How to Cut a 45-Degree Angle on a Miter Saw

Updated February 21, 2017

Building frames around mirrors, pictures, windows and other corners requires a special angled cut known as a mitre. This angle is formed by cutting across the width of a piece of wood as it lays flat. Traditionally a slotted box, known as a mitre box, has been used to make 45 degree cuts. Powered mitre saws -- sometimes called "chop saws" -- brought advancements by allowing the user to set the saw to different angles for more complex cuts. Two pieces of wood cut at a 45-degree angle will let you turn a 90-degree corner, making the 45-degree mitre a good beginner's cut.

Place your mitre box onto a flat surface. Move all obstructions out of the work area to provide a safe place to cut.

Lay a piece of wood trim flat on the bottom of the mitre box. Slide the wood so that your measurement line lays next to the 45-degree slot in the box.

Hold the trim with the fingertips of one hand with your thumb on the near wall of the mitre box. Pull the piece of trim back against the near wall of the box and hold it firmly.

Slip the blade of the back saw into the 45-degree slots in the mitre box. Let the blade of the saw rest on the trim.

Push and pull the back saw to cut the wood. Hold the wood firmly and keep the saw blade in the slots of the mitre box during the cut.

Place the mitre saw on a flat surface that is clear of obstructions and plug it into the closest electric receptacle.

Twist the locking knob on the front of the saw and pull it to the right until the indicator arrow points at the 45-degree notch on the marked dial. Twist the knob to lock the blade assembly in place.

Lay a piece of wood trim onto the cutting surface of the saw. Slide the wood from side-to-side and line up your measurement mark with the centre point of the blade.

Squeeze the trigger and pull the handle down to lower the blade and cut through the wood. Hold the trim firmly against the guide fence during the cut.


Safety glasses or other eye protection are required when using hand and power tools. Hearing protection is required when using a power saw.

Things You'll Need

  • Mitre box with back saw
  • Wood trim
  • Mitre saw
  • Safety glasses
  • Hearing protection
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About the Author

After learning electronics in the U.S. Navy in the 1980s, Danny Donahue spent a lifetime in the construction industry. He has worked with some of the finest construction talent in the Southeastern United States. Donahue has been a freelance writer since 2008, focusing his efforts on his beloved construction projects.