bottom of the door will need to be planed so the door will close. Planes are great for taking off wood in small increments without splintering the edge of the wood in the process. This particular project requires a power plane or a jack plane, which you can rent or purchase from most home improvement stores.
Go outside and close the door until the bottom of the door makes contact with the new threshold. Trace the top of the threshold onto the door by setting a pencil on one end of the threshold with the lead touching the door, then sliding the pencil over the length of the threshold.
Open the door and remove the centre pins from the hinges with a flathead screwdriver and hammer. The centre pins connect the door hinge leaf and the jamb hinge leaf. Insert a flathead screwdriver under the head of the pin and tap the screwdriver handle with the hammer. Remove the middle hinge pin first and then the upper and lower hinge pins.
Place the door, with the tracing mark facing up, on a pair of sawhorses. Ask a friend to hold the door steady while you plane the bottom edge.
Adjust the blade depth on the power plane to 3 mm (1/8 inch). Loosen the adjusting wheel on the front handle of the plane and move the blade up or down until you have 3 mm (1/8 inch) between the blade and the base of the plane. Tighten the adjustment screw to secure the blade.
Start at one end of the door and make long shaves on the edge. You want to obtain a long, continuous cut from one end of the door to the other. Adjust the plane to make a thinner cut, if necessary.
Move the plane in long strokes across the door edge until you reach the trace mark. Hand sand the edge with fine-grit sandpaper to smooth the wood. Wipe the edge down with a lightly damp cloth to remove sawdust, and paint the bottom edge or stain the edge.
Set the door back to the opening and secure the hinge leafs together by inserting the hinge pins.