Xem Studiomeasured geometryLibrary › Joinery › Scarf & splice joints ·
Bird's mouth joint (rafter seat)
How deep is a bird's mouth cut? · Hardware · basis: Xem Studio design — geometry computed in the generator from traditional proportions
Also called: birds mouth, bird's mouth cut, birdsmouth joint, rafter seat cut, boca de pájaro, corte de pájaro, Kerve, Sparrenkerve
Exact dimensions. True size, with no printing tolerance added.
- length
- 153.6 mm
- width
- 80.0 mm
- height
- 106.0 mm
Notes
- Woodworking joint drawn for 3D printing: the parts lock together by shape, so a print can be joined without glue or screws. Drawn at true size with the parts line to line (zero gap) in their assembled position — add your printer's fit allowance to the mating faces (your AI or slicer can do this).
- The V notch that seats a sloping rafter on a wall plate: a level seat cut and a plumb heel cut.
Bird's mouth joint size chart
| dimension | value |
|---|---|
| stock | 20 × 20 plate, 15 × 30 rafter |
| parts | plate, rafter |
| pitch | 30° |
| notch | seat cut and heel cut, about a third of the rafter depth |
| assembles | the rafter sits on the plate |
| holds | the rafter from sliding off the plate |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Xem Studio | Joinery design (geometry computed in the generator from traditional proportions) | web | Xem Studio design |
Free files
★ Free files 3 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json
| birds-mouth-joint-plate | Wall plate (20 × 20) | STEP · STL |
| birds-mouth-joint-rafter | Rafter 15 × 30 at 30° with the bird's mouth notch | STEP · STL |
| birds-mouth-joint-assembled | All parts in their assembled position (each part its own solid) | STEP · STL |
Let your AI pull this. Add
Set it up →https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.Plain text: sheet.txt · JSON: /api/geometry?object=birds-mouth-joint
Fits with
Questions
How deep can a bird's mouth be?
No more than a third of the rafter depth.