If you use metal shears to cut thin sheet metal such as duct metal it curls and can be difficult to flaten properly.
Cutting aluminum sheet clean.
This jet of water eats away at the metal and leaving a clean smooth edge.
This weakens the aluminium and creates a fracture line.
Place the fracture line over the edge of a table and bend the overhang slightly downwards.
Sheet aluminium can be cut without the need for a guillotine or tin snips which tend to deform the metal.
With the aid of a straight edge and a sharp knife score both sides of the aluminium sheet.
Clamp the aluminum down.
The illustrations are for a small bracket but i have cut 3 foot.
To cut the sheets of metal rathe.
2 mark the start and stopping point of your cut.
These photo steps show that it can be done using a utility knife.