This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Miters. A miter is a joint between two pieces which come together at a corner at an angle of ninety degrees with each other. Strictly such a joint can be called a mitered joint only when each piece is beveled off so that each will come to a sharp edge at the corner. There are, however, a number of different methods of cutting the pieces so that they will come together in this way.
The simplest method is to cut off each piece along the edge at a bevel of forty-five degrees, so that when they are put together they will make an angle of ninety degrees with each other. This method is shown in Fig. 74. In practice, however, it is very difficult to make a perfect joint of this kind. The joint is very apt to open on the outside of the corner and leave an unsightly crack there, and great care must be exercised to see that the bevels are cut to exactly forty-five degrees, as the least variation will cause endless trouble.