Building a spud cannon can be exciting and fun, giving you hours of enjoyment both in the process of creating it and when using it. These cannons can, however, be dangerous to operate. You are firing potatoes out of a pipe using combustion, which can make for a volatile situation. Make sure you take great care in making your spud cannon so it doesn't malfunction, and also be careful when firing it.
Using the hacksaw, cut the 3-inch diameter ABS pipe to approximately 14 inches in length, creating the combustion chamber. Quickly check to see if the reducer fits over the cut end of the pipe, making adjustments where you need to ensure a snug, overlapping fit. Use the file to sharpen the firing end of the barrel, which will allow for easier loading by slicing through the excess parts of the potato.
Spread a generous amount of cement along the interior of the reducer and slather it over the exterior of the cut end of the pipe. Place the reducer on the pipe, pushing it into place and securing it snugly. Repeat the cementing with the threaded adaptor on the opposite end of the pipe from where you put the reducer. Again, repeat the cementing step, generously applying it to the open end of the reducer and along the exterior of the 1 1/2-inch diameter pipe, creating the long barrel of the cannon. Allow the cement to cure before proceeding.
Drill a hole midway down the combustion chamber and fit the flint igniter in place using the materials that came with it. Use cement to secure the flint in place, covering any open area to completely seal the combustion chamber. Allow the cement to cure before proceeding.
Inspect the finished product, ensuring all sections are properly cemented and completely dried. Secure the cap on the back end of the cannon to make sure it threads cleanly onto the end of the combustion chamber.
Firing the cannon is simple but requires excessive amounts of caution and should never be done without having others around in case of an accident. To load and fire the cannon, unscrew the cap end and leave it open. On the other end of the cannon, force a potato into the barrel and shove it into place with the handle of a shovel or similar device. Make sure the potato is secure in the barrel and isn't exiting into the combustion chamber. Using hairspray (you should verify it's combustible before applying it), spray into the combustion chamber for approximately 3 seconds. Quickly replace the cap end and secure tightly. Lift the cannon to your side, resting it on your hip or similar fashion, and click the igniter. The fuel inside will ignite, firing the potato out the end of the barrel.
PVC pipe can also be used instead of ABS pipe. There has been no proven difference in the capabilities of a spud cannon used with either kind of material. The combustion chamber can be cut to any size you prefer, but the more area in which the fuel can be placed, the more powerful the spud cannon is going to be. Cleaning the pipe before applying the cement will allow for better bonding between the materials. Make sure to let the cement cure overnight before attempting to fire your spud cannon. Wrapping the combustion chamber in fibre-reinforced shipping tape is also recommended but optional. Pipe tends to shred when it fractures (which it will eventually do over time) and can be dangerous if not reinforced. Consider water testing your cannon by submerging the sealed parts to make sure it does not leak, which will be indicated by no bubbles coming from the submerged section.
Safety! Safety! Safety! The spud cannon can definitely be lethal if used wrong. Make sure you have wide open spaces to fire it and never, ever aim it at anyone. Make sure to use plenty of cement. This cannon is going to be launching potatoes using pressure and combustion. Lack of good cementing will likely lead to it explode in your arms. Always use ear protection when firing a spud cannon. NEVER use gasoline as a fuel in a spud cannon. It will wear down the pipe and cause a dangerous situation.