It is nice to know that artistry is supported by artistry. Although the miter joint is one of the simplest methods of wood joinery, its purposes are dedicated to things that contain beauty. You’ll find the miter joint is the reason why Mona Lisa has been kept inside that frame for so long. A beautifully simple wood joint, but its success derives from the woodworker’s attention to detail.
Related: Tongue and Groove Joint | Dowel Joint | Dovetail Joint | Rabbet Joint | Butt Joint | Lap Joints | Dado Joint | Mortise and Tenon Joint
What it is, and Where it’s Used
The miter joint is the union of two equally angled parts meeting together to form (usually) a 90-degree angle. This is achieved by two perfectly measured pieces of wood at a 45-degree angle.
This type of joint is not the most structurally sound option for wood joinery. It is the likely culprit responsible for holding together every picture frame you’ve ever seen. The miter joint will also be found in the corners of the molding of your ceiling, or the trim near the floor, and all of your door frames! This method is also applied to join together piping that needs to navigate around corners.
Since all of these areas don’t require all that much weight-bearing, the miter joint is the perfect choice for ease of assembly, and aesthetic appeal. The angle in which they meet enables a greater connection of surface area, and a good quality wood glue will keep the edges together in harmony.
How to Achieve a Miter Joint
First and foremost, PRECISION IS CRITICAL. It becomes very obvious when two pieces of wood are cut and even the slightest incorrect angle and the disjointed union is hard to ignore. A good rule of thumb to live by is: Measure Thrice, Look Twice, Cut Once.
Using Electrical Saws
The two main backsaws that can be used to achieve a miter joint are the table saw, the miter saw. Once the desired angles are made, glue the edges together, and then clamp the joint until the glue is completely dry.
The table saw is a circular blade mounted on an arbor, which is powered by an electrical motor. The table itself will commonly have measurements and angles printed onto it to help with measurements, but don’t rely solely on that. Ensure that the plank of wood you are using is clamped into place, as the power of the table saw will likely move it, and knock your perfect measurement out of alignment.
The miter saw is very similar to the circular blade, but it is attached to a frame that can adjust the angle of the blade according to what you desire. It is not attached to an entire table, it is handheld.
Achieving a Miter Joint by Hand
Since this is a very common and traditional method of wood joinery, a nifty tool called a miter box was invented to help with this risky angling business.
The miter box is a kind of tabletop scaffolding where slots are incorporated at the most commonly used angles. This is a guiding point where you will glide your tenon saw (hand saw with rough teeth) through the angled slot according to the angle you’re looking for. This is used as more of a rough cutting guide, where you will then use a miter shooting board to adjust and finesse the final angle.
A miter shooting board is basically a lifted 90-degree angle in which you can place your rough draft, which will hold it in place while you complete your final measuring.
Reinforcing a Miter Joint
Say you have a very valuable or large painting that requires a custom frame. A special piece of art deserves the confidence of a proper casing, and so reinforcing your miter joint with a spline is well worth the work.
A spline is a thin wafer of wood that will be inserted into a slot on the two edges of your frame pieces, that is the appropriate width for the spline. A spline is arranged with the long grain of the spline across the short grain of the frame pieces. (This is very similar to a biscuit butt joint or a dowel butt joint.)
The spline will align the two frame pieces, and be further reinforced with wood glue. It is important to clamp the joint until the wood glue is entirely dry.
If you’re looking to get more creative with your framework, perhaps try a joint that isn’t at a 90-degree angle! The math is very simple to achieve this. If you’d like an acute or obtuse angle for your corners, all that needs to be done is divide that overall desired angle by 2, and you’ll have the angle you’ll need to apply to each wood member. If you’d like an overall angle of 120 degrees, you’ll need to cut your corresponding members each at 60 degrees. Comprende?
Try a hexagon! Try a tetrahedron! Get crazy with it!
Can I create a miter joint by hand?
Absolutely! You will still require a number of tools to help you achieve this (wood glue, hand saw, miter box, etc) but it can be done. It may just require more finesse to finish off the job.
What does a miter joint look like?
It is the joining of two 45 degree angled pieces of material that join in a corner at a 90-degree angle.
When should I use a miter joint?
This type of joint isn’t particularly weight-bearing and should be saved for things like picture frames, door frames, molding, and trim.
How to spline a miter joint?
Some extra handiwork is required to create a spline. You’ll need to measure out the proper hole dimension for your spline at either end of your frame pieces, and glue the spline itself into those holes and clamp it all down until the glue is completely dried.
Does a miter joint have to be at 90 degrees?
Absolutely not! You can get creative with it, but it will make the math more complicated for each corner, depending on the angle you choose.