The concave surface

Fig: The concave surface (above the grinding plate, below the surface)

You can clearly see the problem: the chance of getting a flat surface is very small. Unfortunately, here you sand only with the outermost edge of the sanding disc, not with the entire surface. If you find something like this, you will probably have to straighten the area first.

How you do that is up to you. In principle, there are a few possibilities:

• Planing

• use a particularly coarse grit

• use a smaller grinding wheel

• use a smaller grinding wheel