A butterfly joint (also known as a bow-tie joint or dovetail key) is a butterfly-shaped piece of timber, metal or plastic that is inlaid into two adjoining workpieces to hold them together or to stabilise a crack. The shape resembles a bow tie: wide at both ends and narrow in the middle.
Characteristics of a butterfly joint
| Characteristic | Description |
|---|---|
| Shape | Double trapezium (butterfly / hourglass shape) |
| Material | Hardwood, plywood, metal or plastic |
| Function | Joining two parts or arresting cracks |
| Fixing | Inlaid (routed) into the timber |
Applications
- Crack repair: arresting and stabilising cracks in solid timber
- Board joining: connecting two timber boards (for example in a table top)
- Decorative: visible butterfly joints in a contrasting timber species as an ornamental feature
- Structural: additional reinforcement at a timber joint
How to make a butterfly joint
- Make a template in the desired butterfly shape
- Cut or rout the butterfly joint from a piece of timber
- Place the butterfly joint on the workpiece and trace the outline
- Rout or chisel the recess in the workpiece (to the exact depth)
- Glue the butterfly joint into the recess and plane flush
Tips for the DIYer
- Use a router with a flush-trim bit and a template for accurate work
- Choose a contrasting timber species if you want the butterfly joint to be visible
- The butterfly joint must fit tightly: too loose gives no strength, too tight may split the timber
- For crack repair: first drill the ends of the crack to arrest further growth
- Place the butterfly joint perpendicular to the crack for maximum effectiveness
Dimensions (rule of thumb)
| Application | Width of butterfly joint | Depth |
|---|---|---|
| Crack repair | 2-3x the crack width | 1/3 of the timber thickness |
| Board joining | 50-80 mm | 1/3 of the board thickness |
| Decorative | As desired | 5-10 mm |
Related terms
- Dowel: round timber pin used as a connector
- Dovetail joint: similar wedge shape for corner joints
- Biscuit: oval connecting plate (lamello)
- Inlaying: setting an element flush into the timber