Here's the video version of the instructions:
Step 1: Clean off the paint
However, skipping this step altogether makes it quite hard to see what you're doing in subsequent steps.
By far the easiest time to do this is when the can is still full and sealed, because the liquid inside will support the walls as you press on them with the abrasive.
Step 2: Cut the can open
This should leave you with a rectangle-shaped piece of thin metal.
The edges may be incredibly sharp and jagged. Please be really careful!
Trim off the jagged edges of the rectangle, but try not to remove too much material.
Step 3: Tape the metal to a slightly springy board
Step 4: Mark out the net of the box
- starting with a two-inch square right in the middle, then a four-inch square surrounding it, followed by another (approx) 5 inch square surrounding that.
Extend the lines right off the edge of the metal in both directions - when you're done, you should end up with a quite complicated-looking grid pattern (take a look at the pictures for details).
The above dimensions are based on a tall 440ml can - if you're starting with a smaller one, you might need to scale things down to fit the available materials