A scarf joint is a woodworking joinery used in carpentry for emergency purposes. Carpenters use this joint when long timbers are unavailable by connecting the ends of two pieces of long timber to create a sturdy and long piece of wood plank or board.
History of Scarf Joints
Numerous records talk about the early beginnings of scarf joinery. The year of its birth is unknown, but archaeological findings revealed the discovery of a 7th-century Anglo-Saxon ship along the English riverbank. Archaeologists uncovered that the early shipbuilders used the scarf joints in connecting the stern and stem timbers to the keel’s center.
Some documented scarf joints had an epic failure, but others remain unfazed by the test of time. It was in the 16th century that carpenters began using the double-bladed scarf joint. This scarf joinery is the sturdiest method of extending two board pieces to achieve their desired length.
When to Use a Scarf Joint?
Scarf joints are a popular joinery technique that creates a strong bond between two workpieces and turns them into a single, sturdy board. Its uses are not limited to wood; you can join two pieces of metal. Carpenters and woodworkers use it out of necessity when long pieces of timber are challenging to find in the forest.
If you take a closer look at the mechanics of scarf joints, you will discover that it is the simplest form of lap joints, which requires two workpieces to join their ends and hide the seams for aesthetic appeal. This method is versatile because you can apply it horizontally or vertically. You can use it when you cut the timber short or run out of a long piece of wood.
Scarf joints are easy to identify, as you can see them in crown moldings of the boundary between the ceiling and wall in expansive rooms. The moldings require long timber to create an attractive design that can cover the entire area. The scarf joints come into the picture to join two crown molding pieces to create a single wood piece.
Scarf-joined members lack strength, so carpenters use high-quality adhesives to reinforce their structural performance. Ships, rowboats, canoes, sea vessels, and sailboats use scarf joints to connect short plank pieces to form their entire mast staves. If you have visited Japan, you will notice that typical Japanese homes use scarf joints to connect those short pieces of timber to form decorative moldings and trims.
Steps on Making the Scarf Joints
Scarf joints are an essential woodworking joinery to join two pieces of timber and form a single and continuous long board for a particular carpentry or woodworking project. The finished project can minimize cost as you can create long wood planks by joining short timber pieces and making the project look aesthetically appealing.
For example, you can increase the length of the wood from 1.5 inches to 6 inches. It would be best to have an accurate layout to save time fitting the members using the right tools. Such tools include a wooden mallet, chisel, and mortising machine to form a sturdy locking joint.
Here are the guidelines for making a scarf joint.
Step 1: Scribble a Layout Mark
To achieve a clean cut, you need to scribble the end of the cut. Use a chisel to groove the end grain of the wood parts where you join the ends. Accuracy is vital to avoid tearing out the members. Rip the scribbled center line on each side. The mortised part will clean out everything that the stopped cuts have left.
Step 2: Cutting the Joint
Fitting the ends of the members can be challenging. Back-cutting makes the fitting easier to do. You can excavate the housing using a chisel and drill or a chain mortiser to have a tight and neat blade housing. The chisel will relieve the housing’s back end. This technique minimizes additional adjustments. You can make some adjustments to the blade’s exposed edges.
Step 3: Fitting
After you assemble the two members, ensure that everything is clear to achieve a perfect fitting.
Crown moldings use mitered identical 45-degree angles to join the corners. In some carpentry applications and boat building, like boat trim, the mitered joints should be 30 degrees or lesser to provide mechanical strength to the joints and extra space for gluing.
Tools for Making a Scarf Joint
Scarf joints are a product of cutting two tapered ends from opposing members where the fitting occurs. This technique is vital to reinforce the joint, which a simple butt joint cannot provide.
A circular saw with a 16.5- or 16-inches diameter blade can cut a 90-degree angled ¼ inch member. The tapered ends could have an angled cut from 1:8-1:10. When working on big timbers, you will need an electric chainsaw on an indexing frame and a chain mortiser to save time in cutting a mortise.
In boat building, a scarfer is a must-have tool for cutting several pieces of accurate scarf joineries in various thicknesses of plywood of up to 3/8 inches. A scarfer is easy to install by attaching to a circular saw with a base plate extension of half an inch or more expansive.
Conclusion
Scarf joints have been favorite joineries in boat and shipbuilding construction for hundreds of years. The purpose of a scarf joint is to join short pieces of members to form long and continuous planks when long timbers are unavailable. These joints may not stabilize the members unless you apply a stronger adhesive. Crown moldings in wall-ceiling boundaries in an enormous room benefit from scarf joints.