After a long break form Instructables, I'm back and with a new project: A deceptively simple and incredibly effective propane-powered noisemaker (it goes BOOM!) I don't have any real photos yet, so I'll make so with some crappy MS-Paint diagrams, and any photos I can find online. It's simple enough that you really don't need anything more.
Before we get to the good part, there are definitely a few disclaimers to be observed when building and/or using this thing. It uses propane as a fuel source, which means you could burn yourself or someone else, or set your house or other things on fire. The construction involves working with and cutting pieces out of thin steel food cans ("tin cans") and the edges of the lids and all the cut pieces are usually VERY sharp, and I've cut myself enough to have a healthy respect for them. This device uses the very rapid combustion of a propane-air mixture to produce a lot of pressure inside a semi-confined space, so if you try to fire anything out of the barrel, or obstruct it with anything (hell, even if you just don't use enough tape to hold it together) it may explode in your hands. Chances are that it will just fail at the tape and not cause any real damage to the cans or you, but it's scary and not recommended. Don't build this if you or anyone around you are very sensitive to loud noises because this is LOUD. Don't be stupid and point it at people or animals, and don't use any fuels other than propane and air. I've tried many others and they either don't work or they work WAY too well, with shrapnel and bleeding and screaming being the result.
Now that all that is out of the way, let's get started!
Step 1: Parts and Basic Structure
This noisemaker is made from between 5 and 8 tin cans held securely together by strong packing tape. Do not use duct tape, it's not as strong for this application (I've had a duct-tape one fail but my packing-tape ones are fine) and is less dependable. The photos I found online depict duct tape, and one of them has a tennis ball in it. DON'T TRY TO SHOOT A TENNIS BALL OR ANYTHING ELSE WITH THIS NOISEMAKER, I canon stress this enough. Propane is far more potent than the lighter fluid (naphtha) used in tennis ball cannons of similar design, and is probably unsafe for projectile use, at least with cans and tape. The other part of this setup is a propane torch, AKA a plumber's torch. The overall design of this noisemaker is almost identical to Sonnimo1234's instructable here on tennis ball mortars and I have included an image from his instructible here to illustrate the internal structure. As you can see in the aforementioned image, the cans are stacked and the bottoms of them are cut out only partially for most of the cans. In my design, I alternate fully removing the bottom of one can and leaving half of the bottom on the next one, until I get to the muzzle end which has three can-lengths unobstructed. The can bottoms serve an important role, don't just tape cans together and think it will work if it's essentially a simple pipe. The "baffles" (can bottoms) cause the speed of the flame to increase every time it has to pass through a baffle, which greatly improves the loudness and pitch of the noise made. A simple tube closed at one end will usually just make a "whoosh" or "thump" sound, but a properly fueled and constructed noisemaker sounds like a shotgun blast.
Step 2: Cutting the Cans
This step is the most risky aside from actually firing the thing. It involves sharp tools and sharp metal pieces. Wear heavy-duty work gloves if you're not okay with using your bare hands, or get an adult to help you. I've cut myself plenty of times and it usually happens when you go at something with the attitude "how hard could it be? I can do this!" and then you start bleeding. Be careful, take it slow and try to cut away from yourself as much as possible. Making the straight-through sections is obviously as easy as using a can opener on both ends of a can. When I first made this cannon, I didn't have access to a good pair of tin-ships or sheet metal shears, so I got creative and used a different method to make the baffles. I used an "exacto" type hobby knife and scored all the way around the can bottom halfway from the center, then went over the same line twice more. This deepened the score line and weakened the metal of a can enough that I could use a flat blade screwdriver to break the score line at one spot and then use a pair of pliers to tear the rest of the bottom off along the score line. This works pretty well, but it is time-consuming and involves an extra sharp tool, so if you have a pair of shears, use those. For the bottom can, use a drill with a bit just a little bigger than the nozzle of your propane torch, mine is about 3/8" in diameter so I used a 7/16" bit or so. Drill the fuel/ignition hole in the center of the bottom of the last can, and be careful because the drill but can rip the sides of the hole, making sharp edges and making the hole irregular. The best way to avoid this is to use a "spade" pr "paddle" bit which has a sharp point in the middle and two more at the outer edge that actually do the cutting, so there's less chance of tearing the thin steel.
Step 3: Final Assembly
This is pretty simple, line up the cans, use some tape to hold them together securely, then tape the crap out of the joints and all up and down the whole tube for reinforcement. I usually do a couple spiral wraps too for good measure. Remember, DON'T use duct tape, only strong plastic packaging tape. If you're really worried about the cans coming apart, use fiber-reinforced packaging tape, it's way stronger than the regular stuff. You can't have too much tape, so go crazy if you have enough tape on hand. Make sure the cans are in the right order and all that before you start taping.
Step 4: FIRE IN THE HOLE!
The last step! The one you've been waiting for! Actually using this funny-looking contraption to raise eyebrows and turn heads from a quarter-mile away! I have a torch that has a built-in ignition system operated by a trigger, so all I have to do is stick the torch in the hole, turn it on for about 6-10 seconds, then click the trigger and I am immediately gratified by a very loud BOOOM and a blue fireball blasting out the front. If out don't have an auto-light torch like mine, you have to take the torch out after filling and then put a lit match or a long-handled lighter up to the hole. Watch out for the open hole when you light it though, it tends to shoot a bit of hot gases back at you and it might singe hair or fingers that are in the way.