A lap joint is one of the most popular joinery techniques to join the ends of metals, plastic, and wood. In woodworking, this method can either be half lap joint or a full-lap joint. Both types involve joining two joinery members in overlapping positions so that their ends or edges connect, resulting in a continuous surface.
Lap joints have different kinds to join the edges, depending on their applications and materials. Full-lap joints do not require the removal of one of the members for joining; the thickness of both members adds strength to the joints.
Half-lap joints need to remove the pieces from both members to get the thickness of the thickest wood piece. Half of the wood piece has to be removed from each other if both members have the same thickness.
Are Lap Joints Strong?
Lap joints can be permanent or temporary joinery for some applications. In machinery, for example, it requires temporary joinery when two machine parts join together or needs replacement.
Mechanical fasteners, such as rivets, nails, screws, and bolts, are helpful in temporary lap joinery. Permanent lap joinery in machine works uses various methods, such as welding, brazing, flame joints, soldering, fasteners, and adhesives.
Since we are discussing woodworking, lap joints provide strong resistance against heavy pressure. Gluing two overlapping long-grain wood members (faces, ends, or edges) makes the joints stronger than mortise, tenon, and other joineries.
Full-lap and half-lap joints offer strength to the members using their unique features. As discussed earlier, a full-lap joint involves two overlapping boards in the same fashion. The wood pieces overlap to create a joint thickness similar to the board’s combined thickness. It becomes a full-lap joint when a piece of wood has the same thickness as the other panel.
For example, each board has half an inch, and the full joint will have a one-inch thickness. In a half-lap joint, the overlapping wood sections will have a reduced thickness before they overlap.
Advantages & Disadvantages of Lap Joints
Lap joints offer many advantages in carpentry, woodworking, and manufacturing metals and plastics. They help fabricate regular and odd-shaped wood planks, sheets, boards, and other materials when the need arises for more extended parts.
Vehicle, motorcycle, and aircraft parts use lap joints in making fuselages and frames. Lap joints might be strong joinery, but they also possess some disadvantages. Find out its advantages and disadvantages.
Advantages of Lap Joints
Easy to Create
Lap joints take less effort and time to create as they are easy to make. It does not require special equipment, tools, or cut faces to become perfectly flat or parallel. The essential tools in making lap joints include saws, hammers, and chisels. This joinery is also called novice-friendly woodworking joinery.
Stronger
Lap joints are known for their strength and resilience against shear force. Their strength can stand against heavy pressure, stress, and extreme conditions. Their power is more robust if you dry them well. They are an excellent joinery in furniture making and construction of log houses and cottages.
The two overlapping workpieces bond correctly even if they are full-lap or half-lap joints, as they perform well under stress without resulting in deformation on the structure. They become more secure after applying glue that fills the gap or void between the joints.
Adaptable
Lap joints are adaptable to various applications as you can quickly form them using two different metals like copper or aluminum. They work well in different board thicknesses, where you must weld the thinner piece on top.
There are many versions of lap joints according to your specifications for a specific project. In woodworking, lap joints are excellent joinery for making furniture pieces, flat frames, and wooden boxes. You can also join thin materials like foils and diaphragms.
Less Complex
The simplicity of lap joints makes them ideal for modern and contemporary designs. The absence of ornate and complex designs makes them easy to prepare and cut. If you want a less cumbersome design for your woodworking project, this joinery will make your finished product simple and neat.
If you make it correctly, this joinery can hide the ends and faces of the boards. The surface ends with a beautiful exterior without having to add some finishing touches.
Disadvantages of Lap Joints
Like some wood joineries, lap joints are no exception in their imperfections. There are times when lap joints could be better for specific projects. Here are the disadvantages of lap joints.
Not Eye-Catching
Its simplicity makes lap joints less popular in some woodworking projects that require ornate and intricate designs. Vintage and antique furniture pieces that speak of a particular era look stunning with their complicated patterns and designs.
Minimalists prefer lap joints due to their simplicity and less maintenance. They may be challenging to create, yet the finished product looks pleasing to the onlookers. Lap joints are only suitable for some projects that do not require showing off the joints.
Not User-Friendly
Lap joints are friendly to woodworking beginners as they are easy to make. However, they are not easy to uninstall. Since they are not stable and robust compared to some joineries, removing one piece of plank could take more time than removing several boards in one sitting. Changing the design could be limited because you must uninstall and re-assemble the whole thing.
Gluing Takes Time
Gluing the end or faces of the joints can be problematic as they do not hold together. You need to clamp or fasten the board pieces to stay in place while leaving the glue dry.
Working on small woodworking projects can be challenging as the pieces are so small to allow them to dry individually before moving on to your next task.
