Splines are a great way to give projects a little extra beautification and strength to a miter joint. A miter joint is joining to joints that are cut at specific angles. Usually this is seen with two 45 degree angles that form a 90 degree angle. These joints use only one surface to connect so they are not the strongest if the joint will see some stress. Adding a spline will increase the strength of the joint and add a little extra style.
A spline is a piece of material glued to a mitered joint to add strength. Splines can be easily made by cutting strips of material to the desired thickness of the intended spline. These can then be cut down to size and stored for later use if desired. Splines are usually a third of the thickness of the material but, is completely up to you what size is best for the project. Making a spline jig is pretty simple so let’s get started making a spline cutting jig.
Materials: 1/2″ Plywood
First, I cut 2 6″x15″ pieces from plywood. Then I used angled clamps to butt joint them together. This will create the frame for the spline jig. The clamps I use here are from Woodpeckers. They are a little bit more expensive but regular 90 degree clamps will work.
While the glue is drying for about 30 minutes. I cut two pieces of 5″x11″ plywood. I overcut the 11″ side by 1/2″ so I can sneak up on the 11″ cut. These two pieces will sit at an angle which gives you the ability to cut the splines. Using a digital angle finder, I set the table saw blade to 45 degrees and cut both pieces down to 11″ on one side.
After the clue has had about 30 minutes to dry. I put three screws into the joint to hold it together for extra strength. I leave the clamps on so I don’t stress the joint during this process.
Next, I cut 4 braces at 45 degrees to support the angles pieces of the spline. You will want to mark a line in the middle of the spline to line up the pieces. While holding one of the angled pieces against the brace to ensure 45 degree fit, I super glued two braces to one side. I then repeated this step with the other side. This will create a 90 degree angle.
Use a 90 degree measuring device to check for accuracy. If you have a 90 degree angle you are all set! You have just built a spline which can be used on picture frames or boxes.
A spline jig is a fairly easy jig to make that will take your projects up a level. You can build this jig in a few different configurations depending on your needs.
