A roll is a tooling that comes either as 1st operation or 2nd operation variant. The first operation roll is designed to start the process by rotating around the can and creating the first operation seam.
The profile of the 1st operation roll and its position against the chuck is critical in a proper formation of the double seam. Most of the issues in double seaming stem from incorrect setup of the 1st operation roll.
This the typical shape of the output of the first operation roll .
Most problems with first operation rolls come from the following issues: