A castle joint, also known as Shiro joint, is a combination of a half-lap cross joint and an intersecting bridle joint, resulting in a 3-way interlocking joint. The combination of these two joints makes the overall bond very strong, making the castle joint one of the strongest woodworking joints. The way how the wood pieces are assembled not only guarantees the strength of the joint but also makes the joint stand out aesthetically.
Its application can be found mainly in the production of furniture where a solid connection is needed but at the same time, a nice appearance is desired. Very often the castle joint is used in connecting corners of bed frames, making tables, and connecting table aprons.
Although the castle joint looks complicated it is actually one of the easiest woodworking joints.
There are multiple options and ways how to make a castle joint. It can be made by using an oscillating tool with a chisel a dado stack or a coping saw. All of these options will provide the desired outcome. But probably the easiest (quickest) and most accurate way to ensure the best result is by using a tenoning jig and a crosscut sled together with a table saw.
For the purposes of this article, I leaned toward the traditional way of cutting a castle joint, using a Japanese saw, a coping saw, and a chisel. Among the available choices, this approach is the most budget-friendly but also requires the most skill.
The final result not only looks fantastic but also showcases the joint’s strength. It is no wonder the castle joint is chosen for furniture that demands both durability and beauty. The extra effort spent on this joint is definitely worth it.
Keep reading to find out how to cut a castle joint and assemble all the parts together.
How to Make a Castle Joint Video
If you want to see how it is done, watch the video below for a step-by-step guide on how to cut a castle joint.
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Table of Contents
- Material you will need
- General Questions
- What is a half lap cross joint?
- What is a bridle joint?
- How strong is a castle joint?
- Should you glue a castle joint?
- Castle Joint Step by Step
- Different Ways to Making a Castle Joint
- Woodworking jigs used
*Safety is your responsibility. Make sure you know what you’re doing and take all necessary safety precautions while working with power tools. Safety comes first!
Always be cautious and careful when using any power tool.
Material you will need to make a Castle Joint
3 Pieces of Wood (The thickness of the pieces doesn’t matter)
For this project:
1 Spruce Wood (40 x 40 mm) – for the tower
2x Beech Wood (3 x 15 mm) – for the horizontal pieces
What is a half lap cross joint?
A half-lap joint or a cross-lap joint is a 90-degree interlocking joint of two pieces of wood that are cut halfway through their depth and the width of the cut equals the thickness of the wood piece. The pieces slide together and overlap one another on an even plane.
Making a cross-lap joint is quite easy. Tools of choice for making this joint include routers or table saws with a miter gauge or a crosscut sled.
With a router, you will end up with a clean and precise cut. Nevertheless, using a router is mainly possible with thinner pieces of wood since they won’t have the reach for thicker lumber.
If you want to make deep cross laps then a circular saw is a better option. Circular saws typically have enough clearance to make deep cuts.
What is a bridle joint?
A bridle joint is very similar to the mortise and tenon joint. Actually, it is an easier alternative to the mortise and tenon joint. Both joints are much alike but there is a difference between these two, which is mainly reflected in the length of the tenon and the depth of the mortise.
In the case of a bridle joint, a recessed end from both sides of one wood piece fits into another wood piece recessed in the middle – one accepts the other provides. When locked together you can see the end grain of the tenon which makes the joint quite attractive. Since the bridle joint provides good strength and looks neat it is often used to make benches, tables, or narrow frames for furniture.
The joint is quite strong on its own, however, wood glue, pins, or mechanical fasteners can be additionally used to keep the joint together.
How strong is a castle joint?
The combination of the half-lap cross joint and the intersecting bridle joint makes the castle joint one of the strongest woodworking joints. The Castle joint is known for its impressive strength under vertical loads, it excels in bearing weight. However, when subjected to horizontal forces or lateral pressures, there’s a possibility that it might weaken over time, leading to potential cracks.
To fortify the joint further, consider using wood glue which binds the wooden pieces seamlessly. If you’re looking for even more stability, mechanical fasteners are a good choice, ensuring the joint remains intact and robust for a longer duration.
Should you glue a castle joint?
A significant benefit of the castle joint is its flexibility; you can put it together or take it apart as needed. For a heavy piece of furniture like a castle joint bed frame, this means you can transport the individual pieces and then assemble them right where you want it.
Once you’re happy with the placement and have no plans to disassemble it, I’d suggest firmly securing it with either glue or bolts to ensure it stays intact.
The castle joint naturally interlocks, eliminating the need for extra fasteners or adhesives. Its design inherently provides ample strength and support.
However, when deciding whether to add glue or screws for additional strength, several factors come into play:
- The direction of stress (vertical vs. horizontal)
- How visible the joint is
- The presence of gaps in the joint
Take tables and beds, for instance. For tables, glue can be an excellent addition. It not only secures the joint under less lateral stress but also enhances its appearance by filling in minor gaps. For beds, which experience more side-to-side pressure, it’s wise to use fasteners in spots that remain hidden.
