Cracked gears

Cracked plastic gears are nightmare of every technician. Once it happens, help is very difficult. These parts are not produced anymore. Current level of 3D printing technology hod as its limits, like material quality and resolution. Production of new ones using injection molding is very expensive, initial cost is very high. Investment to such production will not return, unless thousands of spare gears are sold. Another option is to make them using CNC technology. Negative side is that it is not easy to find producer with experienced technicians able yo make such small and complex parts. Initial cost is acceptable, however price per one piece can be quite high, as lot of effort is needed to produce one piece.

Some players are known to have serious issues with cracked plastic parts, while other not. Good advice is to do some research before buying them. Is this player notoriously know to have broken plastic parts? If yes, is there anyone producing them? Is it possible to fix it, or is it hopeless?

Why do they crack?

They’re usually made of POM material. This material is very reliable, long lasting and has very good friction properties. However, it has one negative property. It tends to shrink. It shrinks when it is heated, for example when player is left on sun or in car. By heating POM matrial to 60 C, it will shrink permanently about several percent. It also shrinks with time.
Problem is, when this gear is installed on some other part, for example on metal axle. Plastic material shrinks, while meta one doesn’t. High tension in plastic part will cause that it cracks. Some parts are made of other than POM material. This can be short lasting material, fragile, that breaks into several pieces after some time.

How to fix them?

It depends on particular application, there is no universal how-to. Each part is different and each part needs different fixing method. Here are some examples, how I fixed some plastic parts of DD walkmans.