2.008 is one of the reasons why I chose to go to MIT. Where else would I find a school where an entire class is dedicated to learning how to manufacture yo-yos???
Some finished yo-yos!
The goal of this class is to design and manufacture 50 injection molded yo-yos within a certain budget limit.
Every group has a theme (some past ones include Star Wars, Sushi, Monopoly, etc), but I mainly wanted to focus on performance of the yo-yo. As a result, I managed to convince my group that we should have a multi-configuration yo-yo that can have an aesthetic rim, or the high performance rim.
The key to this modularity is in the details. A nut is insert molded into the outer rim (red piece), along with an oversized McMaster shim (for weight). The rim has a taper that matches a taper on the blue body piece. Thus the taper serves to keep the pieces concentric (which is uber important when you want your yo-yo spinning ~6000 rpm to be vibration free), and the nut allows us to squish the whole yo-yo together during assembly. Other standard yo-yo pieces- a 1/2″ OD 1/4″ ID ball bearing, and silicone rings are incorporated into the body design for performance.
The captive nut is molded in by pressing in a pin that has a nut threaded on the end (aka shoulder bolt where we turned off the head) before each molding. The pin is unscrewed from the finished part and then reused.
The shims are held in place by magnets pressed into the mold and a locating ID.
The mold were made on a CNC lathe with some post machining (runner/gate/various holes) done on a CNC mill.
These yo-yos work so well I may even compete with them at some point!
A core and cavity for the rim and body (respectively). Surface finish for facing is dubious because the lathe we’re using has issues facing with CSS.
Some of the first molded body pieces.
First working yo-yo!
Printed prototype done on a Form 2 3d printer.