• One use of splines is to make clean corners on picture frames.picture frame corner image by Jim Mills from Fotolia.com
  
  Splines are pieces of wood that are glued into pre-cut grooves to reinforce wooden joints. Because wood splits more easily along its grain than across it, splines are made so their grain is perpendicular to the grain of the wood they are reinforcing. Splines are used to reinforce corner and angle joints as well as the entire lengths of laminated boards.
  
  

Reinforce Mitered Joints

• Any time you join wood to form a geometric shape, you must cut the ends of the boards at an angle, which is called making a miter cut. An effective way to reinforce mitered joints is to pre-cut grooves in the ends of the boards and glue in splines that are just thick enough to fit in the grooves. An example of the method for joining two mitered boards with splines is to cut 3/4-inch grooves in the ends of both boards by passing them through the blade of a table saw. Cut a 1 1/2-inch spline that is the same thickness of the saw blade and longer than the width of the boards you are joining. Spread glue on both sides of the spline, insert it into the groove on one of the boards, join the other board and clamp them together. When the glue has dried, cut off the ends of the spline with a hand saw.
  
  

Corner Keys

• Corner keys are another way to reinforce mitered joints, especially 90 degree ones, and can be glued in after the boards themselves are already glued. Keys are commonly used on picture frames. Once the frame has been glued together and the glue is dry, pass each corner of the frame over a table saw blade while holding it at a 45-degree angle. Cut the spline so that it slides snugly into the groove and is longer than you need. Glue it in place, and when the glue dries, cut off the ends flush with the joined wood. When you sand the wood, the spline blends in to make an interesting feature, especially if you use an attractive or contrasting hardwood.
  
  

Blind Splines

• Blind splines are used when joining two pieces of wood lengthwise, as in lamination. To use blind splines, you must cut grooves carefully into the sides of the pieces you will join. One way to do this is to plunge cut with a table saw. Hold the wood over the saw blade, and gently lower it onto the blade, then push the wood through the blade and stop before you get to the end. Only do this if you have a fair amount of confidence and experience using a table saw. Cut the spline so that it fits tightly in the groove, and spread glue on both sides of it. Fit it into the groove in one of the boards, clamp the other board to the first and let the glue dry. Factory lamination is often done with machines that use pre-cut splines, called biscuits, to join the wood in this way.