1. As the can has no support inside, it is hard to estimate how hard to push the cutter.
2. The can is a cylinder that may roll and slip away when cutting it open.
In order to do it safely. This instructable shows how I have the job done.
Step 1: Tools
1. a cloth
2. a cutting mat
3. some blu-tack
4. a cutter (wide blade preferred)
5. a screwdriver with hard plastic handle
6. a bottle (slightly smaller than the can in diameter)
7. an old megazine
8. a pair of scissors
Step 2: Cloth Support
If it still rolling, may also apply some blu-tack between the can and the cutting mat to make it stay still.
Suggest starting to cut near the can top first.
while holding the can still, apply force on the cutter against the can surface above the cloth. The cloth supports your wrist therefore you can hold the cutter more stable and steady. Even the can slips away, the cloth can stop hand movements and prevent cutter blade to cut anything or anyone.
To cut the can effectively, apply force gently towards the centre point of the can, i.e. move the blade back and forth along the blade. By this way the can is cut open bit by bit. Don't rush.
Roll the can a bit when the cut is close to the cloth. Continue to work until the can top is separated.
Step 3: Smoothing the Edge
Step 4: Support by a Bottle
Find a bottle slightly smaller than the can, wrap it by an old magazine and place it inside the can.This forms a support inside the can that avoids deformation.
Step 5: Cut the Bottom
Repeat step 2 - smooth the edge.
When done, the top and bottom is removed and you will get a metallic tube.