If you've seen a vortex cannon in science class you're probably expecting a garbage can with a hole cut in the bottom and a diaphragm on the back. While you can make low velocity vortex rings this way, to make a really high power slug of air a cone shaped barrel is the way to go. Making such a barrel can be a difficult task. In previous iterations of this cannon I used fiberglass to form a cone over a paper mold; a messy process that is likely to have you breathing toxic resin fumes and spending quite a bit of money on materials.

For my new design we'll be using a roll of plastic terrace board, 4" wide by 40' long. Terrace board is sold in slightly smaller rolls which I have found work just as well. The 40' roll might be overkill but I decided I may as well go big for the tutorial.

To make a cone from this roll of plastic the first step is to secure the outside layer so it won't unravel once the straps are cut that bundle it together on the store shelves. We need the outside layer secured, but the inner portion of the coil free to be pulled out. To do this the simplest method is to wrap the roll in fiberglass reinforced tape, but an even more secure method is plastic welding.

There are only a few types of plastic that can be safely welded without giving off horrible chemicals, and fortunately HDPE, high density polyethylene is one of them. HDPE is a close relative to paraffin candle wax, and when burned the similarity is apparent as it smells just like a blown out candle.

Using a torch on low heat we can melt the outer edge of the roll until the plastic pools and begins to merge into the layer beneath. To make sure we only melt the very edge of the roll a piece of thick metal (I used a wrench) should be placed where we would like the melting to stop. Once the plastic has been sufficiently melted together and cooled it should be strong enough that we can cut the straps on the roll without it unraveling.

Safety note: Though HDPE burns cleanly compared to other plastics, it is still wise to weld in an area with a lot of ventilation. It's best to avoid breathing smoke from even the cleanest forms of combustion. If the smoke stinks like a burning tire or is marked with something other than "HDPE" or "LDPE" it's not a safe plastic to weld and you should use a different method to secure the roll.