How to Join Two Boards Lengthwise: Step-by-Step Guide

Whether you’re a handyman or a woodworker or a construction worker, or maybe just a hobbyist beginner, there are a few basics that you need to eventually learn.

One of these is the ability to join wood boards together! Whether it’s for a fence or the wooden wall of a shed, or something else, it’s a pretty easy but basic piece of knowledge that you need!

We go over the four main methods that are commonly used for joining two boards lengthwise. With a few other methods that can be equally as useful which we will go over as well.

TIP: We’ll give you a step-by-step instructions for each method so you know exactly what to do.

What is Edge Joining Boards?

If you’re a complete beginner and this is your first time joining two boards together lengthwise, then you should know others refer to it as edge joining or joining boards side by side.

Joining two boards lengthwise or edge joining is the act of joining the boards so that they’re fastened together on their long sides. This then creates a broader seamless piece of wood that can be used on a larger woodworking project such as a table or benchtop or another project.

And although most of the methods are fairly easy to perform some require additional tools you may not have.

Before you start, read through all of our methods listed here to find out which method best suits the project you are working on. In each method, we list the tools and supplies required for each one.

Four methods on how to join two boards lengthwise (side by side):

There are a few main methods that are commonly used to join two boards together lengthwise: the biscuit joiner, the dowels, the Kreg jig, and the wood glue method. Let’s look at them all in detail:

Edge joining with a Biscuit Joiner:

The biscuit joiner method is one of the least popular, as it requires the most specialized tools. It basically consists of creating several long, thin channels in each board, and then using a joiner piece that is inserted into the channels to keep the boards pressed together through tension.

Tools and supplies you will need with biscuit joiner:

  • Two wooden boards
  • Biscuits of the right size
  • A biscuit joiner like this one here on Amazon
  • A pencil
  • A ruler or tape measure
  • A spray bottle with water
  • A clamp

Step by step guide to joining 2 boards with biscuit joiner:

1. Align and mark the boards:

Start off by aligning the two wooden boards together, in the desired position in which you want them joined. Try and match the grain colors of the wood for a more seamless and professional finish.

Once you’re happy with the alignment, use the pencil to mark a few lines between the two boards, at equidistant points. Then, separate the boards and use the marked lines to mark the slot locations for where the biscuits will be inserted.

2. Set the joiner and make the cuts:

And that you’ve marked the slot positions, you can use the biscuit joiner and start making the cuts. For the best results, make sure each cut is as half as deep as the width of the biscuits you’re using. Once you’ve made the cuts, clean out any excess dust to ensure the cuts are clean and ready to be used.

3. Inserting the biscuits:

Take the biscuits, and insert them into the arranged slots of one of the two boards. Now you can take the spray bottle of water and spray the biscuits so that they become activated.

Then, take this board and slide it into the other board, ensuring that the side of the biscuits that are poking out is fitted into the other board’s slots. The two boards should be fitted together seamlessly.

4. Let the biscuits set:

Clamp both boards together so that they remain properly aligned while the biscuits set and harden. You should let them sit for a few hours before they are ready to withstand any other type of pressure or use.

  • The main advantage of using the biscuit joiner method is that it gives the end result a completely seamless appearance, as it has joined both wooden boards from within. It is also a pretty durable method to use.
  • The main disadvantage, however, is that it requires very specialized tools, and therefore it isn’t an easy or accessible method to use. Biscuit joints also aren’t the best at maintaining lateral pressure, so there’s a risk of the boards bowing.

How to join 2 boards with dowels:

The technique of using dowels is quite a common one for joining two wooden boards lengthwise. It essentially cuts dowels that then act as a tension point between the boards, keeping them firmly joined together.

This method allows the boards to remain sturdy, while also maintaining some flexibility, which is great for overall durability.

Tools and supplies needed for edge joining boards with dowels:

  • Two wooden boards
  • Pre-cut dowels
  • Masking tape
  • A pencil and ruler
  • A depth gauge
  • A mallet
  • A clamp
  • A cordless drill

Joining 2 boards with dowels step by step guide:

1. Measure and mark the dowel locations:

Use the depth gauge, the pencil, and the ruler, and mark the different locations for the dowels. Make sure that these points are equidistant to ensure the boards are joined securely all the way through.

You should also take into account the size of the dowels compared to the width of the boards. It’s important to measure everything correctly so that the end result is as seamless as possible.

2. Drill the first hole:

Make sure you’re using a drill that is the correct size in diameter for dowel rods that you’ll be using. Drill the first hole, and test to make sure the dowel fits and that everything is correct. The dowel should fit quite snuggly, and should not have any room to spare around it!

3. Finish the joint:

If everything checks out, go ahead and drill the rest of the holes. It’s important that both depth and width are as accurate as possible. Once the holes are done, get rid of any sawdust, and insert the dowel rods into each hole.

4. Clamp and leave to set:

Take the board without the dowel rods, and slide it onto the other board so that they become connected by the dowels and fit together seamlessly.

Some people like to apply adhesive onto the dowel rods before doing this, for extra security. You might have to use the mallet to have the boards join completely. Then hold them together with the clamp, and leave them to set.

