Plywood Bridge

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Your task is to build a bridge using 1/8" thick plywood and wood glue only. Our objectives are that you will learn how to use 3d design tools, a laser cutter, and also that you learn a bit about structure. This project is inspired by the "toothpick" bridge project (google it).

dimensions of the bridge

Requirements and constraints

You are to design and build a bridge that meets the following constraints:

  • Your bridge will rest on two pillars (that are provided).
  • Each pillar measures 2.5" x 2'5", they are separated by 7". Pillars are the wood colored items in the diagram.
  • Your bridge must fit within a 12" x 2.5" x 6" rectangular prism (blue region in the diagram).
  • No portion of the bridge may extend below the plane defined by the top surfaces of the two pillars.
  • There must be a 2.5" x 2.5" flat area centered at the top of the bridge upon which weight will be applied (red region in the diagram).


You may use only the following provided materials:

  • One piece of 1/8" by 12" x 12" plywood (i.e. 1/2 of a 12" by 24" piece)
  • Titebond wood glue

Design & Building Process

You should design your bridge using a 3D design tool such as solid works. You should use a laser cutter to cut the parts from the plywood provided to you, then glue them together using titebond wood glue.


We will evaluate your bridge in four ways:

  • Overall strength: How much downward force can be applied on the bridge before it begins to fail? We expect your bridge to hold at least 50 pounds.
    • 85% if it holds 50 pounds. 1 additional point for each additional 20 pounds, up to a total of 90 (150 pounds)
  • Strength to weight ratio: We will divide the strength determined above by the weight of your bridge.
    • Additional 2.5 points for S/W > 200.
  • Beauty.
    • Up to 2.5 points for beauty
  • Craftsmanship.
    • Up to 2.5 points for craftsmanship.

An award will be provided to the builder of the best bridge in each category above.

Example Design

To help you get started, I include some images of a basic design that you can copy. There are some important flaws in this design though. With a few adjustments you should be able to make a much stronger bridge.

view 1
view 2
view 3