In a previous project I built an air cannon (video tutorial embedded below in the first step of this Instructable). The main part of that cannon was a custom piston valve, which I specifically designed to be easily interchangeable with different barrels and chambers. In this project I'll be taking advantage of that feature, and I'll show how you can make a specialty cannon barrel that shreds your projectiles. In this way I can fire a barrage of french fries like a shotgun, and provide all my neighbors with fresh cut apple slices from the comfort of my own backyard. Hey, you can't get more neighborly than that.
Step 1: Readying the Cannon
First things first, take a look at my video embedded above where I build the valve used in this cannon. In that video I made a smaller cannon using a high performance piston valve as the main component, using it to fire ping pong balls and other small projectiles. The chamber of that first cannon is too small to provide enough air for a larger barrel, so I'll put together a new one.
I used a T fitting at the end of a length of 2” pipe to make a chamber that has two legs going outward, this will allow the cannon to sit upright on a flat surface. All pipe and fittings must be pressure rated. End caps close off both legs, and to attach the chamber to my cannon a threaded 2” elbow is cemented to the far opening.
I like to use teflon tape on any threaded PVC fittings just to be sure there are no air leaks. Using the threaded elbow, my chamber attaches directly to the piston valve.
Step 2: Assembling the Cutting Head
I found an apple slicer set for about $10 online (Amazon), and it has three blade configurations. While wandering the isles of my local hardware store with these slicers in hand I found that they were a perfect fit in the outer rim of a 4 by 3 inch PVC closet flange. Pretty convenient right?
By installing four carriage bolts through the evenly distributed holes in the flange (secured by nuts and washers), a second flange placed upside down can be used to secure the cutter. There are built in grooves that the heads of the bolts fit through that allow the cutter to be locked in place with a twist.
Step 3: Finishing the Cutter
I wanted the outer flange to allow a clear view of the blades as the cannon fires, so the extra bit of fitting on that flange was cut flush with the base.
Step 4: Finishing & Mounting the Barrel
The remaining flange is glued to what will be the business end of my cannon barrel, a 2 foot long section of 3 inch diameter PVC pipe. The output of my piston valve uses a 1 and a half inch threaded fitting, so at the other end of this pipe I glue on a reducer, paired with a threaded fitting to match my valve.
To thread the now completed barrel into the rest of the cannon a wooden support is used to take some of the strain off the valve. A large hose clamp works well to keep it in place. I later added some small rubber strips between the hose clamp and the PVC to keep the metal from scratching the paint which I added as I waited for the PVC cement to cure.
Step 5: Firing the Cannon
And the cannon is finished. The rotation lock on the outer closet flange allows easy removal and reattachment of the cutters for loading.
I obviously wanted to get some flying french fry's out of this build, but I ran into the problem of potatoes being too small to properly fit in 3 inch diameter pipe. I ended up using some leaves of cabbage as a sabot/wadding to make a good seal in the barrel. This worked quite well. Apples are also an excellent choice that doesn't require wadding for a proper fit.
Though the pipe and fittings I am using are rated to several hundred PSI I never recommend anyone take PVC cannons to anywhere near those pressures. All it takes is one poorly cemented fitting to blow loose and cause injury. I took this cannon to about 60 PSI for the shots in my video.
I hope you enjoyed this project! Thanks for reading, and be sure to watch the full video on my YouTube channel to see this cannon in action.