In general, the first sanding belt is used for stock removal, while the following belts are only used for creating an even surface finish.
Typically, the first sanding unit consists of a drum made of materials such as steel or hard rubber. The drum, in combination with coarse grit (P36–P100) belts, is ideal for efficient stock removal. When it comes to producing an even surface finish, sanding units that incorporate soft rubber drums or sanding pads are normally used. In these units the grit range varies from P120–P320. For sanding between coats or intermediate sanding, grits P320–P800 are most commonly used along with a very soft rubber drum or a soft sanding pad.
When choosing a grit size the recommendation is to select belts that are only one step from each other in grit sizes. For example, P80–P120–P180 are appropriate steps, whereas P60–P120–P220 often results in problems with the surface finish and product lifespan.