How to Make a Tea Mat with a Butterfly Key
Put the power tools away and make a chashiki, a small Japanese tea mat, accented with a butterfly key (chigiri)—one of Japan's traditional woodworking techniques. The result lands somewhere between traditional and modern, and it looks at home in any setting.
A saw, a chisel, and a little care are all you need. Start small with a piece like this and you will get a real feel for how much there is to Japanese woodworking.
What Is a Chigiri (Butterfly Key)? Reinforcement That's Meant to Be Seen
A butterfly key is a small, bow-tie-shaped piece of wood set into the surface of a board to reinforce a crack or a seam. Japanese woodworkers have used the technique for generations, and it is valued as much for how it looks as for what it does.
There are no fixed dimensions. You size the key, and its angle, to suit the crack or joint you are reinforcing.
What Is a Chashiki? A Small Mat for Japanese Tea Time
A chashiki is a small mat used to serve tea sweets, or set under a teacup as a saucer. Think of it as something between a coaster and a small tray—a simple way to give your tea time a little Japanese character.
Materials and Tools
Materials
- A board about 100 mm wide and 10 mm thick, for the body of the mat
- A piece of hardwood for the butterfly key
- Wood glue
Change the size and the wood species to suit you. For this project we used cherry (sakura) for the board and karin for the key. A light board paired with a dark key gives you a beautiful contrast.
Pro Tip: The key is easier to work with if your stock is about twice as thick as the depth of the recess. We are cutting a 3 to 4 mm recess here, so we started with stock around 8 mm thick.
Tools
- Marking: pencil, Japanese carpenter's square (Sashigane)
- Cutting and shaping: Hand Saw, Flush Cut Saw, for trimming the butterfly key flush with the surface, Oire Nomi Chisels, Genno Hammer, Wooden Mallet (Kizuchi)
- Finishing: Hand Plane, sandpaper
- Other: Double-sided tape or similar
Nice to have:
- Kiridashi Knife: For scoring guide lines before chiseling.
- Protractor: For marking the angle of the butterfly key accurately.
- Chamfer Plane: For chamfering the edges at a consistent angle.
Step-by-Step: Making a Tea Mat with a Butterfly Key (Chigiri)
Step 1: Cut the Board to Size
We are making a square, so set the width at 100 mm. Mark the cut line with a carpenter's square and cut it with a saw.
Step 2: Decide the Size and Position of the Butterfly Key
Size the butterfly key by eye, balancing it against the board as a whole. On our 100 mm board we made the key 55 mm wide, a little wider than half the board, and 35 mm long. The angle is 14 degrees, which works out to a 1:4 slope.
Mark the position so the key ends up centered.
Pro Tip: There are no set dimensions. Adjust the size and angle of the key to suit your board and the look you are after.
Step 3: Shape the Butterfly Key
Marking
Lay out the shape of the key on your hardwood. Draw a line for the width, find the center, and mark the shape so it is symmetrical on both sides. Use a protractor for the angled lines: for a 1:4 slope, that is 76 and 104 degrees.
Pro Tip: A butterfly key is small and angled, which makes it awkward to cut. Leave some spare material around your layout. That way you can cut in from the corners toward the center, and the corners are far less likely to chip.
Sawing the Key
Saw along your lines. To cut straight, line up your eye and the saw with the marking line. Clamping the piece so the line sits square to you means you can put all of your attention on the cut.
As you go, check the lines on both the top face and the side, and keep an eye on whether the saw is drifting.
Dozuki Saws: The Right Saw for Precision Work
Step 4: Transfer the Outline to the Board
Now transfer the outline of the key onto the board. Stick a piece of double-sided tape to the key and set it on the position marks you made earlier. Trace around it in pencil. Going over that pencil line with a Kiridashi knife gives your chisel a crisp edge to register against.
Once the outline is on, lift the key off and put a small mark on both the key and the board so you can fit it back the same way around.
Step 5: Chisel the Recess
Chisel out a recess 3 to 4 mm deep. Start 1 to 2 mm inside your line and work carefully out to the line itself. Keep the bottom flat.
Line up your orientation marks and test-fit the key. Aim for a slightly tight fit so it seats with no gaps around the edges.
How to Use Japanese Chisels: Tips & Techniques
Step 6: Fit the Butterfly Key
Take the smallest shaving off each of the four bottom corners of the key. It helps the key start into the recess. Brush on a thin coat of glue, then tap the key down with a wooden mallet, alternating from side to side in small taps so it goes in level rather than tipping.
Pro Tip: Striking too hard can split the board or the key. If it is too tight to go in, do not force it. Lift it out and take a little more off the recess.
Step 7: Trim the Butterfly Key Flush
Run a Flush Cut Saw along the surface of the board to cut off the part standing proud. Then take the surface down with a Hand Plane until it is level.
Step 8: Chamfer the Edges
Turn the board over and draw a line 10 mm in from each edge. That is your guide for how far to take the chamfer. Work all four edges with a hand plane. A chamfer plane helps create a consistent angle.
The corner where you finish the stroke tends to splinter, so back it with a scrap block to prevent that. Take the chamfer to whatever angle you like.
Step 9: Finishing
If you would like to add a finish:
Use a food-safe plant oil such as flaxseed or perilla oil, or a wood finish rated safe for contact with food. A finish helps keep moisture and dirt from soaking in, and it keeps the grain from raising.
It also brings out the figure in the wood, so the contrast between the board and the butterfly key stands out that much more.
Try Japanese Woodworking for Yourself
A butterfly key takes a flaw, a crack in the wood, and turns it into the thing you notice first. That way of thinking, and that eye for beauty, runs right through Japanese woodworking.
Working without power tools, shaping each part patiently with a saw and a chisel, is one of the pleasures of Japanese woodworking.
Tools Used in This Project
These are the Japanese hand tools we used here. They will serve you well for butterfly keys and for plenty of other woodworking besides.
