Choosing bearings for the 3d printed gears. 

The dial will drive the rotary encoder using a "planetary gear" type setup. One of the planet gears will have the encoder as the shaft but the other two gears, which work as support, will rotate freely over bearings. The free-rotating gears will be fixed to the PCB by a M3 screw and separated from it by a washer.

These are the requirements that I was considering:

• The outer diameter needs to be small enough so it leaves enough space for the 3d printed gears to be strong enough.
• The inner diameter needs to be 3mm so it fits an M3 screw.
• The width needs to be small enough so it leaves space for a washer and a nut in the space between the PCB and the top lid of the device.

I ended up settling for the following open bearings with OD: 8mm, ID: 3mm, width: 3mm