3 inch thickness sander

[Frank S]

You really only need 1 belt in a centerless but you do need dissimilar size rollers or speeds there are quite a few videos showing the operations of a centerless belt grinder. It is actually better to have a plain or rubber wheel rotating in the same direction. Depending on which direction your belt is running depends on whether you position the cylinder above or below the center line. there is also a chart showing the distance offset from center relative to the diameter of the cylinder being ground or polished
Thrufeed Centerless OD Grinding Parameters and Troubleshooting.pdf