Finger joints are one of the most common and stable types of wood-length joints used in woodworking. It is a remarkable joinery technique characterized by interlocking fingers with angled profiles, resembling the teeth of a comb, giving it its name. This method enables the perpendicular joining of two boards, resulting in a connection that offers exceptional strength and stability. The name "Finger Joint" aptly captures the functionality and appearance of this joint. Just as interlocking our fingers produces a strong grip, the finger joint exhibits remarkable strength once interlocked. This joint highlights its exceptional resistance to pulling forces, further emphasizing its robustness. In this guide, we are going to take a look at exactly what a finger joint is, and how to make perfect finger joints.
What is a Finger Joint?
A finger joint, also referred to as a box joint or comb joint, is a woodworking technique used to join two pieces of wood together at a right angle. This joint is created by cutting complementary interlocking profiles into the wood pieces, resembling the interlocking of fingers. It is simpler than dovetail joints and consists of interlocking fingers and grooves along the edges of two wood pieces, which are glued together. The resulting joint provides a large surface area for gluing, resulting in a strong and seamless structure. The most common variation, a tapered or scarfed finger joint, is used to create long lumber pieces from solid boards, resulting in finger-jointed lumber. This joint is valuable in producing baseboards, doors, molding, trim, and floorboards.
Finger joints are commonly used in various woodworking applications, including boxes, cabinets, drawers, frames, and even construction and furniture industries. There are two main types of finger joints: non-structural and structural. Non-structural finger joints feature shorter fingers (pins) and are predominantly used in furniture making. On the other hand, structural finger joints have longer, pointed fingers, providing the necessary strength for applications like flooring and roofing.
Box Joint & Finger Joint
The box joint, also known as a finger joint, is a method of joining two boards at a corner by interlocking them. The terms can be used interchangeably. Box joints, also known as square joints, are typically used on corners to join two pieces of wood together at a right angle. While it shares similarities with the dovetail joint, unlike the dovetail joints which feature angled tails and pins, the box joint consists of straight fingers that mesh together. This joint consists of square fingers and slots that interlock with each other, creating a visually appealing symmetrical pattern. In contrast, finger joints, also referred to as tapered joints, serve a different purpose. They are used to join two pieces of wood together end-to-end, allowing for the creation of longer lengths. Unlike box joints, finger joints have tapered fingers and slots that interlock with each other.
In addition, "finger joint" is often used more broadly in various joinery applications where a strong and interlocking joint is required, this interlocking design provides strength and stability to the joint. Finger joints are used for joining wood pieces longitudinally and at right angles in various woodworking applications; whereas "box joint" is specifically associated with the construction of boxes, cabinets, frames, and similar items. Both joints are valued for their combination of strength and aesthetic appeal in woodworking projects.
Why Choose a Finger Joint?
One advantage of finger joints is that they allow for the efficient use of smaller wood pieces, resulting in materials with good mechanical properties. By connecting individual pieces of wood with finger joints, they can be transformed into finger-jointed lumber, which can exhibit strength properties comparable to solid wood. However, the suitability of the joint depends on factors such as the wood type, dimensions of the fingers, and adhesive used.
In addition to their strength, finger joints also offer a visually appealing symmetrical design to corner assemblies. The uniform and symmetrical nature of finger joints can add a clean and professional appearance to woodworking projects. Moreover, a significant benefit of this joint is its ease of assembly. Interlocking fingers make it easy to properly align the pieces for a precise fit. Unlike dovetails, they do not interlock mechanically, but their substantial glue surface area ensures their strength when combined with modern adhesives.
However, One drawback of the finger joint is that it can represent a significant initial investment for hobbyists or small workshops. Making finger joints often requires specialized jigs and tools, such as a router with a finger joint bit or a table saw with a dado blade, which might not be available to all woodworkers.
How to Make Finger Joints?
Using a router table with a properly positioned fence and the router bit ensures accurate and repeatable cuts. Here's a step-by-step guide on how to finish a finger joint.
Step one: Set up the router table
To begin, mount your finger joint bit on a router table so that the bearing and fence are aligned. This increases safety, especially when routing end pieces, and provides the finest support for your board. Position the router table fence so that the front of the router bit’s cutting edge and the face of the fence are aligned. Using a straight edge or ruler to verify this alignment, will ensure accurate finger profiles.
Step two: Make test cuts
Perform test cuts on two scrapboards. Make a test cut on the first board and invert the second board to create the adjoining cut. If the pieces don't fit accurately, adjust the cutter height and repeat the test cuts until you achieve a snug joint.
Step three: Make final cuts
Make any final adjustments to the cutter if the test cuts are not perfect. Once the setup is correct, proceed with cutting your final wood pieces. Ensure each pair of boards interlocks with flush top and bottom edges when the fingers are interlocked. Once cutting has been done, test the fit of the joints. They should fit snugly without any gaps and the glue ensures that they are practically durable.
Step four: Gluing and assembling the pieces
Here we finish cutting the grooves and fingers before it is glued together. The fingers are lined up with each other and they should slide and interlock together. Once satisfied with the fit, apply wood glue to all the mating surfaces of the fingers. Interlock the fingers of the two pieces, ensuring that the edges are flush and the joint is tight.
What do You Need for Finger Joints?
Usually, a router table-mounted router bit is used to create this kind of joint. What would be your best choice for a bit to make the finger joints? While there are no hard rules, bit selection is based first on board thickness. When boards of different thicknesses are joined together, the selected bits must have sufficient cutting depth to accommodate the thickest board. Simultaneously choose the bit that best suits your needs and budget.
A finger joint router bit is the most widely used and optimal tool for joining wood both end-to-end and edge-to-edge. Findbuytool provides a full selection of industrial-grade finger joint router bits with high-grade welding technology, stable quality, and high efficiency. These bits can be used to make wooden planks’ edge styling precise, resulting in smooth and detailed cuts. Ideal for projects of any level of complexity, they are the preferred choice of professionals and hobbyists alike.
A straight router bit or a spiral upcut router bit also works well. Both make a square cut, with the spiral bit doing the cleanest cut. The spiral upcut design routs cleaner, and faster, leaves a smoother finish, and dramatically reduces tear out.
