Miter joints are angled connections between two pieces of material. The joint is made by mitering each corner at 45-degree angles. It is used on outside corners and enables trim and molding to continue smoothly around corners without having to make an abrupt stop and then start again.
Miter Joint Tools
Power miter saws are an excellent tool for cutting miter joints. A handsaw and miter box combination of tools also works well. Power saws cut faster and are more accurate. A miter box is accurate but manual cutting using a hand saw takes longer. For limited trimming or molding projects, a miter box is the most cost effective tool.
Practice Cutting Miter Joints
If you have no or limited experience making miter joints, its best to practice your skill and accuracy. Use scrap wood for your practice work. Cut a 45-degree angle to the left. Then cut a 45-degree angle to the right. Hold your practice pieces of wood together to check to see if your cut was accurate. You should not be able to see any gaps between the pieces. When cutting your boards, accuracy is best. However, it is better to cut your board too long because you can always go back and trim off excess length. If you cut it too short, you will have to go back and start the process again with that board.
Marking the Cut
Hold the trim in position and use a pencil to mark the location of the miter cut. If accuracy is extremely important, use a sharp utility knife to mark the location.
Securing Miter Joints
The pieces of wood can be secured together with corrugated nails. Be sure to set the nails in from the surface of the board. Be careful not to secure the nails too close to the edges. You can then fill the hole with wood putty. The putty can be painted to match the wood you are using.
Strengthening Miter Joints
A miter joint does not work well in areas that may have excess weight or strain. A miter joint can be made stronger by adding a spline. A spline is inserted into a groove that is cut into the wood. The groove can be cut into the wood before the ends are mitered. Once the groove and miter cuts have been made, the spline can be cut. The spline can be cut in a triangular shape, a biscuit shape or a football shape. Apply a quality adhesive to the spline before inserting it into the groove.
If you find a subtle gap between the trim and the wall, use a shim to fill the space. A playing card can be used as a shim to fill the gap if necessary. Insert the shim between the trim and the wall and then secure the outside edge. You can also fill any visible shim work or gaps with caulk.