Quarter Iso-grid Cardboard Longboard

Skills: Fusion360, Digital Fabrication

Build Instructions: https://www.instructables.com/Quarter-Iso-grid-Cardboard-Longboard/

Project Overview

The goal of this project was to attempt to successfully build a structurally stable longboard deck using cardboard and no adhesives. We began the process by modelling the conceptual design on Fusion360, a 3D CAD software. Next we ran various stress and load tests on our design in the simulation environment of Fusion360. Once we were confident with the results, we began to fabricate it using cardboard with the help of CAM tools. Finally we tested the deck by mounting longboard trucks and wheels. The deck held up to the forces successfully and we have been using it ever since. This project won the Judge’s Prize for the best use of Fusion360 in the Instructables Skateboard Contest 2019.

Choosing the Design and Structure

We began the design process by studying various interlocking grid structures and we came across the isogrid and quarter isogrid structure. The quarter iso-grid pattern is a partially hollowed-out structure formed with two opposite facing equilateral triangles forming a star shape. Structures made using this grid pattern has proven to be extremely light and yet rigid due to the partial hollowness and the interlocking ribs. This structure is generally used in the aerospace industry which encouraged us to attempt to build a longboard deck using it.

Simulations

Fusion360 provides a simulation environment that allows us to apply various stresses and loads on our design. This gives us an accurate idea of how the physical model will react to various forces before having to fabricate it. We began by constraining the regions that would attach to the trucks and applied a force on the top of the deck in the middle that would simulate the weight of an average person (65kgs). The results showed that the force applied would satisfy the safety factors that we set. For experiment's sake, we increased the force to a value that would simulate a weight that is greater than that of an average person (100kg+) and observed minor warps towards the center.

Fabrication

The pieces were laser cut out of cardboard making a total of 61 pieces that interlocked together to create the quarter isogrid structure in the form of the longboard deck. We designed the pieces such that no adhesives are required for the assembly. Next we embedded ½ inch plywood pieces cut to size into the front and back regions of the board and mounted the longboard trucks to the wood. We decided to add an extra layer of laser cut clear acrylic on either side of the deck for an extra layer of reinforcement.

Conclusion

Once the build was complete, we thoroughly tested the longboard. We have been using the board regularly and we have noticed minor wear and tear. Thus we have successfully fabricated a longboard entirely out of cardboard.