  • One of the main advantages of using dowels is that they’re a pretty basic tool within woodworking, so you’re likely to have access to them. It’s also a fairly fast and easy method to use, and it provides you with a great end result.
  • One of the main disadvantages of this method, on the other hand, is that it requires a very high precision when marking and prepping the dowels. A slight mistake or being slightly off can completely unsettle the end result and will ruin the seamless joining of the boards.

Kreg Jig:

This is a method used for joining two boards lengthwise, that makes use of pocket holes. It’s the most commonly used method for home furniture like tables, or similar. The pocket hole is angled, and then a screw is inserted that essentially holds both boards together.

You will need:

  • Two wooden boards
  • A kreg jig (you can get a kit set)
  • Compatible screws
  • A cordless drill
  • Measuring tape
  • A clamp

Step by step guide:

1. Measure and set the depth collar:

Start off by measuring the width of the board, so that you can suitably adjust the depth collar. It’s important that the hole is only as deep as necessary, and no more.

Most Kreg jig sets will come with a very helpful guide to make sure you get these measurements as exact as possible. Mark some guide holes for the drilling.

2. Clamp the wood and drill:

Clamp the board in place so that it’s easier to drill. Make sure the guide holes are also aligned! Now you can insert the drill and make the pocket holes.

It’s always recommended that you make at least around two or three sets of pocket holes so that the joint is as stable and secure as possible.

3. Finish the joint:

Take the other board, and align it with the one you’ve just drilled. Make sure everything aligns as perfectly as possible. Then, clamp them together.

Take the screws and insert them into each pocket hole, screwing them in until they pierce and grab onto the other board as well. This should allow both boards to be securely joined together.

Pros and Cons:

One of the main advantages of using the Kreg jig method when joining two boards together lengthwise is that the end result is very sturdy. The screw and its positioning hold them in place perfectly and makes the joint highly durable and resistant, which is why it’s so popular for home furniture.

One of the main disadvantages of using the Kreg jig method, on the other hand, is that it requires a professional and specialized tool. You can find a Kreg jig kit, but they’re only ever used for this specific purpose, and they take some practice to perfect.

Wood Glue:

Using wood glue is the easiest and most accessible way to join two boards lengthwise, so it’s no wonder that it’s one of the most commonly used!

This method is as easy as it sounds, you’re just using glue to stick the two boards together.

Then you wipe off the excess glue, so that they look seamless, and it’s all done! Of course, you need a good and high-quality wood glue to make sure that this method works properly. 

You will need:

  • Two wooden boards
  • Wood glue
  • Clamps
  • Wood chisel
  • Chalk

Step by step guide:

1. Mark the boards:

Start off by aligning the two boards together, in the way that you want them to be joined. Make sure that the sides match perfectly, and if you want, you can also ensure that the shade of the wood matches too for a more seamless finish.

To mark the boards, use the chalk and draw a wide U across the two so that you can align them easier later on. You can use different marking techniques, instead of the U.

Just make sure that the markings allow you to perfectly match the boards in the exact position you want them in! 

  1. Applying the wood glue:

Take one of the wooden boards and tip it on its side, so that the edge that needs gluing is facing upwards. Then take the wood glue of your choice, and apply it along the entire length of the board’s edge.

Don’t worry about putting on too much glue, as you will deal with the excess later on. What’s important is that you use enough glue to firmly join the boards together. 

  1. Clamp the boards together:

Following the chalk markings, slide the two boards back together, into the desired position. Then, use the clamps to hold them together.

This will not only keep them in place while the glue dries, but will also add pressure so that they’re stuck together a lot better.

Wait for the amount of time indicated for the wood glue that you’re using. On average, this will be around 20 minutes. 

  1. Remove any excess glue:

Before the glue has dried completely, use a wood chisel to remove the excess glue spilling out from in between the boards.

It’s important that you wait until after the glue has begun to settle, but before it dries out completely and is too hard to remove. 

Pros and Cons:

The main advantage of using wood glue to join two boards together is that it’s a very easy method. It’s fast, and it’s accessible, making it the most common amongst beginners and hobbyists. If done right, it also has a very seamless look, so that you can’t even tell the two pieces of wood apart! 

The main disadvantage that wood glue has, is that it’s the weakest method of them all. Despite modern wood glue being impressively strong, it’s still not as strong as the other methods, so it’s not as favored among professionals. 

Other methods of joining two boards together:

There are other methods that can be used to create a joint, and join two boards together. And depending on the end goal, they might be more useful than the four main methods we’ve already covered.

So let’s take a look at the half-lap joint, the tabled lap joint, and the bevel cut scarf joint.

Half lap joint:

With this method, the two boards will be reduced to half their original thickness, in the part where they will lap over each other to be joined. This forms a strong joint, with a big surface for gluing and reinforcing. It is typically used with a door frame, dressers, and different types of outdoor furniture.

