grandpa-amus-bridge

Model of the traditional chinese bridge constructed by Grandpa Amu

grandpa-amus-bridge

Model of the traditional Chinese bridge constructed by Grandpa Amu

Grandpa Amu’s Bridge

I found this traditional Chinese bridge design and construction captivating. The interlocking pieces mean that no fasteners or glue is required and it gets stronger under load.

Construction video and more, because who can get enough?

Bridge from the side

Bridge from the emd

CAD model

First I created a CAD model using DeclaraCAD.

bridge.enaml source

This worked pretty well as there are lots of repeated parts, and by using the Cut operation, mortises could be automatically created in exactly the right locations for the tenons.

Rendered CAD model

Transparency helps see the structure and joints:

Transparent render

I was able to export a bridge.step file which could be imported into FreeCAD to generate a drawing.

Technical drawing detail

Full page drawing with other elevation views.

Scale model

Even though I created the CAD model and drawings, construction was done by eye.

First steps Base structure Side rails Final assembly

The final model would hold together without glue, but it’s a bit fragile that way and I’ve spent enough time assembling it, so I glued it with PVA craft glue.

It was then finished with a few coats of shellac.

Finished bridge model Detail Underside detail

Tools & Materials

  • Craft knife
  • Mini-hacksaw
  • Sandpaper

Craft knife

  • 8mm x 1200mm Tasmanian oak round dowel (2 pieces)
  • 6mm x 6mm x 1200mm Tasmanian oak dressed all round moulding (2 pieces)
  • 2.5mm x 100mm x 915mm balsa sheet (1/3 of a piece)

I cut mortises with the craft knife when it would have been more sensible to make a jig to drill out mortise holes.

Rails were created by splitting the square dowel.

There wasn’t much waste, probably about 20mm left from each of the round and square dowels.

Next steps?

  • 3D printed plastic model
  • Paper model