• Molding trim is the thin wood that borders the room, along the top and bottom of the walls and around doors and windows. The purpose is mainly aesthetic and to seal joints between different angles and different materials. It also can have some effect on helping to insulate the room by preventing air movement through those joints. There are many different ways to install molding trim, depending upon your circumstances and the type of molding you're using.
  
  

Basic Miters

• The most basic cut that you use when installing molding trim is a miter cut, which is simply an angled cut in the wood that butts against other angled cuts to make your corners. The cuts are made with a miter saw, which is a circular blade mounted on a swiveling platform. The angle of the cuts may vary based on your circumstances, but most generally you will be cutting a 45-degree angle into the end of the wood, so that it butts up against another 45-degree angle to form a 90-degree corner. For inside corners, make the mitered angles point inward, toward the main span of the trim. For outside corners, make both miter cuts point outward, away from the main part of the trim. It's a good idea to cut the miters for one corner first, while leaving the trim longer than it has to be on the wall, then make your second cut based on the measurement of the wall.
  
  

Coping Cuts

• One of the more complicated cuts that you may need is a coping cut, which is a miter cut that you alter by hand in order to form a perfect inside corner. Inside corners are seldom actually square, so if you use a regular miter cut on one, you often have problems with gaps or spaces developing at the miters. To make a coping cut, you install the first piece of trim into the corner, straight-cutting the edge of it and putting it up against the adjacent wall. Then you miter cut the second piece, as if you are cutting a regular miter, then cut around the miter by hand with a coping saw. The shape of the miter, after you cut it out, will fit right across the face of the first peice, which gives the impression of a miter cut but is actually not. Since the second piece fits snugly around the first piece, you don't have to worry about a miter gap.
  
  

Splice Cuts

• It's preferable to have each wall or other span covered by a single piece of trim. However that's not always possible. If the area is so long that you have to use two pieces of trim in order to span it, you'll have to make a splice cut to make it look like one piece. The process is similar to that of a miter cut, except instead of cutting both the pieces either inward or outward, you cut one inward and the other outward. When you put them together, the angle cuts will form a straight line without leaving a gap or space that's obvious when looking at it from the front.