Kumiko birdsmouth jig:
pare the notch that locks kumiko together.

Half of every kumiko joint is a small V-notch cut into the end of a strip: the birdsmouth (also written bird's mouth or birds mouth; in Japanese, the jaguchi 蛇口). It is the cut behind every 60° hexagonal pattern, asanoha and mitsukude included, and the 45° cloverleaf. This 3D printed kumiko birdsmouth jig holds your strip flat while a chisel rides two fixed guide faces, one for each flank of the notch, so every joint closes at exactly the angle you set. Saw the notch to rough shape first, then pare the flanks in the jig with a chisel: the saw removes the bulk, the jig gives the precision. Both jaws adjust independently, strips gang flush side by side, and the notch-cutting head slides onto the body with a printed dovetail — like a timber sliding dovetail — so one body serves every angle pair you print. The STL set is free. Or order the jig printed to your spec.

Every STL free · printed to order in tough PETG & posted by a one-person workshop.