Cross braking is done using benders like this one from roto die.
How to bend sheet metal for ductwork.
V notches are the bending notches on straight duct on slip drive.
Cut a piece of foil tape to length.
Monkeys spinning monkeys by kevin macleod.
Slide the backing up and over the pipe.
Simple sheet metal bender using a hand roller clamps and plywood.
In some cases as with thicker sheet of metal you may need to use a sheet metal brake to apply your bend.
A second bend is made across this initial one leaving an x impression on the sheet.
To form the operator marks the bend line on the sheet as a guide then lines it up with punch tip and performs a shallow bend.
How do you bend a flat sheet of metal into a rectangle or l section if there is a profile rollformed on the two vertical edges of the blank as it approaches the braking station.
Peel off part of the backing.
Leave backing on the tape on metal ductwork.