How to Cut a Perfect 45 Degree

The simplest, and traditional, way to cut a perfect 45 degree angle is with a miter box and back saw. They are both inexpensive, often sold as a set and available any place that sells carpentry tools. Miter boxes hold a piece of work, usually a molding, and allows you to cut both 45 and 90 degree angles. Back saws are short, light saws with small teeth that make smooth narrow cuts. They are called back saws because they cut on the back, or pull, stroke - not the front, or push, stroke of the saw. Both tools were invented to, and are still used to, cut crown and trim moldings and picture frames.

Precise angles are important when making picture frames.
  1. Measure and mark the apex of your cut with a ruler and a pencil. For example, if you are cutting molding for a frame that has outside dimensions of 10 inches by 10 inches, make a pencil mark 10 inches from the end of the molding.

  2. Lay a scrap piece of 2x4 or similar scrap of lumber in the bottom of the miter box. The scrap wood will allow you to cut completely through your molding or other piece without scarring the bottom of the box.

  3. Set the miter box on a flat surface. Arrange the molding in the miter box so that the pencil mark you made on the molding aligns with the apex of the 45 degree slot in the miter box

  4. Hold the molding against the back of the miter box with one hand. Insert the miter saw into the 45 degree slot in the miter box with your other hand. Saw through the molding.