After receiving the comment regarding using a can-opener I found the following instructable which gives excellent instructions on how to do just that: Make a Pen Holder
Step 1: Tools You May Require
First up your safety is paramount, do be careful when handling cuttings from the can and wear eye protection. Adult supervision is strongly suggested for anyone who is not used to crafting with such materials.
For this task you will generally need:
3. a file
4. hot glue, epoxy glue or similar
Step 2: Preperations
With the contents removed give the can a good wash out.
Use the opening to get started and work in reasonably big pieces to clear up to the groove. Use a mix of snipping and bending the metal back and forth. Take care working around the cut metal.
Step 3: Clear the Top of Metal and Fold in the Lip
Use a file to clear the last of the metal or fold the cut under the lip as I have done.
I used a pair of pliers and a strip of plastic to push the lip in.
Step 4: Hot Glue
I used hot melt glue to seal the cut edge of metal so that it would not injure anyone. A similar solution might be epoxy glue or electrical tape, duct/duck tape etc. Be sure that you leave the edge in as safe a way as possible, probably best to keep this out of reach of children and small animals.
You'll notice I added a lot of hot glue to the base of the can. This was firstly to balance the weight of the glue in the top of the can. Also, from previous experience with making pen holders out of cans they tend to get top heavy when they're full of pens. The same could be achieved by adding blue tac or plastercine to the bottom, inside and/or out.
Step 5: Done!
As this is my first instructable please let me know what you think. If you follow this instructable please let me know how you get on (and also please take care when working with cut metal, did I mention that already?)