Of course this technique extends pretty easily to any material that can be pixelated (i.e. used as a building block to make a larger picture). LEGOs (TM) operate on this principle, pop cans would work, milk cartons, bottle caps, Rubik's Cubes, ... the sky's the limit.
Step 1: Tools and Materials
Some experimentation led me to the use of zip ties and a slightly-thicker-than-paneling backing piece for the mounting along with a couple of framing pieces serving the dual purpose of stabilizing the piece and providing a surface for my clever catch phrase.
The framing was just scrap 1" x 2" wood painted in a contrasting color. The picture in the front needed to be a bit stable so I opted for the foam board you can get from any art/craft supply store.
Step 2: Overall Layout
This first part was pretty easy. The main reason I did it was to get dimensions for the backing piece, the only thing I didn't have lying around in my spare parts. I decided that some contrast was needed so that the "50" would stand out. After drawing a simple pair of 5x5 grids (don't you love it when the numbers work out for you?) I determined that I would need 17 of one color and 33 of another. The "50" label was a necessity, and the other was chosen according to my friend's tastes.
With this tight arrangement set up I was able to measure the minimum dimensions needed for the backing piece, allowing for a slight bit of horizontal spacing between them in order to accommodate the zip ties that would be fastening the cans to the back.
Step 3: Finding the Spacing
To figure out the zip tie length I used a fabric tape measure to get the size of the can and the added a few inches for slack. The 11" ties were just barely long enough. I could have opted for the 14" ties just to be sure but there weren't enough in the rack at the time.
Step 4: Choosing the Backing
This little piece was hiding in the cabinetry section. It was too long for what I needed, 48" when I only needed 32". The width was perfect and the inlay was an unexpected bonus, especially since the size almost perfectly matched where my two numbers would go. A little trimming on the table saw and I had my backing.
Step 5: Fashioning the Backing
For the holes I was very carefuly about vertical and horizontal alignment since I didn't want the cans crooked, and less so about that actual distance since really the zip ties could go anywhere on the can and do the job just as well.
After the holes were drilled it seemed like a nice touch to color the backing with the number 50 as well so that as cans were removed the number was still visible. Again I opted for the direct approach, putting the cans in place and using painter's tape to mask off the unpainted areas.
As you can see even though the paint job itself was sloppy (again that time constraint thing) the edges turned out nice and even after the tape was removed. The few drips you see were mostly due to the paint running down into the inlay.
Step 6: Creating the Frame
The picture was printed on a standard computer printer then cut out to minimize the edges.
Originally my plan was to paint the letters on to the frame until I found these wonderful paper letters, kind of like post-it notes, at the craft store. They were thin enough that I could attach them to the frame boards with craft glue. The layout was first made in place so that I could confirm the spacing.
Now that I knew everything was going to work the way I expected I glued the letters to the frame and the picture to the foam board using craft glue. A coating was applied over the top as well to minimize lifting.
It was somewhere around this point that I realized that a can was much taller than my frame board and the picture could not be affixed to the frame with the cans in place. I decided to leave the gap in the middle for the time being and figure it out later.
Step 7: Attaching the Frame
When attaching the frame to the back I used a countersink on the screws so that they wouldn't be sticking up from the board. Of course the zip ties would be but I like the permanent parts at least to be neat.
Step 8: Creating the Infrastructure
Second I pushed the other end through the other hole so that there were loops in the front.
Finally I lightly attached each tie so that they wouldn't slip back through as I moved things around. Emphasis was on lightly here since there wasn't a huge amount of slack for the cans to fit in. All of the loops were then ready for final assembly.
Step 9: Final Assembly
The ties had to hold the cans firmly so this was a two-handed job. After several rounds of tiring my fingers out I settle on the technique of holding down the tie with one hand and pulling the end with the other.
As you can see this firmly tightened the ties flush to the board with minimal strain to my fingers.
Lastly I used the side-cutters to clip off all of the loose ends. When the time came to remove one of the cans a knife, pair of scissors, or side cutters could be used to release the tie in the back and free the refreshing beverage!
Step 10: Final Decor
The easiest solution to moving the picture up higher was a simple post made from a scrap 3" piece. It was attached to the back with a couple of screws.
Lastly the foamboard was trimmed to the shape of the picture and attached to the post. I left a little space beside it so that I could sign my birthday wishes right on the piece as well.
And there you have it. Not including the paint drying time and a run to the stores it was probably no more than 4 hours of effort. It's winter up here in Canada right now so this particular piece can sit outside and stay frosty until needed. The cans can even be replaced once empty (if you don't cut the zip ties) to keep a permanent monument to this historic milestone.