To get a piece of moulding to look and fit just right, an angle needs to be cut properly. This is done using a mitre box and a hand saw, or using a protractor to measure the angle. Proper measurements are key to cutting correct angles A mitre box is a wood or plastic box that has corresponding slots on either side that are placed for cutting different angles. A protractor, like the ones found in high school geometry classes, can also be used, which, when the angle is determined, identifies the proper path to cut.
Measure the length of the wood with a tape measure at the position you want the 90-degree angle to be. Mark the outside of the wood, identifying the longest point of the angle.
Place a piece of scrap wood in the mitre box to prevent the saw from damaging the box.
Place the wood to be cut inside the mitre box, aligning the pencil mark with the uppermost point of the 90-degree angle slot. Pace the hand saw in the 90-degree angle slot and cut the wood, making sure to hold the wood firmly to prevent it from moving.
Measure the wood with a tape measure to determine the farthest point of the angle location and mark it with a pencil.
Align the middle of the protractor's flat side so that the pencil mark appears in the middle, which is marked on the protractor. Find the corresponding 90-degree angle mark on the curved portion of the protractor and mark the wood directly under it.
Draw a line connecting the two marks on the piece of wood. This is your 90-degree angle. Cut the wood with either a hand or power saw, making sure the wood is firmly held to prevent slippage.