Let's Build It
Before starting with your project, you should consider what will be the joint used for and how much pressure should it take. For a small coffee table, you might not need as thick wood pieces as in the case of a bed.
A castle joint can be made using wood pieces of different sizes (thicknesses). Generally, you will find joints made out of 3 equal size pieces. In my case, the thickness of the castle is different from the thickness of the horizontal pieces.
In any case, regardless of the thickness of the wood, the principle is still the same.
Also, take into account that when building the castle joint there will be several cutouts both on the castle piece as well as on the horizontal pieces. Mind that the wood pieces will lose some of their strength after the cutouts. Select the wood thickness according to your project. The remaining wood thickness after the cutouts should still make up for a strong and tight fit.
How To Make a Castle Joint Step by Step
Step 1: Cut the Castle
The wood piece I am using for the castle is a square piece of spruce wood 40 x 40 mm.
First, mark the vertical lines to be cut off. Measure the width of the wood piece and divide it by three. It doesn’t have to be perfect, but it has to be the same on all four sides of the wood piece.
TIP: Mark the lines by using a marking gauge or a combination square
Then mark the horizontal lines. The distance (from the top) equals the width of the horizontal wood pieces to be used.
Start with the cuts. To cut the bridle joint I am using a Japanese saw for the vertical cuts and a Coping saw to make the cutoffs. For precise cleaning of both the vertical and horizontal cuts, I am using a chisel. Cutting can be also done easily on a table saw with a tenoning jig.
TIP: Don’t cut on the line but on the inner side of the line. Fine cleaning will be done with a chisel.
Once finished with all four sides you should be left with a 3×3 pattern.
After that, you can go ahead and clear out the bulk of the material using a coping saw from the middle of the joint. Clean the sides and surfaces with a sharp chisel.
Now you should have a piece looking like a tower of a castle.
Step 2: Cut the Tenons in the Horizontal Parts
The horizontal parts are two identical pieces that will slide together and overlap one another on an even plane. The tenons’ width equals the width of the middle part of the tower piece.
To cut the tenons mark the places for the vertical cuts. Cut as deep on both sides of the piece to end up with the desired width. I am using a chisel to get rid of the shoulders. In my case, the cuts are quite shallow but if the wood pieces were thicker, I would use a coping saw to get rid of the material.
TIP: If you are cutting a tenon in the middle of the wood piece or anywhere near the end (but not precisely at the end) leave the distance from the edge a little bit longer. If the distance is too short the end can be brittle and break off. If you leave them longer you can always trim them afterward.
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Step 3: Cut Cross Lap Joints
The final cut that needs to be done is the cross-lap joint on the recently created tenons. Mark the edges for the cut by sliding the tenon into the tower. The depth of the cut is equal to half the width of the horizontal wood piece.
Again, start cutting on the inner side of the line and clean with a chisel afterward.
You should end up with a piece that looks like this.
TIP: Depending on the type of wood (soft x hard) you can add a diagonal offset to make sure the joint doesn’t break. This is especially the case with softwood. The good thing is the offset will not be seen as it will be hidden inside the tower joint itself.
Slowly add to the depth of the cut until both pieces are completely flush after assembly.
Step 4: Assemble all the Pieces of the Castle Joint
Once all the pieces are cut, you can start assembling the castle joint. Take one of the horizontal pieces and slide it into the tower piece. Make sure the socket faces upwards.
Take the second horizontal piece, make sure the socket faces downwards, and slide it into the castle. The two horizontal pieces will slide together, overlap one another, and interlock at 90 degrees. If done well you will get a really nice snug fit.
Below is a picture of a finished Castle Joint.
When to Glue a Castle Joint
If necessary, the castle joint can be additionally secured either with wood glue or screws. The decisive factor is the type of pressure to which the joint will be exposed and the visibility of the joint.
NOTE: If the joint is not perfectly snug after assembly and you want to get rid of the gaps you can put some paste created from glue and wood sawdust into the gaps between the joints. Sand it and the gaps will be gone. It is always good to keep some wood sawdust stored in the shop.
Different Ways to Making a Castle Joint
Using just a hand saw and chisel is one way to make a castle joint, but if you have some common power tools like a table saw or router, you can get the job done even quicker. Pairing them with the right woodworking jigs, can help a lot.
Choosing this way means you’ll likely get the job done quicker, with sharper and more accurate cuts. Plus, it often looks neater. The trick is picking the right jigs for your tool. If you’re using a table saw, tools like a crosscut sled or a tenoning jig can help. With a router, a mortising jig might be what you need.
KEEP READING: How to cut a Castle Joint on a Table Saw
So, this is the castle joint (3 way wood joint). Despite how complicated it looks it is actually quite a simple joint and easy to learn. So, a good candidate from the field of woodworking joinery to start with.