"Rotating Parts" Yo-Yo
MIT, Spring 2008

Class: Design and Manufacturing II
Team Size: 6 people
Duration: 3 months
Project: Design and produce a yo-yo consisting of two injection-molded parts and one thermoformed part.


A yo-yo rotates at high speeds and can become a dangerous spinning projectile when used in the hands of a clumsy novice (such as myself). Playing on this fact, our team custom designed a yo-yo with an image of the "rotating parts hazard" warning label that is commonly seen in machine shops. This detail-heavy image met our desire for an intricate design that would fully test the limits of our skills.


We conducted a production run of fifty yo-yos. The main yo-yo body and the yellow insert are both injection molded, while the black hand-and-gears insert is thermoformed. The three parts are sized to snap-fit together. The design was first created as a CAD model. A CAM package was used to transfer the design into CNC mill- and lathe-readable code, from which the injection molding and thermoforming molds were produced.

During the production run some machine parameters - such as pressure, temperature, or time - were also varied to study their effect on quality. This allowed us to better optimize the production process.


Two of the CNC machined molds. The left is the body mold used for injection molding. The right is the insert mold used for the black thermoformed insert.