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 The five working steps for cutting and fitting 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
