The Bird's Mouth Joint has been around for a long time and gets its unusual name because it resembles the open beak of a baby bird waiting to be fed. Boatbuilders were some of the first to adopt the bird's mouth joint for making hollow sailboat masts that are incredibly strong and light. The Infinity Tools Bird's Mouth Router Bits are available in three sizes that allow you to make projects with 6 or 12 sides (57-505) 8 sides (57-506) or 16 sides (57-507), and we now offer a precision setup block for each to eliminate setup frustration.
The beauty of the Bird's Mouth Joint is that only one edge of each "stave" needs to be routed. This simplifies setup, increases accuracy, and speeds up production. The beak shape lets the 90° edge of the adjoining stave nest in place providing an excellent glue surface and a mechanical corner to help keep the parts in alignment during assembly.
Another nice feature of the Bird's Mouth Joint is that you can produce projects with three different looks. Smooth joint transitions, stepped joint transitions, and even turned round projects are all possible.
Here at Infinity Tools, we offer a setup block for each of the Bird's Mouth router bits that are designed to work with stock of specific thicknesses. For 6, 8, and 16-sided projects use 3/4" material for an outer edge that can easily be sanded smooth. For 12-sided projects use 1/2" material. Thicker and thinner material can be used but may require bit height and/or fence adjustments to achieve your desired results. Choosing thicker material or adjusting the bit slightly allows a stepped profile to be created that can be very attractive and adds a look similar to overlapping shingles.
A simple equation is used to figure out how wide each stave needs to be to make a project of a certain diameter. You can find and print this handy "Cheat Sheet" in the "Documents" tab on the Bird's Mouth Router Bit product page. Here is an example of how easy it is. First, decide how many sides your project will have and choose the correct router bit. Let's go with 8 sides and use router bit 57-506. Second, decide the diameter you want your project to be. let's go with 12". Now we can use the formula found in the instructions for 57-506. (Project Diameter ÷ 2.4 = Stave Width) to find our stave width. 12 ÷ 2.4 = 5, so we will need 8 staves that are 5" wide.
The Bird's Mouth Bits can be used to make elongated shapes like ovals where at least two of the staves are wider than the others. They can also be used to make mitered corner details for cabinets. For those that would like to sand, plane, or turn your projects round we include an easy-to-use formula in the Instructions to determine how thick each stave will need to be in order to make your project completely round.
When it comes time to glue up your project I recommend reaching for a band clamp. The band puts equal pressure all the way around your project pulling all sides together equally and takes advantage of this joint's tendency to "self square". If you don't already have a few band clamps we recommend the Bessey Variable Angle Band Clamp (100-594) because it also includes a reel that keeps the extra band from getting tangled up. Painters tape can also be helpful at keeping all of the pieces aligned while getting the clamps in place, especially for 12 and 16-sided projects.
Don't be afraid to give these bits a try and add some non-90 ° corners to your projects. With the help of the Infinity Tools Birds Mouth Router Bits, setup blocks, and a little easy math you can create projects that definitely qualify as out of the box.
