Octagonal moulding is used almost exclusively to trim around octagon windows. As its name implies, this type of window has eight sides, so trimming it out can be very tedious work. With the proper tools and the right angle measurement, though, these pieces can be cut out and fit together to go perfectly around a window.
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Things you need
- Safety goggles
- Tape measure
- Mitre saw
Count the number of sides on the window to make sure there are eight and divide 360 by 8 to get the measurement for each angle that will need to be cut.
Run a tape measure along each side of the octagon to record the measurement. All measurements should be the same length, but verify just to be sure.
Measure out the distance for the first piece on the desired type of moulding. Mark it with a pencil. Slide the piece of moulding into the mitre saw and turn the blade of the saw to 45 degrees in either direction. Plug in the saw and line up the blade with the mark on the moulding. Turn on the saw and pull on the lever to bring the blade down through the moulding to completely cut the piece. Release the lever and let the blade go back up to turn off the saw.
Mark the next piece at the same length and turn the saw to 45 degrees in the opposite direction. Cut the moulding in the same manner as the previous step and line up the two pieces to make sure they fit together properly.
Cut the other six pieces of moulding the exact same way, making sure to turn the blade of the saw so that there are four right-handed, 45-degree angles and four left-handed 45-degree angles. Line up all of the pieces in the octagon shape around the window to verify that they butt together properly.
Tips and warnings
- The number of sides is divided by 360 because that is how many degrees a complete circle is and this number also equals the number of degrees an octagon would have.
- Always wear safety goggles when working with a compound mitre saw to prevent wood or other material from entering your eyes.
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