You will need:

  • Two wooden boards
  • Circular saw
  • Wood chisel
  • Ruler and pencil
  • Clamp
  • Mechanical fastener

Step by step guide:

  1. Start by placing the two boards together, side by side, with their ends even. And clamp them together.
  2. Measure a distance from the end of the board, along, equal to the width of one board, and mark it. (The mark should go across both boards).
  3. Set the depth of the cut so that it is half the depth of the thickness of the boards, and cut along the line.
  4. Next, you need to cut a few saw kerfs across the boards, closely spaced together.
  5. Unclamp the boards and place them cheek to cheek so that they form a 90-degree angle.
  6. To finish it off, assemble the joint. Depending on the thickness, you might have to use a mechanical fastener.

Pros and Cons:

One of the main advantages of using a half-lap joint is that it’s very easy to use, and can be done with very few materials. Plus, it also provides a large surface area that can be glued or reinforced.

One of the main disadvantages of the half-lap joint is that it can be quite weak, especially because you’re removing thickness from the boards, in order to have them overlap at one of the edges.

Tabled lap joint:

The tabled lap joint can be very useful, as it combines the strength of the interconnecting parts, and also provides a large glue surface to work with.

You will need:

  • Two wooden boards
  • A cordless drill
  • Measuring tape and a marker
  • A clamp

Step by step guide:

  1. Place the two boards side by side and clamp them together. Measure a distance along the board that is equal to the width of one board, plus ¼ of that width, and mark it. This step is almost identical to the set up of the half lap joint.
  2. Set the cutting depth to a third of the thickness of the boards. Then rabbet across both boards.
  3. Next, set the cutting depth to two thirds of the thickness of the boards. Measure from the shoulder of the dado to a distance of on-half of the width of the entire workpiece, and marl it. Make two passes, then cut the remaining dadoes.
  4. Apply glue to both boards, and piece them together. They should fit like a puzzle piece, thanks to the dadoes. Clamp them together so that the pressure helps the glue set even stronger.

Pros and Cons:

One of the main advantages of the tabled lap joint is that it is very strong and durable. It also shows off your skill and effort, as a well-made tabled lap joint will look good and professional, and is usually ideal for furniture in which the joint will be displayed outwards.

One of the main disadvantages of the tabled lap joint, on the other hand, is that it is very time-consuming and demanding to make.

Bevel cut scarf joint:

You will need:

  • Two wooden boards
  • Wood glue
  • Power saw
  • Marker and measuring tape
  • Clamp
  • Triangle

Step by step guide:

  1. Align the boards and mark out an equal angle on both ends, so that they’ll be able to mate properly. This angle should be at least 45 degrees.
  2. Make the 45 degree cut on one side, and have the mating end on the other side.
  3. Line the edges together and make sure they fit perfectly. If they don’t, make some amends or tidy up the edges by cutting them a little more.
  4. Apply glue and push them together so that they fit in place. Use the clamp to ensure they stick together with the right pressure, and let them dry!

Pros and Cons:

One of the main advantages of the bevel cut scarf joint is that it is incredibly easy and simple to cut on a table saw. They also have around 40% more adhesion than other types of similar joints, and if done well they can be almost completely seamless in appearance, making them a very desirable option.

One of the main disadvantages of the bevel cut scarf joint, on the other hand, is that they’re not very easy to reinforce, so they aren’t the most durable of joints you can use for the job.

What is the best method for joining two boards lengthwise? 

Now that we’ve explained all the main methods for joining two boards lengthwise, you can decide for yourself which is most suitable to your specific needs and preferences, as well as which you are able to perform according to the tools and materials you have access to.

It’s pretty clear that wood glue and dowels are the two methods better suited to beginners or hobbyists, or for those that want an easy and fast method that is overall pretty accessible.

The biscuit joiner and Kreg jig, on the other hand, are both methods that require specialized and more professional tools, plus they require a lot more practice in order to get right.

Also, the other three methods we’ve explained can be equally as useful and convenient, if you have the right tools and you’re willing to give them a go. Although they aren’t as popularly used amongst beginners, which is why we didn’t include them as part of our main four!

Truth is, all methods provide a good end result if done right, and all are decently sturdy and durable. Although the wood glue method depends on the quality of the wood glue that you’re using.

But if you had equal access to all methods, which one would be the overall best?

Assuming specialized tools aren’t an issue, the best overall method would be to use the Kreg jig. It is the most durable, thanks to how secure the screws are, and it offers one of the best results while being fast and easy to perform.


In Conclusion

So, to sum everything up, how do you join two boards lengthwise? There are a few main methods that you can use: the biscuit joiner, dowels, the Kreg Jig, and wood glue.

The biscuit joiner and the Kreg jig both require the use of specialized tools and are usually used by professional woodworkers. Dowels are in between, as they are easy to use but require high precision in order to get a good result.

And wood glue is the most accessible and easiest method to use, preferred by beginners and hobbyists, as you’re essentially just gluing the two boards together.

You can choose whichever method is better suited to your means and preferences, and you can go back to our step-by-step guides for each for an easy follow-through explanation on how to use each one of them.

And remember, sometimes it takes a little patience and a few tries to get the desired end result, just keep at it!

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Dean Luoma

As a long-time homeowner, Dean has been working on his own home projects for over 30 years. He is a licensed real estate agent in the state of Minnesota, helping clients with the buying and selling of their homes.

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