First, before telling you how to replace a door, measure the outside dimensions of the door and buy a standard door that is as close to the one that I will be replacing. Doors come in standard widths and heights. It is not a big deal to go to a DIY store and buy the door of your choice.
Then, take down te original door by pulling the hinge pins then unscrewing the hinge plate from the door. Place the new door tightly to the door that it is replacing and scribe any edges onto the new door that must be adjusted, especially the bottom of the new door. Trim the new door at the bottom and the top.
The third step is to place the new door against the old one and scribe the locations of the old hinges and lock fittings and transfer them to the new door. Cut the mortises for the hinges and install the hinge plates into the new door. Lift the new door into position and slide the hinge pins into place. Now you can scribe to the latch side of the door. Use a plane to bevel the latch side with a 1/8″ bevel to the front of the door. This will allow for good clearance for the door to close and leave a nice close and clean edge for the inside of the door.
Finally, drill out the lock including the cross bore for the latching mechanism by aligning the center of the hole with the latch on the door jamb. Put all the hardware back in place and you will have a beautiful new door that is properly hung. All of this should take less than an hour. Remember the adage of carpentry: Measure twice and cut once.
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