How should a mandrel be sized for the duct it will be used in?

When sizing a mandrel for a duct, it is essential to ensure a proper fit that allows for the intended operation without compromising the integrity of the ductwork. Sizing the mandrel to be 1/2" smaller than the duct is appropriate because it accommodates the materials used in the duct and provides enough clearance for easy insertion and removal. This slight reduction allows flexibility during the installation process and prevents any obstruction or damage to the duct's internal surface.

Choosing a mandrel that is equal to the size of the duct might create difficulties in maneuverability and could result in damages if there is too tight a fit. On the other hand, selecting a mandrel that is 1/4" larger or 1" larger could lead to issues such as insufficient support during the forming process and a risk of collapsing or wrinkling the ductwork. Therefore, opting for a mandrel that is sized 1/2" smaller strikes the right balance for functionality and operability in ductwork applications.