This PDF can be downloaded and shows the way we mark and form the rim. First a compass is used to draw an inner line, which will be the high point of the rim. The compass should be set so that the width is a half inch or more. It will be a constant distance from the red line and it will be determined by a stave that does not have anything left inside it.
Bullnosing the Rim
Once the lines are drawn, we start with the belt sander to make the outside curve. The curve should be pretty bulky as it needs to withstand potentially vigorous rim hits. After a rough forming with the belt sander, the curve can be finished off with the orbital sander. It is better to leave more to the orbital sander, because the rim is so important and it is best to go slower and be careful to get it smooth and not take off too much.