Bird's mouth joint (rafter seat) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/birds-mouth-joint/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design — geometry computed in the generator from traditional proportions
Catalog version: 2026-10-20

Overall (mm): length 153.6, width 80.0, height 106.0
- 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.

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

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Xem Studio: Joinery design (geometry computed in the generator from traditional proportions) — web — Xem Studio design — https://xemstudio.com/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/birds-mouth-joint/index.json
API: https://xemstudio.com/api/geometry?object=birds-mouth-joint