Creating a seam in those delicate parts can be a cumbersome experience as the members may separate, leading to splitting, warping, or cracking the gluing surface area.
Not Durable
Professional woodworkers can attest that lap points are less robust than some bloggers say. Why? It has a lower tensile strength, so it is unsuitable for large furniture, such as chairs, tables, and cabinets. The base materials are less rigid as the weld may cause them to pivot.
The overlapping joints are not suitable for mechanical reasons. The joints may store moisture causing the hidden area to deteriorate over time, especially when working on metals.
Creates Gaps
No matter how careful a woodworker is in creating lap joints, gaps between the board pieces are more likely to occur. The workpieces do not have a straight formation as the wood moves often when you are working on it. Lap joints are challenging to stay in place, making them unsuitable for outdoor structures, such as decks, rails, and fences.
The gaps can look unsightly to onlookers, affecting your reputation as a woodworker. The unappealing look of indoor structures is less noticeable once you apply varnish or paint.
You must scribble a line where the workpieces meet and work outwards to prevent gaps in the finished project.
Should I Use a Lap Joint?
A lap joint is an excellent joinery if you are starting a woodworking hobby or want to refresh what you learned in the subject of your industrial art in grade school. But some things influence your decision to use it or not in your next woodworking project.
Size & Weight Considerations
A lap joint is unsuitable for heavy and oversized carpentry projects. The joints are not robust to keep them in place. Lap joints cannot tackle stress and force to keep two furniture pieces. Why not use a miter joint or a butt joint, as they can hold the members together. Mortise and tenon, and dowel joints have the strength for this application.
Mechanical & Aesthetic Reasons
Since lap joints cannot conceal the ugly joinery in outdoor structures, it is not advisable to use them. Their visibility makes the outside of your project unappealing. If you are a meticulous person, there are better recommendations than lap joints. Rabbet and dado joints make the joints less visible to the onlookers.
Different Types of Lap Joints
1) Basic Lap Joint
The simplest lap joint type is the basic lap joint. It does not require a lot of work. All you have to do is to cut the boards according to your desired length and overlap their ends, faces, or edge. You do not have to remove a piece of wood to perform a full-lap joint to fuse the thickness of the workpieces for reinforcement. Use a mechanical fastener or adhesive to hold the members together.
2) Halving Lap Joint
This lap joint type is popular in framing for cabinetry. It is a half-lap joint because you will remove half of the material from the workpieces before facing them together. Like the basic lap joints, it is easy and quick to create.
The board’s long grain to long grain gluing surface offers high strength to the finished project. This method secures bonds while providing even thickness and smooth flow in your woodworking project. The board’s shoulders can withstand racking and twisting if you reinforce the wood with mechanical fasteners or dowels.
3) Cross Lap Joint
This method of lap joinery is popular in making inside framing of cabinetry and basic bracing and structure. It works like the basic half-lap, but the joints lie in the center of two members. Place the members at their correct angles where one piece ends at the joint or extends. The members that end at the shin are known as the middle or tee lap joint.
4) Dovetail Lap Joint
Dovetail lap joints have similarities with cross-lap joints. Their difference is that dovetail lap joints lie between the board’s end and the center of the other board. Its form looks like a dove’s tail or letter V. It is common joinery in furniture and cabinetry framing applications to resist shear forces and stress.
5) End Lap Joint
Known by its different names as corner lap and pull lap joint, the end lap joint is ideal for forming a corner in a rectangular frame. It enables the members to join end to end at the right or parallel angles. It is suitable for internal framing in cabinetry and visible framing in furniture pieces.
6) Mitered Half-Lap Joint
Woodworkers use mitered half-lap joinery for visible framing that requires mitered corners. It is not ideal for heavy and oversized furniture pieces as the gluing surface is narrow, making it a weak joinery.
Reinforcing this joinery means you have to cut a forty-five degrees angle on a piece of wood and take out half of the mitered section’s thickness to form a triangular relief of the board’s back.
The woodworker will cut a forty-five-degree angle halfway through the opposing board before they remove half of the members between the board’s end and a 45-degree cut to form a similar space for the other wood piece.
The two mitered angles are in direct contact, overlapping where you remove the material to form a mitered face, shoulder, and a wide gluing area.
How to Make Lap Joints?
Lap joints are easy to make using glue with two long grain boards to join their faces. Ensure you clamp or fasten the boards to keep them together while allowing the adhesive to dry naturally. Have enough patience before removing the clamp to ensure that the faces or ends of the joints adhere to the glue.
What are the Uses of Lap Joints?
Lap joints have many applications, such as tabling, temporary framing, cabinetry, boxes, and indoor and outdoor structures. It is ideal for framing assembly of cabinets and dressers and timber frame construction.